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The influence of zeolite support materials and their impact on CH4 oxidation activity was studied utilizing Pd supported on H-beta and H-SSZ-13. A correlation between CH4 oxidation activity, Si/Al ratio (SAR), the type of zeolite framework, reduction-oxidation behaviour, and Pd species present was found by combining catalytic activity measurements with a variety of characterization methods (operando XAS, NH3-TPD, SAXS, STEM and NaCl titration). Operando XAS analysis indicated that catalysts with high CH4 oxidation activity experienced rapid transitions between metallic- and oxidized-Pd states when switching between rich and lean conditions. This behaviour was exhibited by catalysts with dispersed Pd particles. By contrast, the formation of ion-exchanged Pd2+ and large Pd particles appeared to have a detrimental effect on the oxidation-reduction behaviour and the conversion of CH4. The formation of ion-exchanged Pd2+ and large Pd particles was limited by using a highly siliceous beta zeolite support with a low capacity for cation exchange. The same effect was also found using a small-pore SSZ-13 zeolite due to the lower mobility of Pd species. It was found that the zeolite support material should be carefully selected so that the well-dispersed Pd particles remain, and the formation of ion-exchanged Pd2+ is minimized.

Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.

A concept of a layered Pd/SSZ-13 with Cu/SSZ-13 as PNA-SCR dual-layer monolith catalyst for NOx abatement is demonstrated. NO-TPD was employed for determining the NOx storage, and the samples are characterized in detail using SEM-EDX, CO/NO-DRIFTS, XPS and H2-TPR. 750 °C hydrothermal treatment greatly promotes the NOx storage capacity and the addition of CO promotes NOx storage capacity and also shifts the NOx desorption temperature. The dual-layer sample (Pd/SSZ-13+Cu/SSZ-13) maintains most of the NOx storage capacity while the NOx desorption temperature is modified due to Cu/SSZ-13 as the top layer. The layered sample work well for NH3-SCR reaction. Notably, for Pd/SSZ-13+Cu/SSZ-13, more than 80 % of the NOx trapped at low temperature (i.e., 80 °C) can desorb in the suitable SCR temperature region where NOx conversion higher than 80 % is found. However, some loss of NO storage is found after SCR experiments. Overall, the dual-layer concept shows interesting potential for NOx abatement, but requires further developments on the PNA material to ensure stable storage capacity.

The efficient conversion of CO2 to hydrocarbons offers a way to replace the dependency on fossil fuels and mitigate the accumulation of surplus CO2 in the atmosphere that causes global warming. Therefore, various efforts have been made in recent years to convert CO2 to fuels and value-added chemicals. In this review, the direct and indirect hydrogenation of CO2 to hydrocarbons via methanol as an intermediate is spotlighted. We discuss the most recent approaches in the direct hydrogenation of CO2 into hydrocarbons via the methanol route wherein catalyst design, catalyst performance, and the reaction mechanism of CO2 hydrogenation are discussed in detail. As a comparison, various studies related to CO2 to methanol on transition metals and metal oxide-based catalysts and methanol to hydrocarbons are also provided, and the performance of various zeolite catalysts in H2, CO2, and H2O rich environments is discussed during the conversion of methanol to hydrocarbons. In addition, a detailed analysis of the performance and mechanisms of the CO2 hydrogenation reactions is summarized based on different kinetic modeling studies. The challenges remaining in this field are analyzed and future directions associated with direct synthesis of hydrocarbons from CO2 are outlined.

Sulfides of NiMo over a series of commercial ultra-stable Y zeolites were studied in an autoclave reactor to elucidate the effect of silica/alumina ratio (SAR = 12, 30, and 80) on the cleavage of etheric C–O (β-O-4) and C–C (both sp3–sp2 and sp2–sp2) linkages present in native/technical lignin and lignin derived bio-oils. 2-Phenethyl phenyl ether (PPE), 4,4-dihydroxydiphenylmethane (DHDPM), and 2-phenylphenol, (2PP) were examined as model dimers at 345 °C and 50 bar of total pressure using dodecane as the solvent. The etheric C–O hydrogenolysis activity was found to be in the order NiMoY30 > NiMoY12 > NiMoY80, despite a high initial rate of C–O cleavage over NiMoY12 owing to its high acid density. A high degree of hydrodeoxygenation (HDO) and hydrocracking reactions were observed with NiMoY30 yielding >80% of deoxygenated products of which ∼58% are benzene, toluene, and ethylbenzenes. A similar experiment with DHDPM showed the rapid cleavage of the methylene-linked C–C dimer (sp3–sp2) to phenols and cresols even with the low acid density (high SAR) catalyst, NiMoY80. Direct hydrocracking of the recalcitrant 5-5′ linkage in 2PP is very slow, however, it cleaved via a cascade of HDO, ring-hydrogenation, and hydrocracking reactions. A high degree of hydrogenolysis and hydrocracking occurs over NiMoY30 due to suitable balance between acidity and pore accessibility, enhanced proximity between acidic and deoxygenation sites leading to a slightly higher dispersion of Ni promoted MoS2 crystallites. Overall, the product spectrum consisted of a high yield of deoxygenated products. The carbon content on the recovered catalyst was in the range of 3–7 wt%. These results pave the way for effective catalysts to break recalcitrant linkages present in lignin to obtain a hydrocarbon-rich liquid transportation fuel. An experiment with Kraft lignin over NiMoY30 shows good selectivity for deoxygenated aromatics and cycloalkanes in the liquid phase.

NiMoS on alumina, USY and mixed alumina-USY supports was studied in a batch reactor to assess the effect of support acidity in valorizing lignin dimers by hydrodeoxygenation (HDO). The reactivity of α-O-4 (benzyl phenyl ether), β-O-4 (2-phenethyl phenyl ether) and 5-5′ (2,2′-dihydroxybiphenyl) linkages was investigated in dodecane at 593 K and a H2 pressure of 5 MPa. A relatively fast rate of hydrogenolysis of the sp3 hybridized etheric bonds was observed for the catalyst supported on the mixed support. With the α-O-4 linkage, the USY supported catalyst selectively yielded deoxygenated aromatics including BTX products with fewer residual C–C dimers. For the β-O-4 linkage, analogous trends have been observed but with more aromatics. Interestingly, with 5-5′ linkages the catalyst on USY and mixed supports can break the C–C linkages without producing other intermediate C–C dimer byproducts. The results show high hydrocracking and isomerization activities of the catalyst supported on USY and mixed supports. This is consistent with XRD, Raman, XPS and TEM measurements, where enhanced dispersion of the active phase was observed. However, hydrogenation activity on the USY support is reduced to a significant degree which results in a large amount of benzene compared to NiMoS–Al2O3 that produces mostly cyclohexane. In addition, elemental analysis revealed that carbon deposition is higher on the USY-based catalyst compared to the alumina-based catalyst owing to its higher acidity. However, the potential for superior C–C bond cleavage on NiMoS-USY opens the possibility to valorize technical lignin in biorefinery processes.

Thermochemical processing of lignin ends up with a major problem which is the high yield of char remained from lignin conversion, causing low yields of desired products. The ReS2/Al2O3 catalyst, used in this work, exhibited a high char-suppressing potential and high hydrodeoxygenation efficiency in the reductive liquefaction of kraft lignin. Compared to NiMo/Al2O3, as a conventional sulfide catalyst, ReS2/Al2O3 showed significantly better catalytic performance with 72.4 % lower char yield, due to its high efficiency in stabilizing the lignin-depolymerized fragments. The remarkable catalytic performance of ReS2/Al2O3 is attributed to its high oxophilicity, the metal-like behavior of rhenium sulfide and sufficient acidity. The effects of reaction temperature and different catalyst supports (Al2O3, ZrO2 and desilicated HY zeolite) were also studied. In an alkali (NaOH)-assisted depolymerization of lignin, it was revealed that ReS2/Al2O3-to-NaOH (stabilization-to-depolymerization) ratio plays a crucial role in determining the reaction pathway toward either solid char residues or liquid monomeric products.

The catalytic properties of palladium supported on H-beta and H-SSZ-13 zeolite with different silica to alumina ratio (SAR) have been evaluated for complete CH 4 oxidation in the presence and absence of water vapor and together with SO 2 . Different SAR was successfully obtained by dealumination of the zeolites in an acidic solution at elevated temperature. Flow reactor experiments showed that the SAR of the zeolite support greatly impacts the catalytic activity, especially in the presence of water vapor. Pd supported on a highly siliceous beta zeolite expressed high and stable CH 4 conversion in the presence of water vapor, whereas the activity for Pd supported on zeolites with low SAR or Al 2 O 3 decreased over time due to accumulative water deactivation. Hence, an increased SAR of the zeolite support clearly correlates to a lower degree of water deactivation. We suggest that this is a result of the high hydrophobicity of the siliceous zeolites. The results also imply that the catalytic activity in the presence of water vapor is influenced more by the SAR than the type of the zeolite framework. The CH 4 oxidation activity was also enhanced with increasing SAR under dry conditions. This was addressed to the formation of more Pd particles in relation to ion-exchanged Pd 2+ species and changes of the oxidation-reduction behavior of the Pd. The high number of acidic sites in zeolites with low SAR provided higher dispersion of Pd particles and formation of more monoatomic Pd 2+ species, whereas almost exclusively Pd particles of larger sizes were formed on the highly siliceous zeolites. The monoatomic Pd 2+ species, mostly formed on zeolites with low SAR, were oxidized and reduced at significantly higher temperatures than Pd in the particle form. Hence, complete reduction or oxidation of the Pd supported on highly siliceous zeolites can be achieved at lower temperatures. Moreover, compared to Pd/Al 2 O 3 , the zeolite supported Pd expressed higher sensitivity to SO 2 . However, the major part of the catalytic activity could be regenerated more easily using siliceous zeolites as supports compared to Al 2 O 3 . We suggest that this is an effect of the lower SO 2 adsorption on the zeolite supports than on the Al 2 O 3 support, which results in the formation of more PdSO x species upon SO 2 exposure. On the other hand, the low SO 2 adsorption on the zeolites also results in less spillover of sulfur species from the support to the active PdO, which explains the facilitated regeneration.

Recently copper ion-exchanged LTA zeolites were proved to be robust for NH3-SCR reaction. In this study, Cu/LTA catalysts with Si/Al = 15 and Cu/Al = 0.4 were synthesized via incipient wetness impregnation (IWI) method, following degreening/hydrothermal aging at different temperatures (750, 800, 850, 900 °C), and used to catalyze standard SCR, fast SCR and NH3/NO oxidation reactions. Catalysts were characterized with surface area/pore volume, powder X-Ray diffraction (XRD), nuclear magnetic resonance (NMR), H2-temperature programmed reduction (H2-TPR) and in situ Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS). Through the BET surface areas, XRD and NMR results, it can be found that the framework structure stability of Cu/LTA catalysts during hydrothermal aging was outstanding, even after harsh aging at 900 °C. Moreover, various Cu species, including Z-Cu2+, Z-[Cu(OH)]+ and CuOx clusters, were quantified for Cu/LTA catalysts hydrothermally aged under various temperatures with H2-TPR and in situ DRIFTS. An imperative finding in this study is the exceptional hydrothermal stability of [Cu(OH)]+ and the gradual conversions of both Cu2+ and CuOx clusters to [Cu(OH)]+ with increasing aging temperature. It is worth noting that this phenomenon is exactly the opposite of Cu/SSZ-13. As it is known from the literature (Song et al., 2017), the formation of CuOx not only decreases the selectivity of NOx conversion, but also can cause deterioration of zeolite structure, since the ion-exchanged copper stabilizes the zeolite. This may also explain why the hydrothermal stability of Cu/LTA samples is outstanding.

The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.

The effects of phosphorous and zinc on the performance of Pt/Ba/Al2O3 catalysts were investigated through wet impregnation of ammonium phosphate and zinc acetate aqueous solutions. Six different sample combinations were studied; 1 wt-% P, 1 wt-% Zn, 1 wt-% P with 1 wt-% Zn, 2 wt-% P, 2 wt-% Zn, 2 wt-% P with 2 wt-% Zn. NOx storage and reduction (NSR) activity and NO2 temperature programmed desorption (TPD) profiles were measured before and after impregnation of P and Zn. Samples containing P performed significantly worse than samples only containing Zn in both NSR activity and TPD measurements. The increased NOx slip during lean phase in activity measurements for P-poisoned samples is mainly related to an increased slip of NO2. This was found for both NO and NO2 in the gas feed during lean phase and suggests that it is mainly the storage component that is poisoned and not the noble metal. Furthermore, the combination (1 wt-% P and 1 wt-% Zn) proved to result in slightly worse performance than only 1 wt-% P, however this was not the case for samples containing 2 wt-%, where the addition of zinc reduced the negative effect of phosphorous. Measurements from NO2-TPD experiments showed that NOx release at low temperature was not affected by the addition of P, while desorption in the temperature range 425–475 °C was significantly reduced. It can therefore be concluded that the poisoning mainly is related to barium NOx storage sites and not to alumina sites. Moreover, X-ray diffraction measurements indicate that some of the barium species are affected by phosphorous. Images from scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX) mapping were in line with the results seen in both the activity tests and NO2-TPD experiments. Phosphorous was concentrated at the same position as barium in the observed images, whereas zinc was more evenly distributed over the surface. For the sample with both 2 wt-% P and 2 wt-% Zn, X-ray photoelectron spectroscopy measurements indicate that Zn and P have a low interaction and this suggests that most of the zinc and phosphorous are separated. However, STEM-EDX showed agglomerates of some zinc and phosphorous, which could be zinc phosphates. This is a plausible explanation of the decreased deactivation observed after introducing 2 wt-% Zn compared to the sample only containing 2 wt-% P.

In this study, we have reproduced a DOC-upstream-of-SCR configuration in the laboratory, with washcoated model Pt/Al2O3, Pd-Pt/Al2O3and Pd/Al2O3catalysts, as well as a commercial DOC, upstream of an alumina-washcoated core. We studied vapour-phase noble metal poisoning of the alumina core, as noble metal from the model DOC catalysts deposited on the downstream alumina core. The mobile species were predominantly volatile platinum oxides, whereas Pd volatilised in such small traces that it was close or below detection limit by Inductively Coupled Plasma – Sector Field Mass Spectrometry (ICP-SFMS), even when the model DOC had only Pd as active species. Even after volatilisation at temperatures as low as 550 °C, the deposited trace amounts of noble metal were highly active for ammonia oxidation. The deposited platinum appears to be finely dispersed, but when subjected to reaction conditions, it likely undergoes sintering, causing a further increase of the ammonia oxidation ability, which will affect the extent of poisoning in a real exhaust aftertreament system. We investigated the dependence of volatilization on temperature, and, as predicted, found it to be exponential. Exposure to increasing temperatures causes different degrees of sintering of the noble metal particles and we found qualitative evidence that sintering decreases the amount of volatilisation. Adding a small amount of Pd (Pd:Pt = 0.5:1) to the catalyst had no effect on volatilisation. However, larger Pd concentrations (Pd:Pt = 1:1 or 2:1) decrease volatilisation. The results for the model DOCs were confirmed by volatilisation from a commercial DOC, where in fact the capturing core exhibited even higher ammonia oxidation ability compared to those downstream of the model DOCs, after evaporation at 700 °C.

© 2018 Elsevier B.V. SCR coated filters have recently been introduced. These combine soot capture through diesel particulate filters (DPF) and NOxremoval through ammonia selective catalytic reduction (NH3SCR). This study investigates the impact of soot on the reactions being important for the SCR process on Cu/SSZ-13, as well as the impact of different gases on soot oxidation using flow reactor measurements. A limited impact of soot on the SCR reactions and a clear inhibiting effect of NH3on soot oxidation, is found. Ammonia TPD, in-situ DRIFT, and XPS experiments are used to investigate the interaction between soot and ammonia. Amines/amides are found on the soot when exposed to NH3and H2O. The results are used to develop a kinetic model for soot oxidation over DPF and a soot coated Cu/SSZ-13 catalyst using diesel soot generated from an engine bench. It is found that it is important to incorporate a random pore model and a free edge site mechanism through which ammonia block these free edge carbons. The model describes well soot oxidation in the presence of NH3over DPF, as well as soot oxidation and the SCR mechanism over soot loaded Cu/SSZ-13.

Automotive catalysts are continuously exposed to different poisons and to high temperature, which result in hydrothermal aging. Phosphorus is one of the poisons that the catalyst could be exposed to and it originates from the lubricant oil. In this work, we study the influence of phosphorus poisoning on the catalytic performance and the deactivation mechanism in the hydrothermal aging of Cu-SSZ-13 catalysts. Phosphorus poisoning was performed by impregnating the Cu-SSZ-13 catalysts with (NH4)2HPO4solution using the incipient wetness impregnation method, which allowed us to precisely control the amount of phosphorus poison on the catalyst. XPS results show that phosphorus oxide (P2O5), metaphosphate (PO3–) and phosphate (PO43–) are formed on the surface of phosphorus-poisoned catalysts, and metaphosphate is the main compound among those species. Phosphorus tends to interact with copper sites and strongly impacts the electronic and reduction property of Cu, as disclosed using EDX mapping, UV–vis DRS and H2-TPR. Results of catalytic activities show that phosphorus poisoning is more severe on ammonia and NO oxidation reactions than on standard ammonia-SCR. This is possibly due to the formation of copper phosphates in the large cages, as revealed using H2-TPR, which reduces the oxidation capacity. Moreover, results of XRD and27Al and31P solid-state NMR reveal that phosphorus not only interacts with copper by forming a P–O–Cu linkage but also partially inserts into the zeolite framework by forming a localized AlPO4phase. Both non-poisoned and P-poisoned catalysts lose their active sites and chabazite structures due to dealumination after successively aging in hydrothermal conditions (8 vol.% O2, 5 vol.% H2O in Ar) at different temperatures (800, 850, and 900 °C), which results in a large decrease in SCR performance. Specifically, the P-poisoned catalysts degrade faster than the non-poisoned catalysts. Results demonstrate that phosphorus induces the extensive formation of AlPO4that accelerates the dealumination during hydrothermal aging. This work provides new insight into understanding the deactivation mechanism in Cu-SSZ-13 from the perspectives of phosphorus-poisoning and hydrothermal aging, and it clearly shows that it is crucial to examine poisoning and hydrothermal aging simultaneously.

The low temperature hydrothermal stability of Cu/SAPO-34 catalysts for the NH3-SCR reaction, prepared by three different structure directing agents (SDAs), i.e., morpholine (MO), triethylamine (TEA), and tetraethylammonium hydroxide (TEAOH), was investigated by exposing them to various amounts of water vapor. XRD and BET studies indicate that there was no sign of Cu/SAPO-34 catalyst's chabazite (CHA) structural collapse due to water vapor exposure up to 55 h regardless of SDA choice. However, a multinuclear solid-state magic angle spinning (SS-MAS) NMR study of Cu/SAPO-34(MO, TEA, TEAOH) suggests that the water vapor exposure had significantly altered the coordination environment of Al, P, and Si, the extent of which depends on the choice of SDA along with water vapor exposure time. NO-DRIFTS and H2-TPR studies suggest different mobility for Cu ions between the 6MR and 8MR of the CHA structure in Cu/SAPO-34(MO, TEA, TEAOH) as the result of water vapor exposure and during the NH3-SCR reaction. The mechanisms for low temperature deactivation of Cu/SAPO-34 were proposed as follows: 1) irreversible Si condensation in the support and 2) Cu migration to less accessible sites and/or formation of CuOx clusters depending on Cu mobility.

In this study, inhibition of tall oil fatty acid hydrodeoxygenation (HDO) activity due to addition of rosin acid over sulfided NiMo/Al2O3 was investigated. Oleic acid and abietic acid were used as model compounds for fatty acid and rosin acid respectively in tall oil. After completion of each HDO experiment, the NiMo catalysts were recovered and used again under the same conditions. The results showed that the oleic acid HDO activity of sulfided catalysts was inhibited by addition of abietic acid due to competitive adsorption and increased coke deposition. The rate of carbon deposition on the catalysts increased when abietic acid was added to oleic acid feed. Moreover, the coke was in a more advanced form with higher stability for the catalysts exposed to both oleic acid and abietic acid. Furthermore, a clear correlation between the rate of coke formation and concentration of abietic acid was observed.

In the combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept, the SCR catalyst can be exposed to rich conditions during deSOx of the LNT. Aging of Cu/SSZ-13 SCR catalysts, deposited on a cordierite monolith, was therefore studied in rich, lean and cycling lean/rich operations at 800 °C (lean condition: 500 ppm NO, 8% O2, 10% H2O and 10% CO2; rich condition: 500 ppm NO, 1% H2, 10% H2O and 10% CO2). The structure of the catalyst was investigated by X-ray diffraction (XRD), surface area measurements and scanning transmission electron microscopy (STEM). In general, aging decreased the SCR activity and NH3 oxidation. However, rich conditions showed a very rapid and intense deactivation, while lean aging led to only a small low-temperature activity decrease. The XRD results showed no sign of structure collapse, but the number of active sites, as titrated by NH3 temperature-programed desorption (NH3-TPD) and in situ DRIFTS, revealed an important loss of acid sites. NH3 storage was significantly more depleted after rich aging than after lean aging. The Lewis sites, corresponding to exchange Cu2+, were preserved to some extent in lean conditions. Lean aging also decreased the enthalpy of NH3 adsorption from −158 kJ mol−1 to −136 kJ mol−1. Moreover, a comparison of aging in lean-rich cycling conditions with aging only in rich conditions revealed that adding lean events did not hinder or reverse the deactivation, and it was mainly the time in rich conditions that determined the extent of the deactivation. The STEM images coupled with elemental analysis revealed the formation of large Cu particles during rich aging. Conversely, Cu remained well dispersed after lean aging. These results suggest that the copper migration and agglomeration in large extra-framework particles, accelerated by the action of hydrogen, caused the observed severe deactivation.

Al2O3/ZrO2/TiO2 (AZT) ternary mixed oxides functionalized with Pt and BaO were synthesized in powder and monolithic forms and were utilized in NOx Storage Reduction/Lean NOx Trap (NSR/LNT) catalysis as novel catalytic materials. Adsorption of NOx and SOx species and their interactions with the catalyst surfaces were systematically investigated via in-situ FTIR technique revealing different NOx coordination geometries governed by the presence and the loading of BaO in the powder catalyst formulation. While BaO-free Pt/AZT stored NOx as surface nitrates, BaO incorporation also led to the formation of bulk-like ionic nitrate species. NOx adsorption results obtained from the current Temperature Programmed Desorption (TPD) data indicated that NOx Storage Capacity (NSC) was enhanced due to BaO incorporation into the powder catalyst and NSC was found to increase in the following order: Pt/AZT < Pt/8BaO/AZT < Pt/20BaO/Al2O3 < Pt/20BaO/AZT. Increase in the NSC with increasing BaO loading was found to be at the expense of the formation of bulk-like sulfates after SOx exposures. These bulk-like sulfates were observed to require higher temperatures for complete regeneration with H-2(g). Catalytic activity results at 473 K and 573 K obtained via flow reactor tests with monolithic catalysts suggested that Pt/AZT and Pt/8BaO/AZT catalysts with stronger surface acidity also revealed higher resistance against sulfur poisoning and superior SOx regeneration in spite of their relatively lower NSC. Monolithic Pt/20BaO/AZT catalyst revealed superior NSC with respect to the conventional Pt/20BaO/Al2O3 benchmark catalyst at 573 K after sulfur regeneration. On the other hand, this trend was reversed at high-temperatures (i.e. 673 K). Preliminary results were presented demonstrating the enhancement of the high-temperature NSC of AZT-based materials by exploiting multiple NOx-storage components where BaO functioned as the low/mid-temperature NOx-storage domain and K2O served as the high-temperature NOx storage domain. Enhancement in the high-temperature NOx-storage in the BaO-K2O multiple storage domain systems was attributed to the formation of additional thermally stable bulk-like nitrates upon K2O incorporation.

Hydrocarbon traps can be used to bridge the temperature gap from the cold start of a vehicle until the exhaust after-treatment catalyst has reached its operating temperature. In this work, we investigate the effect of zeolite structure (ZSM-5, BEA, SSZ-13) and the effect of La addition to H-BEA and H-ZSM-5 on the hydrocarbon storage capacity by temperature-programmed desorption and DRIFT spectroscopy. The results show that the presence of La has a significant effect on the adsorption characteristics of toluene on the BEA-supported La materials. A low loading of La onto zeolite BEA (2% La-BEA) improves not only the toluene adsorption capacity but also the retention of toluene. However, a higher loading of La results in a decrease in the adsorbed amount of toluene, which likely is due to partial blocking of the pore of the support. High loadings of La in BEA result in a contraction of the unit cell of the zeolite as evidenced by XRD. A synergetic effect of having simultaneously different types of hydrocarbons (toluene, propene, and propane) in the feed is found for samples containing ZSM-5, where the desorption temperature of propane increases, and the quantity that desorbed increases by a factor of four. This is found to be due to the interaction between toluene and propane inside the structure of the zeolite.

The inhibiting effect of SO2 on the catalytic activity of the monometallic Pt/Al2O3 and Pd/Al2O3, as well as on bimetallic PtPd/Al2O3 catalyst for the complete oxidation of methane under lean conditions has been studied. Flow reactor experiments, in-situ DRIFT spectroscopy and characterization with XPS, STEM-EDX were performed. It was found that the addition of Pt to the Pd/Al2O3 resulted in a catalyst that was more robust towards sulfur poisoning. XPS results revealed residual sulfates on catalyst surface after regeneration. This was confirmed with EDX analysis, which demonstrated that sulfur was accumulated in noble metal particles and especially in the region of the particle rich in Pt. Although the catalyst has been deactivated in the presence of both SO2 and H2O, an additional presence of NO in the gas mixture of reactants resulted in an increased lifetime of the sample under reaction conditions. This NO effect strongly depends on the temperature of experiments and is most intense at a temperature close to 550 degrees C A postponed inhibition caused by the addition of NO may be explained by the DRIFTS results, which demonstrated that the presence of NO lowers the sulfate formation and mostly surface sulfites are observed that increase the lifetime of the catalyst during SO2 exposure.

The effect on complete methane (CH4) oxidation activity by an addition of up to 2 wt.% barium (Ba) promoter to alumina supported palladium (Pd/Al2O3, 2 wt.% Pd) was investigated. The catalyst samples were characterized with various techniques; temperature programmed oxidation (TPO), temperature programmed reduction with CH4 (CH4-TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). Flow reactor was used to investigate the CH4 oxidation activity in the presence and in the absence of water vapor and also to evaluate the possibility to regenerate the catalytic activity after water vapor exposure. The results from the TPO and the CH4-TPR experiments together with the XPS analysis gave no evidences for electronic promotion of the catalytic activity by addition of 0.5–2 wt.% Ba. This goes in line with the CH4 conversion in dry gas condition, which was not affected by the Ba addition. However, we observed that an addition of Ba to Pd/Al2O3 enhances the CH4 oxidation activity in the presence of water vapor, hence mitigates the effect of water deactivation. Interestingly, it was also seen that after water vapor exposure, the CH4 oxidation activity could be regenerated to greater extent for the Ba promoted samples, particularly for the regeneration temperatures of 500–600 °C. Our results clearly show that the support influences the water deactivation of the active palladium sites and that the addition of barium is beneficial for the catalyst regeneration.

The mitigation of cold-start emissions involves the development of passive NOx adsorbers (PNA) systems that store NOx at low temperature, being designed to release the trapped NOx at higher temperatures, where downstream NOx reduction catalysts are efficient. Pd-based zeolites (BEA, SSZ-13) with different SAR (Si-to-Al ratio) were used for PNA investigation, and Pd/Ce/Al2O3 catalyst was used as a reference for comparison. In this study, NOx adsorption is investigated at low temperature (80 °C) and it is released during a temperature ramp (to 400 °C) under various gas feed composition. Moreover, detailed characterization was performed using BET, XRD, XPS, TPO, STEM and ICP-SFMS and the stored NO species was studied using in-situ DRIFTS. The addition of CO to the storage mixture resulted in that for Pd/zeolites with low and medium SAR the binding energy for NO was increased. In addition, NO was stored in larger quantities, especially for the Pd/SSZ-13 samples. However, for Pd/BEA (SAR = 300) no such stable NO species was formed and for Pd/Ce/Al2O3 the CO addition was even negative. Moreover, in-situ NO DRIFTS showed that there was large amount of nitrosyls on ionic palladium for the Pd/zeolites with low and medium SAR, indicating that a significant fraction of the palladium was in ion-exchanged positions, while this peak was small for the Pd/BEA (SAR = 300) and non-existing for Pd/Ce/Al2O3. Thus, CO addition is beneficial for Pd species that are in ion-exchanged positions, but this is not the case for Pd particles and this can explain the observations that CO is only beneficial for Pd/zeolites with low and medium SAR. Moreover, experiments with similar SAR [Pd/BEA (SAR = 25) and Pd/SSZ-13 (SAR = 24)], showed that there is larger stability of the stored NOx in the small pore Pd/SSZ-13.

The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) over molybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 °C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Nipromoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C18 hydrocarbons)increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C18 hydrocarbons) products and an increase in yield of decarbonated products (C17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.

Commercial lean NOx trap (LNT) catalysts were aged and characterized to elucidate the effect of aging on their performances and examine the deactivation of a rapid-aged catalyst toward an improved correlation with respect to a vehicle-aged catalyst. Detailed characterization studies were carried out on the flow reactor with small cylindrical cores extracted from the commercial LNT catalysts. Physicochemical characterization techniques were also implemented. The catalyst evaluation revealed that aging resulted in a significant deterioration of NOx storage and reduction functions as a consequence of precious metal sintering, loss of surface area of the NOx storage and support materials, phase transitions of the adsorber compounds, and large accumulation of poison species. Among the aged samples examined, the middle (lengthwise) vehicle-aged sample showed the highest NOx conversion, while the oven-aged catalyst was the most active of the aged samples for water gas shift reaction and oxygen storage.

The impact of hydrothermal ageing on the copper sites, crystalline order and critical reactions of a Cu/SSZ-13 was studied. The investigated catalyst had a low Si/Al ratio of 3.7 and was underexchanged at 65%. We propose that this catalyst had nearly saturated ion exchange positions in the 6-membered ring units (6MR) with copper ions, but still contained a significant amount of protonic sites in the large cages (8MR units). Investigation of a broad range of ageing temperatures (550–850 °C) allowed us to observe that no significant number of copper ions moved from the large cages into the 6MR units. Nevertheless, the Cu ions experienced a significant increase in reducibility above ageing temperatures of 700 °C. However, these changes appeared not to have a large impact on catalyst activity, which was more significantly correlated with long and short-range loss of crystallinity. Thus dealumination occurred at all temperatures above 550 °C and was correlated with significantly reduced ammonia storage capacity and ammonia oxidation ability. Low-temperature SCR activity was not much affected below 850 °C, but decreased significantly when total collapse of the zeolite framework occurred at this temperature. At ageing temperatures above 750 °C, formation of oxidic copper species was observed and correlated partially with increased high-temperature ammonia oxidation capacity, though it is possible that oxidation in parallel occurs on non-oxidic sites in ion-exchange positions. On the other hand, low-temperature ammonia oxidation was shown to occur on ionic copper sites (likely in the 6MR units) and decrease with increasing ageing temperature. We further found some evidence that low-temperature formation of N 2 O during standard SCR may occur on different sites or via different mechanisms.

In this study, we have investigated the effect of changing the gas feed composition on soot oxidation over diesel particulate filter (DPF) and SCR-coated filter during temperature ramp experiments from 200 to 750 °C. For DPF, the increasing NO2/NOx ratio promoted soot oxidation across a fairly low temperature range (200–500 °C) and, in addition, soot oxidation was enhanced by water. Interestingly, the presence of NH3 in the gas feed inhibited the soot oxidation under various feed compositions for the DPF. Moreover, ammonia oxidation was also observed over the filter and based on these experiments together with experiments without soot, we conclude that ammonia oxidation is actually occurring on soot particles and that the interaction of the ammonia with the soot is inhibiting soot oxidation. Further, fast and NO2 SCR reactions were found to occur on soot particles, while no reactions with NO under standard SCR conditions was observed. Thus, the NH3 and NO2 molecules are interacting with the soot. When comparing the DPF and SCR-filter we found that the SCR material enhanced the soot oxidation under standard and fast SCR conditions, because of the fact that soot oxidation was inhibited by NH3 and would be rapidly consumed under SCR reactions with the Cu-zeolite in the SCR-filter. Furthermore, during fast SCR conditions, because NO2 is consumed during fast SCR reaction for the SCR-filter, the opposite results were found where soot oxidation occurred at lower temperature for the DPF.

Cu/SAPO-34 and Cu/SSZ-13 having chabazite structure (CHA) have attracted significant attention because of their high activity and N2 selectivity during SCR reaction as well as superior resistance to hydrocarbon poisoning. Cu/SAPO-34 has shown better hydrothermal durability than Cu/SSZ-13 at high temperature. However, we have observed earlier that Cu/SAPO-34 prepared using morpholine as a structure directing agent (SDA) deteriorated under water exposure at low temperature, where the NOx conversion activity decreased from 87% to 6% after 9 h of low temperature exposure. In this study, Cu/SAPO-34 catalysts prepared using three different SDAs, i.e., morpholine (MO), triethylamine (TEA), and tetraethylammonium hydroxide (TEAOH), were prepared by the incipient wetness impregnation (IWI) method. A commercially purchased SAPO-34 (SAPO-34(ACS)) was also used for comparison purposes. After low temperature water deactivation, Cu/SAPO-34(TEA) and (TEAOH) mostly recovered their activities while Cu/SAPO-34(MO) and (ACS) only regained part of their activities after regeneration tests under a series of experimental conditions for the NH3-SCR reaction. Solid-state MAS NMR was employed to study the impact of SDAs on the coordination of Al, P, and Si in the SAPO-34 supports and Cu/SAPO-34 catalysts. CO-DRIFTS, NO-DRIFTS, and H2-TPR employed in this study collectively propose the presence of two different Cu locations in Cu/SAPO-34(MO, TEA, TEAOH, and ACS). It is suggested that the concentrations of Cu in two distinct locations within Cu/SAPO-34 catalysts characterized by CO-DRIFTS, NO-DRIFTS, and H2-TPR studies are significantly influenced by the choice of SDA, which will be important for understanding the deactivation mechanism of Cu/SAPO-34 catalysts during low temperature NH3-SCR reaction.

Methane catalytic combustion was studied on Pd/Al2O3 catalysts modified with alkali and alkaline earth metals (K, Na, Ca and Ba). Temperature-programmed reactions were performed in flow reactor on washcoated monolithic samples. CO chemisorption was carried out and BET surface area was measured in order to characterize the catalysts. Addition of alkaline metals was either beneficial or detrimental for methane oxidation, depending on the catalyst composition and pretreatment. High loading of alkaline modifiers and cooling in reaction mixture increased the light-off temperature of methane oxidation. However, promotion was achieved by doping with calcium after cooling in inert atmosphere. Furthermore, calcium doping was more beneficial in presence of NO, which inhibits the methane oxidation. Higher Pd loading enhanced CH4 oxidation, whereas the effect of calcium depends on Ca and Pd loading. Indeed, the promotion by calcium was more pronounced on catalysts with 5% Pd than with 2.5% Pd. On 2.5% Pd catalyst, high Ca loading was detrimental for CH4 oxidation. In contrary, on 5% Pd catalyst, even 1.51 wt% calcium (the highest loading used) induced promotion, which demonstrates a correlation between Ca: Pd ratio and promotion/inhibition effect. Samples with a mass ratio of 0.15 showed the best activity.

One-pot deoxygenation of kraft lignin to aromatics and hydrocarbons of fuel-range quality is a promising way to improve its added value. Since most of the commercially resourced kraft lignins are impure (Na, S, K, Ca, etc., present as impurities), the effect of these impurities on the deoxygenation activity of a catalyst is critical and was scrutinized in this study using a NiMoS/Al2O3 catalyst. The removal of impurities from the lignin indicated that they obstructed the depolymerization. In addition, they deposited on the catalyst during depolymerization, of which the major element was the alkali metal Na which existed in kraft lignin as Na2S and single-site ionic Na+. Conditional experiments have shown that at lower loadings of impurities on the catalyst, their promotor effect was prevalent, and at their higher loadings, a poisoning effect. The number of moles of impurities, their strength, and the synergism among the impurity elements on the catalyst were the major critical factors responsible for the catalyst’s deactivation. The promotor effects of deposited impurities on the catalyst, however, could counteract the negative effects of impurities on the depolymerization.

Catalytic hydrogenation of CO2 to methanol has gained considerable interest for its significant role in CO2 utilization using heterogeneous catalysts. This study is the first to propose a kinetic model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism for CO2 hydrogenation to methanol over a highly effective indium oxide (In2O3) catalyst. The work focuses on different reaction conditions mainly revolving around the variation of operating temperature, total reactor pressure, H2/CO2 molar feed ratio and weight hourly space velocity (WHSV) of the system. The experimental data were modeled using a competitive single-site kinetic model based on LHHW rate equations. A parameter optimization procedure was undertaken to determine the kinetic parameters of the developed rate equations. The model predicts that when the methanol synthesis reaction becomes equilibrium limited, the progress of the RWGS reaction forces the methanol yield to decrease due to the reversal of the methanol synthesis reaction. A mixture of CO2 and H2 has been used as the reactor feed in all the cases. Significantly w.r.t. the CO2 partial pressure, the reaction rate for methanol synthesis initially increased and then slightly decreased indicating a varying order. The single-site model accurately predicted the trends in the experimental data which would enable the development of reliable reactor and process designs.

This study focuses on the effect of gas composition during SO2 poisoning over Cu/SSZ-13 for NH3-SCR application and was performed by conducting SO2-TPD experiments in a variety of lean gas compositions. In addition, the poisoned monoliths were characterized in detail using ICP-SFMS, UV–vis and XPS. During SO2 poisoning under dry and lean conditions, two different sulfur species were found, which were assigned to weakly bound SO2 and copper sulfate like species. Moreover, a significantly larger amount of copper sulfates was present in humid environment. The presence of NH3 during the poisoning resulted in the formation of ammonium sulfate species which were decomposed at the same temperature independently if the poisoning with SO2 was conducted in ammonia oxidation conditions or under standard or fast SCR conditions. Moreover, if the temperature ramp was conducted with O2 and H2O compared to Ar alone, more stable sulfate species were formed. In addition, SO2 poisoning under standard SCR conditions resulted in mostly ammonium sulfate formation at 200 °C, whereas copper sulfates were predominant after poisoning at 400 °C. After hydrothermal aging at 800 °C, more reducible copper species were noticeable and UV–vis showed that copper oxides had been formed. Sulfur poisoning of the hydrothermally aged sample resulted in the additional formation of copper sulfates during poisoning at 200 °C, which was not the case for poisoning of the fresh catalyst. Thus, the copper oxide species enhanced the copper sulfate formation.

The influence of phosphorus on Cu-SSZ-13 NH3-SCR catalysts was investigated in order to reveal the deactivation behavior of Cu-SSZ-13 in the presence of phosphorus-containing poisons in the exhaust of diesel engines. The phosphorus-poisoning was simulated by treating the Cu-SSZ-13 catalysts with (NH4)(2)HPO4 aqueous solution using incipient wetness impregnation method. The focus of the study was the effect of phosphorous on the different reactions occurring on the SCR catalyst, including ammonia oxidation, NO oxidation and standard SCR using monolith catalysts. Moreover, characterization such as ICP-SFMS, N-2-physisorption, and NH3-TPD were employed for the evaluation of the physical and chemical properties of the P-impregnated catalysts. Physically blocking of pores and poisoning of acidic sites were observed on the P-impregnated catalysts. In addition, we observed that phosphorus severely suppressed ammonia oxidation and NO oxidation, while its impact on standard SCR reaction was nearly negligible below 300 degrees C. Interestingly, a promotive effect was found at higher temperatures, likely due to the severely inhibiting effect on NH3 oxidation caused by the formation of copper phosphates in the large cages (i.e. 8-membered rings) of Cu-SSZ-13.

The water inhibition of methane oxidation over a bimetallic Pt-Pd on CeO2–Al2O3 catalyst was investigated and the experimental data were used to develop a kinetic model, consisting of only three reaction steps. In the model, the water effect was assigned to the adsorption of H2O on surface sites, as well as to the formation and accumulation of surface hydroxyl groups. These two effects were accounted by the model, which could well describe the experimental data obtained under various conditions.

The adsorption of NO2 on Pt/BaO/gamma Al2O3 catalyst has been investigated by micro calorimetry at atmospheric pressure, NOx storage tests and temperature-programmed desorption (TPD). The heat of adsorption of NO2 (Delta H-ads(NO2)) was determined over a wide range of NOx coverages, as the catalyst was exposed to 500/900 ppm NO2 in the absence/presence of 5% CO2 in the range of 423-773 K. The temperature dependent changes of Delta H-ads(NO2) verified the presence of energetically different NOx storage sites with different binding strength. The Delta H-ads(NO2) was found to follow a linear correlation versus temperature, ranging for example from -134.5 to -178.8 kJ/mol for NOx storage over Pt/BaO/gamma Al2O3 at 423-673 K. Thus, at high temperature mostly strongly bound nitrates were formed, while at lower temperature more loosely bound species were also present. Interestingly, the heat of adsorption was higher when using higher NO2 concentration, indicating more bulk barium nitrate formation. This is consistent with the TPD data where a clear high temperature peak was visible after adsorption using 900 ppm NO2 at 423 and 473 K, which was not the case for 500 ppm NO2. Moreover, the micro-calorimetric data also provided evidence in support of the detrimental effect of CO2 on the NOx uptake process. The heat released during the NOx storage in 500 ppm NO2 + 5% CO2 was determined to be significantly reduced ca. -97.8 kJ mol(-1) at 423 K, but ca. -134.5 kJ mol(-1) without CO2. Furthermore, our results show that it is critical to measure heat of adsorption for surface compounds since they are significantly different compared to thermodynamic data for bulk materials.

The purpose of this study is to attribute NH3-TPD peaks observed over Cu/SSZ-13 catalysts to different catalytic sites. This is done by comparing a large number of copper loadings, especially below 40% ion exchange, to be able to see effects relevant to sites in both 6-membered and 8-membered rings. We found that intermediate (200–300 °C) and high (400–500 °C) temperature NH3-TPD peaks followed similar trends to the copper species in 6-membered and 8-membered rings respectively, as seen by H2-TPR and NO-DRIFTS. Thus we propose that these two TPD peaks represent ammonia stored on H and Cu sites in 6 and 8-membered rings, respectively. This assignment is further supported by the finding that the intermediate and high temperature NH3-TPD peaks of samples with different Si/Al ratios also follow the same trend. Moreover, we observe that the activation energy for ammonia oxidation is significantly lower for Cu in 6MR compared to Cu in 8MR rings.

Alumina supported NiMo catalysts were synthesized. The prepared NiMo catalysts were activated by DMDS in a sulfidation process and characterized. The sulfided NiMo catalysts were next used in hydrodeoxygenation (HDO) of oleic acid in a batch reactor. Afterward, the NiMo catalysts were recovered and used in another set of HDO reactions of oleic acid under the same conditions used in the previous HDO reactions. After the HDO experiments, the active phase and deposited coke on spent catalysts were characterized. The results indicated that higher concentrations of DMDS promoted the production of heptadecane (C17) but had no effect on the production of octadecane (C18). Moreover, the XPS results revealed the promotional effect of DMDS concentration on maintenance of the sulfidity of the catalysts. In addition, the results for the experiments with the second run catalyst revealed a clear deactivation due to increased coke depositions. Furthermore, after two repeated experiments with first run and second run cat...

Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NOx storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, and one reason for this could be limited NO oxidation. In addition, the oven-aged sample was found to be well correlated to the vehicle-aged catalyst. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance under real driving conditions and monitor the gradual deterioration of the vehicle-aged catalyst during the vehicle aging testing.

The individual influence, as well as the combined effect of H2O and NO on the activity of Pd/Al2O3, PtPd/Al2O3 and PtPd/CeAl2O3 catalysts in complete methane oxidation under lean conditions were investigated. Under temperature-programmed ramping experiments the activity was severely inhibited in the presence of 5 vol.% H2O in the reaction mixture. We propose that this is due to blocking by both water and hydroxyl species. Under the influence of NO without water in the gas flow, it was found that the methane oxidation activity was partly suppressed, due to blocking of active sites. Indeed TPD performed after ramping experiments showed NOx storage on the catalyst. Contrary to the negative effect of NO in the dry case, the promotional NO effect on the activity was observed when water was co-fed, comparing the case with only water presence. The promotional NO effect was confirmed with isothermal experiments, where e.g. the methane conversion decreased from initial 96% to 25% after 10 h of exposure in CH4-O-2-H2O mixture at 450 degrees C over the Pd/Al2O3 sample, while the decrease was only from 88% to 60% when catalyst was exposed to CH4-O-2-H2O-NO mixture. We propose that the reason is that the NO reacts with the hydroxyl species to form HNO2, which reduces the water deactivation effect.

In this study, the effect of oxygen concentration and the presence of water on methane oxidation were examined over a Pd/Al2O3 catalyst. The physicochemical properties of the catalyst were investigated in detail using BET, XRD, STEM, O2-TPO and CH4-TPR. Ramping experiments from 150 to 700 °C were conducted using rich, stoichiometric and lean gas mixtures in the absence and presence of water. It was found that increasing the oxygen concentration in a dry atmosphere resulted in higher methane oxidation activity, which can be connected to the facilitation of palladium oxide formation. The TPO data showed that only minor amounts of PdO up to 700 °C were decomposed; however, in the stoichiometric and rich reaction mixture, PdO was still decomposed because of the oxygen limitation. This fact resulted in a “negative activation” during cooling, with increased activity because of palladium re-oxidation. Moreover, methane steam reforming and water gas shift reactions were important reactions under rich conditions over the metallic palladium sites. A significant inhibiting effect of water on the Pd-catalyst with loss of methane activity was found. Interestingly, the inhibition effect was much greater using high oxygen concentration in the gas mixture (500 ppm CH4, 8% O2, 5% H2O) than that at lower oxygen levels (800–1200 ppm) and we propose that the hydroxyl species formation, which blocks the active sites, are facilitated by a large oxygen excess. In addition, the re-oxidation of palladium occurring during the cooling ramp in dry feed using rich and stoichiometric gas mixtures was also significantly suppressed in the presence of a large amount of water. Thus, water impedes the oxidation of palladium, which significantly deactivates the Pd catalyst.

The selective oxidation of NH3 to N-2 on bi-functional mixed and dual-layer Cu-SSZ-13 and Pt/Al2O3 washcoated monolith catalysts is investigated under several reaction conditions to probe the effects of the added mass transfer barrier, in terms of the SCR loading (layer thickness), on the activity and selectivity of the catalyst. The combination of Cu-SSZ-13, itself shown to have high activity in reducing NOx, to N-2 with NH3, and Pt/Al2O3 is effective in converting the NOx produced by the very active but poorly selective precious metal catalyst. The data reveal a trade-off between NH3 conversion and N-2 selectivity due to the mass transport barrier afforded by the added Cu-SSZ-13 top-layer: NH3 conversion decreases while N-2 selectivity increases as Cu-SSZ-13 loading is increased. In the presence of feed NOx the NOx conversion of the dual-layer catalyst increases with an increase in the Cu-SSZ-13 washcoat loading. In the absence of feed NOx the dual-layer catalyst has a high selectivity to N-2 due to the selective reaction in the Cu-SSZ-13 layer between NH3 from the bulk and counter-diffusing NOx formed in the underlying Pt/Al2O3. For the same catalyst loadings, the mixed washcoat catalyst gives a higher NH3 conversion at high space velocity than the dual-layer catalyst. This is attributed to NH3 conversion on Pt/Al2O3 sites not impeded by a SCR catalyst top-layer. In the presence of feed NOx the dual-layer catalyst shows a high NOx to N-2 conversion as a result of the high SCR activity of the Cu-SSZ-13 top-layer. The mixed catalyst is more selective to NOx because the Pt catalyst in proximity to the SCR catalyst leads to the oxidation of NH3 back to NOx. Finally, we demonstrate that a hybrid catalyst having dual-layer and mixed catalyst attributes exhibits good performance by exploiting the beneficial effects of both catalyst types. (C) 2016 Elsevier B.V. All rights reserved.

In this study, we have developed a multi-site kinetic model that describes the sulfur poisoning and gradual sulfur removal over Cu/SSZ-13 used for NH3-SCR. Sulfur poisoning was conducted under SCR conditions and thereafter, repeated SCR experiments were conducted to examine the effect of such poisoning and the subsequent gradual removal of sulfur. In addition, the effect of sulfur poisoning was examined on NH3 TPD and ammonia oxidation experiments. The following sites were used in the kinetic model: copper in the six-membered rings as described by S1Cu, copper in the larger cages with S2 and S3 as a site where physisorbed ammonia can attach. Further, ammonia was also adsorbed on the Bronsted sites, represented by S1Bron in the model, but in order not to further complicate the model, small amounts of ammonia storage on Bronsted sites were also lumped into S2. In the model, SO2 was adsorbed on the sites containing copper, which are S1Cu and S2. It should be noted that S1Cu and S2 represents hydrated copper sites. Interestingly, we observed experimentally that ammonia storage was larger after sulfur poisoning compared to before, which is why we added ammonia storage and desorption to the S1Cu-SO2 and S2-SO2 sites. However, ammonia was already adsorbing on the copper site; thus, these steps did not result in increased storage. Consequently, reaction steps were added where additional ammonia was adsorbed to form S1Cu-SO2-(NH3)2 and S2-SO2-(NH3)2 species, which could be interpreted as precursors to ammonium sulfates. Another aspect that must be addressed in the model is the observation in the literature that SO2 is more easily desorbed in SO2+NH3+O2 TPD than SO2+O2 TPD. Reversible reaction steps were therefore added whereby the S1Cu-SO2-NH3 and S2-SO2-NH3 species were decomposed to form SO2. A final reaction step was incorporated into the model to describe the SCR reaction with ammonia attached to the sulfur sites. The developed model could well describe the sulfur poisoning and gradual regeneration during repeated SCR experiments. In addition, the model well described the NH3 TPD and NH3 oxidation before and after sulfur poisoning.

A deactivation study of Cu-SSZ-13 has been conducted using SO2 exposure under SCR conditions and examining its effect on different reactions involving NH3-SCR. Several reactions, including NH3 storage/TPD, NO/NH3 oxidation, standard SCR, fast SCR and SCR with 75% NO2, as well as NH3–NO2 storage/TPD, were investigated at a temperature range of 100–400 °C after exposing the catalyst to 30 ppm SO2 under SCR conditions at 300 °C for 90 min. The catalyst was characterized using XRD, BET, ICP-SFMS and H2-TPR. The BET surface area and pore volume decreased after the sulfur treatment presumably due to blocking by sulfur and/or ammonium–sulfur species. It was found that sulfur was not uniformly deposited along the monolith channel. The deposition occurred from the inlet towards the outlet, as evident from ICP-SFMS measurements. Part of the sulfur was removed after an SCR experiment up to 400 °C. However, this removal was observed only in the inlet half of the sample and not in the outlet. Ammonia TPD experiments revealed that the sulfur poisoning resulted in additional sites that were capable of adsorbing ammonia, resulting in increased ammonia storage. Moreover, standard SCR was significantly deactivated by SO2 poisoning under SCR conditions. Due to the site-blocking effect of the ammonium–sulfur species, fewer copper sites are likely available for the redox SCR cycle. Furthermore, the effect of sulfur poisoning on NH3 oxidation and NO2-SCR as well as N2O production in various SCR reactions were observed. Finally, it was found that the conditions for the sulfur poisoning were critical in which SO2 deactivation under SCR conditions (NH3 + NO + O2 + H2O) was more severe compared to SO2 poisoning in O2 + H2O alone.

The current commercially-available technique for NOx reduction for diesel engines is the selective catalytic reduction (SCR) of NOx with NH3 over Cu zeolites. One of the problems of this technique is their limited ability to convert NOx at diesel particulate filter (DPF) regeneration temperatures. In addition, during regeneration of the DPF there is a risk of thermally deactivating the SCR catalyst. Thus, the aim of the current work was the development of a catalytic system that can reduce NOx both at low as well as high temperature and in addition is stable at high temperature. In order to reach this goal, a Fe/SAPO-34 with chabazite (CHA) structure was combined in a system with a commercial Cu/CHA catalyst. Earlier studies have shown that it is difficult to ion-exchange Fe into CHA structures due to steric hindrance, and we have therefore used a novel synthesis procedure which incorporated iron directly into the zeolite structure. Fe/SAPO-34 with three different Fe-loadings (0.27; 0.47 and 1.03 wt.% Fe) were synthesized and the catalysts were characterized using inductively coupled plasma atomic spectroscopy (ICP-AES), N-2 adsorption-desorption isotherms, BET area measurements and X-ray diffraction (XRD). The chemical composition, porous and crystalline structure of the parent SAPO-34 sample were found to be only slightly affected by addition of small amounts of Fe in the framework zeolite structure. However, more visible changes in the crystallinity were observed in the Fe/SAPO-34 catalysts with higher Fe content, which were attributed to the unit cell size expansion provoked by integration of higher amounts of Fe into the zeolite SAPO-34 framework. The Fe/SAPO-34 with the lowest Fe-loading (0.27 wt.%) was found to be the best catalyst when considering activity as well as high temperature stability. The synthesized Fe/SAPO-34 catalyst demonstrated a significantly improved NOx reduction performance at high temperatures (600-750 degrees C) when compared to a commercial Cu/CHA SCR system, and the combined system (Fe/SAPO-34+ Cu/CHA) exhibited a very good performance in a large temperature interval (200-800 degrees C) that encompasses most diesel exhaust gas conditions.

In this study, Pd/LTA and Pd/SSZ-13 were prepared and then hydrothermally aged at the temperature of 750, 800, 850, and 900 °C. Multiple Pd species, including isolated Pd ions (Pd2+ and [Pd(OH)]+) and 1∼2 nm PdOx nanoparticles, were presented in two fresh samples. The Pd/LTA sample showed remarkable hydrothermal stability, but the Pd/SSZ-13 sample experienced severe damage after aging at 900 °C. The destruction of the aged Pd/SSZ-13 sample led to the migration and sintering of PdOx nanoparticles, which formed bulk PdOx particles on the surface of the zeolite crystallite. A large number of PdOx nanoparticles were retained after aging of the Pd/LTA sample. Pd/LTA contained a higher concentration of Pd2+ sites, while Pd/SSZ-13 had more [Pd(OH)]+ sites. It is found that the improvement of NO adsorption ability with CO addition onto Pd2+ was more significant than onto [Pd(OH)]+.

In this study, Cu/LTA and Cu/SSZ-13 catalysts are examined for sulfur poisoning and regeneration. The nature of the Cu species was probed with H2-TPR and in-situ DRIFTS. These characterizations collectively indicate that primarily Z2Cu is present in Cu/LTA, whereas Cu/SSZ-13 contains a higher concentration of ZCuOH. ZCuOH is proved to be more vulnerable to SO2 poisoning than Z2Cu sites in both Cu/zeolites. H2-TPR results suggest that the interaction of ZCuOH with the framework in Cu/LTA is much weaker than in Cu/SSZ-13, thereby leading to more susceptibility to SO2 adsorption. Moreover, Cu/LTA can store more SO2 under NH3-SCR conditions in the presence of SO2, and it also has a slower deactivation rate due to the different location of generated (NH4)2SO4. Cu/LTA can be fully restored after regeneration at 750 °C. However, Cu/SSZ-13 experiences a loss of activity at high temperature, which is attributed to newly formed CuOx clusters.

Non-poisoned and P-poisoned Cu/SSZ-13 catalysts with different types of Cu sites, i.e., [Cu(OH)]+ and Cu2+, were investigated for NH3-SCR. Phosphorus was found to interact more with [Cu(OH)]+ than Cu2+. Moreover, less phosphorus was required per Cu for poisoning in the samples with a high content of [Cu(OH)]+. We propose a phosphorus poisoning mechanism based on H2-TPR and XPS: poisoning of one Cu2+ involved two P atoms, i.e., P2O5, but for [Cu(OH)]+ contamination, only one P atom (PO3− or PO43−) is needed. Furthermore, phosphorus poisoning resulted in a decline in NH3/NO oxidation and an improvement in SCR activity at high temperatures. Upon hydrothermal aging, [Cu(OH)]+−phosphate/metaphosphate complexes were likely easier detached from the framework than the Cu2+−P2O5 species. This resulted in that the P-poisoned catalyst with high content [Cu(OH)]+ experienced more severe deactivation and dealumination than the non-poisoned catalyst. Additionally, 27Al-NMR suggested that the formation of AlPO4 has a linear relationship with [Cu(OH)]+/Cu2+ ratios.

Hydrodeoxygenation (HDO) activity of a typical hydrotreating catalyst, sulfided NiMo/γ-Al2O3 for deoxygenation of a fatty acid has been explored in a batch reactor at 54 bar and 320 °C in the presence of contaminants, like phospholipids, which are known to be present in renewable feeds. Oleic acid was used for the investigation. Freshly sulfided catalyst showed a high degree of deoxygenation activity, products were predominantly composed of alkanes (C17 and C18). Experiments with a major phospholipid showed that activity for C17 was greatly reduced while activity to C18 was not altered significantly in the studied conditions. Characterization of the spent catalyst revealed the formation of aluminum phosphate (AlPO4), which affects the active phase dispersion, blocks the active sites, and causes pore blockage. In addition, choline, formed from the decomposition of phospholipid, partially contributes to the observed deactivation. Furthermore, a direct correlation was observed in the accumulation of coke on the catalyst and the amount of phospholipid introduced in the feed. We therefore propose that the reason for the increased deactivation is due to the dual effects of an irreversible change in phase to aluminum phosphate and the formation of choline.

The effect of phosphorous exposure on the NOx storage capacity of a Pt/Ba/Al2O3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H2O and O2. The NOx storage capacity was measured before and after the phosphorus exposure and a significant loss of the NOx storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N2-physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P4O10. However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO3−). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample.

Advanced quaternary mixed oxide materials in the form of BaO/Al2O3/ZrO2/TiO2 functionalized with Pt active sites (i.e. Pt/BaO/AZT) were synthesized and structurally characterized via XRD and BET in comparison to a conventional Pt/20BaO/Al benchmark NSR/LNT catalyst. The interactions of these catalysts' surfaces with SOx and NOx gases were monitored via in situ FTIR and TPD. There exists a delicate trade-off between NOx storage capacity (NSC) and sulfur uptake/poisoning which is strongly governed by the BaO loading/dispersion as well as the surface structure and acidity of the support material. Flow reactor measurements performed under realistic catalytic conditions show the high NOx activity for the Pt/20BaO/AZT catalyst at 573 K. After sulfur poisoning and subsequent regeneration at 773 and 973 K, Pt/20BaO/AZT surpassed the NOx catalytic performance at 573 K of all other investigated materials including the conventional Pt/20BaO/Al benchmark catalyst. © The Royal Society of Chemistry 2017.

Phosphorus in vehicle exhaust is one of the typical derivatives from fuels and lubricant oils that cause irreversible deactivation of automotive catalysts. In this work, we investigate the deactivation of Cu-SSZ-13 by vapor-phase phosphorus poisoning (100 ppm H3PO4) under NH3-free lean conditions and NH3-SCR operating conditions. The poisoned monolith catalysts were characterized with XPS, ICP-SFMS, SEM-EDX mapping, and H2-TPR. The influence of phosphorus on catalytic performance (i.e. standard NH3-SCR, NH3 oxidation, NO oxidation, NH3 storage, and NO storage) was evaluated. Phosphorus is mainly stored in the form of metaphosphate in poisoned catalysts, and it possesses axial and radial gradients on catalyst washcoats. Phosphorus strongly affects the copper reduction property, as revealed by the shifts in copper reduction to higher temperature in H2-TPR experiments. Variations in phosphorus poisoning conditions are found to mainly impact the amounts of phosphorus captured and stored in the monolith catalysts. In order to elucidate the deactivation mechanism, the deactivation is correlated with the P/Cu ratio. The temperature shift for copper reduction significantly increases with the P/Cu ratio and levels at high Cu/P ratios. The deactivation degrees of NH3 oxidation and NO oxidation as a function of the P/Cu ratio follow the same trend as the copper reduction temperature. This is possibly due to the formation of copper phosphates in the large cages, which deactivates the copper sites for NH3 and NO oxidation. The deactivation for standard NH3-SCR, NH3 storage, and NO storage is proportional to the P/Cu ratio. The impact of phosphorus on NO storage is significantly stronger than on NH3 storage, indicating that greater contribution to deactivation is brought about by the decreased capacity of NO chemisorption.