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A series of Al2O3-modified CuO-CeO2 (CuCeAlx) was synthesized to reveal the effect of Al2O3 addition on catalytic performance and the proposed mechanism for simultaneous removal of NO and toluene at a broad temperature range. BET, XRD, TEM, XPS, NH3-TPD, H2-TPR, and in situ DRIFTS were used to characterize these catalysts. Results demonstrated that Al2O3-modified CuO-CeO2 catalysts showed the excellent NH3-SCR performance at a broad temperature range (200–400 °C) and good low-temperature activity for toluene oxidation. The modification of Al2O3 significantly tunes the physical and textural properties and induces the formation of oxygen vacancies via the interaction between Ce4+/Ce3+ and Cu2+/Cu+ (Ce4+ + Cu+ ↔ Ce3+ + Cu2+). Besides, the inhibition effect of NH3 on toluene oxidation was confirmed in that the active oxygen species reacted preferentially with NH3 rather than the oxidation intermediates of toluene, while NO had a promotional effect on toluene oxidation owing to the reaction of C7H8 + 18NO = 9 N2 + 7CO2 + 4H2O. At the same time, toluene could also be reducing agents of NO, which was beneficial to NH3-SCR reaction, Based on the results, the proposed mechanism for simultaneous removal of toluene and NO over Al2O3-modified CuO-CeO2 catalysts was revealed.

It is well-known that single-phase metal oxides can be prepared by using metal-organic frameworks (MOFs) as sacrificial templates. In this contribution, we report a facile and scalable route for the preparation of multicomponent metal oxide nanomaterials (MMONs) with high dispersion and tailorable chemical compositions. Specifically, a series of MMONs have been prepared from the calcination of Mn-BTC nanorods together with various transition-metal acetylacetonate complexes (M(acac)2), wherein M(acac)2 was chemically anchored to the porous Mn-BTC with molecular-level dispersion during the one-pot synthesis. The large acac ligands benefit the uniform dispersion of the hetero-metals in the composites during the calcination in air. As a proof of concept application, we have demonstrated that the as-derived MMONs exhibited remarkable catalytic activities in the thermal oxidation of benzene and CO, respectively, which were superior to the traditional mixed metal oxides prepared from the coprecipitation method. The apparent activation energy was calculated and the surface chemical compositions of MMONs were characterized to assess the catalytic roles. In addition, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was also used to reveal the catalytic mechanisms and the synergistic effects of the obtained MMONs.

In this work and for the first time, an alkali metal potassium (K) as a promoter was loaded on an activated carbon (AC) to be used for selective catalytic reduction of NO from industrial flue gas. The denitrification activity of K-modified AC samples was investigated and compared with those of acid- and Cu-modified AC samples. The three modifications can enhance the denitrification activity of AC samples. To investigate the enhanced mechanisms of denitrification and SO2 resistance, various AC samples were characterized by SEM, EDX, XRF, ICP, XRD, N2 physisorption, H2-TPR, XPS, in situ DRIFTS and TPD. For the acid modification, the content of phenolic hydroxyl increases and then promotes the adsorption of NH3. For the loading of Cu, the appearance of Cu2+/Cu+ sites with high catalytic activity promotes NH3 and NO adsorption and changes the reaction pathway. For the loading of K, the adsorption capacity for NO increases nearly 12 times higher than that on Raw-AC, of which 85.0% is chemical adsorption. Moreover, three kinds of active nitrate species additionally forms, including nitro compounds, monodentate nitrate and nitrous oxide, which promote the denitrification reaction path. AC-Cu has poor sulfur resistance due to the sulfation of Cu, while AC-K show good sulfur resistance due to the enhanced adsorption of NO. The catalytic dissociation activity of N2O on AC-K makes the formation and decomposition of N2O into a dynamic equilibrium. As a result, AC-K has a high N2 selectivity, while AC-Cu has poor N2 selectivity.

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.

In order to gain an understanding of the role of oxygen vacancy in enhancing gaseous formaldehyde oxidation, mesoporous NaInO2 compounds were synthesized with different amount of oxygen vacancies while maintaining similar BET surface area. The NaInO2 compounds were designed as the support for platinum (Pt) nanoparticles loaded catalytic oxidation, exhibiting the best performance with a formaldehyde degradation ratio of 96.11%. Interfacial lattice mismatch was considered as the cause of oxygen vacancies and simulated by density functional theory (DFT). Special bridged bidentate species were observed in Pt/NaInO2 with oxygen vacancies during HCHO oxidation using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Based on our observations we propose, for the first time, that superoxide (O2 −) is the effective species that oxidizes formaldehyde, while oxygen vacancies provide pathways to transport O2 − from Pt nanoparticles to support surface thus offering more active sites for the reaction to take place.

A single atom Pt/CeO2 catalyst for the direct non-oxidative methane coupling (NOCM) operation to C2 hydrocarbon product species was prepared, mechanisms were evaluated, and kinetics based on elementary step reaction scheme equations were determined. The catalyst was characterized by a number of techniques; scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were implemented. CO DRIFTS showed the presence of single Pt atoms. Temperature, CH4 flow and functional weight hourly space velocity were varied in the ranges of 780–910 °C, 0.9–2.6 mL min - 1 and 0.094–0.29 h−1, respectively. The applied total pressure, used was 1.5 bar. The highest reactant conversion achieved was 4.3 mol.%, the selectivity to C2 was 60 mol.%, and to ethene alone, maximally 80 mol.% among C2 products. Also some coke was forming, but processing remained stable for 245 h of the time on stream. System’s kinetic parameters were fitted to quantitative data values, non-linear regression analyses were being reiterated, and a relatively good agreement with the space–time point sets for CH4, ethylene, acetylene and hydrogen was reached. The sensitivity analysis of fixed rate constants showed which reaction steps influence reacting CH4, the reactivity towards transformed C2 and yields the most. It was shown that the important physico-chemical transformations are CH4 adsorption, the abstraction of the first H • from its neutral CH4 molecule on the surface and the sorption/desorption of H2. Fast C–C bond processes only have a limited measurable effect on CH4 converted. C2 are primarily affected by the Pt adhesion/release of CH4, synthesized C2 and H2. Modelling may be translated to other catalytic NOCM understanding, designing and optimizing, as an alternative to steam methane reforming.

Herein, a series of CenTiOx (n = 0.068, 0.15, 0.21 and 0.30) flakes with hierarchical structure was prepared by alcoholysis under solvothermal conditions and explored for the selective catalytic reduction (SCR) of NOx with NH3. The morphology of the CenTiOx flakes was related to the Ce doping content. Remarkably, the flakes morphology of catalyst greatly promoted the SCR activity derived from the strong interaction between the Ce and Ti oxides. Among these samples, the Ce0.21TiOx with rod-like hierarchical structures demonstrated good SCR activity that the NO conversion was still over 90% from 270 °C to 450 °C even under SO2 and H2O. Various characterizations clarified that the good activity over Ce0.21TiOx was due to the increase of BET surface area (195 m2/g), surface Ce3+ amount and surface Oα species. In-situ DRIFTS was conducted to determine the distribution and reactivity of surface acid sites. The results demonstrated that there was a direct correlation between the coverage of the Bronsted acid sites and the NO conversion. Eley-Rideal (E-R) mechanism is the most likely to represent the reaction mechanism on Ce0.21TiOx catalyst.

A highly efficient Ni-Pt bimetallic catalyst over Al2O3 for the conversion of oleic acid to heptadecane without using external hydrogen source is synthesized by the atomic layer deposition (ALD). The combined characterizations of HAADF-STEM, in-situ XAFS and CO-DRIFTS confirmed that Ni-Pt-ALD formed a Pt-skin structure over the sub-surface Ni particles. With the modification of Ni, the Pt-skin bimetallic particles exhibit excellent activity and selectivity in the upgrade reaction of oleic acid to aviation fuels. The yield of heptadecane reaches 91%, near the theoretical upper limit of the “self-hydrogen supply-consumption”. The remarkable catalytic performance of the Ni-Pt-ALD catalyst demonstrates that the subsurface Ni-modulated Pt skin structure is capable of integrating the dehydrogenation, decarboxylation and hydrogenation reactions. The undesired side reactions such as alkyl chain aromatization and polymerization could be effectively inhibited.

Photocatalysis is regarded as a promising method for indoor formaldehyde (HCHO) removal, and there remains a strong demand for the development of highly efficient photocatalysts for HCHO oxidation under visible light. Herein, by grafting nano CuOx clusters onto TiO2, the higher performance is achieved over Cu-TiO2 for the photocatalytic oxidation of HCHO under visible light compared with the typical photocatalysts N-TiO2 and g-C3N4. It is found that the presence of water greatly promotes the activity of HCHO oxidation on Cu-TiO2. The characterization results indicate that the CuOx clusters on TiO2 exhibit high redox reversibility between Cu (II) and Cu (I) and greatly facilitate the migration of electrons. The mechanism of photocatalytic oxidation of HCHO was explored by using in situ DRIFTS measurements and DFT calculations. It is shown that HCHO is firstly oxidized to dioxymethylene (DOM), and then DOM is transformed into formate species under visible light irradiation. DFT calculations results indicate that the OH species are responsible for surface formate decomposition, which is the rate-determining step, while O2− radical is not active in formate decomposition. Our findings improve the understanding on the photocatalytic oxidation of HCHO, and the Cu-TiO2 catalyst is a promising candidate for practical application in indoor air purification.

Bisphenol A (BPA) is known as an endocrine-disrupting chemical, generally present in the environment. It has a harmful effect on aquatic lives and human health, therefore it is needful to exploit highly efficient innovative treatment methods for its removal. Herein, we report a Co-BiVO4 photoanode to activate peroxymonosulfate (PMS) for the complete removal of BPA via a photoelectrochemical (PEC) process. The Co-BiVO4 could degrade 99.16% of BPA in the presence of 2 mM PMS within 60 min, whereas the degradation rate constant is 0.08034 min−1, which was 20.86 times higher than the electrocatalytic (EC) and 5.35 times higher than the photocatalytic (PC) process. Notably, Co-BiVO4 showed significant activity toward PMS activation and BPA degradation as compared to other synthesized photocatalysts. Their photoelectrocatalytic performance followed the sequence Co-BiVO4 > Fe-BiVO4 > Ni-BiVO4 > pure-BiVO4 > without catalysts. Several influencing factors on the decomposition process, such as the effect of PMS concentration, applied potential, illumination time, initial pH, BPA concentration, Co loading, and co-existing anions were studied in detail. Radical scavenging experiment and transient absorption result showed that sulfate radicals (SO4•─) were the dominant reactive species. Moreover, a significant synergistic effect was noticed in Co-BiVO4/PEC/PMS system for BPA degradation. Degradation mechanism and reaction intermediates were studied by in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and liquid chromatography-mass spectroscopy (LC-MS) presenting the enhanced bond cleavage in PEC activated PMS system. The BPA showed 92.47% and 87.27% removal in tap and river water samples after 60 min of reaction using Co-BiVO4/PMS PEC system. Our finding proposed an efficient method for wastewater treatment in an eco-friendly way.

The reaction kinetics for the CO2 methanation and reverse water gas shift reaction over an ordered-mesoporous Ni/Al2O3 catalyst were determined. For the parameter estimation and model discrimination, the kinetic data were obtained by means of spatially-resolved measurement in a catalytic plate reactor. In detail, ~21,000 high-resolution gas composition data were gathered along the reactor axis using a movable sampling capillary connected to a mass spectrometer. Additionally, the catalyst surface temperature was determined via infrared thermography. The influence of reaction temperature (320–420 °C), total pressure (1.2–7.3 barabs), and GHSV, as well as possible inhibition of products such as CH4 and H2O, were investigated. A one-dimensional model of the reactor was developed describing the conservation of mass in the bulk gas and catalyst phase. The Bayesian approach was used to estimate the kinetic parameters of 20 proposed Langmuir-Hinshelwood rate expressions for the CO2 methanation that were derived based on three different mechanisms (i.e., direct dissociation, hydrogen assisted dissociation, and hybrid mechanism). Two kinetic models reflected the measured data very well. The most probable models suggest that the rate determining step includes the reaction of an oxygenated complex (COH* or HCOO*) with an active site (*) or an adsorbed hydrogen (H*). Furthermore, water was assumed to be adsorbed as a hydroxyl species (OH*), while methane did not influence the reaction. Temperature- and time-resolved Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) measurements confirmed the presence of both adsorbed surface intermediates.

A novel bifunctional BaWO4/g-C3N4 photocatalyst with heterojunction was first synthesized by a hydrothermal-calcination method. The as-prepared catalysts were imposed in treatment of NOx in air and hydrogen produced from water. The chemical composition of BaWO4/g-C3N4 was optimized and composites with 7% BaWO4 (7%-Ba-CN) exhibited the best photocatalytic performance. In 30 min, the NOx removal ratio of the composite photocatalyst increased by 14% compared with the pure g-C3N4. According to in situ DRIFTS spectra analysis, the transformation pathways of photocatalytic purification of NO on pure g-C3N4 and 7%-Ba-CN were elucidated and compared, and a new adsorption band at 2164 cm−1 associated with NO+ intermediate was discovered on 7%-Ba-CN. In addition, the photocatalytic hydrogen production rate of 7%-Ba-CN was 2743.98 μmol/g/h, which was 4 times higher than that of pure g-C3N4. This research highlights that charge transfer rates can be controlled by constructing heterojunctions. The promotion of the charge separation, transmission and conversion could simultaneously enhance the oxidation and reduction capacity of the composite photocatalyst.

Catalytic combustion of methane was studied over Ce0.5Zr0.5O2 and CeO2 supported Pd (Pd/CZ and Pd/Ce) catalysts in the presence of SO2. The effect of sulfation (air including 100 ppm SO2 for 6 h at 500 °C) on the sulfur-tolerant performance of the catalysts was also investigated. Results indicated that there is a considerable promotion effect for CH4 complete oxidation on Pd/CZ catalyst, while the activity of Pd/Ce catalyst was inevitably inhibited. Further, the superior sulfur-tolerant behavior of Pd/CZ was verified through a 50 h time-on-stream stability test. Mechanistic insights into the synergistic effect between the support and Pd were unveiled by Raman, H2-TPR, XPS, NH3-TPD, DRIFTS, HAADF-STEM, etc. It was deduced that the formation of sulfates at the Pd-support interface could promote the dissociative adsorption of methane on Pd/CZ catalyst. Meanwhile, the higher relative acid strength and the acid amount were also decisive factors for the high sulfur-resistant performance. The enhanced acid strength and acid amount prevented the further formation of bulk-like sulfate species for the SO2 treated Pd/CZ catalyst, thus enhancing the sulfur-tolerant ability of the catalyst.

This study focuses on investigating the influence of ion-exchange method (ION-F and ION-A) and one-pot method (ONE-F and ONE-A) on catalytic properties and hydrothermal stability of Cu/SSZ-13. It was found that ONE-F catalyst showed better SCR activity, especially at low temperature range below 400 °C. After hydrothermal aging, ION-A exhibited higher low temperature efficiency than ONE-A. The effect of synthesis method on the physicochemical structure, acidity intensity, and Cu species migration or transformation of the fresh and aged Cu/SSZ-13 catalysts were comprehensively characterized by NH3-TPO, H2-TPR, NH3-TPD, ICP, XRF, BET, XRD, SEM, and TEM. ONE-F has more isolated Cu2+ sites, higher ratio of active sites Cu2+-2Z/[Cu(OH)]+-Z, more Lewis acid sites, and smaller particle size than ION-F. However, hydrothermal aging had severe effect on Cu/SSZ-13 prepared by one-pot method, leading to particle aggregation and decrease of active copper sites. According to NH3-SCR kinetic studies, smaller particle size and more uniformly distributed active sites over ONE-F resulted in less effect of pore diffusion limitation. Furthermore, in situ DRIFTS results indicated that more monodentate nitrates adsorbed sites and Lewis acid sites existed in ONE-F. On the other hand, monodentate nitrates were identified to be the most active nitrate species, and Lewis acid sites were ascertained to be more active than Bronsted acid sites. Therefore, ONE-F showed more excellent SCR performance than ION-F. However, hydrothermal aging resulted in loss of majority of nitrate adsorbed sites and acid sites over catalyst prepared by one-pot method, leading to lower SCR performance. In conclusion, Cu/SSZ-13 prepared by ion-exchange method has higher hydrothermal stability, however, fresh Cu/SSZ-13 prepared by one-pot method has excellent catalytic properties.

A series of MnaZrbCrcOx catalysts with different Cr/Mn molar ratios were synthesized via co-precipitation for the selective catalytic reduction of NOx with NH3 (NH3-SCR). It was found that a Mn5Zr2Cr2.5Ox catalyst with a Mn:Zr:Cr ratio of 5:2:2.5 exhibited excellent low-temperature activity and the best levels of H2O resistance at a high weight hourly space velocity (WHSV) of 54,000 ml/(h·g). NO conversion levels were measured as greater than 87% within a temperature range of 150–250 °C, and catalytic performance levels reached 90% even 50 h after reactions occurred in the presence of 15% H2O at 230 °C. The characterization results show that strong interactions occurring between Mn, Zr and Cr oxides and higher quantities of Mn4+ and Lewis acid sites improved the redox properties and facilitated H2O resistance. In situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) show that coordinated NH3 on Lewis acid sites and bidentate nitrates play important roles in SCR reactions and that such reactions follow both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. The competitive adsorption of H2O and NO may be the main cause of the adverse effects of H2O on catalytic performance.

Oxidation of low-concentration nitrogen oxides (NOx) to nitrate with solar energy is an efficient way to remove them from atmospheric environment under semi-enclosed or ill-airflow conditions. However, conventional photocatalysts applied in NOx removal face the challenges of low efficiency and generation of toxic byproducts (nitrogen dioxide, NO2) leading to secondary pollution. To tackle these issues, monodisperse gold nanoparticles supported on graphitic carbon nitride (Au@CN) was designed and fabricated by a facile method. The Au@CN exhibited a highly enhanced nitric oxide (NO) oxidation activity and superior NO2 inhibition ability. The microstructures, optical properties and electronic structure of the photocatalysts were analyzed with advanced tools. The in situ diffuse reflectance infrared spectroscopy (DRIFTS) was applied to dynamically monitor and reveal the reaction process at time sequence. Density functional theory (DFT) and electron spin resonance (ESR) were combined to explore the oxidation mechanism at molecular level. It was found that (1) the presence of Au metal site favored the adsorption and activation of the gas molecules; (2) the high separation efficiency of the photogenerated electron-hole pairs enhanced the production of radicals for NO oxidation; (3) the unique electronic structure of Au@CN prefers nitrate formation with a low rate-determining barrier and largely suppress the toxic intermediate NO2, thus effectively controlling the secondary pollution. The present work could provide a novel mechanistic insight into visible-light photocatalytic NO oxidation and selectivity on Au@CN which is beneficial for designing efficient and safe photocatalyst with low environmental risk.

A series of ceria supported perovskite-based lean-burn NOx trap (LNT) catalysts 10 wt.% LaCoO3/xK(2)CO(3)/CeO2 (denoted as L/xK/C, x = 1, 3, 5, 8 wt.%) were prepared by successive impregnation. They display excellent performance for NOx storage and reduction, especially the one with 3% K2CO3. The formation of supported perovskite LaCoO3 on CeO2 is confirmed by XAFS characterization. The results of XPS and O-2-TPD reveal that the supported perovskite LaCoO3 contains considerable amounts of surface adsorbed oxygen, which are responsible for NO to NO2 oxidation during NOx storage. The catalyst L/3K/C exhibits fast and complete NOx trapping in lean condition, showing little NOx leak for long time, over which a particularly high NOx reduction percentage (97.7%) and NOx to N-2 selectivity (98.5%) are simultaneously achieved in cyclic lean/rich atmospheres. FT-IR and CO2-TPD results demonstrate the diversity of K species including -OK groups, dispersed surface K2CO3 species and bulk or bulk-like K2CO3 species. The dispersion and states of K species show big impact on NOx storage pathways. In situ DRIFTS results indicate that on L/xK/C NOx is stored as diverse nitrates without evident nitrite species detected during NOx adsorption and storage, which further verifies their excellent oxidation ability. (C) 2014 Elsevier B.V. All rights reserved.

The effect of Pt dispersion on the different supports was evaluated. The Pt structural and textural properties have been analyzed by XRD, HRTEM and CO pulse chemisorptions. The redox and structure property between Pt and supports was characterized by H 2 -TPR and Raman. CO-DRIFTS characterized the identification of Pt coordination. Results demonstrate that the Pt dispersion is dependent of Ce contents of supports. The Pt supports interaction tends to become weak as Ce content decreasing, leading to higher reduction temperature for active oxygen at low temperature. The stronger interaction for Pt loaded on CeO 2 and Ce 0.7 Zr 0.3 O 2 results in superior CO oxidation performance. The TOF for Pt loaded on Ce based supports presents linear increasing as Pt dispersion increasing.

The selective non-catalytic reduction (SNCR) deNOx process was influenced by high-concentration CaO particles in the pre-calciners when applied to cement industry. The influence of CaO on the SNCR deNOx process was investigated using a fixed bed reactor at temperature that ranges from 873 K to 1373 K and the mechanism of the process was analyzed. The experimental results demonstrated that CaO has catalytic effects on NH3 decomposition, NO reduction by NH3, and NH3 oxidation. It inhibits the SNCR deNOx process mainly via catalyzing NH3 oxidation to NO. The catalytic effect of CaO can be ignored at temperatures higher than 1273 K. NH3 was found that first adsorbed onto the CaO surface and then dissociated to NH2 by Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The mechanism analysis of CaO catalysis during the SNCR deNOx process showed that NH3 dissociation on the CaO surface is the rate-controlling step, and the intermediate substance, NH2, reacts with O2 or NO to produce NO or N2. The competition of the two reactions determines the product selectivity. A kinetic model including CaO-catalyzed NH3 conversion and gas phase SNCR deNOx reaction was developed, which well predicted the CaO-involved SNCR deNOx process.

MnO x –CeO 2 –ZrO 2 /γ-Al 2 O 3 catalyst was prepared by the sol–gel method and then investigated on the selective catalytic reduction (SCR) of NO x (NO and NO 2 ) by NH 3 . The catalytic activity was enhanced by the addition of Zr in the broad temperature range of 100–400 °C. This catalyst could also be well-behaved under high GHSV and in the presence of SO 2 and H 2 O. The XRD and XPS results showed that the Zr 4+ ions incorporated into the CeO 2 crystal lattice and formed the solid solution, resulting that the BET surface area and pore volume of this catalyst increased obviously. The detailed SCR mechanism was researched using the in situ DRIFTS. It showed that NO could be adsorbed on the catalyst and formed different kinds of nitrates at 150 °C, which almost converted to the stable bidentate and bridged nitrates in the presence of O 2 . NH 3 could be adsorbed on both Lewis sites (coordinated NH 3 species) and Bronsted sites ( NH 4 + ) at 150 °C. These adsorption products were enhanced by introducing O 2 . The results of the SCR reaction on the catalyst indicated that the reaction route could follow the Eley–Rideal mechanism as NH 3 pre-adsorbed on the catalyst, it could also follow the Langmuir–Hinshelwood mechanism when NO pre-adsorbed on the catalyst.

The present work investigates the lean NO x trapping performance of BaO (1, 3, 5 wt.%) modified CeO 2 (BC) NO x storage catalysts, where 2 wt.% Pt/Al 2 O 3 (PA) part was mechanically blended in. Before mixture, the storage catalysts (BaO/CeO 2 ) were treated at 800 °C for 5 h in a steam and CO 2 -containing air. The storage catalysts were characterized in detail by X-ray diffraction (XRD), nitrogen adsorption–desorption, energy-filtered transmission electron microscopy (EFTEM), and X-ray photoelectron spectroscopy (XPS). Results show highest Ba dispersion on CeO 2 for 3BC sample. 5BC sample forms large BaCO 3 particle leading to lower Ba dispersion than 3BC sample. NO x storage capacity was investigated in steady-state and transient NO/O 2 adsorption reactions in the temperature range from 100 °C to 300 °C. As BaO loading increases, the PA–BC catalysts exhibit nonlinear enhancement for NO x storage capacity (NSC) compared with PA–Ce sample. And PA–3BC sample possesses superior NO x storage capacity. The evolution and stability of NO x adsorbed species at 100 °C were explored by in situ DRITFS. DRIFTS results show that PA–3BC and PA–5BC samples present obviously different NO x adsorbed species from PA–Ce sample. Besides, nitrate formation is more facilitated for PA–3BC sample compared with the PA–5BC sample. These results can be contributed to high Ba dispersion on CeO 2 , which is advantageous to Ba–Ce contact and NO x trapping. And the Ba sites in intimate contact with CeO 2 can effectively utilize the Ba sites and oxygen from CeO 2 to form nitrates at low temperature, which possess higher stability than Ce nitrates.

In this paper, diamine modified montmorillonite was prepared by water aided exfoliation/grafting method. The materials were characterized by elemental analysis (EA), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectrometer (DRIFTS), automated surface area and porosity analyser (ASAP 2420) and thermogravimetric analysis (TGA). Adsorption of carbon dioxide on modified montmorillonite was investigated by isothermal CO2 adsorption, temperature ramp CO2 adsorption, regeneration screening test with adsorption/desorption cycles, and multiple cyclic test. The maximum adsorption capacity for modified montmorillonite is 2.4 mmol g−1 at 100 °C. In a 15% CO2 in N2 mixture, the material achieves a maximum adsorption capacity of 1.8 mmol g−1, which is 75% of its maximum capacity in pure CO2. The optimum adsorption and desorption temperature are found to be 80 and 160 °C, respectively, by regeneration testing. The long term performance was also studied in pure CO2, 15% CO2 in N2 and 15% CO2 in N2 with 1000 ppm SO2. The material is stable in pure CO2 and 15% CO2 in N2, while the adsorption capacity drops dramatically with the presence of SO2. In order to understand the kinetics of CO2 adsorption, four kinetics models were evaluated, with the Avrami equation providing the best experimental-simulation fit.

A series of Fe/HBEA catalysts was prepared by conventional impregnation (IMP) and liquid ion exchange (LIE) methods with various levels of iron contents, all of which was used to identify and quantify iron species and study the roles of different iron species in NO x conversion efficiencies, catalytic selectivity, and temperature dependencies. The composition and distribution of the iron species strongly depended on iron contents and preparation methods. LIE method preferred to produce more iron ions at ion exchange sites than IMP method, and then obtained highly active and selective Fe/HBEA catalysts. Isolated iron species at ion exchange sites was active in the NO x reduction with ammonia reaction (including N 2 O reduction with ammonia reaction), and iron oxide particles mainly contributed to the ammonia oxidation at the whole temperature range. The results of DRIFTS showed that nitrate species, Fe 2+ mononitrosyls [Fe 2+ (NO)], and Fe 2+ dinitrosyls [Fe 2+ (NO) 2 ] were coadsorbed on the Fe/HBEA samples, yet the LIE samples preferred to yield much more nitrate and nitrosyl species than the IMP samples. Fe 2+ mononitrosyls was found to be the key intermediates in the SCR reaction at 200 °C, while the nitrates species, mainly generated on iron ion sites and adsorbed on zeolite support, did not take part in the SCR reaction. NH 3 -TPD and ammonia oxidation results showed zeolite acidity might not be critical for SCR reaction on Fe/HBEA catalysts, and would be inhibited with the introduction of iron.

Catalytic removal of indoor HCHO was proposed to proceed in a “storage-oxidation” cycling process. Two kinds of supported silver catalysts, namely Ag/HZSM-5 and Ag–MnO x –CeO 2, were investigated as catalysts for this cycling process. Due to the highly dispersed silver clusters formed and its good redox properties, the Ag–MnO x –CeO 2 catalyst showed better HCHO oxidation properties in both the storage phase (HCHO partial oxidation to HCOO − at room temperature) and oxidation-regeneration phase (total oxidation of the formates into CO 2 and H 2 O at elevated temperatures). The presence of H 2 O (RH = 50%, 25 °C) was found to enhance the HCHO storage capacity for Ag–MnO x –CeO 2 catalyst, while competitive adsorption of HCHO with H 2 O was observed over Ag/HZ catalyst. The results of DRIFTS indicate that the partial oxidation of HCHO into HCOO − is accelerated by the presence of H 2 O over the Ag–MnO x –CeO 2 catalyst. In addition, the catalyst saturated with HCHO can be in situ regenerated without production of secondary pollutants and can be used repeatly. It is suggested that this is a promising approach for indoor HCHO elimination.

This study focuses on investigating the effect of ignition temperature for the combustion synthesis (CS) on the selective catalytic reduction of NO x with NH 3 over Ti 0.9 Ce 0.05 V 0.05 O 2− δ nanocomposites serial catalysts prepared by the solution combustion method. Ti 0.9 Ce 0.05 V 0.05 O 2− δ -350 °C showed the best SCR activity and N 2 selectivity in a broad temperature window of 150–400 °C, in which more than 83% NO x was reduced with the superior N 2 selectivity above 95%. The influence of the ignition temperature for CS on the physical and morphological properties, the crystalline phase, the microstructure, the redox behavior, the oxidation state, the reactants adsorption capability, and the evolution of the surface nitrate and acid sites after the adsorption of NO x and NH 3 was extensively investigated in detail using comprehensive characterization techniques including N 2 physisorption, XRD, SEM, TEM, FTIR, EPR, and XPS. The increase of the ignition temperature, the decrease of the specific surface area, the total desorption pore volume, the surface fractal dimension, and the concentration of the chemisorbed oxygen, and the increase of the average pore diameter and the particle size, which may be the main reasons for the decline of the NO x removal efficiency and the N 2 selectivity. In addition, the NO x /NH 3 -TPD results suggest that the Ti 0.9 Ce 0.05 V 0.05 O 2− δ catalysts prepared at lower ignition temperatures could provide more chemisorption NO x and NH 3 species, and simultaneously enhance the activation of both species that result in the improvement of the SCR activity. Furthermore, the in situ DRIFTS results indicate that the active monodentate nitrate and bridging nitrate species come from the NO x adsorption and that the ionic NH 4 + bound to the BrOnsted acid sites are active species and essential for the SCR process. The increase of the ignition temperature decreases the key surface nitrate species and acid sites, and thus the relevant NH 3 -SCR activity and selectivity.

The performance of pure and aluminum containing SBA-type catalysts prepared using different aluminum sources and different Al/Si ratios were investigated in the polypropylene degradation reaction using a thermogravimetric analyzer. For the synthesis of catalysts, aluminum isopropoxide and aluminum sulphate were used as the aluminum sources. Synthesized materials had high surface areas and exhibited nitrogen adsorption isotherms of type IV. EDS results showed that the aluminum incorporation into the structure was very effective. 27 Al MAS NMR spectra of the catalysts exhibited tetrahedrally and octahedrally coordinated aluminum species in the structure. TEM images of synthesized catalysts showed well-ordered hexagonal arrays of uniform mesopores with cylindrical channels. With the aluminum loading, DRIFTS analysis of the pyridine adsorbed materials revealed the existence of Bronsted acid sites in the synthesized catalysts in addition to Lewis acid sites. Thermogravimetric analysis results showed a marked reduction in the degradation temperature in the presence of aluminum containing SBA-type catalysts. The activation energy value of the degradation reaction decreased to about 51–70 kJ/mole in the presence of catalysts synthesized using aluminum sulphate as the aluminum source and when aluminum isopropoxide was used as the aluminum source activation energy value of the reaction decreased to 82–89 kJ/mol.

We describe here the performance of a novel MgO–CeO2-supported Pt nanocatalyst (∼1.5 nm mean Pt particle size) towards the selective conversion of NO (XNO > 90%) into N2 ( S N 2 > 80 % ) using H2 (H2-SCR) in the low-temperature range of 120–180 °C for a wide range of O2, H2 and CO2 feed concentrations. This catalytic system showed remarkable performance under industrial process conditions of NOx control [1] , [2] , [3] , [4] , [5] . Using a feed composition containing 150 ppm NO, 2 vol% O2 and H2 in the 0.2–0.8 vol% range (GHSV = 33,000 h−1), the NO conversion, XNO (%) and N2-selectivity, S N 2 (%) were found to increase with increasing H2 feed concentration in the 120–180 °C range, where NO conversions in the 97–100% range and N2-selectivities in the 83–93% range were obtained. By increasing the O2 feed concentration from zero to 5 vol%, both the XNO (%) and the S N 2 (%) were found to decrease by an extent which was dependent of reaction temperature. The effect of CO2 in the feed stream (0–12 vol%) was found to be slightly negative for the NO conversion, while an opposite behavior was found for the S N 2 (%), likely due to competitive adsorption of CO2 and NO on the same non-selective NOx adsorption sites. In situ DRIFTS studies have shown that the oxygen feed concentration largely influenced the surface concentration of inactive NOx and only slightly that of active NOx intermediates of H2-SCR but not their chemical structure.

The nano TiO2 supported V2O5–WO3/TiO2 catalysts (VWTi) were prepared by impregnation method assisted with ultrasonic energy. Their poisoning on activity by alkali metals (Na, K, Ca and Mg) was investigated. The degree of the poisoning effect for all the alkali metal doped catalysts was shown as follows: K > Na > Ca > Mg. Further investigations were carried by NH3-TPD, DRIFTS, XPS and H2-TPR characterization. Na and K could decrease the amount and stability of the Bronsted acid sites to a greater extent than Mg and Ca. Surface chemisorbed oxygen could also be reduced and the downward trend was in good agreement with SCR activity. In addition, the reducibility of vanadium species on the Ca and Mg doped catalysts are higher than that on the Na and K doped catalysts with the same alkali metal oxides loadings. Furthermore, Na and K ions could also affect the reduction degree of tungsten species, while no obvious changes have happened for the tungsten species over Ca- and Mg-VWTi catalysts. Consequently, the different poisoning effects of these four alkali metals doped nano V2O5–WO3/TiO2 catalysts are correlated not only to the surface acidity but also to the reducibility of vanadium and tungsten species.

This study investigated the effect of adding CeO2 to an Rh/Al2O3 catalyst on the decomposition of nitrous oxide (N2O). The Rh/CeO2 catalyst was shown to have a high catalytic activity but was significantly affected by oxygen. In contrast, the Rh/Al2O3 catalyst has moderate catalytic activity and was unaffected by oxygen. In order to avoid the adverse effects of oxygen while simultaneously enhancing catalytic activity, we developed a new catalyst, Rh/CeO2–Al2O3, which was prepared using three different methods (impregnation, co-precipitation, and ball milling). Activity tests, H2 TPR, DRIFTS, and O2 off/on tests confirmed that the Rh/CeO2–Al2O3 catalyst prepared using the co-precipitation method had the highest catalytic activity and inhibition by oxygen was reduced.

High temperature processing of solvothermally synthesised MgO nanoparticles promotes striking changes in their morphology, and surface chemical and electronic structure. As-prepared NanoMgO comprised ∼4 nm cubic periclase nanocrystals, interspersed within an amorphous Mg(OH)(OCH3) matrix. These crystallites appear predominantly (1 0 0) terminated, and the overall material exhibits carbonate and hydroxyl surface functionalities of predominantly weak/moderate base character. Heating promotes gradual crystallisation and growth of the MgO nanoparticles, and concomitant loss of Mg(OH)(OCH3). In situ DRIFTS confirms the residual precursor and surface carbonate begin to decompose above 300 ◦C, while in situ XPS shows these morphological changes are accompanied by the disappearance of surface hydroxyl/methoxide species and genesis of O− centres which enhance both the surface density and basicity of the resulting stepped and defective MgO nanocrystals. The catalytic performance in tributyrin transesterification with methanol is directly proportional to the density of strong surface base sites.

Passive NOx adsorption (PNA) has been recently developed as a promising technology for controlling the NOx emissions during the cold start period. In this work, we illustrate a CO-assisted mechanism by combining experimental and kinetic modeling studies. Pd/SSZ-13 has been synthesized, characterized and evaluated as a PNA in low-temperature NOx adsorption and temperature program desorption cycles, to represent multiple cold start periods. The gas compositions were also systemically changed, where both the effect of varying NOx and CO feed was evaluated in the presence of high water and oxygen contents. A kinetic model was developed to simulate the profiles of NO and NO2, including three initial Pd sites (Z-Pd(II)Z-, Z-[Pd(II)OH]+ and PdO). It is concluded from XPS and in situ DRIFTS experiments, flow reactor measurements and modelling observations that CO reduces Pd(II) species to Pd(I)/Pd(0) species, which increases the stability of the stored NOx species, resulting in a release above the urea dosing temperature. The model could well describe the experimental features, including the effect of CO. In addition, the model was used for full-scale catalytic converter simulations.

Oxygen carrier materials (OCM) are usually exposed to sulfur-contained gases in the fuel reactor for chemical looping combustion. This work provides both experimental and model work to understand the SO2 effect on the heterogeneous redox kinetics of a CaMn0.375Ti0.5Fe0.125O3-δ-based perovskite oxygen carrier. The cycle reactivity and redox kinetics under reducing conditions were conducted with and without SO2 in a micro-fluidized bed thermogravimetric analysis technology (MFB-TGA). The redox kinetic behaviors were simulated by a bubbling fluidized bed reactor model coupled with a two-stage kinetic model. The SO2 can react with the perovskite to increase the oxygen transfer capacity from 4 wt% to 5 wt%. When the temperature is higher than 1173 K, SO2 has almost no effect on the H2 reduction reactivity, while the oxidation reactivity decreases by 50%, but the oxidation is still fast enough to achieve 4 wt% capacity within 8 s. When the temperature is lower than 1173 K, there is a significant sulfur-poisoning effect during oxidation and reduction. The analyses of XRD, SEM-EDS, and in-situ DRIFTS indicated that most of the absorbed sulfur mainly existed in the sulfate/sulfide shell on the particle surface. The chemical kinetics and physical structure of CaMn0.375Ti0.5Fe0.125O3-δ perovskite can be completely recovered in the absence of SO2, and this perovskite oxygen carrier is chemically memorable and reversible in its solid structure. The fundamental understanding of the sulfur effect on the redox kinetics and solid structure of the perovskite oxygen carrier provides a new insight to the material development and corresponding reaction mechanisms.