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We have reported a LaMnO-based, Pt free lean NO trap (LNT) catalyst shows promising NO reduction activities, but the mechanism of NO reduction or the role of the perovskite over this catalyst has not been addressed. This paper presented our investigation on the mechanistic aspects of NO adsorption and reduction over several LaMnO-based LNT catalysts. NO can be effectively oxidized to NO on LaMnO at 350 °C, while little NO (NO + NO) can be stored verified by the following temperature programmed desorption experiment; under the same conditions, a significant amount of NO (41 μmol NO/g washcoat) were stored over BaO/AlO/LaMnO indicating NO are adsorbed mainly on the BaO/AlO. The temperature programmed surface reaction with CO demonstrated that although it can store NO during the lean period, failed to reduce NO by CO over the BaO/AlO/LaMnO catalyst. After adding Pd into BaO/AlO/LaMnO, NO can not only be stored during the lean conditions but also reduced. It could be concluded that the Pd catalyst, not perovskite, is responsible for NO reduction during the rich conditions. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ti-SBA-15 and Ti-MCM-41 were synthesized and evaluated as possible photocatalysts for the reduction of CO, and for the photo-Kolbe decomposition of acetic acid. UV-Raman was used to study the adsorption of carbon dioxide, water, formic acid, and acetic acid over Ti-MCM-41 by monitoring the UV enhanced resonance peak of the totally symmetric stretching band of the grafted Ti species at 1,085 cm. Acetic and formic acid dissociate on Ti-SBA-15 and Ti-MCM-41 to form acetate and formate, respectively. The conjugate bases subsequently interact strongly with Ti sites. Water interacts with the Ti sites, while no change in the amplitude of the 1,085 cm band is observed in the presence of CO. Photocatalysis experiments indicate that these mesoporous silicalites are active in the photo-Kolbe decomposition of acetic acid. CO is formed by reaction of a hole with the acetate carboxylate groups. The methyl radical co-products react with a surface proton and an electron to form methane. No products resulting from the dimerization of methyl radicals are observed, presumably because of the highly dispersed active sites. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Direct carbonyl reduction to methylene has been achieved by mild reductant system obtained from the combination of organosilane and gallium (III) trifluoromethanesulfonate {Ga(OTf)}, a water tolerant, recyclable, catalyst. Among a series of organosilanes studied, dimethylchlorosilane (MeSiHCl, DMCS) showed the highest efficiency. Both aromatic and aliphatic ketones were effectively reduced to the corresponding methylene products with high functional groups tolerance, under very mild conditions in a relatively short period of time with good to excellent yields. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The addition of gold, by deposition precipitation, to a mixed copper manganese oxide catalyst (Hopcalite) has been studied for ambient temperature carbon monoxide oxidation. The deposition of gold on the catalyst surface enhanced the activity of the Hopcalite. The catalyst containing 1 wt% gold was the most active and showed higher activity than Hopcalite containing 0.5 and 2 wt% gold. It is expected that the introduction of gold will introduce new active sites to the Hopcalite that are associated with the gold nanoparticles. However, gold addition also increased the reducibility of the catalyst significantly compared to unmodified Hopcalite, and the most easily reduced catalyst was the most active, indicating that the lability of lattice oxygen was an important factor influencing activity. Graphical Abstract: The activity of a copper-manganese oxide catalyst for ambient temperature CO oxidation is significantly promoted by the addition of gold using deposition precipitation.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Pd/CeO2, Pd/ZrO2 and Pd/CeO2–ZrO2, were prepared by impregnation on a well defined alumina support. The oxides are finely dispersed over alumina support. TPR results on promoted Zr and Ce catalysts indicate partial reduction of CeO4 and ZrO2. The dispersions for Pd/Al2O3 and Pd/Zr/Al2O3 are similar but very different on Pd/Ce/Al2O3 and Pd/Ce/Zr/Al2O3, increasing 4 and 7 times in relation to the Pd/Al2O3, suggesting re-dispersion of Pd, mainly due to the promoting effect of Ce. EPR signals of Pd/Ce/Al2O3 are related with O2− species of Ce4+–O2−. DRIFTS studies with NO and CH4 reaction showed that the Pdδ+ species interacts with Ce+δ, modifying significantly the NO + CH4 reaction route. Pd/CeO2, Pd/ZrO2 and Pd/ CeO2–ZrO2, were prepared on a well defined alumina support. The structural and surface properties were studied under different characterization analyses in situ. EPR signals of Pd/Ce/Al2O3 are related with O2- species of Ce4+–O2. The NO reduction by CH4 was also studied by DRIFTS. It shows that the Pdδ+ species interacts with Ce+δ and that Ce and Zr modifies significantly the NO + CH4 reaction route.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The carbon support (C) is modified by its functionalized surface with Ti species and used as a support of Pt catalyst for oxygen reduction reaction (ORR). Anatase TiO2 nanoparticles with the size of 3–5 nm are uniformly dispersed on the modified carbon support (C-Ti). It is shown that the C-Ti is well dispersed in the solution of Pt precursor due to the hydrophilic TiO2 nanoparticles. This causes a uniform distribution of Pt nanoparticles on C-Ti support. The average particle sizes are 2.9, 2.6, and 3.1 nm, respectively, for Pt/C, Pt/C-Ti, and Pt-commercial. The ORR performance is evaluated in terms of both mass-activity and specific activity. It is found that the Pt/C-Ti revealed the highest performance. The enhancement factors of ORR performance on the Pt/C-Ti at the potentials of 0.75, 0.8, and 0.85 V was more than two for both mass activity and specific activity compared to those on the Pt/C. The large surface area of Pt with a favorable electronic structure would be responsible for a superior performance of the Pt/C-Ti in ORR. Carbon support (C) was modified by reacting Ti species with its functionalized surface and used as a support of Pt catalyst for oxygen reduction reaction (ORR). Due to the hydrophilic TiO2 nanoparticles, the modified support (C-Ti) revealed enhanced dispersion in the solution of Pt precursor, which made Pt nanoparticles highly dispersed on its surface. The enhancement factors of ORR performance on Pt/C-Ti was more than two for both mass activity and specific activity compared to those on the Pt supported on unmodified carbon (Pt/C).[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A fluidizable, Ni/Mg/K/AD90(90% α-Al2O3) catalyst was evaluated in a pilot-scale study with oak-derived syngas for tar and methane reforming at 900 °C. The catalyst was operated in a semi-batch mode for ten individual reaction cycles, each separated by a regeneration protocol consisting of steaming followed by H2 reduction. During the experiment, subsequent reaction cycles showed a decrease in activity as indicated by decreased initial methane conversion. During each reaction cycle, H2S poisoning was the dominant deactivation mechanism, while coking was deemed to be minor in comparison. Catalyst characterization by XRD and TPR suggest that the loss of activity for subsequent reaction cycles coincides with the formation of a NiAl2O4 species that is not fully reduced under process conditions, which in turn results in a decreased number of potential metallic nickel (Ni0) sites available for hydrocarbon steam reforming. An increase in nickel crystallite size with time-on-stream was also observed using XRD, indicating that sintering may also play a role in loss of catalyst activity, although this is not considered the primary deactivation mechanism because activity loss was observed even when nickel crystallite sizes remained nearly constant. [ABSTRACT FROM AUTHOR]

Single-crystalline La0.6Sr0.4MnO3+ δ microcubes of cubic perovskite phase were prepared hydrothermally. The adopted temperature and time of hydrothermal treatment and the amount of KOH used had great effects on the low-temperature reducibility of La0.6Sr0.4MnO3+ δ. The initial H2 consumption rate of La0.6Sr0.4MnO3+ δ played a vital role in determining its catalytic activity for toluene combustion. It is concluded that the perovskite-type oxide catalyst with a higher initial H2 consumption rate displayed a higher catalytic activity for the addressed reaction. [ABSTRACT FROM AUTHOR]

In NO/CO reaction, there is a competition between NO reduction by CO and Mo2C oxidation by oxygen generated during NO dissociation. A complete equality of NO conversion and NO reduction degree can be achieved after increasing CO concentration in the system, which makes establishing a catalytic cycle on Mo2C catalyst possible. [ABSTRACT FROM AUTHOR]

Copper catalysts supported on magnesia promoted ceria are synthesized and used for NO reduction by CO. The supports and the subsequent Cu catalysts are prepared by citric acid sol–gel and impregnation methods, respectively. The results of N2-physisorption, XRD, EPR and TPR measurements indicate that the Mg addition promotes not only the dispersion of CuO, but also the formation of Cu–O–Ce solid solution. The highest amount of Cu–O–Ce solid solution is found in catalyst modified with 5 wt.% MgO. Based on the catalytic performance, two active sites for the reduction NO by CO are proposed: copper matrix and Cu–O–Ce solid solution. The former does not require the involvement of oxygen vacancy and is more active at low temperature range (T < 200 °C), while the latter shows higher NO conversion at temperature above 200 °C, due to the easy regeneration of oxygen vacancy. Also, it is found that the NO conversion over copper matrix is suppressed, while that over Cu–O–Ce solid solution is stimulated in high CO concentration. [ABSTRACT FROM AUTHOR]

Alumina supported 5% Co catalyst was prepared, by the controlled nanocrystal deposition method using oleic acid as a capping agent, and tested for its activity and selectivity in Fischer–Tropsch synthesis. The catalyst exhibited facile reducibility of the cobalt species. The CO conversion and C5+ selectivity obtained on this size-controlled catalyst were higher than those observed on the catalysts prepared by impregnation and precipitation techniques. Decrease in the mobility of the nanoparticle towards the tetrahedral sites of alumina could be the reason for high reducibility, as the formation of cobalt aluminate was found to be considerably reduced during temperature programmed reduction. [ABSTRACT FROM AUTHOR]

An amorphous Co-B catalyst was prepared by chemical reduction method and characterized by isothermal N2 adsorption/desorption, XRD, ICP-AES and HR-TEM. The catalytic activity of the Co-B catalyst in the hydroformylation of 1-octene was evaluated in a 100 mL stainless autoclave. Fresh amorphous Co-B catalyst showed a relatively high activity in the hydroformylation of 1-octene. The thermal stability of fresh Co-B catalyst was also examined. When fresh Co-B catalyst was thermally treated in N2 or H2 atmosphere at 200–500 °C for 2 h, the specific surface area and the catalytic activity of the Co-B catalyst decreased. When Co-B was supported on SiO2, the activity of the catalyst increased obviously. Compared with conventional supported Co/SiO2 catalyst, Co-B/SiO2 showed much higher activity than Co/SiO2. The influences of solvents and reaction conditions on the catalytic activity of the amorphous Co-B catalyst were also studied. The recycle test of the amorphous Co-B catalyst was done. [ABSTRACT FROM AUTHOR]

Iron-containing zeolites are known to be promising catalysts for the NH3-SCR reaction. Here, we will investigate the catalytic activity of iron-based BEA catalysts, which was found to exhibit improved activities compared to previously described iron-containing zeolite catalysts, such as ZSM-5 and ZSM-12. Series of Fe-BEA zeolite catalysts were prepared using a range of different preparation methods. Furthermore, we found that an iron concentration around 3 wt% on BEA showed a small optimum in SCR activity compared to the other iron loadings studied. [ABSTRACT FROM AUTHOR]

The influence of syntheses parameters of zeolite ZSM-5 on the lean NO x reduction activity and hydrothermal stability of Cu-ZSM-5 has been investigated. The hydrothermal stability of Cu-ZSM-5 was found to depend on the aluminium source used and on the presence of Ca(OH)2 in the synthesis mixture for ZSM-5. [ABSTRACT FROM AUTHOR]

This study tested the selectivity and sustainability of an alumina-supported Pd–In bimetallic catalyst for nitrate reduction with H2 in a continuous-flow packed-bed reactor in the presence of: (i) dissolved oxygen (DO), an alternative electron acceptor to nitrate, (ii) variable NO3 −:H2 influent loadings, and (iii) the presence of a known foulant, sulfide. The sustainability of the catalyst was promising, as the catalyst was found to be stable under all conditions tested with respect to metal leaching. The presence of DO at concentrations typical of treatment conditions will increase H2 demand for NO3 − reduction, but has no negative impact on the selectivity of the catalyst. Under optimal conditions, i.e., a pH of 5.0 and a high NO3 −:H2 influent loading, low NH3 selectivity (5%) was achieved for extended periods (36 days), resulting in sustained levels of NH3 that approached the European legal limit. The biggest challenge to the sustainability of the catalyst was the addition of sulfide, that initially increased NH3 selectivity and ultimately resulted in complete deactivation of the catalyst. Further work is required to identify regeneration methods to restore sulfide-fouled catalyst activity and selectivity; however, the most effective use would be to remove sulfide prior to catalytic treatment. [ABSTRACT FROM AUTHOR]

Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m2/g) exhibited higher C5+ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH4 selectivity. [ABSTRACT FROM AUTHOR]

The effects of using NO or NO2 as the NO X source on the performance of a NO X storage/reduction catalyst were investigated from 200 to 500 °C. The evaluation included comparison with constant cycling times and trapping the same amount of NO X during the lean phase. With NO2 as the NO X source, better trapping and reduction performance was attained in comparison to NO, at all operating temperatures except 300 °C. This exception, under the conditions tested, was likely due to high NO oxidation activity and rapid trapping of NO2, although it is expected that extending the trapping time would lead to consistent differences. Several reasons for the observed improvements at 200, 400 and 500 °C with NO2 relative to NO are discussed. One that can explain the data, for both trapping and release improvement, is treating the monolith as an integral reactor. With NO2, more NO X is trapped at the very inlet of the catalyst, whereas with NO, the maximum in trapping during cycling occurs slightly downstream. Thus more of the catalyst can be used for trapping with NO2 as the NO X source. The decreased release during catalyst regeneration is similarly explained; with more being released at the very inlet, there is more residence time and therefore contact with downstream Pt sites, but more importantly more interaction between reductant and stored NO X. NH3 and N2O measurements support this conclusion. [ABSTRACT FROM AUTHOR]

Redox reactions catalyzed by cobalt nitrides should be carried out below the critical temperature at which bulk oxidation of the nitrides occurs. Then, a catalytic redox cycle could be established by introducing a reducing agent into the system below this temperature so that the oxygen could be removed prior to the occurrence of bulk oxidation. [ABSTRACT FROM AUTHOR]

Ag/SBA-15 catalysts have been prepared by means of in situ reduction methods using hexamethylenetetramine and formaldehyde as reducing agents, respectively, and characterized by N2 adsorption/desorption, XRD, TEM and XPS. Presence of nanoparticles of silver in SBA-15 were confirmed by high angle X-ray diffraction data (peaks between 2 θ = 35–80º) and XPS, and transmission electron microscopy confirmed the diameter of the nanoparticles. When hexamethylenetetramine was used as reducing agent, uniform Ag nanoparticles inside the channels were formed, and diameter of nanoparticles is found to be ~6.0 nm which is coincident with channel diameter of SBA-15. The catalysts were subjected to CO oxidation in a flow reactor at atmospheric pressure and temperatures up to 300 °C. Studies revealed that catalysts prepared with different reducing agents strongly influence their catalytic performance in the CO oxidation, what prepared with hexamethylenetetramine as mild reducing reagent shows a certain low temperature catalytic activity. [ABSTRACT FROM AUTHOR]

Composites of polyaniline (PANI) or polypyrrole (PPy) doped with chloride ions and Pt or Rh particles were prepared by chemical reduction of metal ions conducted in the presence of the polymers. Based on X-ray diffraction studies it was established that the composites contained metal nanoparticles (5–9 in size). However, according to SEM investigations metal particles were agglomerated (40 nm–1.1 μm in size). Redox activity of the composites in the catalytic isopropyl alcohol conversion was ca. ten times higher than the acid–base one. Pt dispersed in polymer matrices showed higher catalytic activity than Rh. PPy doped with chloride ions had a promoting effect on the activity of Pt catalysts. [ABSTRACT FROM AUTHOR]

Fe/ZSM-5 and Cu-ZSM-5 were investigated for selective catalytic reduction of NOx with ammonia. The Fe/ZSM-5 catalyst showed over 90% NO conversion from 350 to 500 °C and Cu-ZSM-5 showed over 90% NO conversion from 250 to 350 °C. After pretreatment in 10% H2O at 700 °C, the Fe/ZSM-5 still exhibited high activities and stability. On the basis of the experiments, Fe/ZSM-5 and Cu-ZSM-5 seem to be promising candidates for diesel-engine NOx emission control. [ABSTRACT FROM AUTHOR]

The role of Ag in simultaneously catalyzing NO reduction and C3H6 oxidation was shown to be strongly dependent on the redox properties of its local environment. Under an atmosphere of 1,000 ppm NO, 3,000 ppm C3H6, and 1% O2 and a GHSV of 30,000 h−1, a perovskite La0.88Ag0.12FeO3 prepared by reactive grinding is active giving a complete NO conversion and 92% C3H6 conversion at 500 °C. These values are much higher than the NO conversion of 55% and C3H6 conversion of 45% obtained over a 3 wt.% Ag/Al2O3 catalyst under the same conditions. Under an excess of oxygen (10% O2) a good SCR performance with a plateau of N2 yield above 97% over a wide temperature window of 350–500 °C along with C3H6 conversion of 90% at 500 °C was observed over Ag/Al2O3, while minor N2 yields (∼10% at 250–350 °C) and high C3H6 conversions (reaching ∼100% at 450 °C) were obtained over La0.88Ag0.12FeO3. Abundant molecular oxygen is desorbed from Ag substituted perovskite after 10% O2 adsorption as verified by O2- temperature programmed desorption (TPD). This reflects the strongly oxidative properties of La0.88Ag0.12FeO3, which lead to a satisfactory NO reduction at 1% O2 due to the ease of nitrate formation but to a significant C3H6 combustion above that value. The formation of nitrate species over the less oxidizing Ag/Al2O3 was accelerated under an excess of oxygen resulting in an excellent lean NO reduction behavior. The redox properties of silver catalysts could be adjusted via mixing perovskite with alumina for an optimal elimination of both NO and C3H6 over the whole range of oxygen concentration between 0 to 10%. [ABSTRACT FROM AUTHOR]

Pd/HZSM-5 catalyst prepared via glow discharge plasma reduction followed by calcination thermally showed enhanced stability for methane combustion. In order to investigate the plasma catalyst preparation mechanism, oxygen glow discharge, initiated at room temperature, has been employed for reduction of Pd/HZSM-5 catalyst. The catalyst characterization using XRD and XPS analyses demonstrates that oxygen glow discharge plasma is also able to reduce Pd/HZSM-5 catalyst. This suggests that the electronic effect plays an important role in the treatment of catalyst using glow discharge. This also confirms that the thermal effect of the glow discharge reduction can be ignored. A highly durable catalyst for methane combustion has been obtained from calcination of the glow discharge reduced sample. [ABSTRACT FROM AUTHOR]

In order to improve the catalytic performance of supported-Ir catalysts for the selective reduction of NO with CO, the effect of H2 was investigated. While adding H2 showed no or negative effect on NO conversion on Ir/SiO2, Ba/Ir/SiO2 and Ir/WO3/SiO2 catalysts, the activity of Ba-doped Ir/WO3/SiO2 catalyst for NO reduction was significantly increased by H2 addition. The role of H2 was found to stabilize the catalytically active Ir-WO x sites during the reaction. [ABSTRACT FROM AUTHOR]

Mono – (Ag/SiO2, Pd/SiO2) and bimetallic (Ag+Pd/SiO2) catalysts have been obtained via sol-gel method from tetra-ethoxy-silane (TEOS) and their activity in reduction of Nitric oxide (NO) with carbon monoxide (CO) has been investigated. The highest activity in the process of reduction of NO with CO possesses the sample Ag + Pd/SiO2. It has been found that the sol-gel method for preparation of bimetallic catalysts allows the formation of various catalytic active centers (CAC) which leads to high activity in reaction of NO reduction. The presence of Ag2O and PdO in these CAC allows the elimination of NO. The process of this elimination includes reduction of NO with CO at temperatures up to 200 оC as well as direct decomposition of NO at higher temperatures. [ABSTRACT FROM AUTHOR]

An unusual behavior was observed during experiments conducted at 371 and 465 °C with a commercial NOX storage/reduction catalyst: the outlet NOX concentration during the trapping phase reached a cycle minimum after regeneration, increased for 20–30 s, as expected, but then surprisingly decreased, indicating the catalyst had become more efficient in trapping the entering NOX. The results reported in this letter indicate that this phenomenon was caused by a superposition of two factors: a substantial exotherm associated with the regeneration event from reductant reacting with surface oxygen species and a negative impact of an evolving temperature profile on the dynamic NOX storage capacity. [ABSTRACT FROM AUTHOR]

The ability of H2S to reduce NO in a fixed bed reactor using a γ-alumina catalyst was studied with the objective of generating new methods for conversion of NO to N2. Compared to the homogenous reaction of NO with H2S, the catalyzed reaction showed improved conversions of NO to N2. Using a gas space velocity of 1000 h−1 and a feed of 1% NO and 1% H2S in argon, it was found that the conversion of NO to N2 was complete at 800 °C. This result compared to a 38% conversion of NO to N2 for the homogeneous gas phase reaction at 800 °C. At temperatures below 800 °C, a short fall in the nitrogen balance was discovered when the γ-alumina was employed as a catalyst. This discrepancy was explained by conversion of NO to NH3 and subsequent reaction of the NH3 with any SO2 in the system to form ammonium sulfur oxy-anion salts. This suggestion is supported by the finding that when larger amounts of H2S were used relative to NO, more NH3 was formed together in tandem with lower N2 mass balances. Several reaction pathways have been proposed for the catalytic reduction of NO by H2S. [ABSTRACT FROM AUTHOR]

CoNdOx (Co/Nd = 1) is a highly promising catalyst for the carbon-free CO2 reforming of methane. Influence of the Co/Nd ratio on the catalyst performance in the CO2 reforming and also on the crystalline phases and reduction by temperature programmed reduction (TPR) of the CoNdOx catalyst has also been investigated. The CoNdOx (CoNd = 1.0) catalyst consisted of mainly NdCoO3 perovskite-type mixed metal oxide and it showed not only a high resistance to carbon formation at different process conditions (viz. temperature = 750-900 °C and gas hourly space velocity (GHSV) = 10000-50000 cm3 g-1 h-1) but also high activity and selectivity in the CO2 reforming process. The high resistance to carbon formation for this catalyst is attributed mostly to strong metal (Co°)-support (Nd2O3) interactions. [ABSTRACT FROM AUTHOR]

We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic reduction (SCR) of NO with ammonia at high temperatures (300-400 °C). In this work, we found that the reaction temperature could be decreased to 200-300 °C when a small amount of noble metal (Pt, Rh, or Pd) was added to the Fe-ZSM-5. The SCR activity follows the order Pt/Fe-ZSM-5>Rh/Fe-ZSM-5>Pd/Fe-ZSM-5 at 250 °C. On the Pt promoted Fe-ZSM-5, 90% NO conversion was obtained at 250 °C at GHSV = 1.1 × 105 h-1. Moreover, the noble metal improved the resistance to H2O and SO2. The presence of H2O and SO2 decreased the SCR performance only very slightly. [ABSTRACT FROM AUTHOR]

Hydrothermal treatment of Co/MFI catalysts at high temperature increases their performance for NOx reduction with methane. As this treatment also shifts the TPR peak of isolated Co ions upward by 20 °C, the results suggest that the hydrothermal treatment induces transport of Co2+ ions from α to β positions. [ABSTRACT FROM AUTHOR]

The H2/NO/O2 reaction under lean-burn conditions has been studied by means of in situ DRIFTS, reactor measurements and temperature-programmed desorption with the aim of understanding the very different behavior of Pd/TiO2 and Pd/Al2O3 catalysts. The former deliver very high NOx conversions (70-80%) with good N2 selectivity whereas the latter show very low activity. In addition, PdTiO2 exhibits two distinct NOx reduction pathways, thus greatly extending the useful temperature range. It is shown that the PdTiO2 low-temperature channel involves adsorption and subsequent dissociation of NO on reduced (Pd0) metal sites. The low activity of PdAl2O3 is a consequence of palladium remaining in an oxidized state under reaction conditions. The high-temperature NO reduction channel found with PdTiO2 is associated with the generation and subsequent reaction of NHx species. [ABSTRACT FROM AUTHOR]

Sn0.5Ti0.5O2 shows excellent catalytic performance both for the CO-SO2 reaction and the CO-SO2-NO reaction. At 350 ° C, 525 ppm SO2/520 ppm NO/2085 ppm CO, SV = 3000 h-1, the conversion of SO2 is nearly complete in the CO-SO2 reaction and above 89% in the CO-SO2-NO reaction; NO conversion is above 98% in the latter reaction. The selectivities of S and N2 are both close to 100%. SO2 shows a significant promoting effect on the activity of the Sn0.5Ti0.5O2 catalyst for NO reduction by CO. Combining transient response experiments, catalytic tests and TPD results, we propose a SO2-assisted NO-CO reaction concept. The existence of a surface sulfur species, which was formed during the CO-SO2 or CO-SO2-NO reaction, is proved by XPS analysis. It is the active site for NO reduction in the CO-SO2-NO reaction, and through which SO2 accomplishes its promoter role. On the basis of the results obtained, the SO2-assisted redox mechanism of simultaneous reduction of SO2 and NO by CO is proposed. [ABSTRACT FROM AUTHOR]

Fe-ZSM-5 catalysts were prepared by subliming FeCl3 into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl3 exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl3 into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl3 at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl3 at 700 °C were found to be more active for NO reduction with NH3 in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl3 at 320 °C. To determine the active sites, the catalysts were characterized by H2-TPR, in situ DRIFTS of NO adsorption, NH3-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH3 could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when γ positions in Fe-ZSM-5, corresponding to Fe2+(NO) band at 1877 cm-1 in DRIFTS, were preferentially occupied. [ABSTRACT FROM AUTHOR]