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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]

This study provides insight into the mechanistic and performance features of the cyclic reduction of NO by CO in the presence and absence of excess water on a Pt-Rh/Ba/AlO NO storage and reduction catalyst. At low temperatures (150-200 °C), CO is ineffective in reducing NO due to self-inhibition while at temperatures exceeding 200 °C, CO effectively reduces NO to main product N (selectivity >70 %) and byproduct NO. The addition of HO at these temperatures has a significant promoting effect on NO conversion while leading to a slight drop in the CO conversion, indicating a more efficient and selective lean reduction process. The appearance of NH as a product is attributed either to isocyanate (NCO) hydrolysis and/or reduction of NO by H formed by the water gas shift chemistry. After the switch from the rich to lean phase, second maxima are observed in the NO and CO concentrations versus time, in addition to the maxima observed during the rich phase. These and other product evolution trends provide evidence for the involvement of NCOs as important intermediates, formed during the CO reduction of NO on the precious metal components, followed by their spillover to the storage component. The reversible storage of the NCOs on the AlO and BaO and their reactivity appears to be an important pathway during cyclic operation on Pt-Rh/Ba/AlO catalyst. In the absence of water the NCOs are not completely reacted away during the rich phase, which leads to their reaction with NO and O upon switching to the subsequent lean phase, as evidenced by the evolution of N, NO and CO. In contrast, negligible product evolution is observed during the lean phase in the presence of water. This is consistent with a rapid hydrolysis of NCOs to NH, which results in a deeper regeneration of the catalyst due in part to the reaction of the NH with stored NO. The data reveal more efficient utilization of CO for reducing NO in the presence of water which further underscores the NCO mechanism. Phenomenological pathways based on the data are proposed that describes the cyclic reduction of NO by CO under dry and wet conditions. [ABSTRACT FROM AUTHOR]

It is shown that palladium-cobalt oxide-cerium catalyst deposited on cordierite catalyzes the reduction of nitrogen(II) oxide with carbon monoxide, and cobalt-iron catalysts in simultaneous reduction of NO + NO with C-C alkanes retained high activity in the presence of water vapor and sulfur dioxide. The Pd-CoO/cordierite catalyst exceeds the Pt-CoO/codierite catalyst in the conversion of NO and CO in the reaction mixture CO + NO + O + HO + SO. Modification of the Pd-CoO/cordierite with cerium oxide considerably increases its sulfur resistance. [ABSTRACT FROM AUTHOR]

This study gives an overview of zeolites used for hydrocarbon trapping, selective catalytic reduction of nitrogen oxides (NO) with NH (NH-SCR) and hydrocarbon NO reduction applications. We also discuss challenges for the use of zeolites in these applications and the material properties that require improvement. [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]

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]

The influence of the combustion products of different lubrication oil additives and impurities in fuel or urea solution on the activity and selectivity of V2O5/WO3-TiO2 catalysts in the selective catalytic reduction (SCR) of nitrogen oxides by ammonia was investigated. Focusing on the deactivation by calcium, phosphate, and potassium, the DeNO x activity followed the order K ? Ca >PO4. This trend was investigated on the structural level of the catalyst by means of temperature programmed desorption of ammonia (NH3-TPD) and a DRIFT characterization of the adsorbed ammonia species. The results suggest that the studied elements strongly reduce the acidity of the SCR catalyst in the order K ? Ca >PO4 by mainly affecting the Brønsted acidity of the surface. [ABSTRACT FROM AUTHOR]

A Pd catalyst is particularly effective for the oxidation of CO and C3H6 at low temperatures, while the Pt/Rh/Ce catalyst is active for NO reduction. The TWC activity of both catalysts generally decreased as the catalyst mileage increased. However, the NO reduction activity was less affected by catalyst aging compared to the oxidation reactions. The selectivity of the catalysts in favor of the CO–O2 reaction (vs. C3H6–O2 reaction) in the O2 partitioning experiments became less pronounced as the catalyst aged. The NO partitioning experiments reveal the superior capability of H2 in NO reduction to the other reductants (CO and C3H6) examined in the present study. The reactivities of NO with both H2 and CO were found to decrease upon catalyst aging, resulting in decreased overall NO removal activity. [ABSTRACT FROM AUTHOR]

In order to elucidate the effect of support in the catalytic performance, two selected potassium-promoted catalysts (K1Cu/beta and KCu2/Al2O3) were tested for the simultaneous NO x /soot removal from a simulated diesel exhaust. For comparative purpose, the behaviour of a platinum catalyst (Pt/beta) was also studied. Isothermal experiments revealed that the potassium-promoted catalysts show a high activity for NO x /soot removal in the 350–450 °C temperature range. In addition, the catalysts present the advantage that the main reaction products are N2 and CO2. Among the catalysts tested, KCu2/Al2O3 presents the best global performance at 450 °C: the highest soot consumption rate, even higher than the platinum catalysts, and a high NO x reduction. [ABSTRACT FROM AUTHOR]

Isothermal storage of NO2 and subsequent reduction with different reducing agents (H2, CO or H2 + CO) in a lean NO x trap catalyst was tested by Temperature Programmed Desorption (TPD) and Temperature Programmed Reduction (TPR) experiments at temperatures representative of automotive “cold-start” conditions (<200 °C) using a commercial NO x trap catalyst. Results from the TPR experiments revealed that no reduction of stored NO2 to N2 was observed at 100–180 °C, and at 200 °C 10% reduction only of NO2 to N2 was measured. A special affinity of H2 to form NH3 was observed during the reduction of stored NO2. The formation of NH3 increases with increasing amount of stored NO2 and decreases with increasing storage temperature. Direct relation exists between the amount of adsorbed and/or stored NO2 and the formation of H2O and NH3. [ABSTRACT FROM AUTHOR]

Isothermal storage and reduction of NO2 with CO, C3H6 and H2 as reducing agents on a lean NOx adsorber was investigated by temperature programmed desorption (TPD) and temperature programmed reduction (TPR) studies. The reduction of NOx was clearly favoured with H2 as reducing agent. Carbon monoxide and C3H6 showed fairly low reduction of NOx. The NOx reduction at low temperatures with H2 as reducing agent was found to be effective, clearly much more effective than for CO. [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]