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Two different routes of synthesis were followed in order to compare the surface properties of two Cu-SAPO-34 catalysts. The direct copper incorporation during the hydrothermal synthesis, compared to the conventional impregnation method, allowed us to study the impact of active centers location on the catalytic activity during both the selective catalytic reduction of NOx by NH3 and the NH3 oxidation. X-ray diffraction, ex-situ diffuse reflectance infrared spectroscopy and X-ray photoelectron spectroscopy analysis were performed to know the copper location and its state for each catalysts. A unique location of the copper oxide at the surface of the synthesized catalyst was observed when the hydrothermal process was used. For similar Cu contents in the catalysts, different catalytic behaviors during the selective catalytic reduction of NOx by NH3 and during the NH3 oxidation were observed as a consequence of the specific activity of the copper clusters. Indeed, some cations in exchanged position were detected when the impregnation method was used, allowing high SCR performance at low temperature. On the other hand, the small copper clusters at the surface and the exchanged cations exhibited a certain NH3 oxidation at low temperature, hindering DeNOx activity. Catalyst with mainly large copper clusters and no appreciable occurrence of exchanged Cu2+ present in a range of temperatures, limited NH3 oxidation and high SCR performance. [ABSTRACT FROM AUTHOR]

In a previous study, a drastic enhancement of the NOx conversion in EtOH-SCR process was achieved by means of ammonia and ethanol co-feeding over Ag/Al2O3 catalyst to avoid the NO2/NOx ratio dependency of conventional implemented urea-SCR technology. The ammonia activation was mainly attributed to the availability of hydrogen H* species resulting from EtOH dehydrogenation, which promoted the H2 assisted NH3-SCR over Ag/Al2O3. Additional conversion gain was reached with a dual-bed configuration in which a NH3-SCR catalyst (WO3/CexZr1−xO2) was added downstream to the silver-based sample (Ag/Al2O3 + NH3-SCR catalyst). This study deals with the influence of the SCR catalyst formulation on the catalytic performances of the dual-bed system. Oxide-based sample (WO3/CexZr1−xO2) and exchanged copper zeolite (Cu2.5-FER) were selected as model NH3-SCR catalysts. Results shows that WO3/CexZr1−xO2 in more appropriate in dual-bed configuration for (EtOH + NH3)-SCR process because ammonia and ethanol (or its by-products) strongly interacted together on Cu2.5-FER. [ABSTRACT FROM AUTHOR]

The effect of steam on NO x reduction over lean NO x trap (LNT) Pt–Ba/Al2O3 and Pt/Al2O3 model catalysts was investigated with reaction protocols of rich steady-state followed by lean–rich cyclic operations using CO and C3H8 as reductants, respectively. Compared to dry atmosphere, steam promoted NO x reduction; however, under rich conditions the primary reduction product was NH3. The results of NO x reduction and NH3 selectivity versus temperature, combined with temperature programmed reduction of stored NO x over Pt–BaO/Al2O3 suggest that steam causes NH3 formation over Pt sites via reduction of NO x by hydrogen that is generated via water gas shift for CO/steam, or via steam reforming for C3H8/steam. During the rich mode of lean–rich cyclic operation with lean–rich duration ratio of 60 /20 s, not only the feed NO, but also the stored NO x contributed to NH3 formation. The NH3 formed under these conditions could be effectively trapped by a downstream bed of Co2+ exchanged Beta zeolite. When the cyclic operation was switched into lean mode at T < 450 °C, the trapped ammonia in turn participated in additional NO x reduction, leading to improved NO x storage efficiency. [ABSTRACT FROM AUTHOR]

A series of gas sensing layers based on indium oxide doped with gold were prepared by using the aerosol technology for deposition as the active contact layer in a metal oxide semiconductor capacitive device. The interaction between the measured species and the insulator surface was quantified as the voltage changes at a constant capacitance of the device. The sensor properties were investigated in the presence of H2, CO, NH3, NO, NO2 and C3H6 at temperatures between 100–400 °C. Significant differences in the morphology of the layer and its sensitivity were noted for different preparation methods and different gas environments. [ABSTRACT FROM AUTHOR]

The influence of the preparation method on the NO–SCR by NH3 activity of Cu-OFF catalysts has been studied on presence of oxygen. The catalysts structure and the nature of copper species have been investigated by XRD, 27Al MAS NMR, UV-visible spectroscopy and H2-TPR. Among the examined preparation methods, the ionic exchange in aqueous solution gives the highest efficient catalyst in NO-SCR. It is shown that Cu cationic species are formed in large extent with this method despite the presence of minor amounts of small oxide clusters. [ABSTRACT FROM AUTHOR]

A catalyst for NOx storage/reduction was prepared to improve the activity of Ba–Pt/?-Al2O3 by replacing Ba with a mixture of Ba and Mg. The catalyst was prepared by impregnating Pt and then co-impregnating Ba and Mg (Mg:Ba molar ratio = 1) on commercial ?-Al2O3. The tests have been carried out in the presence of CO2 at temperatures between 200 and 400 °C in order to understand the role of both the feed and various alkaline-earth metals. The storage capacity of the two catalysts was different like the mechanism in the reduction process. [ABSTRACT FROM AUTHOR]

Flow reactor experiments and kinetic modeling have been performed in order to study the mechanism and kinetics of NOx reduction over Pt/SiO2 catalysts with hydrogen as the reducing agent. The experimental results from NO oxidation and reduction cycles showed that N2O and NH3 are formed when NOx is reduced with H2. The NH3 formation depends on the H2 concentration and the selectivity to NH3 and N2O is temperature dependent. A previous model has been used to simulate NO oxidation and a mechanism for NOx reduction is proposed, which describes the formation/consumption of N2, H2O, NO, NO2, N2O, NH3, O2 and H2. A good agreement was found between the performed experiments and the model. [ABSTRACT FROM AUTHOR]

The use of low-sulfur fuel is known to improve the performance of the three-way catalytic converter (TWC). However, in this work we report how low-sulfur operation of commercial TWC also favors formation of N2O and NH3 as by products. We found that low-sulfur rich operation above 300 °C increases the production of NH3, inhibiting the formation of N2O characteristic of high-sulfur operation. During lean operation, the production of N2O near the stoichiometric point is not significantly affected by the sulfur level. The large production of N2O observed during light-off is not affected by SO2 when the operation is lean, but under rich conditions N2O is produced up to 575 °C. The increased production of NH3 and N2O in TWC as a result of the introduction of low-sulfur gasoline is an area that requires further analysis because of its implication upon public health in large urban settings. [ABSTRACT FROM AUTHOR]