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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]

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]

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]

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]

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]

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]

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]

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]

There are no general accepted models for CO and HC oxidation and NOx reduction in automotive catalysis. Many factors affect the observed kinetics e.g. the catalyst preparation method and conditioning, the composition of the exhaust gases, mass and heat transfer, and all the reaction conditions that the catalyst has been exposed to prior to an experiment. However, most experiments are done under idealized conditions with a fresh catalyst and without water, SO2, etc. Simple models will only describe the individual experiments and more complex models require determination of the parameters from independent measurements under realistic conditions. The kinetic models available in the literature are only reliable for the exact catalyst and reaction conditions for which they have been developed. [ABSTRACT FROM AUTHOR]