Showing papers on "Selective reduction published in 2002"

Al-Free Sn-Beta Zeolite as a Catalyst for the Selective Reduction of Carbonyl Compounds (Meerwein−Ponndorf−Verley Reaction)

Abstract: The catalytic activity of Sn-Beta zeolite in the Meerwein−Ponndorf−Verley (MPV) reduction of carbonyl compounds with secondary alcohols was performed with quantitative yields to the corresponding alcohol. This heterogeneous catalyst exhibits activities and selectivities not observed before with other Me-zeolites.

Selective reduction of NO to N2 in the presence of oxygen over supported silver catalysts

Abstract: Selective reduction of NO (0.1%) with propylene (0.1%) in the presence of oxygen (5%) with He balance was carried out over Ag supported on Al2O3, H-ZSM5 and H-Y catalysts. Although their activities were different, all three catalysts showed high selectivity to N2 (around 95%). Through several characterizations, it was concluded that silver was present in the form of Ag2O clusters, but not in metallic form for the three catalysts. High selectivity to N2 on all the catalysts is attributed to the same active phase of silver oxide. The difference in catalytic activity is considered to be due to the amounts and the size of Ag2O clusters. Normalized activity per Ag site (TOF) was not the same (Ag/Al2O3>Ag-ZSM5>Ag-HY), which is explained by the carbon depositions and facile transformation of Ag species under redox condition over zeolite-based catalysts.

NO reduction with CO in the presence of O2 over Al2O3-supported and Cu-based catalysts

Abstract: NO reduction with CO in the presence of O2 was examined over various kinds of Al2O3-supported and Cu-based catalysts. The effects of loaded elements, supports and calcination temperatures on catalysis for the NO–CO–O2 reaction system were investigated. We found that the most effective catalyst was 0.5 wt.% Cu/γ-Al2O3 calcined at 773 K. The states of Cu species were characterized with XRD, UV/VIS/NIR, EPR, TPR and X-ray absorption spectroscopic techniques. Highly dispersed Cu2+ species on Al2O3 are active species for selective reduction of NO to N2. The aggregated Cu species preferentially oxidize CO without reducing NOx, and the appearance of the aggregated Cu species resulted in drastic reduction in N2 formation capability.

Preparation and Structure of In−ZSM-5 Catalysts for the Selective Reduction of NO by Hydrocarbons

Abstract: The influence of the preparation route on the microstructure of indium species in In−ZSM-5 catalysts for the selective reduction of NO by hydrocarbons has been investigated. Samples were prepared by aqueous ion exchange, by precipitation with or without previous ion exchange step, by reductive solid-state ion exchange of indium precipitates in flowing hydrogen or at the expense of NH4 ions in the zeolite, and by sublimation or solid-state ion exchange with InCl3. These materials have been studied by XPS, X-ray absorption spectroscopy, representative samples also by FTIR, and transmission electron microscopy. It was found that in aqueous exchange undesired precipitation of extra-zeolite aggregates can be avoided only at low pH, where the indium enters the zeolite voids only in low amounts (maximum exchange degree ≈10% (at In/Al = 1)). At near-neutral pH, extra- and intra-zeolite indium species are formed, and the coordination spheres of the latter differs from those of intra-zeolite indium species obtained...

Thermoregulated phase-transfer ligands and catalysis: XV CO selective reduction of nitroarenes catalyzed by Ru3(CO)9(PEO-DPPSA)3 in two-phasic system

Abstract: Aqueous/organic two-phase CO selective reduction of nitroarenes catalyzed by the thermoregulated phase-transfer catalyst Ru 3 (CO) 9 (PEO-DPPSA) 3 (PEO-DPPSA: poly(ethylene oxide)-substituted 4-(diphenylphosphino)benzenesulfonamide) was investigated. The influences of reaction temperature, CO pressure, ratio of substrate/catalyst (mol) and organic/aqueous (vol.%) on the reduction were studied. Under the condition of 140 °C, P CO =4 MPa and 10 h, the conversion of o -ClC 6 H 4 NO 2 was 97.5% and the selectivity of the desired amines was higher than 99%. The reduction proceeded with good activity and selectivity toward nitro group when halogen, carbonyl or cyano groups where present in the substrates. The catalyst in the water phase could be recycled three times with little loss of catalyst activity.

Selective reduction of NO with propylene in the presence of oxygen over Co- and Pt-Co promoted HY

Abstract: Selective reduction of NO with propylene in the presence of oxygen was carried out over Co ion-exchanged HY zeolites (Si/Al=2.55, 20) and Co-Pt combination catalysts based on HY zeolite (Si/Al=2.55). Between the two Co-HY catalysts, selective reduction of NO to N2 was favored over Co-HY zeolite with lower Si/Al ratio, however, oxidation of NO and combustion of C3H6 proceeded easily over that with higher Si/Al ratio. It was further shown that most of Co existed as ion-exchanged Co [Co2+ or Co2+(OH)?] over the catalyst with lower Si/Al ratio, and as Co oxide [Co3O4] over the catalyst with higher Si/Al ratio. When bimetallic Co-Pt/HY catalysts were applied, Pt was present in metallic form in the working catalysts. Over these catalysts, conversion of NO increased with increase in the amount of Pt loading, however, selectivity to N2 decreased. The maximum yield of N2 was achieved over 0.1 wt.% Pt?1.0 wt.% Co-HY catalyst. It is concluded that metallic form of Pt and ion-exchanged Co are essential to obtain high yield of N2, and that the role of Pt is to catalyze the oxidation of NO to NO2, which is successfully reduced by propylene over Co sites to nitrogen.

Adsorption and catalytic reduction of NO with methanol over carbon and carbon-supported catalysts

Abstract: The effect of various metal additives on the catalytic performance of carbon during the selective reduction of NO with methanol has been studied in the absence and in the presence of gas-phase oxygen. The mechanism of this reaction in the use of carbon-supported catalysts was studied by means of in situ FTIR combined with the measurements of catalytic activity. In the absence of oxygen, NO is adsorbed in a very small amount on the surface of carbon. The reaction of NO with the products of the methanol decomposition, results in the formation of adsorbed isocyanate (NCO) species at 2229 cm−1. Formation of gaseous NH3 as a product of the reaction between NO and methanol was observed. Oxygen-containing surface functional groups of carbon effectively promotes the reduction of NO with methanol. IR spectroscopic results of this study show that in the presence of O2 nitric oxide is catalytically oxidized to nitrogen dioxide, which is chemisorbed on the surface of carbon. The surface nitrogen species were identified by FTIR spectroscopy.

Selective Hydrogenation of Aromatic Compounds Containing Epoxy Group over Rh/Graphite

Abstract: Catalytic hydrogenation of aromatic compounds containing epoxy group to alicylic compounds has been investigated. Rh supported on graphite with high surface area exhibited superior performance to other supported catalysts for the selective reduction of the aromatic group while retaining epoxy group.

Method for carrying out the selective catalytic reduction of nitrogen oxides with ammonia in the lean exhaust gas of a combustion process

Abstract: The invention relates to a method for carrying out the selective catalytic reduction of nitrogen oxides with ammonia in the lean exhaust gas of a combustion process executed using a first lean air/fuel mixture. According to the invention, the ammonia required for the selective reduction is obtained from a second rich air/fuel mixture, which contains nitrogen monoxide, by reducing the nitrogen monoxide in a NH3 synthesis stage to ammonia while forming a product gas stream. The ammonia produced thereby is separated out from the product gas stream and is stored in a storage medium for the requirement-orientated use during the selective catalytic reduction.

Sol—Gel Prepared Sn—Al2O3 Catalysts for the Selective Reduction of NO with Propene.

Abstract: Catalytic reduction of NO by propene in the presence of oxygen was studied over Sn–Al2O3 prepared by the sol–gel method. The maximum NO conversion did not change much with Sn loading (1–5 wt%), although the effective temperature window for NO reduction shifted to lower temperatures with increasing Sn loading. X-ray diffraction (XRD), and X-ray absorption spectroscopy (XANES and EXAFS) revealed the formation of finely-divided SnO2 crystallites in Sn–Al2O3. It was deduced that not only the surface vicinity of supported SnO2, which can be reduced at lower temperatures, but also alumina participate in the reaction as catalytically active sites. The catalytic performance of Sn–Al2O3 was markedly improved by an H2O treatment at 873 K. The H2O treatment did not affect the crystal structure of the catalysts and the dispersion state of supported SnO2, but promoted the removal of Cl− ions, which originated from the SnCl4 precursor. The activity enhancement by the H2O treatment was accounted for by an increase in th...

Metal loaded Ti-pillared clays for selective catalytic reduction of NO by propylene†

Abstract: Metal loaded Ti-PILCs have been used as catalysts for the selective reduction of NO by propylene. Cu, Ni, and Fe ion exchanged Ti-PILCs were prepared. The influence of the metal loading was studied. When the metal loading increases, the catalytic activity also increases reaching a maximum of NO conversion and then decreased. Cu-TiPILs exhibited the highest NO conversion. Cu-PILCs prepared by impregnation were compared with those prepared by ion exchange. In general the ion exchange method resulted to be more adequate for the preparation of the catalyst. The presence of Cu 2+ species in the ion-exchanged samples could be the responsible of this behaviour.

Monitoring Aging and Deactivation of Emission Abatement Catalysts for Selective Catalytic Reduction of NOx

Abstract: Titania/vanadia, zeolite, and noble metal catalysts are utilized for selective catalytic reduction (SCR) of NO x using ammonia as the reductant in different temperature ranges. Studies of aging have been carried out to probe deactivation rates and mechanisms. Periodic laboratory testing of samples of NO x reduction catalysts from multi-layer reactors, such as those utilized at electric power plants, allows prediction of catalyst life-times. Testing has been carried out under protocol conditions with monolith, plate-type, and pelleted catalysts so that relative NO reduction rates can be compared, with or without the presence of SO2. The catalysts were analyzed by surface analysis techniques, including electron microscopy and X-ray photoelectron spectroscopy, to probe surface morphology, loss of active components, presence of poisons, and blocking of pores and active sites by ammonium bisulfate to determine the dominant mode(s) of gradual deactivation.

Method for the selective catalytic reduction of nitrogen oxides using ammonia in the lean exhaust gas from a combustion process

Abstract: The invention relates to a method for the selective catalytic reduction of nitrogen oxides using ammonia in the poor exhaust gas from a combustion process which is carried out on a first poor air/fuel mixture. The ammonia necessary for the selective reduction is obtained from a second, rich air/fuel mixture containing nitrogen monoxide, by reducing the nitrogen monoxide to ammonia, in one NH3-synthesis step, forming a product gas flow. The ammonia formed is separated from the product gas flow and is stored in a storage medium to be used if needed in the selective catalytic reduction.

Method for the selective catalytic reduction of nitrogen oxides using ammonia in the poor exhaust gas from a combustion process

Abstract: The invention relates to a method for the selective catalytic reduction of nitrogen oxides using ammonia in the poor exhaust gas from a combustion process which is carried out on a first poor air/fuel mixture. The ammonia necessary for the selective reduction is obtained from a second, rich air/fuel mixture containing nitrogen monoxide, by reducing the nitrogen monoxide to ammonia, in one NH3-synthesis step, forming a product gas flow. The ammonia formed is separated from the product gas flow and is stored in a storage medium to be used if needed in the selective catalytic reduction.

Roles of CoAl2O4, Co3O4, and alumina for selective catalytic reduction of NO with ethene in excess oxygen

Abstract: The catalytic activities of pure CoAl2O4, Co3O4, physical mixture of CoAl2O4 and Al2O3, and Co3O4 free Co/Al2O3 for the reduction of NO with ethene in excess oxygen, the oxidation of NO, and the oxidation of ethene were investigated to elucidate the activities of CoAl2O4, Co3O4 and Al2O3. Pure CoAl2O4 was more active than Al2O3 for oxidation of NO, the initiation step of the selective reduction of NO over Co/Al2O3, but was less active than Co3O4 for oxidation of ethene. Well-mixed CoAl2O4-Al2O3 catalyst calcined at 800°C had higher activity for selective catalytic reduction of NO with ethene in excess oxygen than catalyst calcined at 500°C as well as roughly-mixed CoAl2O4-Al2O3 catalyst. The high activity of CoAl2O4-Al2O3 catalyst depends on the synergy of CoAl2O4 and Al2O3 particles at their interfaces. Selective removal of Co3O4 from cobalt-loaded alumina, Co3O4-free Co/Al2O3, enhanced the activity for selective catalytic reduction of NO with ethene in excess oxygen, indicating that Co3O4 inhibited the reaction, and that the residual CoAl2O4-like species was catalytically active. High activity of Co/Al2O3 calcined at 800°C for the selective reduction of NO with ethene in excess oxygen is due to the fomlation of CoAl2O4 on the Surface layer of γ-Al2O3.

Additive Effect of Rh on the Catalytic Activity of Ag/Al2O3 for the Selective Reduction of NO

Abstract: The additive effect of noble metals (Rh, Ir, Ru, and Pd) on the catalytic activity of Ag/Al2O3 for the selective reduction of NO with n-decane in the presence of O2, H2O and SO2 was investigated. Although NO reduction activity of Ag/Al2O3 was decreased by coexisting SO2 at temperatures below 450°C, the addition of Rh improved the activity at 300-400°C. Optimum Rh loading was 0.05-0.1wt% and the effect was remarkably observed at low concentration of coexisting SO2.

Catalytic Activities of Single Component Metal Oxides for Selective Reduction of NO with Ethene

Abstract: The catalytic activities of thirteen types of single component metal oxides were measured for the selective catalytic reduction (SCR) of NO with ethene in excess oxygen and related reactions to elucidate the characteristic features of catalyst activity. The related reactions were the oxidation of NO2 with O2, the oxidation of C2H4 with O2, the reduction of NO2 with C2H4 in the absence of O2, and the reduction of NO with C2H4 in the absence of O2. Alumina exhibited the highest activity for SCR, followed by ZrO2, SNO2, MgO, CaO, Y2O3, and TiO2; WO3, Co3O4, CuO, Fe2O3, ZnO, and SiO2 showed little activity. The active catalysts including alumina had the characteristic features of high activities for both the oxidation of NO to NO2 and the reduction of NO2 with C2H4 to form N2, as well as low activity for the oxidation of C2H4 with O2. Although Co3O4, CuO, and Fe2O3 showed high activities for the oxidation of NO to NO2, they were also highly active for the oxidation of C2H4 with O2. Therefore, C2H4 was consumed without reduction of NO over these catalysts. The characteristic features for the active catalysts also support the reaction scheme that the SCR proceeds by the successive reactions of the oxidation of NO to NO2 and the reduction of NO2 with C2H4 to form N2.

Selective catalytic reduction

Abstract: A process for the selective catalytic reduction of nitrogen oxides with ammonia in a lean-mix exhaust gas from a combustion process operated with a first, lean-mix air/fuel mixture, wherein the ammonia required for selective reduction is obtained from a second, rich-mix air/fuel mixture which contains nitrogen monoxide by reduction of the nitrogen monoxide in a NH3 synthesis step to give ammonia with the formation of a product gas stream, and where the nitrogen monoxide-containing second air/fuel mixture is supplied to the NH3 synthesis step for reduction of the nitrogen monoxide to ammonia over a three-way converter catalyst and the ammonia formed is separated from the product gas stream and is stored in a storage medium for use as and when required for selective catalytic reduction.

Alumina-supported catalysts for NO reduction in an oxidizing atmosphere

Abstract: Catalytic selective reduction of NOx to N2 using a hydrocarbon in an oxidizing atmosphere is challenging because of the competitive reaction of hydrocarbon combustion. Alumina is a rather effective catalyst for this reaction, but it requires high operating temperatures. The activity can be enhanced by adding other catalytic components, such as Pt, Ag, CoOx, or SnO2. Many of these catalyst systems are bifunctional. A substantial portion of the reaction pathway for propene reduction of NOx has been elucidated for SnO2/Al2O3. The function of SnO2 is to oxidize the propene to acrolein, which is than transterred to alumina where it reacts to form acetaldehyde. Reduction of NOx by acetaldehyde on alumina leads to N2. The bifuncational aspect of the catalyst systems offers the potential to improve the catalytic performance by optimizing the individual components.

Sulfurated Borohydride Exchange Resin: A Novel Reagent for Selective Reduction of Aldehydes.

Abstract: Selective reduction of aldehydes is carried out by using sulfurated borohydride exchange resin as a novel reducing reagent. Other sensitive groups like F, Cl, Br, NO2, CN, OMe, ester and methylenedioxy remain intact under these reaction conditions. The isolation of pure products by simple filtration and evaporation is an important feature of this method.