Megumu Inaba

Role of supported metals in the selective reduction of nitrogen monoxide with hydrocarbons over metal/alumina catalysts

Abstract The promoting effect of supported metals on alumina catalyst was investigated for the reduction of nitrogen monoxide in oxygen-rich atmospheres. For NO reduction with propene over impregnated CoO/A1 2 O 3 , the first reaction step was found to be the oxidation of NO to NO 2 probably catalyzed by dispersed cobalt species. The next reaction step, which is the reaction of NO 2 with propene to form N 2 , was considered to take place on the alumina surface. Although the activity of impregnated FeO/A1 2 O 3 was low because of the presence of large iron oxide particles catalyzing propene oxidation with dioxygen, FeO/A1 2 O 3 prepared with sol-gel method showed excellent deNO x activity.

Infrared study of catalytic reduction of nitrogen monoxide by propene over Ag/TiO2–ZrO2

Abstract The reaction mechanism of NO reduction by propene over silver-supported TiO2–ZrO2 catalyst was studied by means of in situ FT-IR, combined with catalytic activity studies. The catalytic activity studies suggested that silver plays an important role as the active species. In FT-IR measurements under a static condition, organic nitro (R-NO2), nitrite (R-ONO), inorganic NO−3, carbonate, formate and acetate species were detected when TiO2–ZrO2 or Ag/TiO2–ZrO2 was exposed to a gas mixture of NO+C3H6+O2 at room temperature. In the case of Ag/TiO2–ZrO2, an intense IR band assigned to isocyanate (–NCO) species was observed by evacuation at temperatures above 300°C after being exposed to NO+C3H6+O2. Under a dynamic condition, the isocyanate band was not detected on Ag/TiO2–ZrO2, but observed on TiO2–ZrO2. The isocyanate species was found to be highly reactive toward NO2. A reaction mechanism has been proposed that organic nitro and nitrite compounds formed initially on TiO2–ZrO2 are converted on Ag sites to isocyanate, which is then reduced to N2 by the reaction with NO2 on Ag sites.

Enhanced activity of in and Ga-supported sol-gel alumina catalysts for NO reduction by hydrocarbons in lean conditions

Abstract Nitrogen monoxide was reduced efficiently by hydrocarbons in the presence of oxygen over sol-gel alumina supported indium, gallium, cobalt and tin catalysts. The support alumina prepared by a sol-gel method had high surface area and accordingly active alumina sites for the reaction. Particularly indium/alumina showed a high activity to reduce NO preferably by propene, propane and ethene but also by alcohols in the absence and the presence of water vapor. The activities of alumina supported cobalt, silver and tin catalysts were increased when calcinating the catalysts at 800°C instead of 600°C. In the case of gallium/alumina, NO 2 has higher reactivity than NO to nitrogen when propene was used as a reductant, proving the significance of the oxidation step of NO to NO 2 . The step of NO oxidation was promoted by preparing a physical mixture of 5 wt% Mn 3 O 4 with indium/alumina or gallium/alumina. The NO conversion to nitrogen was increased from 58 to 84% with the manganese oxide promotion over indium/alumina in the presence of water. The reaction mechanistic differences between the alumina supported catalysts and Cu/ZSM-5 were also discussed.

Cooperative effect of platinum and alumina for the selective reduction of nitrogen monoxide with propane

Reduction of nitrogen monoxide with propane in the presence of oxygen proceeded not only on alumina-supported platinum but also on physical mixtures of alumina and silica-supported platinum, both of which are inactive for the selective NO reduction. Spillover, gas phase transfer of some reaction intermediates, or homogeneous propane oxidation seems responsible for the cooperative effect.

Production of olefins from ethanol by Fe-supported zeolite catalysts

Ethanol conversion to C3+ olefins over Fe/H-ZSM-5 catalysts was investigated. Fe is a non-toxic and cheap metal. C3+ olefins are useful not only as fuels but also chemicals. Fe catalysts are fully effective even in the presence of water in EtOH. Therefore, there is no need to remove water from water-containing ethanol, such as bio-ethanol. The initial selectivity of C3+ olefins was not affected by the kind of Fe source and calcination temperature significantly, except in the case of iron phosphate used as the iron source, which showed low C3+ olefins selectivity. In general, the selectivity of C3+ olefins was slightly decreased with time-on-stream. As causes of catalytic deactivation, carbon deposition on the catalyst and framework collapse of the zeolite support can be considered. However, in the cases of Fe2(SO4)3- and FeCl3-derived catalysts, calcined at 700 °C, the decrease in C3+ olefins selectivity could be suppressed. In general, selectivity of aromatics was decreased and selectivity of ethylene was increased with time-on-stream. Used catalyst can be regenerated by air treatment at 500 °C, but the degree of regeneration was dependent on the kind of iron starting materials and the calcination temperature. An FeCl3-based catalyst, calcined at 700 °C, and catalysts calcined at 900 °C (irrespective of iron source) can be almost completely regenerated, while Fe(NO3)3- or Fe2(SO4)3-based catalyst, calcined at 700 °C, cannot be completely regenerated by this treatment.

Silica-supported cobalt catalysts for the selective reduction of nitrogen monoxide with propene

Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO2 prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co2+ ions on silica are responsible for the catalytic activity.

Oxide aerogel catalysts

Abstract Aerogels and xerogels of TiO 2 , V 2 O 5 , ZrO 2 , and Al 2 O 3 with and without additives were prepared by hydrolysis of metal alkoxide. The aerogels and the xerogels were obtained by supercritical drying of the wet gels in ethanol and by drying at 90°C for 24 h in air. Catalyst activity of the gels for NO reduction with C 3 H 6 were determined at 200–600°C in a fixed bed flow reactor. The highest NO conversion to N 2 was obtained with Al 2 O 3 aerogel catalysts, about 80% at 500°C. Al 2 O 3 –ZrO 2 and ZrO 2 have higher activities at lower temperatures. TiO 2 and V 2 O 5 have low activities although they have high oxidation activities. Catalyst activity of aerogels is higher than that of xerogels because of the higher effective diffusivity of reaction gas attributed to the high porosity and larger pore size.

Epoxidation of propylene with molecular oxygen in methanol over a peroxo-heteropoly compound immobilized on palladium exchanged HMS

The peroxo-heteropoly compound {HPO4[W(O)(O2)2]2} was synthesized on the surface of HMS by reacting HMS-PrNH(PO3H2) with [W2O3(O2)4(H2O)2]2− solution, and then palladium ions were exchanged into the channels of HMS to form a hybrid catalyst. The novel solid catalyst showed 34.1% propylene conversion and 83.2% selectivity for propylene oxide for the oxidation of propylene using molecular oxygen as an oxidant in methanol at 373 K for 6 h. Because {HPO4[W(O)(O2)2]2} was immobilized on the HMS surface by chemical bonds and palladium particles formed during the reaction were fixed in the HMS channels, the solid catalyst could be reused by a simple filtration method and the active components did not leach into the methanol medium after reaction. The selectivity for propylene oxide over the solid catalyst was similar to that over a homogeneous catalyst containing [(C6H13)4N]2{HPO4[W(O)(O2)2]2} and Pd(OAc)2, but the propylene conversion over the solid catalyst was lower than that over the homogeneous catalyst. The highest yield of propylene oxide obtained over the solid catalyst by increasing catalyst amount was similar to the highest yield of propylene oxide over the homogeneous catalyst.

Effects of Pretreatments of Cu/ZnO-Based Catalysts on Their Activities for the Water–Gas Shift Reaction

The effects of the pretreatments of Cu/ZnO-based catalysts prepared by a coprecipitation method on their activities for the water–gas shift reaction at 523K were investigated. The activity of a Cu/ZnO/ZrO2/Al2O3 catalyst for the water–gas shift reaction was less affected by calcination at temperatures ranging from 673-973K and by H2 treatment at 573 or 723K than that of a Cu/ZnO/Al2O3 catalyst. The catalyst activity could be correlated mainly to the Cu surface area of the catalyst.

Catalytic performance of silver- and indium-supported TiO2ZrO2 binary oxide for the selective reduction of nitrogen monoxide with propene

The catalytic activity of silver- and indium-supported TiO2ZrO2 binary oxide for NO reduction by propene in the presence of oxygen was investigated. Silver and indium enhanced drastically the NO reduction activity of TiO2ZrO2. This metal additive effect was considered to be due to the promotion of the reaction of NO2 with propene leading to the formation of N2 via organic compounds containing oxygen and nitrogen. In fact, in-situ FT-IR measurements suggested that silver on TiO2ZrO2 catalyzes effectively the reaction of adsorbed species to form an isocyanate species which is a possible reaction intermediate in this reaction.