Yoshiaki Kintaichi

Selective reduction of nitrogen oxides with hydrocarbons over solid acid catalysts in oxygen-rich atmospheres

Highly selective reduction of nitrogen oxides to dinitrogen occurs to a high level in oxygen-rich atmospheres by using a small amount of propane as a reducing agent over alumina, silica-alumina, titania and zirconia catalyst. Judging from the data of activity and ammonia TPD measurement on a series of silica-alumina catalysts, acidity is suggested to be one of the main factors that determine catalytic activity.

Role of oxygen in selective reduction of nitrogen monoxide by propane over zeolite and alumina-based catalysts

The role of coexisting oxygen in the selective reduction of nitrogen monoxide by propane on H-zeolites, alumina, Cu-ZSM-5 zeolite and Pt/Al2O3 catalysts was investigated. In the case of H-zeolites and alumina, oxidation of NO to NO2 played an important role for the overall selective reduction of NO. On the other hand, the initial reaction step was considered to be partial oxidation of propane over Cu-ZSM-5 and Pt/Al2O3.

Transition metal-promoted silica and alumina catalysts for the selective reduction of nitrogen monoxide with propane

Abstract The effect of transition metal additives on the catalytic performances of silica and alumina was investigated for the selective reduction of nitrogen monoxide with propane in the presence of high concentrations of oxygen. Some metal-silica catalysts showed the activity although silica was quite inactive. Most of the transition metals were found to promote the catalytic activity of alumina, although the performances were dependent on the preparation conditions. In particular, metal-alumina catalysts containing metal aluminate showed excellent activity at low temperatures and under high space velocity conditions.

Selective reduction of nitrogen monoxide with propane over alumina and HZSM-5 zeolite : Effect of oxygen and nitrogen dioxide intermediate

In this study we investigated the reduction of nitric oxide with propane over alumina or HZSM-5 zeolite under various reaction conditions and found that the presence of oxygen is essential for selective reduction to occur. It was also found that the reduction of nitrogen dioxide takes place more effectively than that of nitric oxide. Thus we think that the oxidation of nitric oxide to nitrogen dioxide is an important step. This paper deals with the reaction mechanism of the new reaction

Alkali metal-doped cobalt oxide catalysts for NO decomposition

The effect of addition of alkali metals was investigated on the catalytic activity of cobalt oxide (Co3O4) for the direct decomposition of NO. Although Co3O4 was totally inactive, NO decomposition over Co3O4 was significantly promoted by the addition of alkali metals (Li, Na, K, Rb and Cs). Potassium was found to be the most effective additive. The addition of alkali metals increased not only the surface area but also the specific activity per unit surface area. This suggests that catalytically active sites are created on the Co3O4 surface as a result of interaction with alkali metals. The interface between alkali metals and Co3O4 is clearly essential in the NO decomposition reaction. Characterization of the catalyst using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and desorption of O2 (O2-TPD) revealed that traces of added alkali metals weaken the CoO bond strength and promote oxygen desorption from Co3O4, resulting in the formation of cobalt species with a slightly lower valence state. We conclude that these effects, caused by addition of alkali metals, are responsible for the activity enhancement of Co3O4.

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.

Remarkable promoting effect of rhodium on the catalytic performance of Ag/Al2O3 for the selective reduction of NO with decane

Abstract The addition of small amounts of rhodium enhanced the activity of Ag/Al 2 O 3 catalyst for the selective reduction of NO with decane at low temperatures. The Rh-promoted Ag/Al 2 O 3 showed its high performance even in the presence of low concentrations of SO 2 . Based on the catalytic activity for elementary reactions, it was suggested that the role of added rhodium is to enhance the reaction between NO x and decane-derived species, leading to NO reduction. Catalyst characterization by UV-Vis spectroscopy indicated that the major silver species on Rh-promoted Ag/Al 2 O 3 is Ag n δ + clusters, which would be responsible for the high activity. FT-IR measurements revealed that the formation rate of isocyanate species, which is a major reaction intermediate, is higher on Rh-promoted Ag/Al 2 O 3 .

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.