Mitsunori Tabata

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.

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

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.

Performance of solid acid type catalysts for the selective reduction of nitrogen oxides by hydrocarbons and alcohols

Abstract The performance and characteristics of solid acid type catalysts such as H-ZSM-5 and alumina for the title reaction were investigated. NO reduction on these catalysts was characterized by high efficiency of reducing agent consumed in the presence of oxygen. The catalytic activity was found to be correlated to the solid acidity of the catalysts. Among various reducing agents, methanol was the most efficient for NO reduction at low temperature. It was suggested that the oxidation of NO to NO2 is an important reaction step in the overall NO reduction. Although coexisting water vapor inhibited the reaction, methanol was still effective for alumina-catalyzed reduction at low temperature. Alumina showed excellent activity and durability for the de-NOx of diesel emissions.

Reduction of NOx in diesel exhaust with methanol over alumina catalyst

Abstract NO x reduction in diesel exhaust using selective catalytic reduction by methanol over alumina catalyst was investigated. Although a slight decrease in catalytic activity took place at the initial stage of the catalyst evaluation, more than 40% NO x conversion was obtained at 400°C and a space velocity of 10 000 h −1 by using a ball type alumina catalyst and methanol ( CH 3 OH/NO x mole ratio = 2) as a reducing agent. The experimental results using synthetic exhaust gases containing SO 2 indicated that the initial catalytic deactivation is ascribed to the formation of Al 2 (SO 4 ) 3 -like species on alumina surface through reaction with SO 2 . However, the formation stopped at a certain point in time. The stable activity following the initial deactivation did not depend on SO 2 concentration. A durability test of a honeycomb type alumina was also conducted, and more than 70% of NO x conversion maintained for more than 4000 h at a CH 3 OH/NO x mole ratio of 6. In this case a gradual decrease in the activity of alumina occurred due to catalyst sintering.

Promotive effect of Sn on the catalytic activity of Al2O3 for the selective reduction of NO by methanol

The effect of various metal additives on the catalytic performance of A12O3 was investigated for the selective reduction of NO by methanol in oxidizing atmosphere. The addition of Sn promoted the catalytic activity of alumina for the NO reduction at low temperatures. Moreover, it was found that Sn/Al2O3 catalyst maintained its high activity even in the presence of SO2.