Toshiyuki Tanaka

Intermediacy of organic nitro and nitrite surface species in selective reduction of nitrogen monoxide by propene in the presence of excess oxygen over silica-supported platinum

Abstract The role of surface species in the selective reduction of nitrogen oxides by propene in the presence of excess oxygen over Pt/SiO 2 has been studied at 393 K mainly with IR spectroscopy. Organic nitro, nitrite and carbonyl species were detected during the reaction. The reactions of those three species with nitrogen dioxide and oxygen took place rapidly, producing N 2 , N 2 O and CO 2 , while the reactivities of those species with nitric oxide and propene were low. Hence, a mechanism is proposed, in which the nitro, nitrite and carbonyl surface species are key reaction intermediates. Similarity in the products between the selective reduction and the oxidation of nitro (nitromethane) or nitrite (n-butylnitrite) compound supported the proposed reaction scheme.

Catalytic removal of nitric oxide with hydrogen and carbon monoxide in the presence of excess oxygen

Catalytic NOx removal with H2 in the presence of an excess of oxygen was studied. A Pt/zeolite catalyst has a high NOx conversion efficiency, but has the disadvantages of being strongly poisoned by CO and HCs such as C3H6 and the formation of N2O as a byproduct from NOx. By reducing the oxidation efficiency of Pt, we have developed an improved catalyst, Pt-Mo-NaSiO2, which has a higher temperature range of NOx conversion and a lower N2O byproduct formation, than conventional Pt catalysts. This idea was supported by IR and XPS data of the catalyst.

Effect of the addition of Mo and Na to Pt catalysts on the selective reduction of NO

The selective reduction of NOx by reductants such as C3H6 and CO in oxidizing feedstreams simulated exhaust from automobile engine and three-way behavior around the stoichiometric point have been investigated on trimetallic PtMoNa/SiO2 catalysts, over a wide range of temperatures compared with bimetallic PtMo/SiO2 catalyst and monometallic Pt/SiO2 catalyst. The simultaneous addition of Mo and Na to Pt catalysts has been found to improve the following reaction characteristics on selective reduction of NOx and three-way activity of conventional Pt catalyst. The temperature window on selective reduction of NOx on trimetallic PtMoNa/SiO2 catalysts was found to be wider and to shift at higher temperature than that on bimetallic PtMo/SiO2 and monometallic Pt/SiO2 catalysts under lean static conditions. The redox ratio window, in which three-way activity occurred on trimetallic PtMoNa/SiO2 catalysts, was also found to be wider than that on bimetallic PtMo/SiO2 catalysts and monometallic Pt/SiO2 around stoichiometric point. On the other hand, XPS, IR and CO adsorption data indicated that the oxidation of Pt on PtMoNa/SiO2 catalysts was depressed by the added Mo and Na even under excess oxygen conditions, so that the reaction characteristics of trimetallic PtMoNa/SiO2 catalysts was improved.