Nitrogen oxides reduction with hydrocarbons under oxidizing conditions over alumina supported metal catalysts

摘要

A single step sol-gel procedure has been developed and applied to synthesize Pt/alumina, Ag/alumina and Au/alumina catalysts. Also, an activation procedure has been found to be crucial to get highly active Au/alumina and Ag/alumina catalysts. In contrast, Pt/alumina catalyst was active after the calcination step. Although all catalysts are calcined at 600°C, their surface areas are ∼300 m2/g with a uniform pore size distribution, having pores less than 10 nm. In addition, the metal particle size in all catalysts is found to be independent of the metal loading.;The catalytic activity results show that the single step sol-gel prepared Pt/alumina, Ag/alumina and Au/alumina catalysts are very active and also selective toward N2 in comparison to impregnation catalysts. In addition, the temperature window for activity of all sol-gel catalysts is larger than that for impregnation catalysts under the same reaction conditions. Their NOx activity is observed to increase as a function of oxygen concentration. Especially, in the case of Pt/alumina catalyst, the N2 selectivity at maximum NOx conversion increases to ∼80% when the oxygen concentration is 14%.;The presence of water in the reactant gas mixture does not hinder the NOx activity and N2 selectivity of Pt and Au sol-gel catalysts but the activity of Ag sol-gel catalyst is affected by the presence of water. In addition, the presence of 25 ppm SO2 slightly decreases the activity of Au and Ag sol-gel catalysts but it does not change the activity and N2 selectivity of Pt sol-gel catalyst.