(A) study on the characteristics of mesoporous materials supported catalyst for the destruction of $NO_x$ and VOCs

Abstract

Nitrogen oxides $(NO_x)$ and volatile organic compounds (VOCs) are among the major air pollutants in the lower atmosphere evolving energy conversion process today. The catalytic destruction of these compounds has been recognized as the most available technology to control of these air pollutants. Platinum containing catalysts were prepared using the mesoporous silicates as support materials and tested for the SCR of NO with hydrocarbon. Pt/MCM-41, Pt/MCM-48 and Pt/SBA-15 catalysts showed better activity for the reduction of NOx with hydrocarbon than the conventional Pt/ZSM-5 catalyst. Among them, Pt/SBA-15 showed the good hydrothermal stability under 10 vol.% $H_2O$ flow at 500℃. From the catalytic reduction of NO over Pt/SBA-15 with different meal loading and $H_2-TPR$ experiment, it can be concluded that the highly dispersed Pt species are more active for NO reduction (especially $N_2O$ formation) in the lower temperature region while bulk Pt species contribute to $N_2$ formation in higher temperature region. XPS results indicate that the Pt species over Pt/SBA-15 are reduced during the reaction of NO-SCR even in the presence of excess oxygen. The reduced Pt species could not be completely oxidized after they have been in contact with NO or $O_2$ at the reaction temperature. Complete NO conversion can only be reached when the concentration of oxygen is less than the critical oxygen concentration. Above the critical oxygen concentration, an optimal reaction temperature exists for the maximum NO conversion, which occurs at the temperature required for complete oxidation of $C_3H_6$. Both maximum NO conversion and $N_2$ selectivity decrease with the increase of oxygen concentration. A higher NO conversion obtained with the higher $C_3H_6/NO$ ratio implies that the adsorption and activation of $C_3H_6$ may be the controlling step for the SCR of NO on Pt/SBA-15. NO conversion is found to be increased by the incorporation of Al species due to the enhancement of...