Identification of Main Active Sites and the Role of NO 2 on NO x Reduction with CH 4 over In/BEA Catalyst: A Computational Study

摘要

The main active sites and the catalytic process in selective catalytic reduction of NO x by CH 4 (CH 4 -SCR) on In/BEA catalyst were investigated by density functional theory (DFT) using a periodic model. The [InO] + and [InOH] 2+ moieties were constructed in the channel of periodic BEA zeolite representing the Lewis and Br?nsted acid sites. The electronic structures [InO] + and [InOH] 2+ were analyzed, and it was found that the [InO] + group were the main active sites for CH 4 activation and NO/NO 2 adsorption in the CH 4 -SCR process. CH 4 molecules could be activated on the O site of the [InO] + group in In/BEA, which was resulted from the strong interactions between the C-p orbital of the CH 4 molecule and the O-p orbital of the [InO] + group. CH 4 activation was the initial step in CH 4 -SCR on In/BEA catalyst. NO 2 molecules were essential in the SCR process, and they could be produced by NO reacting with gaseous O 2 or the O atom of the [InO] + group. The presence of NO 2 could facilitate the key intermediate nitromethane (CH 3 NO 2 ) formation and lower the reaction barrier in the SCR process.