Study on the monolayer dispersion behavior of SnO 2 on ZSM-5 for NO x -SCR by C 3 H 6 : the remarkable promotional effects of air plasma treatment.

Aiming to fabricate more practical catalysts for NO x -SCR with C 3 H 6 , SnO 2 /ZSM-5 having different SnO 2 loadings was prepared and treated with DBD air plasma. The dispersion of SnO 2 on the H-ZSM-5 support and their interactions were investigated with both experimental methods and DFT calculations. SnO 2 displays evident monolayer dispersion behavior, getting a threshold of 0.271 mmol 100 m -2 support. Plasma treatment improves significantly the SnO 2 dispersion, hence amplifying the monolayer dispersion threshold to 0.380 mmol 100 m -2 . XPS and DFT calculations have testified that plasma treatment strengthens strongly the SnO 2 -ZSM-5 support interaction, mainly through donating electrons from Sn 4+ to Al 3+ in the support, thus improving the dispersion of SnO 2 at the same loadings. Consequently, the catalytic performance is remarkably improved because of the generation of more abundant surface acid sites and superoxide species devoted to the reaction. The sample having a SnO 2 loading near the monolayer dispersion threshold shows the optimal activity in the corresponding catalyst series, demonstrating an evident threshold effect. Over SnO 2 /ZSM-5, the reaction goes through a Langmuir-Hinshelwood pathway, involving the adsorption and activation of both NO and C 3 H 6 molecules. Surface mono-dentate/bridged-nitrate and carbonate species are the main reaction intermediates.