Study on the monolayer dispersion behavior of SnO2 on ZSM-5 for NOx-SCR by C3H6: the remarkable promotional effects of air plasma treatment

Aiming to fabricate more practical catalysts for NOx-SCR with C3H6, SnO2/ZSM-5 having different SnO2 loadings was prepared and treated with DBD air plasma. The dispersion of SnO2 on the H-ZSM-5 support and their interactions were investigated with both experimental methods and DFT calculations. SnO2 displays evident monolayer dispersion behavior, getting a threshold of 0.271 mmol 100 m(-2) support. Plasma treatment improves significantly the SnO2 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 SnO2-ZSM-5 support interaction, mainly through donating electrons from Sn4+ to Al3+ in the support, thus improving the dispersion of SnO2 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 SnO2 loading near the monolayer dispersion threshold shows the optimal activity in the corresponding catalyst series, demonstrating an evident threshold effect. Over SnO2/ZSM-5, the reaction goes through a Langmuir-Hinshelwood pathway, involving the adsorption and activation of both NO and C3H6 molecules. Surface mono-dentate/bridged-nitrate and carbonate species are the main reaction intermediates.