Probing the effects of plasma-induced surface species in ring-opening process of toluene decomposition via plasma-excited TPD and in situ DRIFTS

Aromatic ring-opening process is considered as the rate-determining step for catalytic toluene decomposition. However, the ring-opening pathway has not been fully revealed, especially the effect of the surface species in plasma catalytic hybrid system. Herein, a series of Mn based catalysts (with the low Mn content of 1 wt %), Mn/ gamma-Al2O3, Au-Mn/gamma-Al2O3 and Ag-Mn/gamma-Al2O3, were used to clarify the mechanism of plasma catalytic toluene degradation by a closely combined temperature-programmed desorption (TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Effects of plasma on surface oxygen species were investigated by a comparison study of O2-TPD and plasma-excited O2-TPD. A strong interaction between plasma and Ag-Mn/ gamma-Al2O3 could make better use of plasma-induced active oxygen species (i.e. O3, O*, O2* etc.) and considerably increase the amount of chemically adsorbed oxygen. Moreover, modified NH3-TPD experiments proved that O2 excited by plasma would greatly change the surface acidity of Ag-Mn/gamma-Al2O3, resulting in the desorption activation energy (Ed) of toluene increasing to 19.5 kJ/mol. Finally, possible ring-opening mechanisms over different catalysts were proposed after the evolution of typical intermediates being systematically analyzed by in situ DRIFTS. It was found that the toluene ring-opening reaction on different catalysts might be selectively started at hydroquinone. The present work could provide both a more detailed toluene ring-opening process and new insights into the understanding of the plasma exciting effect on the surface species in VOCs decomposition.

Automated summary

This study investigated the mechanism of plasma catalytic toluene degradation using a series of Mn-based catalysts. The interaction between plasma and Ag-Mn/γ-Al2O3 was found to enhance the utilization of plasma-induced active oxygen species and chemically adsorbed oxygen. The possible ring-opening mechanisms over different catalysts were proposed after analyzing the evolution of typical intermediates.