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/γ-Al 2 O 3 , Au-Mn/γ-Al 2 O 3 and Ag-Mn/γ-Al 2 O 3 , 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 O 2 -TPD and plasma-excited O 2 -TPD. A strong interaction between plasma and Ag-Mn/γ-Al 2 O 3 could make better use of plasma-induced active oxygen species ( i.e. O 3 , O*, O 2 * etc. ) and considerably increase the amount of chemically adsorbed oxygen. Moreover, modified NH 3 -TPD experiments proved that O 2 excited by plasma would greatly change the surface acidity of Ag-Mn/γ-Al 2 O 3 , resulting in the desorption activation energy (E d ) 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.