Degradation mechanism of toluene over Ce-M (Cu, Co and Fe) catalysts: Effect of oxygen vacancies on reaction intermediates

Abstract

A series of CeO2 samples modified with various metals M (M = Cu, Co and Fe) were synthesized via a simple sol–gel approach. The experimental results showed that there were significant differences in the catalytic activities between different metal-doped Ce-based catalysts. The Ce-Cu sample possessed excellent catalytic activity at low temperatures, and 90 % conversion of toluene was at 255 ℃, which was due to the presence of ample oxygen vacancies (Ov). Three degradation pathways for toluene oxidation were inferred based on the in situ DRIFTS. The Ce-Cu catalysts possessed abundant Ov, which improved the conversion between Oads → Olatt and the breakage of aromatic rings, thus reducing the production of intermediates. The Ce-Co and Ce-Fe catalysts owned few amounts of Ov species, leading to an extensive amount of by-products. Furthermore, the loss of active sites inhibited the reaction rate, causing the inferior catalytic performance of the Ce-Co and Ce-Fe samples.