Mechanism of Carbon Deposit/Removal in Methane Dry Reforming on Supported Metal Catalysts

The greater resistance to coke deposition for Pt/ZrO2 compared to Pt/Al2O3 in the CH4/CO2 reaction has been attributed to the higher reactivity of coke with CO2 on Pt/ZrO2 [1]. Hence, in this communication, the reaction of coke derived from methane (CHx: which is an intermediated in the reforming reaction and also a source of coke deposition) with CO2 was studied on Pt/Al2O3 and Pt/ZrO2 at 1070 K. The reactivity of coke itself on Pt, as measured by its reaction with H2, was higher on Pt/Al2O3 than on Pt/ZrO2. However, the reactivity of coke toward CO2 was lower. Hence, the difference between the two catalysts cannot be attributed to the difference in the reactivity of coke itself. Next, the ability of the active site to activate CO2 (probably oxygen defect sites on the support), as shown by CO evolution measurement in CO2 stream, was higher on Pt/ZrO2 than on Pt/Al2O3. Therefore, the high reactivity of coke toward CO2 on Pt/ZrO2 is attributed not to the intrinsic reactivity of coke itself but to the high activity of CO2 at oxygen defect sites of ZrO2 that are in the vicinity of Pt particles.