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 intermediate in the reforming reaction and also a source of coke deposition) with CO₂ was studied on Pt/Al203 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.