Activation mechanism of methane-derived coke (CHx) by CO2 during dry reforming of methane - comparison for Pt/Al2O3 and Pt/ZrO2

The reaction of methane-derived coke (CHx: intermediate of the reforming reaction and also a source of coke deposition) with CO2 was studied on supported Pt catalysts in relation with CO2 reforming of methane. Temperature-programmed hydrogenation (TPH) was performed to investigate the reactivity of coke deposition after the catalyst was exposed to CH4/He at 1070 K. Coke on Pt/Al2O3 could be hydrogenated around 873 K, while for Pt/ZrO2 this was above 1073 K. The results indicate that the reactivity of coke with hydrogen was higher on Pt/Al2O3 than on Pt/ZrO2, which was different from the reactivity of coke towards CO2. Thus, the reactivity of CO2 was studied and compared on these catalysts by several technics. The amount of CO evolution was measured during CO2 flow at 1070 and 875 K. Rate and amount of converted CO2 were higher on Pt/ZrO2 than on Pt/Al2O3. Pt/ZrO2 was proven to react with CO2 to produce CO and active oxygen (CO2 --> CO + O) (probably on its oxygen defect site) more easily than Pt/Al2O3.