Evidence of undissociated CO2 involved in the process of C-H bond activation in dry reforming of CH4

We investigate here systematically C-H bond activation mechanism on Pt/MgO with O-2,O- H2O and CO2, and find that dry reforming of CH4 (DRM) experiences a weak activity compared with reforming or partial oxidation of CH4. Pressure dependence shows negligible effect of CO determined within a broad CO pressure regime (< 10 kPa at high-pressure CH4/CO2 (20.3 kPa) and < 0.3 kPa at low-pressure CH4/CO2 (0.8 kPa)) and competitive adsorption between CH4 and CO2 (0.8 kPa), suggesting that CO2 is involved in CH4 activation as an entire molecule. Based on established Langmuir-Hinshelwood model, reaction between adsorbed CH4 and CO2 to yield formate and methyl species was kinetically relevant. Both CO2 and CH4 derivatives are the most abundant surface intermediates, being confirmed by in situ FTIR and quasi -in-situ XPS. The oxidizability of oxidant was quantitatively evaluated; CO2 has the weakest oxidizability, probably making DRM less active. DRM is structure-sensitive with terrace site of Pt as active component. The influence of reverse water-gas shift was dominant in modifying selectivity. This work will certainly reconcile contradictories on CH4 activation mechanism and push the industrial application of CH4 forward. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

This study systematically investigates the C-H bond activation mechanism on Pt/MgO catalyst with O-2, O-H2O, and CO2. It is found that dry reforming of CH4 (DRM) exhibits weaker activity compared to reforming or partial oxidation of CH4. Pressure dependence shows that CO has negligible effect, suggesting the involvement of CO2 in CH4 activation as a whole molecule. The reaction between adsorbed CH4 and CO2 to form formate and methyl species is kinetically relevant. Experimental results confirm that both CO2 and CH4 derivatives are the most abundant surface intermediates.