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

We investigate herein the reaction mechanism of dry reforming of methane over Pt clusters in combination with kinetic measurements and in-situ characterizations, proposing that the undissociated CO 2 involves in C-H bond activation and the direct reaction between CO 2 * and CH 4 * is considered as the kinetically relevant step. [Display omitted] • CO 2 is probably undissociatively involved in the process of CH 4 activation over Pt/MgO. • A Langmuir-Hinshelwood model is established to explain the DRM reaction mechanism. • Rates of dry reforming of CH 4 are lower than those of CH 4 -O 2 and CH 4 -H 2 O due to different oxidation capacities. • The reaction between CH 4 * and CO 2 * to form HCOO* and CH 3 * is probably the RDS. We investigate here systematically C-H bond activation mechanism on Pt/MgO with O 2 , H 2 O and CO 2 , and find that dry reforming of CH 4 (DRM) experiences a weak activity compared with reforming or partial oxidation of CH 4. Pressure dependence shows negligible effect of CO determined within a broad CO pressure regime (<10 kPa at high-pressure CH 4 /CO 2 (20.3 kPa) and <0.3 kPa at low-pressure CH 4 /CO 2 (0.8 kPa)) and competitive adsorption between CH 4 and CO 2 (0.8 kPa), suggesting that CO 2 is involved in CH 4 activation as an entire molecule. Based on established Langmuir-Hinshelwood model, reaction between adsorbed CH 4 and CO 2 to yield formate and methyl species was kinetically relevant. Both CO 2 and CH 4 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; CO 2 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 CH 4 activation mechanism and push the industrial application of CH 4 forward. [ABSTRACT FROM AUTHOR]