International Journal of Hydrogen Energy, Vol.44, No.8, 4167-4176, 2019
Dry reforming of methane with isotopic gas mixture over Ni-based pyrochlore catalyst
Dry reforming of methane was carried out using isotopic (CO2)-C-13 and (CO2)-O-18 gases over a Ni-based pyrochlore catalyst that was synthesized using the modified Pechini method. In this method, 1 wt% Ni was doped into the La2Zr2O7 pyrochlore structure. The catalyst was characterized by H-2-TPR, TPO, and XRD and tested for its methane reforming activity under CO2 dry-reforming reaction conditions. The results of repeated TPR/TPO cycles up to 950 degrees C showed that the consecutive TPR profiles were nearly identical, indicating that the catalyst was stable at high temperatures, and that the nickel oxidation/reduction processes were reversible. The dry-reforming experimental results using labelled (CO2)-C-13 gas showed the syngas production for this material proceeded through the activation of CH4 with O that came from breaking one of the C-O bonds of CO2 with the latter reaction (CO2 activation) likely occurring at oxygen vacancies at or near the Ni particle-pyrochlore interface. It was also found that only a small portion of the CO originated from CH4. A variation of the same experimental test, but using (CO2)-C-12-O-18, revealed only (CO)-C-12-O-18 was formed and no (CO)-C-12-O-16 was detected, ruling out the possibility of reaction with the lattice oxygen in the catalyst structure with this material. Over this catalyst, the activated CH4 appeared to dissociate to elemental carbon on the catalyst surface, which was determined to be the source of carbon from a post reaction TPO of the catalyst that was exposed to the (CO2)-C-13-(CH4)-C-12 mixture. No carbon deposition appeared to originate from (CO2)-C-13. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.