Dry reforming of methane with isotopic gas mixture over Ni-based pyrochlore catalyst

Dry reforming of methane was carried out using isotopic ¹³CO₂ and C¹⁸O₂ 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 H₂-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 °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 ¹³CO₂ gas showed the syngas production for this material proceeded through the activation of CH₄ with O that came from breaking one of the CO 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 ¹²C¹⁸O₂, revealed only ¹²C¹⁸O was formed and no ¹²C¹⁶O 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 ¹³CO₂¹²CH₄ mixture. No carbon deposition appeared to originate from ¹³CO₂.