(439c) Reforming of Methane over Ni and Ca Based Pyrochlore Catalysts to Produce Syngas

Catalytic conversion of methane and carbon dioxide to syngas is the most studied and feasible option to utilize these gases. Further, syngas can be converted to high value chemicals. Some of the processes involving conversion of CH₄ and CO₂ to syngas are Dry Reforming, Oxy-CO₂ Reforming and Bi-Reforming of methane. In the current work, we focus on the former two, Dry reforming (DRM) and Oxy-CO₂ reforming of methane (OCRM). Nobel metals are most active and stable for reforming reactions, but, are expensive. Hence, comparatively inexpensive Ni based catalysts, which are significantly active and stable, are explored for these reactions. However, these catalysts are prone to deactivation by coking and sintering at high temperatures. Pyrochlores are thermally and chemically stable crystalline metal oxides with general formula A₂B₂O₇ which are tolerant at reforming conditions. In our work, Lanthanum Zirconate pyrochlore (La₂Zr₂O₇) was doped with Ni in Zr site and Ca at La site to produce an active and stable catalyst. A modified Pechini method was used to produce 3wt% Ni loading of La₂Zr₂O₇ catalyst (LCNZ3) and tested for reforming reactions. 1:1 ratio of CH4:CO2 was used for DRM, while 1:3:1 ratio of CO2:CH4:O2 was used for OCRM. Additionally, spectroscopic and thermal characterizations were carried out to study the catalyst.

XRD of fresh catalyst showed peaks corresponding to the base pyrochlore (La₂Zr₂O­₇) and small peaks of NiO. Additionally, a perovskite phase was also observed in the catalyst. A significant increase in the lattice constant value of the pyrochlore was seen, suggesting Ni substitution into the pyrochlore structure. Ni⁺² and Ni⁺³ states were observed to be present on the surface from XPS. XPS and SEM-EDS analysis were done to compare the surface and bulk compositions of the catalysts. TPR showed reduction peaks at different temperatures, indicating different interaction strengths of Ni in the structure. Catalyst showed higher activity, i.e., higher conversion values of reactants for OCRM compared to DRM. Also, DRM deactivated the catalyst more significantly compared to OCRM. This could be due to limitation of carbon formation on the surface because of presence of additional oxidizing agent, i.e., oxygen. Post run TPO were also carried out to characterized the coke deposited on the surface. Carbon deposited was observed to be present in more than one phase, i.e., amorphous and polymeric.