(439e) Dry Reforming of Methane over Ni Based Lanthanum Zirconate Pyrochlore Catalysts: Deactivation Study

Dry reforming of methane (DRM) is one promising method for conversion of methane and carbon dioxide to syngas (CO+H₂). Typically, nickel-based catalysts are widely used in methane reforming due to availability and cost but are prone to deactivation by coking and sintering[1]. Various types of catalysts have been studied to optimize conversion and minimize deactivation. Pyrochlores are thermally stable crystalline metal oxides with general formula A₂B₂O₇ and are tolerant at methane reforming conditions. In our work, a modified Pechini[2] method was used to prepare Lanthanum Zirconate pyrochlore catalyst with Ni doped in Zr sites to produce 3wt%Ni catalyst. Spectroscopic and thermal characterizations of the catalyst were carried out.

Due to low Ni loading, XRD spectra did not show significant difference to the base pyrochlore spectra, except for few small peaks of NiO. In XPS, Ni⁺² and Ni⁺³ were detected from Ni3p and O1s peaks as reported by Voevodin et al.[3] TPR of fresh catalysts showed a large peak above 550°C (Fig shown), which can be attributed to highly dispersed and strongly interacting Ni species with the support. Two other small peaks were also observed at lower temperatures which could be due to possible reduction of Ni⁺³ to Ni⁺² and Ni⁺² to Ni⁰[4]. A temperature programmed reaction was carried out to observe activity and possible deactivation of the catalyst. Catalyst was reduced under hydrogen at high temperatures to activate the catalyst prior to the reaction. Around 700°C, the reactants, CO₂ and CH₄ started to react. Temperature was held for 90 min each at 700°C, 750°C, 800°C and 850°C and then brought back to 700°C. During this process, the product stream was monitored continuously using a Mass Spectrometer. Initial experiment at 700°C showed 93% and 88% conversions of CO₂ and CH₄ respectively. These conversions are higher than the those obtained for 4%Ni/Al₂O₃ from MónicaGarcía-Diéguez et al.[5], and 5%Ni/CeO₂-ZrO­2­ from Kambolis et al.[6], at the same operating temperature of 700°C. As the temperature was increased, increase in both CO₂ and CH₄ conversion values was observed and reached equilibrium at around 850°C. When the reaction temperature was brought back to 700°C, there was a significant drop in the conversion values indicating catalyst deactivation. Post reaction TPO showed two peaks indicating carbon deposition (Fig shown). Peak at 345°C can be assigned to amorphous carbon, while the peak at 610°C can be assigned to polymeric carbon. SEM images also confirmed carbon depoisition.