(439e) Dry Reforming of Methane over Ni Based Lanthanum Zirconate Pyrochlore Catalysts: Deactivation Study
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. 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. 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., and 5%Ni/CeO2-ZrO2 from Kambolis et al., 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.