Improving the Coke Resistance of Ni-Ceria Catalysts for Partial Oxidation of Methane to Syngas: Experimental and Computational Study

The synthesis of syngas (H-2 : CO=2) via catalytic partial oxidation of methane (CPOM) is studied over noble metal doped Ni-CeO2 bimetallic catalysts for CPOM reaction. The catalysts were synthesized via a controlled deposition approach and were characterized using XRD, BET-surface area analysis, H-2-TPR, TEM, Raman and TGA analysis. The catalysts were experimentally and computationally studied for their activity, selectivity, and long-term stability. Although the pure 5Ni/CeO2 catalyst showed high initial activity (similar to 90%) of CH4 conversion, it rapidly deactivates around 20% of its initial activity within 140 hours of TOS. Doping of Ni/CeO2 catalyst with noble metal was found to be coke resistant with the best-performing Ni-Pt/CeO2 catalyst showed similar to 95% methane conversion with >90% selectivity at a temperature of 800 degrees C, having exceptional stability for about 300 hours of time-on-stream (TOS). DFT studies were performed to calculate the activation barrier for the C-H activation of methane over the Ni, Ni3Pt, Ni3Pd, and Ni3Ru (111) surfaces showed nearly equal activation energy over all the studied surfaces. DFT studies showed high coke formation tendency of the pure Ni (111) having a very small C-C coupling activation barrier (14.2 kJ/mol). In contrast, the Ni3Pt, Ni3Pd, and Ni3Ru (111) surfaces show appreciably higher C-C coupling activation barrier (similar to 70 kJ/mol) and hence are more resistant against coke formation as observed in the experiments. The combined experimental and DFT study showed Ni-Pt/CeO2 as a promising CPOM catalyst for producing syngas with high conversion, selectivity and long-term stability suited for future industrial applications.