Study On Pd And Ni Based Catalysts For Partial Oxidation Of Methane To Synthesis Gas

Partial Oxidation of Methane (POM) has drawn great scientific interests due to high reaction rate, low energy consuming, limited operation cost, and producing the syngas with H₂/CO molar ratio of 2:1 that could be directly applied for methanol and Fischer-Tropsch Synthesis.The present works investigate Ni and Pd based POM catalysts concerning preparation methods, modifications, performances and initial industrial applications. The studies combine the analysis of model reactions, XRD, BET, TPR, dispersion measurement, TG-DTA, Raman, SEM and XPS to provide the fundamental references for POM catalysts design.Investigations over Ni based POM catalysts reveal the optimized 10% Ni loading onα-Al₂O₃. Surface areas'threshold is determined to be 4.042m²/g, and higher values induce larger pore volumes and diameters positive for mass transportation efficiency thus benefitting POM performances. Pore volume Vt≥0.0160cm³/g and pore diameter Dp≥13.08nm would be required accordingly. The parameter S_micro/S_BET well describes the correlation between supports'textures and catalytic performances, where the desired activities could be maintained at S_micro/S_BET≤37.79%. Catalytic activity and durability has been significantly improved by CeO₂-ZrO₂ promoters. Mechanical powder mixed POM catalyst shows the best comprehensive performance in comparison with precipitates or precursors mixed samples, which is contributed to the intense Ni-Al₂O₃ interaction resisting active sites sintering, carbon deposit.Investigations of Pd based POM catalysts confirm the advantages of CeO₂-ZrO₂ supports in reducing Pd amount for activity maintenance, promoting catalytic activity and durability. Better dispersion of active components with higher thermal stability on CeO₂-ZrO₂ and the reactive lattice oxygen of the latter are the main factors for those above advantages. Precipitates mixed catalyst performs the best activity in comparison with the mechanical powder or precursors mixed samples. Pd and CeO₂-ZrO₂ interaction is magnified in precipitates mixed catalysts, and the lattice oxygen of CeO₂-ZrO₂ is positive for carbon deposit removal on metal sites. Initial industrial application of the selected Pd catalysts, where CeO₂-ZrO₂ is mixed with Al₂O₃ as the promoter with molar ratio of 1:1, shows the improved sulfur resistance due to the formation of surface oxidative sulfate from SO₂ adsorption. Ignition temperature of the catalysts'bed is managed to be limited at 880℃in metal honeycomb supported materials, lower than 950℃for calcinations, avoiding active sites aggregation, supports sintering, and improving longevity of the catalysts.