Effects of preparation conditions on the CO methanation performance of Co-Mo carbide catalysts

Abstract We prepared activated charcoal-supported Co-Mo carbide catalysts to investigate the effects of solution pH and initial Co/Mo molar ratio. In the absence of Co, no Mo adsorption was observed at pH above the pHzpc of AC, whereas the introduction of Co at pH > 6 resulted in the co-precipitation of Mo and Co and facilitated Mo adsorption. CO conversions for CO methanation at 400 °C and 30 bar achieved over samples prepared at pH 3 were initially high but decreased with increasing reaction time, whereas CO conversions were maintained at >90% with increasing reaction time for samples prepared at pH > 6. XPS analysis of these high-performance catalysts revealed that the predominant state of surface Mo was Mo0 rather than Mo4+ and Mo6+. Catalysts with maximum methanation activity, i.e., those with the highest surface Mo0 content, were obtained at pH 7 and an initial Co/Mo molar ratio of 1.0.