Effects of modifying Ni/Al_2O_3 catalyst with cobalt on the reforming of CH_4 with CO_2 and cracking of CH_4 reactions

摘要

Alumina supported nickel (Ni/Al_2O_3), nickel-cobalt (Ni-Co/Al_2O_3) and cobalt (Co/Al_2O_3) catalysts containing 15% metal were synthesized, characterized and tested for the reforming of CH_4 with CO_2 and CH_4 cracking reactions. In the Ni-Co/Al_2O_3 catalysts Ni-Co alloys were detected and the surface metal sites decreased with decrease in Ni:Co ratio. Turnover frequencies of CH_4 were determined for both reactions. The initial turnover frequencies of reforming (TOF_(DRM)) for Ni-Co/Al_2O_3 were greater than that for Ni/Al_2O_3, which suggested a higher activity of alloy sites. The initial turnover frequencies for cracking (TOF_(CRK)) did not follow this trend. The highest average TOF_(DRM), H_2:CO ratio and TOF_(CRK) were observed for a catalyst containing a Ni:Co ratio of 3:1. This catalyst also had the maximum carbon deposited during reforming and produced the maximum reactive carbon during cracking. It appeared that carbon was an intermediate product of reforming and the best catalyst was able to most effectively crack CH_4 and oxidize carbon to CO by CO_2.