Methane reforming over a high temperature stable-NiCoMgO_x supported on zirconia-hafnia catalyst

Abstract

The unusually high temperature stable NiCoMgO_x (Ni/Co/Mg:1:0.2:1.2)/zirconia-hafnia catalyst has been investigated for syngas generation via the catalytic partial oxidation of methane (CPOM), oxidative steam reforming of methane (OSRM) and oxidative CO₂ reforming of methane (OCRM) processes. The catalyst, even when calcined at 1400°C for 4 h, showed excellent activity/selectivity for the CPOM, OSRM and the OCRM reactions. On account of its high thermal stability, hot spots in the catalyst bed and/or high temperatures prevailing at the catalyst surface during the oxy-reforming processes would have little or no effect on the catalytic activity/selectivity of the NiCoMgO_x/zirconia-hafnia catalyst, thus making the catalyst suitable even for operating under adiabatic conditions. While the selectivity for CO increased considerably with increasing reaction temperature for the CPOM process, the selectivity for H₂ was affected to a much lesser extent. The selectivity for CO and H₂ in the CPOM reaction was found to decrease with increasing space velocity; the H₂ selectivity was however affected to a greater extent. For the OSRM process, the H₂O/CH₄ ratio profoundly influenced the H₂/CO ratio and the heat of the reaction. Depending on the H₂O/CH₄ ratio, the OSRM process could be operated in a mildly exothermic, thermoneutral or mildly endothermic mode. The CO₂ conversion increased rapidly with increasing OCRM temperature and correspondingly the exothermicity of the OCRM reaction was found to decrease with increasing reaction temperature. At 900°C, the OCRM reaction was mildly exothermic and provided high methane conversion and syngas selectivity.