Calcined hydrotalcites of varying Mg/Al ratios supported Rh catalysts: highly active mesoporous and stable catalysts toward catalytic partial oxidation of methane

摘要

Catalytic partial oxidation of methane to produce syngas were studied over calcined hydrotalcites of varying Mg/Al ratios supported Rh catalysts. Hydrotalcites of varying Mg/Al ratios were prepared using their hydroxide precursors and intercalating them with amino acid lysine. Upon calcination, these hydrotalcites converted into their mixed metal oxides having mesoporosity and used directly as support materials for the synthesis of rhodium catalysts. Rh dispersion, size of the nanoparticles, and metal-support interactions were found to strongly influence the activity of the catalyst and their stability. Feed composition, gas hourly space velocity, and temperature were found to influence the catalyst activity, CO/H_2 ratio, and CO/CO_2 selectivity. Alumina and alumina-rich calcined hydrotalcites exhibit higher catalytic activity, but carbon formation and aggregation were prominent. In contrast, MgO and MgO-rich calcined hydrotalcite supported Rh catalysts exhibit moderate activity; however, they were resistant against particle sintering and carbon formation. Long-term testings of these catalysts were carried out, and it was observed that calcined hydrotalcites of varying Mg/Al ratios supported Rh catalysts were promising candidates as stable and active catalysts toward catalytic partial oxidation of methane.