Nickel-Calcium Phosphate/Hydroxyapatite Catalysts for Partial Oxidation of Methane to Syngas: Effect of Composition

Nickel-calcium phosphate/hydroxyapatite catalysts have recently been reported to exhibit high activity and selectivity in partial oxidation of methane (POM). In this work the optimum composition was determined. The optimum mole ratio of Ca/PO₄ was around 10/6 and that of Ni/PO₄ was in a range from 1.0/6 to 3.0/6 with the optimum Ca/PO₄, and the activity could be related with the amount of metallic nickel. In a temperature range from ca. 400 to 700 K, an apparent autothermal reaction was observed to occur in some cases. This is due to the fact that the actual catalyst temperature is higher than the measured temperature, which comes from the exothermic nature of the reaction. The mixing sequence of the precursors during the catalyst preparation does little affect the catalyst activity and characteristics. Deactivation of the catalyst occurred slowly, but the catalyst could easily be regenerated. Moreover, the nickel-calcium phosphate/ hydroxyapatite catalyst showed higher activity than the nickel-strontium phosphate catalyst.