Lead-substituted strontium hydroxyapatite (Sr(10-x)Pb(x)(OH)2(PO4)6) showed remarkably enhanced catalytic performance for the oxidative coupling of methane (OCM) when compared with the unsubstituted strontium hydroxyapatite. Other substituted transition metals such as zinc, cobalt and nickel were not so effective for improving the catalytic performance for the OCM. The Ni-substituted catalyst exhibited quite different catalytic behavior: CO and hydrogen were the major products instead of the C2 products. The catalyst with the extent of Pb substitution(x) of 0.2 showed the highest C2 selectivity and yield (about 47% and 17% at 1,023 K, respectively) and also exhibited quite stable behavior.
Hutchings GJ, Scurrell MS, "Methane Conversion by Oxidative Processes: Fundamental and Engineering Aspects," Wolf, E.E., ed., Van Nostrand Reinhold, New York, 200, 1992