Oxidative coupling of methane over transition-metal-substituted strontium hydroxyapatite

Lead-substituted strontium hydroxyapatite (Sr_10-xPb_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.