Active Phase Structure of the SiO₂-supported Nickel Phosphide Catalysts for Non-oxidative Coupling of Methane (NOCM) Reactions

SiO2-supported NiP binary catalysts show high activity for the non-oxidative coupling of methane (NOCM) reactions, one of the most difficult but important catalytic reactions. We have studied the SiO2-supported NiP binary catalysts by extended X-ray absorption fine structure (EXAFS) with different Ni : P ratios. NiP binary catalyst with the composition of Ni : P = 1 : 1 was the most active among the three different compositions. EXAFS showed that the NiP catalyst with Ni : P = 1 : 1 had a Ni2P structure. The structure was stable after the high temperature (1173 K) NOCM reaction conditions for 12 h. It is interesting that Ni2P shows high catalytic activities in many other reactions such as hydrodesulfurization, hydrogen evolution reaction, and so on. It may be due to the appropriate electronic and geometrical modification of a Ni active site by P.