Catalytically active species in Ni-based catalytic systems for low-temperature methanol synthesis probed by in situ ATR/FTIR in combination with reaction kinetics

An in situ ATR/FTIR technique was employed to probe the transformation of the nickel precursor in a catalyst composed of Ni(OCOCH3)2 and CH3OK for low-temperature methanol synthesis in a liquid medium. Homogeneous nickel species, Ni(CO)4 and a hydridocarbonylnickel anion ([HNi(CO)3]− and/or [HNi2(CO)6]−) were simultaneously derived from Ni(OCOCH3)2 during the reaction. Reaction kinetics in combination with in situ FTIR observation revealed that the ratio of the reaction rate between the catalysts with different nickel precursors, i.e. Ni(OCOCH3)2/CH3OK and Ni(CO)4/CH3OK, agreed with the ratio of the infrared absorption assigned to the nickel anion. This supports the proposed reaction scheme in which methanol is formed through methyl formate and the nickel anion catalyzes the rate-determining hydrogenation step of methyl formate.