Mechanistic insight into effect of doping of Ni on CO2 reduction on the (111) facet of Cu: thermodynamic and kinetic analyses of the elementary steps

摘要

A systematic mechanistic investigation of CO2 reduction on a Ni-modified Cu(111) surface is performed based on an extensive set of density functional theory (DFT) calculations by focusing on the hydrocarbon CH4 formation pathways. By carefully analyzing reduction pathways on the Ni-modified Cu(111) surface, some important mechanistic information is deduced. The presence of Ni stabilizes all reaction intermediates, and thus reduces the activation barrier for almost all CO2 reduction steps. Most importantly, it can considerably lower than the activation barrier of CO2 hydrogenative dissociation into CO, which is the rate-determining step of CO2 reduction on a pure Cu(111) surface. Thus, the doping of Ni atom is able to activate CO2, leading to enhanced surface activity of CO2 reduction into hydrocarbons. Notably, the activation barriers that are required for CH4 and CH3OH formation are almost all easily overcome through the thermoactive process at ambient temperatures after doping of Ni atom. Thus, a higher CH4 and CH3OH yield may be expected in the presence of the doped Ni atom. Thermodynamic analyses indicate that doping of Ni may reduce the overpotential of CO formation through CO2 hydrogenative dissociation. On this basis, two decriptors may be proposed in order to describe the catalytic activity of Cu-based catalysts for CO2 reduction, and a perfect Cu-based alloy in CO2 reduction should moderately bind CO and form and reduce CO more easily. Simutaneously, CO hydrogenation occurs more easily on the (111) facet of Ni-modified Cu than dimerization, thereby the selectivity of (111) facet of Cu on production CH4 is further confirmed to some degree. The present study reveals a rich reaction chemistry and provides new insights to guide the rational design of Cu-based alloy catalysts for hydrocarbons formation from CO2 reduction.