Distinct Roles of Zn and Ga in CO2-to-Methanol Conversion over Inverse ZrO x /Cu under Industrial H2/CO2 Ratios

Abstract CO2 hydrogenation to methanol is a promising route for clean fuel and chemical production. Recently, inverse Cu-based catalysts with high Cu content, particularly the ZrOx/Cu system, have attracted attention due to their cost-efficiency. Zn and Ga are effective promoters for Cu-Zr catalysts, but their dopant-specific roles and active sites remain unclear. In this work, inverse ZrOx/Cu catalysts were selectively doped with Zn or Ga to clarify their distinct promotion mechanisms in methanol synthesis. Under standard conditions, the inverse Zn-doped catalyst achieved a methanol space-time yield of 0.79 g/gcat./h. Combined theoretical and experimental studies support a formate-mediated pathway on both catalysts and suggest that heterolytic H2 dissociation can occur at Ga–O and Zn–O sites, followed by hydrogen spillover to adjacent Cu sites. Despite this common pathway, Zn and Ga promote different elementary functions. Zn doping induces a polarization effect that activates distal Zr sites, thereby enhancing CO2 adsorption and activation at distant Zr sites, whereas Ga doping facilitates H2 dissociation and increases the availability of active hydrogen species. As a result, the relative catalytic performance is strongly governed by the H2/CO2 feed ratio: Zn doping becomes more advantageous under industrial H2-rich conditions, whereas the Ga-doped catalyst is competitive under H2-lean conditions. This work identifies the atomistic origins of the distinct promotional effects of Zn and Ga in inverse ZrOx/Cu catalysts and provides a reaction-condition-oriented strategy for designing efficient Cu-based catalysts for CO2-to-methanol conversion.