Understanding the role of surface Zn species in CO2 hydrogenation to methanol over Cu/ZnO/Al2O3

Abstract

The structural characteristics of surface Zn species are of significance to regulate the activity and selectivity of Cu-based catalysts for CO₂ hydrogenation to methanol. A series of Cu/ZnO/Al₂O₃ catalysts derived from layered double hydroxides (LDH) precursors was systematically optimized and subjected to calcination and reduction at various temperatures to tune the surface Zn species with controlled characteristics of Cu species, including Cu sizes and Cu⁺/Cu⁰ ratios. Structural characterization reveals that formation of a well-defined Cu–ZnO interface with variable surface Zn species (Zn²⁺ and Zn^δ+), and maintained Cu nanoparticle sizes and Cu⁺/Cu⁰ ratios within similar degrees. A strong positive correlation is established between the fraction of surface Zn^δ+ species and methanol productivity, highlighting the critical role of ZnO_x species in Cu–ZnO interface during CO₂ hydrogenation. The optimized catalyst achieved a methanol space-time yield of 610.6 mg·g⁻¹·h⁻¹ at 250 °C and 3.0 MPa, exceeding most reported Cu-based catalysts under comparable conditions. This work provides mechanistic insights into interfacial structure–activity relationships and offers practical guidelines for the rational design of high-performance Cu/ZnO/Al₂O₃ catalysts for CO₂ hydrogenation to methanol.