Enhancing Methanol Yield of CO2 Hydrogenation with the Use of Bifunctional Catalyst/Adsorbent Formulations

In contrast to conventional methanol synthesis using syngas (COand H₂), the use of CO₂ necessitates C=O scission and, consequently, H₂O is formed as a byproduct, which can inhibit the rate of methanol synthesis. Thus, abstraction of H₂O during catalysis enhances rate of methanol synthesis in CO₂ hydrogenation both by alleviating equilibrium constraints and by eliminating H­₂O inhibition. Steady-state CO₂ hydrogenation on commercial Cu/ZnO/Al₂O₃ formulations (1080 μmol_surface-Cu/g_cat) with H₂O co-feed (30 bar total pressure; CO₂ (4.4 bar) + H₂ (13 bar) + Ar (12 bar) + H₂O (0-0.60 bar) + He balance; 523 K) confirmed the inhibitory effect of H₂O observable even at partial pressures below 10% of the inlet CO₂ partial pressure. Conversely, co-processing of methanol (30 bar total pressure; CO₂ (4.4 bar) + H₂ (13 bar) + Ar (12 bar) + methanol (0-0.19 bar) + He balance; 523 K) did not indicate any inhibitory or promotional effect. Transients in rate during CO₂ hydrogenation (60 bar; CO₂:H₂:Ar = 1:3.5:2.7; 503 K) on an interpellet mixture of Cu catalyst and molecular sieve 3A water adsorbent (1:10 by wt.) resulted in ~30% higher methanol synthesis rates attributable to H₂O abstraction as evidenced by a delay in H₂O evolution with respect to methanol evolution. Regeneration of molecular sieve 3A was also possible with temperature treatment at 523 K under ambient pressure, which did not negatively impact the activity of the catalyst. The presented work highlights the cooperation of reaction and transport phenomena during bifunctional catalysis to modulate methanol yield of CO₂ hydrogenation through H₂O abstraction.