The Theoretical Study Of Methanol Synthesis From CO/CO₂ Hydrogenation On Cu-Based Catalyst

Methanol is considered as a clean and efficient fossil energy. As an important basic chemical raw material, methanol can be used to produce formaldehyde, dimethyl sulfate and acetic acid. Therefore, methanol draws more and more attention because of its wide application. Currently, there are three points for active sites of the Cu-based catalysts: Cu0, Cu+ or Cu0-Cu+. To search for the active sites of catalyst and comprehend the effect of Cu0 and Cu+ on reaction mechanisms of methanol synthesis, in this paper, we study the differences of methanol synthesis from CO/CO2 hydrogenation on Cu+ and Cu using DFT+U and DFT, respectively.In the study, Cu2 O and Cu stand for the Cu+ and Cu0 species, which study the differences of methanol synthesis via CO/CO2 hydrogenation and water-gas-shift on Cu+ and Cu to a certain extent. The main conclusions are listed as follows:1. On Cu2O(111) surface, the most probable route of methanol synthesis from syngas is CO â†' HCO â†' H2 CO â†' H2 COH â†' H3 COH, the most energy-demanding step is H2 CO formation from HCO hydrogenation; On Cu(111) surface, the most probable route is CO â†' HCO â†' H2COâ†' H3 CO â†' H3 COH, the most energy-demanding step is HCO formation from CO hydrogenation.2. On Cu2O(111) surface, methanol synthesis from CO2 hydrogenation proceeds via the pathway CO2 â†' HCOO â†' HCOOH â†' H2 COOH â†' H2 CO â†' H2 COH â†' H3 COH. On Cu(111) surface, methanol synthesis is via the sequence CO2 â†' HCOO â†' HCOOH â†' H2COOHâ†' H2 CO â†' H3 CO â†' H3 COH. On Cu2O(111) and Cu(111) surface, the most energy-demanding step is the hydrogenation of HCOOH to H2 COOH.3. On Cu2O(111) surface, WGS is as follow: CO+2H2O â†' CO + 2OH + 2H â†' COOH + OH + 2H â†' CO2 + H2 O + H2, which belongs to associative mechanism, the energy-demanding step is COOH formation through OH reaction with CO. On Cu(111) surface, WGS is via the sequence CO+2H2O â†' CO + 2OH + 2H â†' CO + H2 O + O + 2H â†' CO2 + H2 O + H2, which is redox mechanism, the most energy-demanding step is the first H abstraction from H2 O scission.