CO{sub 2} hydrogenation to methanol on a YBa{sub 2}Cu{sub 3}O{sub 7} catalyst
The synthesis of methanol from CO{sub 2} and H{sub 2} over YBa{sub 2}Cu{sub 3}O{sub 7} was studied. The aim was to clarify (1) the nature of the catalyst in the working state, (2) the redox behavior of copper in various oxidation states, and (3) the formation and transformation of precursor species in methanol synthesis. The effects of reaction pressure, temperature, and space velocity on the catalytic performance were also investigated. The optimum reaction conditions were pressure = 3.0 MPa, space velocity = 3600 h{sup {minus}1}, and temperature = 240 C. After H{sub 2} reduction at 250 C, the YBa{sub 2}Cu{sub 3}O{sub 7} transformed from an orthorhombic to a tetragonal structure, a phase which is active for methanol synthesis. In a H{sub 2}-reduced YBa{sub 2}Cu{sub 3}O{sub 7} sample, there were Cu{sup +} and oxygen vacancies and electrons trapped at the oxygen vacancies. The authors observed that CO{sub 2} adsorption would consume the trapped electrons, resulting in the reoxidation of Cu{sup +} to Cu{sup 2+}. Intermediate species such as formate, methylenebisoxy, formyl, formaldehyde, and methoxide were observed in in situ-FTIR and FT-Raman studies; they were also captured by CD{sub 3}I during methanol synthesis. Based on these experimental results, a reaction mechanism for CO{sub 2} hydrogenation to methanol over YBa{sub 2}Cu{sub 3}O{sub 7} was proposed. In this mechanism, hydrogen adsorbs dissociatively at the Cu{sup +} sites of the CuO{sub x} planes, whereas CO{sub 2} adsorbs at the oxygen vacancies. The spillover of hydrogen atoms from Cu{sup +} to the oxygen atoms and/or carbon atom of adsorbed CO{sub 2} leads to the formation of COOH, COHOH, HCOHOH, and H{sub 2}COHOH species; subsequently, one of the C-O bonds is weakened. Other intermediate species such as formate, methylenebisoxy, formyl, formaldehyde, and methoxide could be formed, and the final products are methanol, bimethyl ether, and CO.
- Research Organization:
- Hong Kong Baptist Univ., Kowloon (HK)
- OSTI ID:
- 20014518
- Journal Information:
- Journal of Catalysis, Vol. 189, Issue 1; Other Information: PBD: 1 Jan 2000; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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