An infrared study of methanol synthesis from CO{sub 2} on clean and potassium-promoted Cu/SiO{sub 2}
- Lawrence Berkeley Lab., CA (United States)
- Univ. of California, Berkeley, CA (United States)
Infrared spectroscopy and temperature-programmed reaction (TPR) spectroscopy were used to study hydrogenation of CO{sub 2} and CO{sub 2}/CO mixtures over Cu/SiO{sub 2} and potassium-promoted Cu/SiO{sub 2} catalysts. Isothermal and temperature-programmed reactions were conducted at temperatures between 303 and 563 K and pressures of 0.1 and 0.72 MPa. The only products observed during the reaction of H{sub 2} and CO{sub 2} are CO, H{sub 2}O, and CH{sub 3}OH. At 0.1 MPa over Cu/SiO{sub 2}, only 1% of the CO{sub 2} reacts to form methanol, the balance forming CO via the reverse water-gas shift (RWGS) reaction. Increasing the total pressure to 0.72 MPa and adding CO to the feed (CO/CO{sub 2} = 1) improve the methanol selectivity to 26%. Apparent activation energies measured at 480 K during H{sub 2}/CO{sub 2}/Ar in the feed does not affect the apparent activation barrier for RWGS but lowers that for methanol synthesis to 16.9 kcal/mol. Infrared spectra reveal the following species on the Cu surface during CO{sub 2} hydrogenation: bidentate formate, monodentate formate, H{sub 2}O, CO, and two forms of carbonate. Small concentrations of methanol and methoxy species are also observed. Addition of CO to the H{sub 2}/CO{sub 2} feed increases both bidentate formate coverage and methanol synthesis TOF by 40%. Potassium promotion of Cu/SiO{sub 2} accelerates the RWGS reaction but hinders methanol synthesis, reducing methanol selectivity to 1% at 0.72 MPa during the reaction of H{sub 2} and CO{sub 2}. Infrared observations show that potassium promotion stabilizes formate and carboxylate species. Based on the species observed during TPR-IR experiments and previous insights from methanol decomposition studies, a mechanism is proposed for CO{sub 2} hydrogenation over Cu. The effects of CO addition to the feed and potassium promotion of Cu can be explained by the proposed scheme. 83 refs., 15 figs., 4 tabs.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 111026
- Journal Information:
- Journal of Catalysis, Vol. 154, Issue 2; Other Information: PBD: Jul 1995
- Country of Publication:
- United States
- Language:
- English
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