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H. Arakawa, H. Kusama, K. Sayama, and K. Okabe
[Proc. of International Conference of Carbon Dioxide Utilization, pp.95-102, 1993]
An effective synthesis of both CH_{3}OH over CuO-ZnO-TiO_{2} catalyst and oxygenates (CH_{3}OH + CH_{3}OCH_{3}) over the hybrid catalyst (combination of acid catalyst and CuO-ZnO-Al_{2}O_{3} catalyst) was studied. CuO-ZnO-TiO_{2} produced CH_{3}OH effectively at a lower temperature compared with the case of CuO-ZnO-Al_{2}O_{3}-Cr_{2}O_{3} catalyst. Methanol was produced with 78% selectivity, 20% yield and 26% CO_{2} conversion at the condition of 220°C, 7 MPa, GHSV=2000h^{-1} and H_{2}/CO_{2}=3/1. TiO_{2} additive improved CH_{3}OH selectivity mainly. An in situ FT-IR spectroscopy of surface species over the catalyst suggested that CO_{2} was directly hydrogenated to CH_{3}OH via carbonate, formate and methoxy intermediates on Cu surface. While, the hybrid catalyst system was very efficient for the effective production of CH_{3}OH + CH_{3}OCH_{3} mixture (17% yield) as one of methods to overcome the restriction of equilibrium yield of CH_{3}OH (10% yield) over CH_{3}OH synthesis catalysts at the condition of 240°C to 260°C and 3 MPa.