The authors have developed CuO-ZnO-Al
2O
3-Ga
2O
3-MgO catalyst for methanol synthesis from CO
2 and H
2, and have been studying a technology for the direct synthesis of dimethyl ether (DME) from CO
2 and H
2 using the combination of the methanol synthesis catalyst above mentioned and a methanol dehydration catalyst.
In the present study, the catalytic activities of three types of γ-Al
2O
3 with different specific surface areas, four types of compound oxides (ZrO
2•Al
2O
3, SiO
2•Al
2O
3, SiO
2•TiO
2, ZrO
2•TiO
2), and a ZSM-5 zeolite for DME synthesis by methanol dehydration were tested. DME synthesis activity increased with higher specific surface area of γ-Al
2O
3 catalyst. Compound oxide catalysts containing Al
2O
3 showed higher DME synthesis activity than catalysts without Al
2O
3, and ZrO
2•Al
2O
3, the best compound oxide, showed higher DME synthesis activity than the best γ-Al
2O
3 with the largest specific surface area (250m
2/g). Addition of a metal oxide as the promoter is effective for improving the DME synthesis activity of Al
2O
3 by methanol dehydration. ZSM-5 zeolite produced more olefins rather than DME. The presence of water in the methanol feed suppressed the DME synthesis reaction by methanol dehydration.
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