Chemistry

Pressuring CO2 to React

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Science  06 Dec 2013:
Vol. 342, Issue 6163, pp. 1149
DOI: 10.1126/science.342.6163.1149-a

One sustainable approach for converting CO2 from large-scale industrial production processes into chemicals and fuels is by reacting it with hydrogen generated from solar or wind energy. The catalytic hydrogenation of CO2 into methanol offers a potential route for conversion, but most commercial catalysts, which use copper and zinc oxide supported on alumina and operate at pressures of 50 to 100 atm, have low single-pass conversions and require product separation and reactant recycling. Bansode and Urakawa, noting that high pressures thermodynamically favor the methanol product, studied this reaction on such catalysts at higher pressures. They could boost single-pass conversions to >95% at 355 atm and 260°C and at high H2 partial pressures (H2/CO2 ratios > 10:1). These conditions should suppress formation of CO as a final product, but the increasing conversion for methanol as temperature was increased to 260°C suggests that the reaction proceeds initially through reduction to CO. This reaction is endothermic and competes with exothermic methanol synthesis. They also show that addition of a solid acid catalyst, H-ZSM-5, as a physical mixture led to the single-pass production of dimethyl ether with selectivities of >80%; when this catalyst was added in a second series reactor, light alkanes or propylene could be produced as well.

J. Catal. 309, 66 (2014).

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