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Quantifying the promotion of Cu catalysts by ZnO for methanol synthesis

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Science  20 May 2016:
Vol. 352, Issue 6288, pp. 969-974
DOI: 10.1126/science.aaf0718

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How zinc helps copper make methanol

Copper nanoparticles can catalyze the formation of methanol from a mixture of CO2, CO, and H2, but adding zinc oxide nanoparticles, themselves inactive in this reaction, greatly boosts the rates. Kuld et al. measured how methanol synthesis activity varies with the coverage of zinc atoms on the copper nanoparticles, as determined experimentally and with density functional theory calculations. The ZnO nanoparticle size determined how much zinc covers the copper surface and in turn controlled the catalyst activity.

Science, this issue p. 969

Abstract

Promoter elements enhance the activity and selectivity of heterogeneous catalysts. Here, we show how methanol synthesis from synthesis gas over copper (Cu) nanoparticles is boosted by zinc oxide (ZnO) nanoparticles. By combining surface area titration, electron microscopy, activity measurement, density functional theory calculations, and modeling, we show that the promotion is related to Zn atoms migrating in the Cu surface. The Zn coverage is quantitatively described as a function of the methanol synthesis conditions and of the size-dependent thermodynamic activities of the Cu and ZnO nanoparticles. Moreover, experimental data reveal a strong interdependency of the methanol synthesis activity and the Zn coverage. These results demonstrate the size-dependent activities of nanoparticles as a general means to design synergetic functionality in binary nanoparticle systems.

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