Understanding Catalyst Activity
In-situ temperature-programmed XRD measurements of a selected Cu/Zn/Al-catalyst precursor
Cu/Zn/Al-oxide catalysts are commonly used in industrial low-pressure methanol synthesis. The reaction, starting from synthesis gas (mixture of CO2, CO, and H2) is catalyzed by a combination of CuO, ZnO, and Al2O3 oxides whereas the final catalyst is obtained by a reduction of CuO to metallic Cu under H2 flow. It is widely accepted that the active species for the methanol synthesis are metallic Cu-clusters. ZnO is supposed to be essential for a homogeneous distribution of the active Cu-species at elevated temperatures. The catalysts are produced by a precipitation process, first forming mixed Cu/Zn/Al hydroxy carbonates. These hydroxy carbonates are calcined in a second step, forming the mixed oxides of Cu, Zn and Al. The role of the hydroxy carbonate phases and their decomposition during the thermal treatment are supposed to have a strong influence on the catalytic behaviour of the final catalysts obtained.
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