Preparation of Cu/ZnO and Cu/ZnO/Al2O3 Methanol Catalysts by Gas-Phase Loading of Mesoporous Silica: Aiming at Superior Catalytic Activity by Molecular Control of their Microstructure

Copper-based catalysts (Cu/ZnO and Cu/ZnO/Al2O3) are the basis of the industrial methanol synthesis and methanol oxidation and are important components of fuel cell technology. For the preparation of these catalysts, metal–organic chemical vapor deposition (MOCVD) technique has proven its potential. Furthermore, studying synergistic metal–support interactions, strategies can be developed to gain molecular control over the interfaces that would provide the basis for the knowledge-driven improvement of heterogeneous catalysts. Since there is in principle no limit in respect to the simultaneous maximization of the specific copper surface area and the Cu/ZnO interface area, there is no limit to the increase of the catalytic activity beyond that which is currently possible. In order to maximize the specific copper surface area and the Cu/ZnO interface area, the loading of copper in the matrices can be increased by the repetition of the loading cycles. Furthermore, the combination of different Cu precursors with different zincand aluminium-oxide precursors opens up a certain degree of freedom to optimize the loading process. Current findings of this work include successful deposition of Cu/ZnO catalysts by the MOCVD using templated silica as a support. The molecular control of the Cu/ZnO interface is achieved by variation of dimension and framework of the pores and by exploration of the precursor chemistry. After the first loading cycle, the specific copper surface area of the obtained Cu/ZnO@PMS samples was in the range of 5-6 mCu/gcat, while the XRD and EXAFS studies revealed exceptionally low copper crystallite size and degree of aggregation. The methanol synthesis performance is found to be 19-130 μmol/gcath, using a special catalytic test set-up referenced to the industrial ternary catalyst having a value of about 450 μmol/gcath.