Microstructural characterization of Cu/ZnO/Al2O3 catalysts for methanol steam reforming-A comparative study

摘要

Microstructural characteristics of various real Cu/ZnO/Al2O3 catalysts for methanol steam reforming(MSR)were investigated by in situ X-ray diffraction(XRD),in situ X-ray absorption spectroscopy(XAS),temperature programmed reduction(TPR)and electron microscopy(TEM).Structure-activity correlations of binary Cu/ZnO model catalysts were compared to microstructural properties of the ternary catalysts obtained from in situ experiments under MSR conditions.Similar to the binary system,in addition to a high specific copper surface area the catalytic activity of Cu/ZnO/Al2O3 catalysts is determined by defects in the bulk structure.The presence of lattice strain in the copper particles as the result of an advanced Cu-ZnO interface was detected only for the most active Cu/ZnO/Al2O3 catalyst in this study.Complementarily,a highly defect rich nature of both Cu and ZnO has been found in the short-range order structure(XAS).Conventional TPR and TEM investigations confirm a homogeneous microstructure of Cu and ZnO particles with a narrow particle size distribution.Conversely,a heterogeneous microstructure with large copper particles and a pronounced bimodal particle size distribution was identified for the less active catalysts.Apparently,lattice strain in the copper nanoparticles is an indicator for a homogeneous microstructure of superior Cu/ZnO/Al2O3 catalyst for methanol chemistry.