Surface characterization of CuO-ZnO methanol-synthesis catalysts by x-ray photoelectron spectroscopy. 2. Reduced catalysts
The surface state of the coprecipitated cupric oxide-zinc oxide (CuO-ZnO) catalysts reduced at 250/sup 0/C with H/sub 2/ was investigated by x-ray photoelectron spectroscopy (XPS). It was found that a monovalent copper species was present in the surface of the catalysts with low copper contents. It was revealed that two distinct types of copper metal species, both of them being negatively charged by electron transfer from ZnO, were produced in the catalyst surface upon the reduction. In the high copper content catalysts (> 25 wt % CuO), the predominant Cu metal species is described by well-dispersed metal particles, whereas in the low copper content catalysts (< 10 wt % CuO), the major copper metal species is best characterized by a two-dimensional epitaxial copper layer over ZnO. It is concluded that both the two-dimensional copper metal and Cu/sup +/ are formed from Cu/sup 2 +/ dissolved in a ZnO lattice, while the copper metal particles are originating mainly from crystalline and amorphous copper oxide phases. The two-dimensional copper metal species was found to be preferentially reoxidized to Cu/sup +/ when exposed to air at room temperature. The two-dimensional Cu/sup 0/-Cu/sup +/ species are suggested to be catalytically active for the methanol synthesis at low temperature and pressure. The reduction of ZnO was observed only when reduced at 500/sup 0/C and in the presence of copper. In the case of the impregnated catalysts, no appreciable interactions were found between Cu metal and ZnO, in contrast to the coprecipitated catalysts. 7 figures, 2 tables.
- Research Organization:
- Osaka Univ., Japan
- OSTI ID:
- 5513844
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 87:19; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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10 SYNTHETIC FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ALCOHOLS
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTIONS
COPPER COMPOUNDS
COPPER OXIDES
COPRECIPITATION
DATA
DISPERSIONS
ELECTRON SPECTROSCOPY
ELECTRONIC STRUCTURE
ELEMENTS
EXPERIMENTAL DATA
HIGH TEMPERATURE
HYDROGEN
HYDROXY COMPOUNDS
IMPREGNATION
INFORMATION
MEDIUM TEMPERATURE
METHANOL
MIXTURES
MOLECULAR STRUCTURE
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PRECIPITATION
QUANTITY RATIO
REDUCTION
SAMPLE PREPARATION
SEPARATION PROCESSES
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
SYNTHESIS
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
ZINC COMPOUNDS
ZINC OXIDES