Synthesis, characterization and activity of CuZnGaOx catalysts for the water-gas shift (WGS) reaction for H2 production and CO removal after reforming

- Preparation of Cu/Zn/Ga catalysts at various pH precipitation conditions
- Structure sensitivity relationship of CuZnGaOx catalyst on water-gas shift activity
- Intrinsic activity is related to the Cu metallic surface area and metal dispersion
- A high CO conversion is obtained at low temperatures and a high H2O/CO ratio

CuZnGaOx catalysts were prepared by co-precipitation synthesis method and their turnover performance was evaluated for the water-gas shift (WGS) reaction. The effects of pH on composition, structure and morphology were investigated. Materials were characterised using powder XRD, physisorption, chemisorption and electron microscopic techniques. Basic preparation conditions produced smaller, uniform and homogenously distributed particles, while a high interface concentration of bulk copper phase was observed at acidic pH. X-ray diffraction peak, corresponding to CuO(111), was broader at neutral/alkaline pH, which indicated small synthesized crystallites, disordered oxide arrangement and polymorphism. The analyses after H2-TPR revealed that all Cu was in the metallic oxidation state after reduction. H2-TPR profiles demonstrated that a stronger comparative interaction between Cu-ZnOx and Cu-GaOx existed for a higher applied syntheses pH. Continuous temperature-programmed surface reaction (TPSR) measurements showed that these also granted the thermodynamic equilibrium CO conversion at 240 °C. Time-on-stream catalytic activities were examined in a fixed bed reactor. An increase in the vaporised steam content in reactant feedstock mixture caused a rise in CO consumption and effluent hydrogen productivity. WGS process was thus structure-sensitive to the supported active metal in CuZnGa-based composite nano-catalysts. Intrinsic kinetic reactivity was proportional to Cu area, dispersion and sites, which could be altered by precipitation composite fabrication pH. The methane, methanol or ethanol reforming design with low-temperature WGS is particularly vital in high-temperature proton-exchange membrane fuel cells (PEMFC), in which thermal unit integration may be used to supply heat from the stack to WGS operation, and in the case of CH3OH, even reformer.

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