CoZr nanocomposites in a ceramic–metal AlOx(OH)y/Al matrix with a different Co/Zr ratio and its potential for syngas processing

Abstract

We investigated the possibility of synthesizing Co nanoparticles in CoZr_nH/AlO_x(OH)_y/Al ceramic–metal catalysts and controlling the catalytic properties of these nanoparticles in syngas conversion by changing the Co/Zr ratio. The CoZr nanocomposites were obtained from metal powders by mechanochemical activation in a high-energy mill under an argon atmosphere, followed by treatment with hydrogen at high pressure and room temperature. Ceramic–metal catalysts were prepared by mixing the corresponding CoZr_nH powder nanocomposite (30 wt%) with powdered aluminum (70 wt%), hydrothermal treatment of the mixture and subsequent calcination. The materials were characterized with a set of physicochemical methods: powder X-ray diffraction, scanning electron microscopy, ⁵⁹Co internal field nuclear magnetic resonance spectroscopy, and temperature programmed reduction. Catalytic studies were performed in a laboratory fixed-bed flow reactor at 2 MPA and 210–270 °C. It is shown that the activity in syngas conversion to C₅₊ hydrocarbons and selectivity to methane and C₂–C₄ hydrocarbons depend on the Co/Zr ratio. Thus, with an increase in the zirconium content in the samples, the interaction of metal cobalt with metal zirconium improves in the process of mechanical activation and subsequent treatment with hydrogen. The destruction of the agglomerates of crystallites of metallic cobalt in the form of β-Co (Co_fcc) occurs as well as their transformation to α-Co (Co_hcp) particles active in the syngas conversion to C₅₊ hydrocarbons. This can explain the highest specific yield of C₅₊ hydrocarbons on a cermet with the lowest Co/Zr ratio.