Unexpected redox mechanism in WGS reaction with Ni-ZnO catalyst through a Solid-State Co-precipitate in solid solution

Abstract

Designing highly dispersed metal nanoparticles (NPs) working at high temperature reductive atmosphere remains a challenge, especially for non-noble metal NPs (e.g., Ni NPs). Here, a solid-state co-precipitate method was developed to prepare sintering-resistance Ni-ZnO catalyst. The catalyst featured as high Ni dispersion by this solid-state co-precipitate method in solid solution, and ∼ 6 nm Ni NPs were obtained even in a long-term reduction pre-treatment (500 °C, H2). Interestingly, a well-established strong metal and support interaction (SMSI) effect of Ni-ZnO was observed during the reduction process. A thin ZnO overlay was clearly deposited on the Ni metal NPs, effectively tuning the geometry and electronic structure of the exposed Ni metallic sites. Combined with the evidence of CO-TPD, H2O-TPD, H2O-titration, and CO-H2O TPSR, the existence of Ni-ZnO SMSI strongly provides the unusual pathway of redox mechanism during water gas shift (WGS) reaction, avoiding the tendency of CO methanation reaction in traditional Ni-based catalytic systems.