Maximizing the number of Rh0–Rh+ sites through metal dispersion control for the synthesis of higher alcohols from syngas†

Abstract

Higher alcohol synthesis (HAS) from syngas presents an effective method for obtaining clean liquid fuels and high-value chemicals. In this study, we regulated the catalytic performance by altering the dispersion of Rh on the CeO₂ support. A comprehensive understanding of the regulatory mechanism of catalytic performance and the key CO adsorption configurations was achieved through a series of characterization experiments. In reduced catalysts, Rh existed in two forms: Rh⁺ at the Rh–CeO₂ interface and Rh⁰ away from the interface. The total length of the Rh–CeO₂ interface perimeter was influenced by the size of Rh nanoparticles, thereby regulating the ratio of Rh⁰ to Rh⁺. A balanced distribution of Rh⁰ to Rh⁺ is necessary to improve the selectivity, indicating that the synthesis of higher alcohols is contingent upon the synergistic effect of Rh⁺ and Rh⁰, and the Rh⁰–Rh⁺ sites are identified as the key sites. Furthermore, we clarified the configurations of CO stably adsorbed on the Rh/CeO₂ surface under reaction conditions: Rh⁺₂H_x–(CO) and Rh⁰_2–(CO). The C–C coupling between the two adsorbed CO was found to be crucial for the production of higher alcohols.