Ammonia synthesis over cesium-promoted mesoporous-carbon-supported ruthenium catalysts: Impact of graphitization degree of the carbon support

Carbon-supported ruthenium catalysts facilitate electrically-assisted Haber–Bosch ammonia synthesis. However, the relationship between carbon supports and catalytic performance remains ambiguous. We developed ordered mesoporous carbon plates (MCPs) with varying graphitization degrees as Cs-promoted Ru catalyst supports, examining correlations between ammonia synthesis rate and key structural parameters, included graphitization degree, Ru nanoparticle size, and Cs/Ru ratio. High-graphitization-degree carbon supports resisted methanation and facilitated formation of reductive activation enabled dynamic Cs0 species as electronic promotor, induced by spillover hydrogen from the Ru surface to CsOH. Density functional theory calculations further revealed that CsOH alleviated hydrogen poisoning. Notably, the catalyst supported on MCP-1100—which exhibited the highest graphitization degree among the supports and superior stability—with 10 wt% 2.3-nm-sized Ru nanoparticles and Cs/Ru = 2.5 achieved high ambient-pressure ammonia synthesis rates (7.9–43 mmolNH3·g−1·h−1) below 410 °C. Furthermore, it functioned under intermittent operating conditions, potentially integrating renewable-electricity-based electrolytic hydrogen production. [Display omitted] •Mesoporous carbon plates (MCPs) with varied graphitization degree are synthesized.•MCPs are used as supports for Cs-promoted Ru (∼2 nm) catalysts for ammonia synthesis.•Metallic Cs0 forms by reduction of CsOH by spillover hydrogen from Ru nanoparticles.•Highly graphitized MCP-1100 resists methanation and facilitates formation of Cs0.•The optimized MCP-1100 supported catalyst excells in intermittent ammonia synthesis.