X-ray absorption spectroscopy of Ba- and Cs-promoted Ru/Mesoporous carbon catalysts for long-term ammonia synthesis under intermittently varied conditions

The structural characteristics of Ba- and Cs-promoted Ru catalysts supported on a mesoporous carbon material were examined by X-ray absorption spectroscopy and several characterization techniques, and correlated to their activities in long-term ammonia synthesis under intermittent operation conditions. 0.5Ba-10 wt% Ru/MPC contains barium species adhered to the surfaces of the Ru nanoparticles, creating more catalytically active sites for the dissociation of nitrogen molecules. By contrast, 2.5Cs-10 wt% Ru/MPC contains cesium hydroxides homogeneously covered on the MPC and Ru interfaces, enhancing the electronic properties of the Ru nanoparticles and consequently facilitating ammonia synthesis. As a result, the catalytic study demonstrated that ammonia synthesis rates over these promoted Ru catalysts could be finely and stably tuned within 22.5-100 mmol g(cat)(-1) h(-1) by quickly varying the reaction temperature in the range of 340-400 degrees C and gas hourly space velocity in the range of 9000-18 000 h(-1), and the intermittent operation conditions could achieve the desired hydrogen production rates derived from a sustainable process.