Well-ordered Cs-Ru/@SBA-15 nanocomposite materials for low pressure ammonia synthesis

A facile route for preparing large-pore SBA-15-supported and Cs-promoted Ru nanocomposite materials (denoted as Cs-Ru/@SBA-15) was developed for catalysing the synthesis of ammonia under low pressure conditions. Aqueous solutions of ruthenium( iii ) nitrosyl nitrate and caesium carbonate were impregnated on the as-prepared SBA-15 mesoporous silica in a step-wise manner. The P123 template not only chelated with the Ru and Cs species but also stabilised the mesoporous silica framework, prior to carbonisation at 400 °C in N 2 . As a result, the Cs-Ru/@SBA-15 catalysts prepared with Ru loadings of 2-6 wt% and a fixed Cs/Ru molar ratio of 2.5 possessed high surface area, porosities, and ordered pore structures. The XRD patterns, CO chemisorption data, and STEM images revealed that the nanostructured Ru particles (1.5 mmol NH 3 g cat −1 h −1 ) of the Cs-Ru/@SBA-15 catalysts at atmospheric pressure. Conversely, the catalysts impregnated with only Ru or Cs species had no effect on the ammonia synthesis. The solid 13Cs-4Ru/@SBA-15 catalyst with a Ru loading of 3.2 wt% and Cs/Ru molar ratio of 3.1 exhibited the highest activity (5.3 mmol NH 3 g cat −1 h −1 ) at 460 °C and a H 2 /N 2 molar ratio of 1 at atmospheric pressure. The high activity was maintained by varying the space velocity, H 2 /N 2 molar ratio, and reaction temperature under low-pressure conditions, which facilitated green ammonia synthesis using low-carbon hydrogen derived from renewable energy-based water hydrolysis. An active and durable Ru-based catalyst using an inert support such as SBA-15 for low pressure ammonia synthesis can be prepared, where the Cs-promoted Ru active sites are delicately built in the nanospace.