Development of ruthenium-based catalysts for ammonia synthesis via polyol reduction method

In this work, ruthenium-based catalysts were synthesized via polyol reduction method with different metal oxides as support and caesium as promoter. The samples were characterized through XRD, ICP-OES, nitrogen physisorption and XPS. Then, the catalysts were tested for ammonia synthesis in the range of temperatures 548–673 K and pressures 1–5 MPa. The synthesized catalysts allowed an ammonia production rate approximately four times higher compared with the performances of similar catalytic formulations in literature (tested at same conditions). The best performance were achieved with the Cs–Ru/CeO₂ (1%_wt Cs, 5%_wt Ru), reaching an ammonia production of nearly 73 mmol h⁻¹∙g_cat⁻¹ at 673 K and 5 MPa. As showed by the XPS analysis, the increased Ce³⁺/Ce⁴⁺ ratio led to an enhancement of oxygen vacancies, which favoured the dissociative adsorption of nitrogen, that is the limiting step in the ammonia synthesis reaction. Such high catalytic activity can be ascribed to the beneficial effect of the polyol reduction method for the maximization of the exposure of active sites.