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The influence of the calcination process on the physicochemical properties and catalytic behavior of the Co/Mg/La catalysts for ammonia synthesis has been investigated. The catalysts were prepared using the different thermal pre-treatment methods prior to the activation, i.e., drying and calcination, and the respective activities for ammonia synthesis were assessed. It was found out that changing from air calcination prior to activation to direct activation of the co-precipitated species led to the different catalytic performances. The most favorable catalytic performance was achieved with Co/Mg/La prepared by calcination in air. Detailed characterization methods, employing e.g., XRPD, H2-TPD, N2-TPD, CO2-TPD, SEM, and TEM, showed that the superior catalytic behavior of this catalyst was attributed to its strong basicity and favorable adsorption properties toward hydrogen and nitrogen. [ABSTRACT FROM AUTHOR]

Ammonia presents a promising hydrogen source and energy carrier for mobile and stationary applications. The development of new and cheaper catalysts for ammonia synthesis is thus of great importance in improving the efficiency of the Haber-Bosch process. Here we report the investigation of ammonia synthesis on cobalt catalysts supported on magnesium–lanthanum mixed oxides with varying Mg/La molar ratios. Our studies revealed that the catalyst's activity is tuneable by varying the support composition, allowing an adjustment of the surface adsorption properties. Owing to the increased basicity of the support and weaker interactions between cobalt and hydrogen atoms, the catalyst supported on mixed MgO–La 2 O 3 oxide with Mg/La molar ratio of 7 demonstrated the highest activity and stability for ammonia synthesis as compared to other reported cobalt catalysts. [Display omitted] • Cobalt catalysts supported on MgO–La 2 O 3 mixed oxides for ammonia synthesis. • Dependence of the surface basicity on the performance of the cobalt catalysts. • Tuning the surface adsorption properties by varying the support composition. [ABSTRACT FROM AUTHOR]

The binding of hydrogen with nitrogen in the ammonia molecule has enormous potential as a hydrogen storage method. The development of efficient ammonia synthesis catalysts with high activity and stability is essential for this reaction. In this study, a series of MgO–Ln 2 O 3 (Ln = La, Nd, Eu) mixed oxides was designed and applied as the support of cobalt catalysts. The tuning of the support composition by selecting lanthanide elements differing in electronegativity led to changes in the physicochemical properties of the catalysts, such as the active phase dispersion, accessibility of active sites for hydrogen, surface density of basic sites. The Co/MgO–Nd 2 O 3 catalyst showed better activity than other studied catalysts in NH 3 synthesis reaction at 470 °C, 6.3 MPa. Its excellent performance is ascribed to the increased density of medium basic sites and the enhancement of electron-donating ability. [Display omitted] • Ammonia synthesis over Co catalysts supported on MgO–Ln 2 O 3 (Ln = La, Nd, Eu) composites. • Variable basic sites and tunable basicity of MgO–Ln 2 O 3 mixed oxides. • A strong influence of support basicity on properties of Co/MgO–Ln 2 O 3 catalysts. • The highest activity and stability of Co supported on MgO–Nd 2 O 3 catalyst. [ABSTRACT FROM AUTHOR]