Influence of Reaction Conditions and Promoting Role of Ammonia Produced at Higher Temperature Conditions in Its Synthesis Process over Cs-Ru/MgO Catalyst

Cs promoted Ru/MgO catalyst was prepared by an impregnation method using Ru(NO3)(3) and Cs(NO3)(2) as precursor compounds. The activity measurements for ammonia (NH3) synthesis were carried out in a fixed-bed flow reactor. A reactant stream of H-2 and N-2 was used for NH3 synthesis. The influences of reaction temperature, pressure and H-2/N-2 ratio on the performance of the catalyst were investigated in detail. The relative concentration of H-2 and N-2 in the reactant stream highly influenced the catalytic activity. The remarkably higher rate of NH3 synthesis was observed for the higher H-2/N-2 ratio at 400 degrees C and lower H-2 concentration in the reactant stream improved the catalytic activity at lower temperature conditions. A sharp increase in the catalytic activity of Cs-Ru/MgO with an increase in pressure was observed at 400 degrees C for a reactant stream with higher H-2 concentration. Relatively less interaction of H-2 with the surface of the catalyst is suggested in the presence of NH3 produced during the reaction conducted at elevated temperature conditions. This less susceptibility for H-2 adsorption on the active sites of the catalyst is a plausible reason for a higher rate of NH3 synthesis at higher temperature conditions. We modified the Temkin equation model by considering the adsorbed species on the surface of the catalyst affecting NH3 synthesis.