Very stable in-operando and low-loaded atomic molybdenum on solid support materials have been prepared and tested to be catalytically active for N₂-into-NH₃ hydrogenation. Ammonia synthesis is reported at atmospheric pressure and 400°C with NH₃ rates of ca. 1.3·10³ μmol h¯¹ gMo¯¹ using a well-defined Mo-hydride grafted on silica (SiO₂-700). DFT modelling on the reaction mechanism suggests that N₂ spontaneously binds on monopodal [(≡Si-O-)MoH₃]. Based on calculations, the fourth hydrogenation step involving the release of the first NH₃ molecule represents the rate-limiting step of the whole reaction. The inclusion of cobalt co-catalyst and an alkali caesium additive impregnated on mesoporous SBA-15 support increases the formation of NH₃ with rates of ca. 3.5·10³ μmol h¯¹ gMo¯¹ under similar operating conditions and maximum yield of 29·10³ μmol h¯¹ gMo¯¹ when pressure is increased to 30 atm.
|Original language||English (US)|
|Number of pages||5|
|Journal||Angewandte Chemie International Edition|
|State||Published - Nov 5 2018|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Authors acknowledge SABIC (Saudi Basic Industries Corporation) and King Abdullah University of Science and Technology (KAUST) for support. Gratitude is also due to the KAUST Supercomputing Laboratory using the supercomputer Shaheen II for providing the computational resources. A.P. also thanks the Spanish MINECO for a project CTQ2014-59832-JIN.