On the possibility of an Eley-Rideal mechanism for ammonia synthesis on Mn6N5+x (x=1)-(111) surfaces

作者：Zeinalipour Yazdi Constantinos D^*

来源：Physical Chemistry Chemical Physics, 2018, 20(27): 18729-18736.

DOI：10.1039/c8cp02381f

Recently we reported an Eley-Rideal/Mars-van Krevelen mechanism for ammonia synthesis on cobalt molybdenum nitride (Co3Mo3N). In this mechanism hydrogenation of activated dinitrogen occurs directly from the gas phase in a low barrier step forming a hydrazinylidene intermediate =NNH2. In this paper we study whether such a mechanism of ammonia synthesis could occur on the (111) surface of another metal nitride, Mn6N5+x (x = 1), as this would explain the low-T ammonia synthesis activity of Co3Mo3N. We find that although N-2 adsorbs more strongly than H-2 on the (111) surface, having also examined the (110) and the (100) surface, N-2 is not significantly activated when adsorbed in an end-on configuration. The hydrogenation reactions via an Eley-Rideal mechanism are all high barrier processes (>182 kJ mol(-1)) and therefore an Eley-Rideal mechanism for ammonia synthesis is predicted to not occur on this material unless there are high temperatures. Our study indicates that the fact that an Eley-Rideal/Mars-van Krevelen mechanism occurs on Co3Mo3N is a result of the stronger activation of dinitrogen at nitrogen vacancies when dinitrogen is adsorbed in an end-on configuration.

• 出版日期2018-7-21