(486e) Early Transition Metal Carbides and Nitrides for Sustainable Ammonia Synthesis

Ammonia synthesis, developed early in the 20^th century, has become a crucial catalytic process that is essential to sustaining the growing global population. Currently, statistics from the Food and Agriculture Organization (FAO) show that artificial fertilizer contributes to more than 40% of global food production. As of 2014, more than 160 MTons of ammonia were synthetically produced, which makes it one of the highest produced chemicals in the chemical industry. Nitrogen fixation via the typical Haber-Bosch process utilizes an Fe-based catalyst at harsh temperatures and pressures above 400 °C and 150 bar, respectively. These operating conditions consume 1-2% of the world energy budget and emit 1.6% of the total CO₂ emitted. To produce ammonia at more economically and environmentally feasible conditions, there is a need to explore and understand the mechanisms of alternative catalysts that would be active at lower temperatures and ambient pressures.

Currently, the doubly-promoted Fe catalyst and supported Ru catalyst are used in major ammonia production plants; however, previous literature have shown that the efficiency and activity of these catalysts are less than those of transition metal carbides and nitrides when operating under atmospheric pressures. To further improve upon these conditions, a variety of supported transition metal carbides and nitrides are used to produce ammonia at atmospheric pressure and significantly lower temperatures (<200 °C). It is hypothesized that these supported Mo₂C and Mo₂N catalysts effectively utilizes a bifunctional mechanism that would allow them to activate the N₂-triple bond on the metal while performing nitrogen hydrogenation on the support. These materials were synthesized via a temperature program reaction followed by wet-incipient impregnation. Initial results indicate that the Mo₂C and Mo₂N-supported metal catalysts increased ammonia production at lower operating temperatures and atmospheric pressure, thus supporting the bifunctional hypothesis.