(5h) Mechanocatalytic Ammonia Synthesis over TiN in Transient Microenvironments
AIChE Annual Meeting
Sunday, November 13, 2022 - 5:36pm to 5:54pm
Mechanochemical N2 fixation was demonstrated with complimentary evidence from XRD and XAS, which showed a substantial transformation of Ti to TiN within 6 h of milling in N2. The synthesized ammonia was qualitatively detected by colorimetry and mass spectrometry of the reactor effluent, and quantitatively with ion chromatography. A transient Mars-van Krevelen mechanism is proposed for mechanocatalytic NH3 synthesis, where nitride formation and ammonia synthesis occur in distinct thermodynamic regimes. By exploiting rapidly evolving, transient microenvironments, effective catalytic activity can be increased by several orders of magnitude while also facilitating difficult chemistry at mild conditions. A preliminary technoeconomic analysis reveals the competitiveness of this approach to other novel methods for ammonia synthesis.
Expanding on this work, we aim to determine the characteristics of an optimal catalyst. Hence, we are comparing the activity of five different transition metals (Ti, Zr, Nb, Mo, V) for their steady-state reactivity toward nitridation and hydrogenation. Correlating reactivity trends with material properties will build the foundation for a rational catalyst design and an optimized catalytic system for ammonia synthesis.