Mechanocatalytic Ammonia Synthesis over TiN in Transient Microenvironments

Abstract

Environmentally friendly and energy-efficient ways to produce ammonia are essential to meet global food demands. Here, a new approach for ammonia production at nominally ambient conditions is introduced. As proof of concept, ammonia is synthesized mechanocatalytically by ball milling titanium in a continuous gas flow. The ammonia synthesis reaction is proposed to follow a transient Mars− van Krevelen mechanism under mechanically activated conditions, where molecular nitrogen incorporation into the titanium lattice and titanium nitride hydrogenation occur in thermodynamically distinct environments. X-ray powder diffraction and X-ray absorption spectroscopy confirm the formation of titanium nitride from titanium and N 2 . The reactivity of nitrided titanium supports that lattice nitrogen plays a role in ammonia formation. The in situ formed titanium nitride is catalytically active, and the nitride regeneration reaction is determined to be the ratelimiting step. A preliminary technoeconomic analysis shows that this approach could be feasible for distributed ammonia production.

Mechanocatalytic Room‐Temperature Synthesis of Ammonia from Its Elements Down to Atmospheric Pressure

“…To finally prove that ammonia formation results from activation of nitrogen and not impurities (e.g. dissolved N in the stainless steel), two control experiments were performed: A batch reaction using 15 N 2 produced exclusively 15 NH 3 (see Table S3, entry 64 and Figure S25) and a continuous-flow experiment under exclusion of nitrogen gas resulted only in insignificant values of 10 ppm of ammonia (see Table S5, entry 81 and Figure S26). Significant amounts of ammonia in this experiment could only be produced after again dosing nitrogen gas.…”

“…In 2020, Tricker et al claimed a mechanocatalytic synthesis of ammonia over TiN in a common laboratory shaker mill. [15] However, during milling no ammonia was observed in the gas phase, and ammonia was determined by washing the milled solid with an aqueous solution, so that hydrolytic ammonia formation from a nitride seems possible, even probable. A true step towards mechanochemical ammonia formation was taken recently in a chemical looping process.…”

Alkali Metal Salt Interference on the Salicylate Method for Quantifying Ammonia from Nitrogen Reduction

“…16 These harsh operation conditions make the Haber-Bosch process a very energy-intensive process 17 (i.e. it consumes between 1% and 2% of the anthropogenic energy [18][19][20] ); and make the distributed ammonia production economically unfeasible, 21 restricting ammonia production to large centralized ammonia production facilities. 22 In addition to its large energy consumption, the current Haber-Bosch process is an important CO 2 source (i.e.…”

“…26 Achieving this goal would make ammonia production more sustainable and economically profitable, enabling smaller local reactors, 27 and thereby distributed ammonia production networks in which ammonia would be directly generated at the consumption point. To present date, several promising strategies are being actively explored, including (mild conditions) thermochemical, [28][29][30] electrochemical, 31-34 photochemical, [35][36][37] photoelectrochemical, [38][39][40] plasma-activated, 41,42 and mechanocatalytical 21,43 ammonia production methods. So far, none of these methods has achieved acceptable ammonia yields and/or selectivities, and therefore the search continues as shown by the increasing number of works dealing with the Nitrogen Reduction Reaction (NRR).…”

Recent Advances and Perspective on Electrochemical Ammonia Synthesis under Ambient Conditions

“…The NH 3 is produced by the lattice N, leading to lattice vacancies which will be further replenished with the gaseous N 2 . [ 50,74,75 ] Moreover, the theoretical study of MN x for the NRR also suggested that transition metal nitrides, such as VN and ZrN, can suppress the HER and achieve the NRR at low onset potentials. [ 50 ]…”