DeWitt Jacob A, Phillips Erin V, Hebisch Karoline L, Tricker Andrew W, Sievers Carsten
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Faraday Discuss. 2023 Jul 19;243(0):65-76. doi: 10.1039/d2fd00164k.
Mechanocatalytic ammonia synthesis is a novel approach toward ammonia synthesis under mild conditions. However, many open questions remain about the mechanism of mechanocatalytic ammonia synthesis, as well as the structure of the active catalysts during milling. Herein, the structural evolution of an synthesized titanium nitride catalyst is explored during extended milling. The yield of ammonia bound to the catalyst surface was found to strongly correlate with an increase in catalyst surface area during milling, although a lower surface concentration of ammonia at earlier milling times suggests a delay in ammonia formation, corresponding to the conversion of the titanium metal pre-catalyst into the nitride. Small pores develop in the catalyst during milling due to interstitial spaces between agglomerated titanium nitride nanoparticles, as shown by SEM and TEM. In the first 6 h, the titanium is both converted to a nitride and fractured to smaller particles, before an equilibrium state is reached. After 18 h of milling, the catalyst nanoparticles appear to crystallize into a denser material, resulting in a loss of surface area and pore volume.
机械催化氨合成是一种在温和条件下合成氨的新方法。然而，关于机械催化氨合成的机理以及球磨过程中活性催化剂的结构，仍存在许多未解决的问题。在此，我们探索了一种合成氮化钛催化剂在长时间球磨过程中的结构演变。发现与催化剂表面结合的氨的产率与球磨过程中催化剂表面积的增加密切相关，尽管在球磨初期氨的表面浓度较低，这表明氨的形成存在延迟，这与金属钛预催化剂向氮化物的转化相对应。扫描电子显微镜（SEM）和透射电子显微镜（TEM）显示，由于团聚的氮化钛纳米颗粒之间的间隙，球磨过程中催化剂内部会形成小孔。在最初的6小时内，钛既转化为氮化物，又破碎成更小的颗粒，然后达到平衡状态。球磨18小时后，催化剂纳米颗粒似乎结晶成一种更致密的材料，导致表面积和孔体积减小。
