Structural evolution of TiN catalysts during mechanocatalytic ammonia synthesis
Structural evolution of TiN catalysts during mechanocatalytic ammonia synthesis
复制标题
机械催化氨合成过程中 TiN 催化剂的结构演变
DOI：
10.1039/d2fd00164k
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发表时间：
2023
影响因子：
3.4
通讯作者：
Sievers, Carsten
中科院分区：
文献类型：
--
作者：
DeWitt, Jacob A.;Phillips, Erin V.;Hebisch, Karoline L.;Tricker, Andrew W.;Sievers, Carsten
机械力催化合成氨是一种温和条件下合成氨的新方法。然而，许多悬而未决的问题仍然是机械催化氨合成的机制，以及在研磨过程中的活性催化剂的结构。在此，原位合成的氮化钛催化剂的结构演变进行了探讨，在延长研磨。发现结合到催化剂表面的氨的产率与研磨期间催化剂表面积的增加强烈相关，尽管在较早的研磨时间下氨的较低表面浓度表明氨形成的延迟，对应于钛金属预催化剂转化成氮化物。如SEM和TEM所示，由于团聚的氮化钛纳米颗粒之间的间隙空间，在研磨期间在催化剂中形成小孔。在第一个6小时内，钛既转化为氮化物，又断裂成较小的颗粒，然后达到平衡状态。研磨18小时后，催化剂纳米颗粒似乎结晶成更致密的材料，导致表面积和孔体积的损失。
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 in situ 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.