Kordatos Apostolos, Mohammed Khaled, Vakili Reza, Goguet Alexandre, Manyar Haresh, Gibson Emma, Carravetta Marina, Wells Peter, Skylaris Chris-Kriton
School of Chemistry, University of Southampton SO17 1BJ UK
School of Chemistry and Chemical Engineering Queen's University Belfast BT7 1NN UK.
RSC Adv. 2023 Feb 14;13(9):5619-5626. doi: 10.1039/d2ra07462a.
The formation of interstitial PdC nanoparticles (NPs) is investigated through DFT calculations. Insights on the mechanisms of carbidisation are obtained whilst the material's behaviour under conditions of increasing C-concentration is examined. Incorporation of C atoms in the Pd octahedral interstitial sites is occurring through the [111] facet with an activation energy barrier of 19.3-35.7 kJ mol whilst migration through the [100] facet corresponds to higher activation energy barriers of 124.5-127.4 kJ mol. Furthermore, interstitial-type diffusion shows that C will preferentially migrate and reside at the octahedral interstitial sites in the subsurface region with limited mobility towards the core of the NP. For low C-concentrations, migration from the surface into the interstitial sites of the NPs is thermodynamically favored, resulting in the formation of interstitial carbide. Carbidisation reaction energies are exothermic up to 11-14% of C-concentration and slightly vary depending on the shape of the structure. The reaction mechanisms turn to endothermic for higher concentration levels showing that C will preferentially reside on the surface making the interstitial carbide formation unfavorable. As experimentally observed, our simulations confirm that there is a maximum concentration of C in Pd carbide NPs opening the way for further computational investigations on the activity of Pd carbides in directed catalysis.
通过密度泛函理论（DFT）计算研究了间隙型PdC纳米颗粒（NPs）的形成。在研究材料在碳浓度增加条件下的行为时，获得了碳化机理的相关见解。碳原子通过[111]晶面掺入钯八面体间隙位置，其活化能垒为19.3 - 35.7 kJ/mol，而通过[100]晶面迁移对应的活化能垒更高，为124.5 - 127.4 kJ/mol。此外，间隙型扩散表明，碳将优先迁移并驻留在次表面区域的八面体间隙位置，向纳米颗粒核心的迁移率有限。对于低碳浓度，从表面迁移到纳米颗粒的间隙位置在热力学上是有利的，从而导致间隙碳化物的形成。碳化反应能量在碳浓度达到11 - 14%之前是放热的，并且会根据结构形状略有变化。对于更高的浓度水平，反应机理变为吸热，这表明碳将优先驻留在表面，使得间隙碳化物的形成变得不利。正如实验观察到的那样，我们的模拟证实，钯碳化物纳米颗粒中存在碳的最大浓度，这为进一步对钯碳化物在定向催化中的活性进行计算研究开辟了道路。
