Department of Chemical Engineering, Texas A&M University, College Station, TX 77843, USA.
Phys Chem Chem Phys. 2019 Nov 28;21(44):24543-24553. doi: 10.1039/c9cp05688b. Epub 2019 Oct 30.
We aim at elucidating the mechanism of the trimethyl aluminum (TMA) decomposition on oxidized nickel (NiO) and metallic nickel (Ni) facets in the absence of a source of hydroxyl groups. This TMA decomposition mechanism constitutes the earliest stage of growth of AlO coatings with the atomic layer decomposition (ALD) method, which stabilizes nickel catalysts in energy-intensive processes such as the dry reforming of methane. Our first-principles calculations suggest thermodynamic favorability for the TMA decomposition on metallic nickel compared to oxidized nickel. Moreover, the decomposition of TMA on metallic nickel showed almost no differences in terms of energy barriers between flat and stepped surfaces. Regarding the impact of the CH radicals formed after TMA decomposition, we calculated stronger adsorption on metallic nickel facets than on oxidized nickel, and these adsorption energies are comparable to the adsorption energies calculated in earlier works on AlO ALD growth on palladium surfaces. These results lead us to believe in the growth of porous AlO coatings triggered by CH contamination rather than due to preferential TMA decomposition on stepped and/or defective facets. The CH radicals are likely to be thermally stable at temperatures used during AlO ALD processes, partially passivating the surface towards further TMA decomposition.
我们旨在阐明在不存在羟基源的情况下，三甲基铝（TMA）在氧化镍（NiO）和金属镍（Ni）晶面上分解的机制。这种 TMA 分解机制构成了原子层分解（ALD）方法生长 AlO 涂层的最早阶段，它稳定了能源密集型过程中的镍催化剂，如甲烷干重整。我们的第一性原理计算表明，TMA 在金属镍上的分解比在氧化镍上热力学上更有利。此外，TMA 在金属镍上的分解在平坦和阶梯表面之间的能垒方面几乎没有差异。关于 TMA 分解后形成的 CH 自由基的影响，我们计算出在金属镍晶面上的吸附比在氧化镍晶面上更强，这些吸附能与在钯表面上进行的 AlO ALD 生长的早期工作中计算的吸附能相当。这些结果使我们相信，多孔 AlO 涂层的生长是由 CH 污染引发的，而不是由于阶梯和/或缺陷晶面优先进行 TMA 分解。在进行 AlO ALD 过程中使用的温度下，CH 自由基可能具有热稳定性，部分钝化表面以阻止进一步的 TMA 分解。
