Nolan Michael
Tyndall National Institute, UCC, Lee Maltings, Dyke Parade, Cork T12 R5CP, Ireland.
ACS Omega. 2018 Oct 12;3(10):13117-13128. doi: 10.1021/acsomega.8b01957. eCollection 2018 Oct 31.
The capture and conversion of CO are of significant importance in enabling the production of sustainable fuels, contributing to alleviating greenhouse gas emissions. While there are a number of key steps required to convert CO, the initial step of adsorption and activation by the catalyst is critical. Well-known metal oxides such as oxidized TiO or CeO are unable to promote this step. In addressing this difficult problem, a recent experimental work shows the potential for bismuth-containing materials to adsorb and convert CO, the origin of which is attributed to the role of the bismuth lone pair. In this paper, we present density functional theory (DFT) simulations of enhanced CO adsorption on heterostructures composed of extended TiO rutile (110) and anatase (101) surfaces modified with BiO nanoclusters, highlighting in particular the role of heterostructure reduction in activating CO. These heterostructures show low coordinated Bi sites in the nanoclusters and a valence band edge that is dominated by Bi-O states, typical of the Bi lone pair. The reduction of BiO-TiO heterostructures can be facile and produces reduced Bi and Ti species. The interaction of CO with this electron-rich, reduced system can produce CO directly, reoxidizing the heterostructure, or form an activated carboxyl species (CO ) through electron transfer from the reduced heterostructure to CO. The oxidized BiO-TiO heterostructures can adsorb CO in carbonate-like adsorption modes, with moderately strong adsorption energies. The hydrogenation of the nanocluster and migration to adsorbed CO is feasible with H-migration barriers less than 0.7 eV, but this forms a stable COOH intermediate rather than breaking C-O bonds or producing formate. These results highlight that a reducible metal oxide heterostructure composed of a semiconducting metal oxide modified with suitable metal oxide nanoclusters can activate CO, potentially overcoming the difficulties associated with the difficult first step in CO conversion.
捕获和转化一氧化碳对于实现可持续燃料的生产具有至关重要的意义，有助于减轻温室气体排放。虽然转化一氧化碳需要多个关键步骤，但催化剂的吸附和活化的初始步骤至关重要。诸如氧化钛或氧化铈等知名金属氧化物无法促进这一步骤。为了解决这一难题，最近的一项实验工作表明含铋材料具有吸附和转化一氧化碳的潜力，其根源归因于铋孤对电子的作用。在本文中，我们展示了密度泛函理论（DFT）模拟，即增强一氧化碳在由扩展的金红石型TiO（110）和用BiO纳米团簇修饰的锐钛矿型（101）表面组成的异质结构上的吸附，特别强调了异质结构还原在活化一氧化碳中的作用。这些异质结构在纳米团簇中显示出低配位的铋位点以及由Bi - O态主导的价带边缘，这是铋孤对电子的典型特征。BiO - TiO异质结构的还原可以很容易地进行，并产生还原的铋和钛物种。一氧化碳与这个富电子的还原体系相互作用可以直接生成一氧化碳，使异质结构再氧化，或者通过从还原的异质结构向一氧化碳的电子转移形成活化的羧基物种（CO）。氧化的BiO - TiO异质结构可以以类似碳酸盐的吸附模式吸附一氧化碳，具有中等强度的吸附能。纳米团簇的氢化以及向吸附的一氧化碳的迁移是可行的，氢迁移势垒小于0.7电子伏特，但这形成了一个稳定的COOH中间体，而不是断裂C - O键或生成甲酸盐。这些结果突出表明，由用合适的金属氧化物纳米团簇修饰的半导体金属氧化物组成的可还原金属氧化物异质结构可以活化一氧化碳，有可能克服与一氧化碳转化中困难的第一步相关的难题。
