Ketrat Sombat, Maihom Thana, Wannakao Sippakorn, Probst Michael, Nokbin Somkiat, Limtrakul Jumras
Department of Chemistry, Faculty of Science and Center for Advanced Studies in Nanotechnology for Chemical, Food and Agricultural Industries, KU Institute for Advanced Studies, Kasetsart University , Bangkok 10900, Thailand.
Department of Chemistry, Faculty of Liberal Arts and Science, Kasetsart University, Kamphaeng Saen Campus , Nakhon Pathom 73140, Thailand.
Inorg Chem. 2017 Nov 20;56(22):14005-14012. doi: 10.1021/acs.inorgchem.7b02143. Epub 2017 Oct 30.
The oxidation of CO by NO over metal-organic framework (MOF) M(btc) (M = Fe, Cr, Co, Ni, Cu, and Zn) catalysts that contain coordinatively unsaturated sites has been investigated by means of density functional theory calculations. The reaction proceeds in two steps. First, the N-O bond of NO is broken to form a metal oxo intermediate. Second, a CO molecule reacts with the oxygen atom of the metal oxo site, forming one C-O bond of CO. The first step is a rate-determining step for both Cu(btc) and Fe(btc), where it requires the highest activation energy (67.3 and 19.6 kcal/mol, respectively). The lower value for the iron compound compared to the copper one can be explained by the larger amount of electron density transferred from the catalytic site to the antibonding of NO molecules. This, in turn, is due to the smaller gap between the highest occupied molecular orbital (HOMO) of the MOF and the lowest unoccupied molecular orbital (LUMO) of NO for Fe(btc) compared to Cu(btc). The results indicate the important role of charge transfer for the N-O bond breaking in NO. We computationally screened other MOF M(btc) (M = Cr, Fe, Co, Ni, Cu, and Zn) compounds in this respect and show some relationships between the activation energy and orbital properties like HOMO energies and the spin densities of the metals at the active sites of the MOFs.
通过密度泛函理论计算研究了含配位不饱和位点的金属有机框架（MOF）M(btc)（M = Fe、Cr、Co、Ni、Cu和Zn）催化剂上CO被NO氧化的反应。该反应分两步进行。首先，NO的N - O键断裂形成金属氧中间体。其次，一个CO分子与金属氧位点的氧原子反应，形成CO的一个C - O键。第一步是Cu(btc)和Fe(btc)的速率决定步骤，在此步骤中需要最高的活化能（分别为67.3和19.6千卡/摩尔）。铁化合物的值比铜化合物低，可以用从催化位点转移到NO分子反键轨道的电子密度量更大来解释。反过来，这是由于与Cu(btc)相比，Fe(btc)的MOF最高占据分子轨道（HOMO）和NO的最低未占据分子轨道（LUMO）之间的能隙更小。结果表明电荷转移在NO的N - O键断裂中起重要作用。我们在此方面通过计算筛选了其他MOF M(btc)（M = Cr、Fe、Co、Ni、Cu和Zn）化合物，并展示了活化能与轨道性质（如HOMO能量和MOF活性位点金属的自旋密度）之间的一些关系。
