Fang Zongtang, Zetterholm Patrick, Dixon David A
Department of Chemistry, The University of Alabama , Shelby Hall, Box 870336, Tuscaloosa, Alabama 35487, United States.
J Phys Chem A. 2016 Mar 24;120(11):1897-907. doi: 10.1021/acs.jpca.6b00158. Epub 2016 Mar 10.
The dehydration and dehydrogenation reactions of one and two 1,2-ethanediol and 1,3-propanediol molecules on (MO3)3 (M = Mo, W) nanoclusters have been studied computationally using density functional and coupled cluster (CCSD(T)) theory. The reactions are initiated by the formation of a Lewis acid-base complex with an additional hydrogen bond. Dehydration is the dominant reaction proceeding via a metal bisdiolate. Acetaldehyde, the major product for 1,2-ethanediol, is produced by α-hydrogen transfer from one CH2 group to the other. For 1,3-propanediol, the C-C bond breaking pathways to produce C2H4 and HCH═O simultaneously and proton transfer to generate propylene oxide have comparable barrier energies. The barrier to produce propanal from the propylene oxide complex is less than that for epoxide release from the cluster. On the Mo3O9 cluster, a redox reaction channel for 1,2-ethanediol to break the C-C bond to form two formaldehyde molecules and then to produce C2H4 is slightly more favorable than the formation of acetaldehyde. For W(VI), the energy barrier for the reduction pathway is larger due to the lower reducibility of W3O9. Similar reduction on Mo(VI) for 1,3-propanediol to form propene is not a favorable pathway compared with the other pathways as additional C-H bond breaking is required in addition to breaking a C-C bond. The dehydrogenation and dehydration activation energies for the selected glycols are larger than the reactions of ethanol and 1-propanol on the same clusters. The CCSD(T) method is required because density functional theory with the M06 and B3LYP functionals does not predict quantitative energies on the potential energy surface. The M06 functional performs better than does the B3LYP functional.
利用密度泛函理论和耦合簇（CCSD(T)）理论，通过计算研究了1,2 - 乙二醇和1,3 - 丙二醇分子在(MO3)3（M = Mo、W）纳米团簇上的脱水和脱氢反应。这些反应通过形成带有额外氢键的路易斯酸碱络合物引发。脱水是通过金属双二醇盐进行的主要反应。1,2 - 乙二醇的主要产物乙醛是通过一个CH2基团的α - 氢转移到另一个CH2基团产生的。对于1,3 - 丙二醇，同时产生C2H4和HCH═O的C - C键断裂途径以及质子转移生成环氧丙烷的途径具有相当的势垒能量。从环氧丙烷络合物生成丙醛的势垒低于从团簇释放环氧化物的势垒。在Mo3O9团簇上，1,2 - 乙二醇通过氧化还原反应通道断裂C - C键形成两个甲醛分子然后生成C2H4的途径比生成乙醛的途径略占优势。对于W(VI)，由于W3O9的还原性较低，还原途径的能垒更大。与其他途径相比，Mo(VI)上1,3 - 丙二醇生成丙烯的类似还原途径不是有利途径，因为除了断裂C - C键外还需要额外断裂C - H键。所选二醇的脱氢和脱水活化能大于乙醇和1 - 丙醇在相同团簇上的反应活化能。需要使用CCSD(T)方法，因为采用M06和B3LYP泛函的密度泛函理论无法预测势能面上的定量能量。M06泛函的表现优于B3LYP泛函。
