Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Box 870336, Tuscaloosa, Alabama 35487-0336, United States.
J Phys Chem A. 2023 Apr 27;127(16):3614-3624. doi: 10.1021/acs.jpca.3c00776. Epub 2023 Apr 12.
Dehydration and dehydrogenation of an ethanol molecule on (TiO), = 2-4, nanoclusters were studied at the correlated molecular orbital theory CCSD(T)/aug-cc-pVDZ(-PP(Ti)) level using density functional theory B3LYP/DZVP2-optimized geometries. Physisorption and chemisorption of ethanol at the bridge Ti site on the trimer and tetramer are thermodynamically preferred over these reactions at the Ti site with a terminal Ti═O. Two possible lowest energy reaction coordinates of dehydration were predicted for the dimer and trimer where the β hydrogen on ethanol transfers to the adjacent terminal oxygen, or to the adjacent bidentate oxygen. Only the latter reaction coordinate was predicted to be the lowest energy one for the tetramer. Removal of ethylene from the (TiO)OH-CH complex for = 2-4 at 0 K requires 2-7 kcal/mol. For dehydrogenation, transfer of the α hydrogen to the adjacent Ti atom results in the lowest energy reaction coordinate following a proton-coupled electron-transfer (PCET) process. Removal of the acetaldehyde molecule requires 14-26 kcal/mol from the (TiO)H-CHO complex. Loss of H from the (TiO)H complex requires 5-8 kcal/mol. Dehydration and dehydrogenation of one ethanol molecule occur below the reactant asymptote for (TiO), = 2-4, whereas for (WO) and (MoO), two ethanol molecules are required for this process to be below the reactant asymptote. Dehydration of ethanol is thermodynamically preferred over dehydrogenation on (TiO), = 2-4. There is an approximate linear correlation of metal Lewis acidity with physisorption of ethanol. A quadratic correlation is predicted between the chemisorption barrier of ethanol and the corresponding proton affinity of oxygen to which the proton is being transferred. There are linear correlations between the basicity of the oxygen site and the acidity of the OH group versus the energy to remove CH from that site. The results for the nanoclusters for = 3 and 4 are consistent with the experimental results for the reactivity of ethanol on Ti rutile TiO (110) surface sites.
在相关分子轨道理论 CCSD(T)/aug-cc-pVDZ(-PP(Ti))水平上，使用密度泛函理论 B3LYP/DZVP2 优化的几何形状，研究了（TiO），= 2-4 纳米团簇上乙醇分子的脱水和脱氢反应。在桥 Ti 位上，乙醇在三聚体和四聚体上的物理吸附和化学吸附比在具有末端 Ti═O 的 Ti 位上的这些反应更具热力学优势。对于二聚体和三聚体，预测了两条可能的最低能量脱水反应坐标，其中乙醇上的β氢转移到相邻的末端氧或相邻的双齿氧。仅预测后一个反应坐标是四聚体的最低能量反应坐标。对于= 2-4，在 0 K 时从（TiO）OH-CH 复合物中除去乙烯需要 2-7 kcal/mol。对于脱氢反应，α 氢转移到相邻的 Ti 原子上导致最低能量反应坐标，遵循质子耦合电子转移（PCET）过程。从（TiO）H-CHO 复合物中除去乙醛分子需要 14-26 kcal/mol。从（TiO）H 复合物中除去 H 需要 5-8 kcal/mol。对于（TiO），= 2-4，一个乙醇分子的脱水和脱氢反应发生在反应物渐近线以下，而对于（WO）和（MoO），这个过程需要两个乙醇分子才能低于反应物渐近线。在（TiO），= 2-4 上，乙醇的脱水反应在热力学上优于脱氢反应。金属路易斯酸度与乙醇的物理吸附之间存在近似线性关系。预测了乙醇的化学吸附势垒与质子转移到的氧的相应质子亲合能之间的二次关系。氧位的碱性与从该位去除 CH 的能量之间存在线性关系。对于= 3 和 4 的纳米团簇，结果与乙醇在 Ti 金红石 TiO（110）表面位上的反应性的实验结果一致。
