Dieu Hang Tran, Hung Huynh Minh, Nguyen Minh Tho
Department of Chemistry, Quy Nhon University, 590000 Quy Nhon, Vietnam.
Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
ACS Omega. 2017 Aug 16;2(8):4563-4574. doi: 10.1021/acsomega.7b00808. eCollection 2017 Aug 31.
High-accuracy quantum chemical calculations were carried out to study the mechanisms and catalytic abilities of various mixed silicon species SiM with M = H, Li, Na, Cu, and Ag toward the first step of methanol activation reaction. Standard heats of formation of these small triatomic Si clusters were determined. Potential-energy profiles were constructed using the coupled-cluster theory with extrapolation to complete basis set CCSD(T)/CBS, and CCSD(T)/aug-cc-pVTZ-PP for SiCu and SiAg. The most stable complexes generated by the interaction of methanol with the mixed clusters SiM possess low-spin states and mainly stem from an M-O connection in preference to Si-O interaction, except for the SiH case. In two competitive pathways including O-H and C-H bond breakings, the cleavage of the O-H bond in the presence of all clusters studied becomes predominant. Of the mixed clusters SiM considered, the dissociation pathways of both O-H and C-H bonds with SiLi turns out to have the lowest energy barriers. The most remarkable finding is the absence of the overall energy barrier for the O-H cleavage with the assistance of SiLi. The breaking of O-H and C-H bonds with the assistance of SiH, SiLi, and SiNa is kinetically preferred with respect to the SiCu and SiAg cases, apart from the case of SiNa for O-H cleavage. In comparison with other transition-metal clusters with the same size, such as Cu, Pt, and PtAu, the energy barriers for the O-H bond activation in the presence of small Si species, especially SiH and SiLi, are found to be lower. Consequently, these small mixed silicon clusters can be regarded as promising alternatives for the expensive metal-based catalysts currently used for methanol activation particularly and other dehydrogenation processes of organic compounds. The present study also suggests a further extensive search for other doped silicon clusters as efficient and more realistic gas-phase catalysts for important dehydrogenation processes in such a way that they can be experimentally prepared and implemented.
进行了高精度量子化学计算，以研究各种混合硅物种SiM（M = H、Li、Na、Cu和Ag）对甲醇活化反应第一步的反应机理和催化能力。确定了这些小三原子硅簇的标准生成热。使用耦合簇理论并外推至完备基组CCSD(T)/CBS构建势能面，对于SiCu和SiAg则使用CCSD(T)/aug-cc-pVTZ-PP。甲醇与混合簇SiM相互作用生成的最稳定络合物具有低自旋态，除SiH情况外，主要源于M-O连接而非Si-O相互作用。在包括O-H和C-H键断裂的两条竞争途径中，在所研究的所有簇存在下，O-H键的断裂占主导。在所考虑的混合簇SiM中，SiLi存在时O-H和C-H键的解离途径具有最低的能垒。最显著的发现是在SiLi的辅助下O-H裂解不存在整体能垒。除了SiNa用于O-H裂解的情况外，在SiH、SiLi和SiNa的辅助下O-H和C-H键的断裂在动力学上比SiCu和SiAg的情况更有利。与其他相同尺寸的过渡金属簇（如Cu、Pt和PtAu）相比，发现小硅物种（特别是SiH和SiLi）存在时O-H键活化的能垒更低。因此，这些小的混合硅簇可被视为目前用于甲醇活化特别是其他有机化合物脱氢过程的昂贵金属基催化剂的有前途的替代品。本研究还建议进一步广泛寻找其他掺杂硅簇，作为重要脱氢过程的高效且更实际的气相催化剂，以便能够通过实验制备和应用。
