当前位置: X-MOL 学术J. Catal. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Experimental and theoretical assessment of the mechanism of hydrogen transfer in alkane-alkene coupling on solid acids
Journal of Catalysis ( IF 7.3 ) Pub Date : 2017-09-19 , DOI: 10.1016/j.jcat.2017.08.002
Michele L. Sarazen , Enrique Iglesia

Experimental and theoretical methods are used to probe the mechanism and site requirements for C–C bond formation and hydride transfer (HT) reactions of alkane-alkene mixtures on solid acids with diverse acid strength and confining voids. Such methods provide quantitative descriptors of reactivity in terms of the properties of molecules and solids for chemistries that enable the practice of alkylation and oligomerization catalysis. In these processes, chain growth is controlled by HT from alkanes to alkene-derived bound alkoxides formed via oligomerization or β-scission. Transition state (TS) treatments of the elementary steps that mediate these reactions show that HT rates depend on the energies required to desorb alkoxides as carbenium ions and to cleave the weakest C–H bond in gaseous alkanes. These energies serve as accurate molecular descriptors of hydride transfer reactivity and, taken together with the acid strength and van der Waals stabilization properties of catalytic solids, provide the kinetic details required to predict the relative rates at which alkoxides react with alkenes (to form C–C bonds and larger alkenes) or alkanes (to accept H-atoms and desorb as alkanes) for chains with a broad range of size and skeletal structure. Confinement effects reflect the size of the TS and its precursors for C–C coupling and HT relative to the dimensions of the confining voids, which determine how guest species form van der Waals contacts with the host without significant distortions. Smaller voids preferentially stabilize the smaller C–C bond formation TS over the larger structures that mediate HT. Acid strength, in turn, influences the stability of conjugate anions at the ion-pair TS: stronger acids lead to higher turnover rates for C–C coupling and HT, but to similar extents, because their TS structures contain fully-formed framework anions that benefit similarly from their more stable character in stronger acids.



中文翻译:

固体酸与烷烃-烯烃偶联过程中氢转移机理的实验和理论评估

使用实验和理论方法来探究烷烃-烯烃混合物在具有不同酸强度和限制空隙的固体酸上进行CC键和氢化物转移(HT)反应的机理和位点要求。这样的方法就分子和固体的化学性质提供了反应性的定量描述,使得能够进行烷基化和低聚催化实践。在这些过程中,链增长受HT控制,从烷烃到通过低聚或β断裂形成的烯烃衍生的键合醇盐。介导这些反应的基本步骤的过渡态(TS)处理表明,HT速率取决于解吸烷氧化物作为碳正离子和裂解气态烷烃中最弱的CH键所需的能量。这些能量可作为氢化物转移反应性的准确分子描述,并与催化固体的酸强度和范德华稳定特性一起,提供了预测烷氧化物与烯烃反应的相对速率(形成C–的相对速率)所需的动力学细节。 C键和较大的烯烃)或烷烃(接受H原子并解吸为烷烃)可用于尺寸和骨架结构广泛的链。约束效应反映了TS及其用于C–C耦合和HT的前驱体的尺寸相对于约束空隙的尺寸,这决定了客体物种如何形成范德华斯与主体的接触而没有明显的变形。较小的空隙优先于较小的C–C键形成TS稳定于介导HT的较大结构。反过来,酸强度

更新日期:2017-09-19
down
wechat
bug