Lessio Martina, Senftle Thomas P, Carter Emily A
Department of Chemistry, Princeton University, Princeton, NJ, 08544-1009, USA.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, 08544-5263, USA.
ChemSusChem. 2018 May 9;11(9):1558-1566. doi: 10.1002/cssc.201800037. Epub 2018 Apr 18.
Adsorbed hydrogenated N-heterocycles have been proposed as co-catalysts in the mechanism of pyridine (Py)-catalyzed CO reduction over semiconductor photoelectrodes. Initially, adsorbed dihydropyridine (DHP*) was hypothesized to catalyze CO reduction through hydride and proton transfer. Formation of DHP* itself, by surface hydride transfer, indeed any hydride transfer away from the surface, was found to be kinetically hindered. Consequently, adsorbed deprotonated dihydropyridine (2-PyH ) was then proposed as a more likely catalytic intermediate because its formation, by transfer of a solvated proton and two electrons from the surface to adsorbed Py, is predicted to be thermodynamically favored on various semiconductor electrode surfaces active for CO reduction, namely GaP(111), CdTe(111), and CuInS (112). Furthermore, this species was found to be a better hydride donor for CO reduction than is DHP. Density functional theory was used to investigate various aspects of 2-PyH * formation and its reaction with CO on GaP(110), a surface found experimentally to be more active than GaP(111). 2-PyH * formation was established to also be thermodynamically viable on this surface under illumination. The full energetics of CO reduction through hydride transfer from 2-PyH * were then investigated and compared to the analogous hydride transfer from DHP*. 2-PyH * was again found to be a better hydride donor for CO reduction. Because of these positive results, full energetics of 2-PyH * formation were investigated and this process was found to be kinetically feasible on the illuminated GaP(110) surface. Overall, the results presented in this contribution support the hypothesis of 2-PyH *-catalyzed CO reduction on p-GaP electrodes.
吸附的氢化氮杂环已被提出作为吡啶（Py）催化半导体光电极上CO还原机制中的助催化剂。最初，人们假设吸附的二氢吡啶（DHP*）通过氢化物和质子转移来催化CO还原。通过表面氢化物转移形成DHP本身，实际上任何从表面转移走的氢化物转移，在动力学上都受到阻碍。因此，随后提出吸附的去质子化二氢吡啶（2-PyH）是更可能的催化中间体，因为通过从表面向吸附的Py转移一个溶剂化质子和两个电子来形成它，预计在各种对CO还原有活性的半导体电极表面，即GaP(111)、CdTe(111)和CuInS(112)上，在热力学上是有利的。此外，发现该物种比DHP是更好的用于CO还原的氢化物供体。密度泛函理论被用于研究2-PyH形成的各个方面及其在GaP(110)上与CO的反应，实验发现该表面比GaP(111)更具活性。在光照下，2-PyH在该表面的形成在热力学上也是可行的。然后研究了通过从2-PyH转移氢化物进行CO还原的完整能量学，并与从DHP进行类似氢化物转移的情况进行了比较。再次发现2-PyH是更好的用于CO还原的氢化物供体。由于这些积极结果，研究了2-PyH形成的完整能量学，发现该过程在光照的GaP(110)表面在动力学上是可行的。总体而言，本论文中给出的结果支持了在p-GaP电极上2-PyH催化CO还原的假设。
