Breaking H₂ with CeO₂: Effect of Surface Termination

Abstract

The ability of ceria to break H 2 in the absence of noble metals has prompted a number of studies because of its potential applications in many technological fields. Most of the theoretical works reported in the literature are focused on the most stable (111) termination. However, recently, the possibility of stabilizing ceria particles with selected terminations has opened new avenues to explore. In the present paper, we investigate the role of termination in H 2 dissociation on stoichiometric ceria. We model (111)-, (110)-, and (100)-terminated slabs together with the stepped (221) and (331) surfaces. Our results support a dissociation mechanism proceeding via the formation of a hydride/hydroxyl CeH/OH intermediate. Both the stability of such an intermediate and the activation energy depend critically on the termination, the (100)-terminated surfaces being the most reactive: the activation energy is 0.16 eV, and the CeH/OH intermediate is stable by −0.64 eV for the (100) slab, whereas the (111) slab presents 0.75 and 0.74 eV, respectively. We provide structural, energetic, electronic, and spectroscopic data, as well as chemical descriptors correlating structure, energy, and reactivity, to guide in the theoretical and experimental characterization of the Ce–H surface intermediate.

Water‐Assisted Homolytic Dissociation of Propyne on a Reduced Ceria Surface

“…Extensive studies on the interaction of H 2 and ceria show that the dissociation of H 2 proceeds through a hydride intermediate . Both oxygen vacancies and surface terminations of ceria play crucial roles in H 2 activation . The formation of surface and bulk hydride species upon H 2 adsorption at elevated temperatures was demonstrated by in situ inelastic neutron spectroscopy studies …”

H2 Dissociation and Oxygen Vacancy Formation on Ce2O3 Surfaces

“…This indicates that Ce 2 O 3 stabilizes the heterolytic product compared to CeO 2 who tends to lead to an unstable (H + ,H -) product. 33,34,38 Furthermore, the activation energy of the dissociation is very low, from 0.04 eV for (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) to 0.13 eV for (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) Table 5. Adsorption energies (in eV) of the species involved in the H 2 dissociation process.…”

“…Recently, ceria has been successfully used in hydrogenation processes [28][29][30][31] with high activity and selectivity, thus opening new avenues in hydrogenation catalysis application in the absence of noble metals. [31][32][33][34][35][36][37][38] The mechanism of the H 2 dissociation on the (111)-CeO 2 surface was proposed by García-Melchor et al 33 and Fernández-Torre et al 34 : the H 2 molecule dissociates according to a heterolytic pathway forming a hydride/proton pair (Ce-H/OH) which is 0.7-0.8 eV endothermic, although the homolytic final product Ce 3+ -OH/Ce 3+ -OH is energetically very favorable, 2-3 eV exothermic with respect to the reactants initial energy. Very recently, H 2 dissociation was also investigated on other CeO 2 surfaces 36,38 and it was found that the surface termination plays a key-role on both the activation energy and the stabilization of the heterolytic product.…”

“…However, the homolytic product reminds systematically the most stable one, disfavoring the presence of hydride species at the surface. 33,34,36,38 Previous work of Vecchietti et al 39 report the formation of Ce-H hydride species as a key step in the semi-hydrogenation of alkyne. Moreover, Vilé et al 28 and Carrasco et al 29 have shown that the presence of oxygen vacancy was detrimental to the alkyne hydrogenation.…”

Wasserunterstützte homolytische Dissoziation von Propin auf reduzierter Ceroxidoberfläche

“…Umfangreiche Untersuchungen zur Wechselwirkung von H 2 und Ceroxid zeigen, dass die Dissoziation von H 2 über ein Hydrid‐Intermediat verläuft . Sowohl die Anwesenheit von Sauerstoff‐Leerstellen als auch die Oberflächenterminierung von Ceroxid spielen eine entscheidende Rolle bei der H 2 ‐Aktivierung . Die Bildung von Hydrid‐Spezies auf Oberfläche und im Volumen von Ceroxid durch H 2 ‐Adsorption bei erhöhter Temperatur wurde durch in situ Untersuchungen mit inelastischer Neutronenstreuung nachgewiesen …”