Hydrogen Spillover and Its Relation to Hydrogenation: Observations on Structurally Defined Single‐Atom Sites**

Abstract

Hydrogen spillover, involving the transfer of H atoms from metal sites onto the catalyst support, is ubiquitous in chemical processes such as catalytic hydrogenation and hydrogen storage. Atomic level information concerning the kinetics of this process, the structural evolution of catalysts during hydrogen spillover, as well as the nature of participation of the spilled over H in catalysis, remain vastly lacking. Here, we provide insights to those questions with a solubilized polyoxometalate-supported single-atom catalyst which allows for the use of characterization techniques generally inaccessible to the study of heterogeneous catalysts. Hydrogenation kinetics together with poisoning studies further reveal that hydrogen spillover can be either detrimental or beneficial for catalysis, the direction and magnitude of which depends mostly on the nature of the reducible functional group. Similar trends were observed on one of the most prototypical hydrogen spillover catalysts-Pt/WO 3 .

H2-reduced phosphomolybdate promotes room-temperature aerobic oxidation of methane to methanol

“…3a and S15). 40 As expected, after introducing 2 equivalents (relative to Pd) BzM to block Pd in Pd/CsPMA before H 2 treatment, PMA was not able to be reduced to enable methane oxidation (BzM-H 2 -CH 4 /O 2 in Fig. 2e).…”

Functionalized ceria–niobium supported nickel catalysts for gas phase semi-hydrogenation of phenylacetylene to styrene

“…15 Similarly, a recent study presented interesting deductions on the role of spillover hydrogen on the catalyst support. 16 The authors found that the spillover of hydrogen occurs as an autocatalytic process, and the spilled over H on metal oxides is decidedly protonic in nature and induces vacancy formation on the support. Furthermore, they observed that the spilled hydrogen on the support has direct participation in the reaction, and lowers the reaction barrier during CO and nitro group hydrogenation.…”

“…The phenomenon depends on the reducibility aptitude of the support and its tendency to offer high interaction with the active metal. 16 Tauster et al 17 were the first to investigate the strong metal–support interaction of non-transition metallic oxides (SiO 2 , Al 2 O 3 , SiO 2 –MgO and Al 2 O 3 –SiO 2 ). However, it was suggested that transition metal oxides would offer more interaction with the metal atoms on their surfaces, and possibly form a metal–metal bonding arising from the overlapping of the d orbitals of the neighboring cations.…”

Sub-nanometric high entropy alloy cluster: hydrogen spillover-driven synthesis on CeO2 and structural reversibility

“…This phenomenon has applications in the elds of hydrogen storage materials, 18 sensor fabrication 19 and heterogeneous catalysis. 20,21 Hydrogen spillover is favored on reducible transition metal oxides such as TiO 2 , CeO 2 and WO 3 because active H atoms are able to migrate over oxide surfaces as proton (H + )/electron (e − ) pairs based on the reaction M n+ + O 2− + H → M (n−1)+ + OH − . 22 Our group previously demonstrated that NPs made of binary solid-solution alloys having non-equilibrium compositions (speci cally, Ru-Ni and Rh-Cu) can be synthesized by utilizing individual H atoms originating from hydrogen spillover as a strong reductant to promote the simultaneous rapid reduction of deposited metal cations at low temperatures.…”