Hydrogen spillover and its relation to catalysis: observations on structurally defined single-atom sites

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 and is therefore of tremendous fundamental and technological interest. However, atomic level information concerning the kinetics of this process, the structural evolution of the 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 the development of a solubilised polyoxometalate-supported single-atom catalyst which allows for the use of characterisation techniques generally inaccessible to study heterogeneous catalysis. 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 predominantly on the nature of the reducible bond in the substrate. Similar trends were observed on one of the most prototypical hydrogen spillover catalysts, Pt/WO3, supporting the generalisability of the observations.