Professor Vannice performed seminal early research investigating hydrogen spillover from supported metals onto reducible oxide surfaces. While hydrogen spillover is well known and often invoked, it remains poorly understood. In tribute to Prof. Vannice’s work, and in celebration of his career, we discuss our most recent work on spillover. Using Au/titania catalysts, we show it is possible to quantify the highly mobile adsorbed hydrogen species that define spillover. We also discuss the differences between spillover and support reduction – a related phenomenon in which the hydrogen spillover “irreversibly” reacts with the support.
Our recent advances allow us to begin understanding the driving forces behind spillover and examine how various changes to the catalyst impact spillover thermodynamics. We show spillover is a rare example of entropically favorable adsorption and is fundamentally tied to the support surface chemistry. This support surface chemistry is largely consistent regardless of the identity of the metal used to adsorb hydrogen. The impact of surface hydroxylation, strongly adsorbed water, and support phase on spillover thermodynamics will be discussed.
