Studying H2 dissociation on heterogenous catalysts is important for improving hydrogenation catalysts. One interesting aspect of heterogenous catalysts is that they have two active sites: one directly at the metal site and the other at the metal-support interface (MSI). We have extensively studied H2 activation on Au/TiO2 catalysts and are extending our studies to other systems such as Ru/TiO2. We use FTIR spectroscopy and volumetric gas adsorption experiments to monitor and quantify the spectroscopic signatures associated with H2 activation. Our previous studies on Au/TiO2 catalysts showed heterolytic H2 dissociation at the MSI results in protons that are transferred to interface hydroxyls and electrons that are distributed across the semiconductor support. In comparison to Au/TiO2, we observed important differences for H2 adsorption on Ru/TiO2 catalysts. We observe proton addition to the interface hydroxyls upon H2 dissociation; however, there is an induction period before we observe electron injection into the semiconductor support. This is consistent with hydrogen adsorption followed by a “spillover” mechanism. We also observed changes in the stretching hydroxyl region of the Ru/TiO2 catalysts under exposure to H2. Free Ti-OH stretches around 3670 cm-1. On Au/TiO2 catalysts, we see the transfer of a proton to the support hydroxyl through a clear loss of Ti-OH in the stretching region at 3620 cm-1 and the growth of the protonated interface hydroxyl (MSITiOH2+) stretching band at 3300 cm-1. For our Ru/TiO2 catalysts, we observe the loss of Ti-OH sites at 3690 cm-1 and the gain of MSITiOH2+ at 3400 cm-1. The hydroxyl stretching features associated with Ru/TiO2 are blue shifted with respect to free Ti-OH while the Au/TiO2 features are red shifted. These shifts indicate the Ru nanoparticles create a more polar interface hydroxyl by withdrawing electron density in contrast to Au nanoparticles which donate electron density. This talk will present further direct comparison of the H2 dissociation mechanism on Au and Ru nanoparticle catalysts contributing to a better understanding of these systems

Monitoring H2 activation using FTIR spectroscopy: Comparison of the spectroscopic signatures on supported Au and Ru catalysts

ACS Spring 2022

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