Hydrogen Radical Detection in Catalytic Hydrogenation Reactions: Background C-H Activation in Solvents

Platinum group metal (PGM) nanoparticle catalysts are commonly used in a wide variety of liquid-phase hydrogenation reactions. Carbon-supported palladium nanoparticles are used extensively in many industrially applied hydrogenation reactions across the pharmaceutical industry and increasingly in the hydrogenolysis of bio-derived molecules. These reactions are often performed in solvents such as toluene or xylene which are considered inert towards mild hydrogenation conditions. Through a series of catalytic studies analysed using 1H/2H Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopies, and Density Functional Theory (DFT) calculations, we present evidence that hydrogen is being constantly exchanged into the methyl groups of the solvent possibly via a radical mechanism at these mild conditions. These effects should be considered in the explanation of any model of catalytic hydrogenation reaction at metal surfaces.