Protons in silica supported phosphotungstic acid catalysts

Acid catalysts use highly mobile protons to activate a range of organic compounds such as olefins. The radicals then react to form long chain olefins. The reaction mechanism can be controlled by adjusting the acidity of the solid catalyst. Phosphorus tungsten acid (PTA) is such a catalyst whose catalytic activity can be enhanced by interaction with oxide supports. Catalysis experiments have demonstrated the efficacy of silica supported PTA, but the origin of the activity, e.g. due to a change in acidity, is debated. We performed X-ray photoelectron spectroscopy experiments, which indicate electronic structure changes due to electron transfer between PTA and oxide. However, electron spectroscopy cannot measure the hydrogen partial density of state, making it difficult to attribute the measured changes to increased acidity. We therefore plan to use neutron inelastic scattering (INS) at TOSCA to measure the hydrogen-dominated vibrational density of states, which will allow us to distinguish between protons and other hydrogen atoms (mainly as water) in the compound.