Gold–palladium colloids as catalysts for hydrogen peroxide synthesis, degradation and methane oxidation: effect of the PVP stabiliser

The reactivity of AuPd nanoparticle catalysts prepared by sol immobilisation is often explained by a structure activity relationship based solely on particle size or composition. In this contribution, we compare colloidal AuPd nanoparticles stabilised with polyvinylpyrrolidone (PVP) with the same AuPd nanoparticles supported on TiO2 for the direct synthesis of hydrogen peroxide and methane oxidation to methanol. We show that while the particles have similar rates of H2O2 synthesis, supporting the particles can affect the rates of H2O2 decomposition and hence the effectiveness of the catalyst for reactions which rely on H2O2 as an initiator or oxidant. We demonstrate that the absence of PVP results in high rates of H2O2 decomposition in methane oxidation experiments but this can be minimised by the addition of PVP to the reactor. These results also show that for AuPd alloys, both polymer stabiliser and support effects need to be taken into account when describing the activity of the nanoparticles and the active sites should in fact be thought of as a metal–support–polymer interface with many degrees of freedom.