Palladium-gold catalysts for H2O2 direct synthesis at room temperature and atmospheric pressure

Introduction Hydrogen peroxide has always been considered a very interesting and environmentally friendly oxidant with applications confined mainly in unselective sectors such as the paper and textile industry and the treatment of waste waters. More recent applications, related to the discovery of TS-1 molecular sieve, are in the large scale selective oxidation processes for the chemical industry. The increasing demand for H2O2 and the general need for greener oxidants has revamped the interest for an alternative to its production by the oxidation of alkyl anthraquinone. Synthesis by direct reaction of hydrogen and oxygen has long been an attractive alternative, but it never found industrial application because of severe drawbacks due mainly to the hazardous nature of the gas mixtures and to the low yield and low selectivity to hydrogen peroxide rather than water that could be reached with known catalysts. Until very recently, the catalysts used in these investigations have been based predominantly on Pd. In the last years it has been reported that catalysts based on Pd-Au alloys supported on Al2O2, Fe2O3, TiO2 can significantly improve the rate of H2O2 formation when compared with the Pd only catalyst. We have recently demonstrated for sulfated zirconia and ceria samples, that while the monometallic gold catalysts are inactive under our experimental conditions, the addition of gold in amount 1:1 to the monometallic Pd sample improves the productivity and especially the selectivity of the process. In this work, in order to better understand the nature of Pd-Au interaction, different bimetallic Pd-Au samples supported on zirconia were prepared by different methods and were tested for the direct synthesis of hydrogen peroxide under very mild conditions (1 bar and 20°C) and outside the explosion range.