Support Effects in Gold-Catalyzed Direct Propylene Epoxidation
Low energy demand, limited generation of waste and undesired products, and economically attractive starting materials are prerequisites for a sustainable process. Propylene oxide is one of the bulk chemicals (production >9 mln t/y) widely used as building block for many every-day products including paints, plastics, foams, artificial leather, etc., that is yet to undergo the adaption to a more sustainable process. Most of propylene oxide is currently synthesized via two main routes: first, a chlorohydrin route, where propylene reacts in two steps with chlorine and a base (e.g. lime) towards the desired propylene oxide and a salt as waste. Second, the hydroperoxidation process involving an organic hydroperoxide as an oxidant and generating the desired product and an organic byproduct.
Currently, in research the most promising waste-free propylene oxide synthesis involves selective gas-phase oxidation of propylene with oxygen in the presence of hydrogen and supported gold nanoparticles on Ti-containing supports as a catalyst. Where propylene oxide can be obtained with high selectivity with water as a by-product.  In this bifunctional system, metallic gold particles are proposed to be crucial for activation of oxygen and hydrogen to peroxides. While the selective oxidation of propylene is proposed to take place at the perimeter between the Au-particles and the metal oxide surface (figure 1). Ti activates H2O2 for the subsequent reaction with propylene.  Yet limited information is available on the effects of the support materials in the selective oxidation of propylene to propylene oxide. In my research I want to gain more insight into how certain support-related parameters affect the catalytic performance of this catalyst.
In our group there is experience both with supported gold-nanoparticles (2-4 nm) on oxidic supports, used in selective butadiene hydrogenation , and selective oxidations, e.g. the selective oxidation of ethylene over supported silver-catalysts.