Dr Jennifer Edwards - BSc (Hons) PhD MRSC
The heterogeneous oxidation of hydrocarbons is of fundamental interest in the production of fine chemicals. When molecular oxygen is used as the oxidant, harsh reaction conditions tend to be employed – typically high temperature and pressure. Today the concept of green chemistry and sustainability is a key consideration and processes are required that can effectively utilise raw materials, reduce waste and avoid the use of toxic intermediates under mild reaction conditions. The discovery that finely dispersed Au nanoparticles are exceptionally active for CO oxidation at sub ambient temperatures was followed by the successful utilisation of Au catalysts for a wide range of highly selective, clean oxidation reactions which operate under very mild conditions. Typically, these catalysts contain high concentrations of Au (2.5-5 wt%). My previous research on the direct synthesis of H2O2 demonstrated for the first time that “clean” (halide/acid free) H2O2 can be generated when a 5 wt% AuPd catalyst is used.
Figure 1 Scanning transmission electron microscopy images of supported AuPd nanocrystals on metal oxide and activated carbon supports. For TiO2 and Al2O3 supports (red) the nanocrystals show a coreshell morphology with the Au rich core (blue) surrounded by a Pd rich shell (green). On activated carbon (red) the nanocrystal shows a homogeneous alloy composition
When the AuPd catalyst is supported on activated carbon, H2 selectivity and synthesis rates are extremely high, ~98% and 160mol.kgcat-1.h-1 respectively, with initial rates even higher (~900 mol.kgcat-1.h-1 ). Whilst the activity of this catalyst is high, the active site on the catalyst surface has not been clearly identified and the presence of a trimodal particle size distribution suggests that not all of the metal present (5 wt%) is active. Precious metals are an expensive, finite resource and it is important that catalysts utilising these materials do not contain inactive, spectator species. I am interesting in developing catalysts which contain far less precious metal than those typically employed, and where all the metal present is participating in the catalytic reaction. The applications for these materials include:
Selective hydrogenation and hydrogenolysis
Selective oxidation and epoxidation
Utilisation of bio renewable feedstocks
Fossil fuel free synthesis of platform chemicals
Analysis of these materials by computational studies and in depth characterisation will allow fundamental insight into the structure of the active site and will help elucidate reaction mechanisms. In turn this information will be used to formulate supported nanostructures which are reaction (hydrogenation, hydrogenolysis, (ep)oxidation) specific.