Assessing and controlling the size, morphology and composition of supported bimetallic catalyst nanoparticles

Supported bimetallic nanoparticles are frequently used for applications in catalysis [1]. Ideally we would like to be able to synthesize stable alloy nanoparticles with (i) a well-defined and narrow size range, (ii) very specific morphologies (i.e. random alloy, ordered alloy, core-shell structures) and (iii) closely controlled compositions. In reality, our ability to simultaneously control all of these physical parameters by conventional catalyst preparation methods is still somewhat lacking. We have found that aberration corrected analytical electron microscopy is an excellent way of performing ‘quality control’ measurements on such bimetallic catalyst systems. In particular, the combination of HAADF imaging and XEDS compositional analysis in the STEM has given us considerable insight into the way in which elemental distributions evolve in these bimetallic catalyst systems during processing and use. Our studies have especially highlighted the need to create simple chemical synthesis protocols which afford a tighter control of composition from particle-to-particle. In this presentation some case studies will be given, using the Au-Pd, Pt-Pd and Au-Pt bimetallic systems as specific examples, to illustrate the complex relationships that can exist between preparation route, compositional homogeneity and catalytic performance.