Novel supported Pd hydrogenation bionanocatalyst for hybrid homogeneous/heterogeneous catalysis

Homogeneous and heterogeneous catalysis approaches to hydrogenation have different advantages and disadvantages and hybrid approaches are sought to maximise the advantages of both. Bacterial cells, of length 1–2 μm, present an economical alternative to conventional micro-scale supports such as graphite and alumina. Certain strains of bacteria can reduce soluble Pd(II), from stock solutions or acid extracts of spent catalysts, forming nanocrystals of Pd, which are supported within the bacterial cell surface layers. The biologically supported nano-Pd contains particles of size ∼5 nm and below, as determined using magnetic measurements (SQUID) and EXAFS spectroscopy. Bio-nano-Pd supported on exemplar Gram negative and Gram positive bacterial types catalysed the hydrogenation of itaconic acid (initial rates 1.1 and 1.2 × 10−2 mol gPd−1 s−1) comparing well with commercial 5% Pd-graphite (1.3 × 10−2 mol gPd−1 s−1).