A biogenic catalyst for hydrogenation, reduction and selective dehalogenation in non-aqueous solvents

We report the activity of a new palladium catalyst supported on fundamentally different Gram negative (Desulfovibrio) and Gram positive (Bacillus) bacterial surfaces (bio-Pd). Under H2 (electron donor), cells of both strains reduced Pd(II) to Pd(0) as discrete nanoparticles located in the periplasmic space of D. desulfuricans or between the peptidoglycan and the proteinaceous surface layer (S-layer) of B. sphaericus. The catalytic activity of the preparations was similar in their ability to reduce Cr(VI) to Cr(III) (aq), and in the hydrogenation of itaconic acid (aq.) Bio-Pd on D. desulfuricans was also an effective catalyst in a range of reactions in methanol, performing comparably to a commercially available catalyst (10% Pd/C) in the conversion of 4-azidoaniline to 1,4-phenylenediamine. In the hydrogenation of 3-nitrostyrene, the bio-Pd showed selectivity for the partly reduced (dehalogenated) product (1-ethyl-3-nitrobenzene — 74%, 1-ethyl-3-aminobenzene — 7%) whereas the commercial catalyst produced only the fully reduced product (1-ethyl-3-aminobenzene — 73%). In the case of 1-bromo-2-nitrobenzene, again bio-Pd was selective for the dehalogenated product, nitrobenzene, whereas the commercial catalyst produced the salt aniline hydrobromide.