Biosynthesis Parameters Control the Physicochemical and Catalytic Properties of Microbially Supported Pd Nanoparticles

Abstract

The biosynthesis of Pd nanoparticles supported on microorganisms (bio‐Pd) is achieved via the enzymatic reduction of Pd(II) to Pd(0) under ambient conditions using inexpensive buffers and electron donors, like organic acids or hydrogen. Sustainable bio‐Pd catalysts are effective for C‐C coupling and hydrogenation reactions, but their industrial application is limited by challenges in controlling nanoparticle properties. Here, using the metal‐reducing bacterium Geobacter sulfurreducens, it is demonstrated that synthesizing bio‐Pd under different Pd loadings and utilizing different electron donors (acetate, formate, hydrogen, no e⁻ donor) influences key properties such as nanoparticle size, Pd(II):Pd(0) ratio, and cellular location. Controlling nanoparticle size and location controls the activity of bio‐Pd for the reduction of 4‐nitrophenol, whereas high Pd loading on cells synthesizes bio‐Pd with high activity, comparable to commercial Pd/C, for Suzuki–Miyaura coupling reactions. Additionally, the study demonstrates the novel synthesis of microbially‐supported ≈2 nm PdO nanoparticles due to the hydrolysis of biosorbed Pd(II) in bicarbonate buffer. Bio‐PdO nanoparticles show superior activity in 4‐nitrophenol reduction compared to commercial Pd/C catalysts. Overall, controlling biosynthesis parameters, such as electron donor, metal loading, and solution chemistry, enables tailoring of bio‐Pd physicochemical and catalytic properties.