Abstract
Bacillus benzeovorans assisted and supported growth of ruthenium (bio-Ru) and palladium/ruthenium (bio-Pd@Ru) core@shell nanoparticles (NPs) as bio-derived catalysts. Characterization of the bio-NPs using various electron microscopy techniques and high-angle annular dark field (HAADF) analysis confirmed two NP populations (1–2 nm and 5–8 nm), with core@shells in the latter. The Pd/Ru NP lattice fringes, 0.231 nm, corresponded to the (110) plane of RuO2. While surface characterization using X-ray photoelectron spectroscopy (XPS) showed the presence of Pd(0), Pd(II), Ru(III) and Ru(VI), X-ray absorption (XAS) studies of the bulk material confirmed the Pd speciation (Pd(0) and Pd(II)- corresponding to PdO), and identified Ru as Ru(III) and Ru(IV). The absence of Ru–Ru or Ru–Pd peaks indicated Ru only exists in oxide forms (RuO2 and RuOH), which are surface-localized. X ray diffraction (XRD) patterns did not identify Pd-Ru alloying. Preliminary catalytic studies explored the conversion of 5-hydroxymethyl furfural (5-HMF) to the fuel precursor 2,5-dimethyl furan (2,5-DMF). Both high-loading (9.7 wt.% Pd, 6 wt.% Ru) and low-loading (2.4 wt.% Pd, 2 wt.% Ru) bio-derived catalysts demonstrated high conversion efficiencies (~95%) and selectivity of ~63% (~20% better than bio-Ru NPs) and 58%, respectively. These materials show promising future scope as efficient low-cost biofuel catalysts.
Highlights
The synthesis of bimetallic nanoparticles (NPs) has attracted major interest, given their ubiquitous catalytic applications and the unique properties ascribed to synergistic interactions between the two metallic components
Intracellular localization of Pd NPs was reported for the Gram-positive organism Bacillus benzeovorans, with co-localization of cytoplasmic Pd with phosphate groups (Supplementary Information Fig. S2) but attempts to fabricate bimetallic NPs on these Pd-‘seeds’ are not reported using Ru; the chemical formation of bimetallic Pd@Ru NPs is under-examined, while their facile biofabrication remains unexplored
Tests using the 20 wt% bio-derived Ru (14 wt% Ru: sample I, Table 1) gave 95% conversion of 5-hydroxymethyl furfural (5-HMF) with a yield of dimethyl furan (DMF) of 47.9 ± 2.0% which was increased to 60.3 ± 3.0% by incorporation of Pd to make the bimetallic
Summary
The synthesis of bimetallic nanoparticles (NPs) has attracted major interest, given their ubiquitous catalytic applications and the unique properties ascribed to synergistic interactions between the two metallic components. The suitability of living organisms, including bacterial cells, to template and form catalytic mono-metallic NPs is well known e.g.2,3, but microbially-assisted fabrication of structured bimetallic NPs is hardly investigated. A paradigm study[4] investigated microbially-assisted production of gold-palladium core@shell NPs (bio-Au@ Pd). Ru(III) was determined in the spent solution by assay using stannous chloride. Under H2 via the Pd(0) ‘seeds’, resulting in the bimetallic[4] This comprises chemical nanoparticles which retain the advantage of bio-scaffolding imprinted in the initial Pd-seeding step. The identification of intracellular Au@Pd core@shell NPs (Supplementary Information Fig. S1) (as opposed to earlier reports of NP growth on bacterial cell surfaces) following deposition of Pd-NPs in the cytoplasm[7] implies cellular uptake and trafficking mechanism(s) for metals with no known biological roles. Intracellular localization of Pd NPs was reported for the Gram-positive organism Bacillus benzeovorans, with co-localization of cytoplasmic Pd with phosphate groups (Supplementary Information Fig. S2) but attempts to fabricate bimetallic NPs on these Pd-‘seeds’ are not reported using Ru; the chemical formation of bimetallic Pd@Ru NPs is under-examined, while their facile biofabrication remains unexplored
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