Alkali metal salts and supported transition metals have been the dominant catalysts used to maximise hydrogen production from supercritical water gasification (SCWG). Recently, FeCl3 has emerged as an alternative to these that has been found to be more effective in some cases reported in literature. However, to these authors’ knowledge, few studies exist that study this catalyst with none that involve microalgae as the feedstock. Investigation is reported into the effect of FeCl3 on the SCWG of Chlorella vulgaris for a range of temperatures (400–600°C) and biomass concentrations (1–3wt%), with comparisons made to other catalysts (KOH, Ru/C and their combinations). A significant decrease in hydrogen yield, carbon conversion and energy efficiency was observed with the addition of FeCl3, due to a reduced pH which suppressed the water gas shift reaction and catalysed of char forming reactions. This was in contrary to Ru/C and KOH catalysts, where those outcomes increased. Additionally, when FeCl3 was used with Ru/C, the ruthenium was poisoned, nullifying its positive effects. Consequently, FeCl3 is not a suitable catalyst for hydrogen production from microalgae, either alone or in conjunction with a ruthenium catalyst.

Supercritical water gasification of microalgae offers a solution to hydrogen production that can simultaneously capture carbon from the atmosphere as both CO2 and solid biochar, without some of the negative environmental impacts of other biomass sources. Investigation into the influences of temperature (400-600 degrees C), biomass concentration (1-3 wt%), Oxidant Coefficient (0-0.5), heterogenous catalysts (Ru/C) and homogenous catalysts (KOH, 0-1 wt%) was carried out by integrating experimental results into a system model in ASPEN plus (R). High temperatures and ruthenium catalyst were found to be preferable for both experimental and whole system approaches at maximising hydrogen yield and efficiency. However, despite being favourable in the reaction, low concentrations were not favourable in the integrated system, due to differences in heat recovery and pumping power. Similarly, the influence of oxidant and KOH showed a more complex influence on the whole system than is currently understood in SCWG reactions. As a result, a maximum hydrogen yield of 12.7 mg/g was achieved, with 38 % and 30 % of the carbon being captured as gas and solid respectively, at 600 degrees C, 2 wt% algae, 1 wt % KOH, Ru/C catalyst and a 0.3 oxidant coefficient.

Due to their potential for a high growth rate microalgae are seen as promising feedstocks for hydrogen production, but their high-water content makes them unsuitable for traditional gasification. An alternative method, such as supercritical water gasification, is required to maximise this potential. This review assesses the literature involving the supercritical water gasification of microalgae and other relevant feedstocks. The impact on hydrogen yield, of biomass composition, catalysts, operating conditions, and the integration of the reactor into larger systems are considered. A high carbohydrate and low protein feed is usually preferable for maximum hydrogen yield. Homogeneous alkali metal salts and heterogeneous transition metals are desirable as catalysts. Issues such as recyclability, deactivation, and poor selectivity towards hydrogen production of these catalysts remain problematic. High temperatures and low biomass concentrations are suitable for high yields but require high energy inputs, so may not be advantageous when considering a whole system energy balance.

Investigation into the supercritical water gasification (SCWG) of microalgae has largely used deionized water as the reaction medium. However, real systems would use the algal growth water directly, containing ions that have been known to catalyse SCWG (K+, Na+, OH-, Fe3+, Cl-). Investigation into the effect of the growth water on SCWG was carried out for a range of temperatures (450-550), biomass concentrations (1-3%wt) and catalysts (KOH, Ru/C), using glucose or Chlorella vulgaris as the feedstock was performed. A significant increase in CO2 and reduction in CO content in the gas was observed without a catalyst and with a Ru/C catalyst. An increase in char/tar was also observed without a catalyst. As a result, the impact of the growth water should be considered for the SCWG of microalgae, in laboratory experiments and the selection of algal growth media in industrial applications.

Urbanisation, population growth, and climate change have put unprecedented pressure on water resources, leading to a global water crisis and the need for water reuse. However, water reuse is unsafe unless persistent chemical pollutants are removed from reclaimed water. State-of-the-art technologies for the reduction of persistent chemical pollutants in wastewater typically impose high operational and energy costs and potentially generate toxic by-products (e.g., bromate from ozonation). Nature-base solutions are preferred to these tech-nologies for their lower environmental impact. However, so far, bio-based tertiary wastewater treatments have been inefficient for industrial-scale applications. Moreover, they often demand significant financial investment and large infrastructure, undermining sustainability objectives. Here, we present a scalable, low-cost, low -car-bon, and retrofittable nature-inspired solution to remove persistent chemical pollutants (pharmaceutical, pes-ticides and industrial chemicals). We showed Daphnia's removal efficiency of individual chemicals and chemicals from wastewater at laboratory scale ranging between 50 % for PFOS and 90 % for diclofenac. We validated the removal efficiency of diclofenac at prototype scale, showing sustained performance over four weeks in outdoor seminatural conditions. A techno-commercial analysis on the Daphnia-based technology suggested several technical, commercial and sustainability advantages over established and emerging treatments at comparable removal efficiency, benchmarked on available data on individual chemicals. Further testing of the technology is underway in open flow environments holding real wastewater. The technology has the potential to improve the quality of wastewater effluent, meeting requirements to produce water appropriate for reuse in irrigation, in-dustrial application, and household use. By preventing persistent chemicals from entering waterways, this technology has the potential to maximise the shift to clean growth, enabling water reuse, reducing resource depletion and preventing environmental pollution.

Hydrogen, an emergent alternative energy vector to fossil fuels, can be produced sustainably by fermentation of cellulose following hydrolysis. Fermentation feedstock was produced hydrolytically using hot compressed water. The addition of CO2 enhanced hydrolysis by ~26% between 240 and 260 °C with comparable hydrolysis products as obtained under N2 but at a 10 °C lower temperature. Co-production of inhibitory 5-hydromethyl furfural was mitigated via activated carbon sorption, facilitating fermentative biohydrogen production from the hydrolysate by Escherichia coli. Post-fermentation E. coli cells were recycled to biomanufacture supported Pd/Ru nanocatalyst to up-convert liquid-extracted 5-HMF to 2,5-dimethyl furan, a precursor of ‘drop in’ liquid fuel, in a one-pot reaction. This side stream up-valorisation mitigates against the high ‘parasitic’ energy demand of cellulose bioenergy, potentially increasing process viability via the coupled generation of two biofuels. This is discussed with respect to example data obtained via a hydrogen biotechnology with catalytic side stream up-conversion from cellulose feedstock.

A heterogeneous Pd catalyst, biologically-mineralized palladium nanoparticles (bio-Pd), was synthesized using sulfidogenic bacteria which reduced soluble Pd(II) to catalytically-active Pd-nanoparticles (NPs). Heat treatment (processing) of bio-Pd (5 or 20 wt% on the cells) made by Desulfovibrio desulfuricans evolved supported Pdcatalyst comprising Pd-NPs held on large spherical hollow structures. The rate of hydrogenation of 2-butyne1,4-diol was similar to 5-fold slower than for a commercial catalyst (similar to twice that of native bio-Pd), but with high selectivity to the alkene, fulfilling a key industrial criterion. In the Heck reaction, while bio-Pd showed a comparable reaction rate in ethyl cinnamate synthesis to that achieved by commercial Pd/C, heat-treated bio-Pd had negligible activity. D. desulfuricans bio-Pd was replaced by bio-Pd made using a consortium of waste acidophilic sulfidogenic bacteria (CAS) supplied from an unrelated primary remediation process. This gave comparable activity to commercial 5 wt% Pd/C in ethyl cinnamate synthesis, signposting an economic, scalable route to catalyst manufacture.

Summary Desulfovibrio desulfuricans reduces Pd(II) to Pd(0)‐nanoparticles (Pd‐NPs) which are catalytically active in 2‐pentyne hydrogenation. To make Pd‐NPs, resting cells are challenged with Pd(II) ions (uptake), followed by addition of electron donor to promote bioreduction of cell‐bound Pd(II) to Pd(0) (bio‐Pd). Application of radiofrequency (RF) radiation to prepared 5 wt% bio‐Pd catalyst (60 W power, 60 min) increased the hydrogenation rate by 70% with no adverse impact on selectivity to cis‐2‐pentene. Such treatment of a 5 wt% Pd/carbon commercial catalyst did not affect the conversion rate but reduced the selectivity. Lower‐dose RF radiation (2–8 W power, 20 min) was applied to the bacteria at various stages before and during synthesis of the bio‐scaffolded Pd‐NPs. The reaction rate (μ mol 2‐pentyne converted s‐1) was increased by ~threefold by treatment during bacterial catalyst synthesis. Application of RF radiation (2 or 4 W power) to resting cells prior to Pd(II) exposure affected the catalyst made subsequently, increasing the reaction rate by 50% as compared to untreated cells, while nearly doubling selectivity for cis 2‐pentene. The results are discussed with respect to published and related work which shows altered dispersion of the Pd‐NPs made following or during RF exposure.

Following early reports, the literature now abounds with many examples of the use of biological materials to support, stabilise and incorporate metallic nanoparticles (NPs). This is noteworthy since precious metals (PMs) have no known biological functions. The use of biosupported PM metallic nanoparticles has been shown in green chemistry, remediation and in catalysts for energy and fuel cell applications, but the high cost of PMs means that the benefits must be clear to achieve cost effectiveness. To minimise cost, bacterial cells can recover metals from wastes. This chapter focuses on the ability of some bacteria to biorefine metals from liquid wastes and waste leachates into neo-catalysts in one-pot reactions. The resulting metallic NPs comprise a mixture of metals including non-active components of wastes. The activities of catalysts made from pure metals are compared with activities of waste-derived counterparts. A second way to minimise cost is to use ‘second life’ bacteria left over from an unrelated process. This chapter describes examples of the use of second life Escherichia. coli cells from a biohydrogen process and a second life sulphate reducing mixed culture from a primary bioremediation process used to treat acidic minewaters.

Functional nanomaterials are employed in a wide range of technological and industrial applications and searches for new and unique particles and production methods are expanding. Microbes now serve as widely available and untapped biotechnological resources due to their abilities to precipitate nanomaterials in systems utilising waste products and process streams as raw materials. Of particular appeal is the potential to offer a green biosynthesis approach to nanomaterial production (compared to traditional processing methods) for precious metal (palladium and gold) nanocatalysts, copper, selenium, tellurium and sulphur-based semi-conductors and quantum dots and magnetic iron-based nanomaterials. This chapter will focus on Fe and precious metal bionanomaterials, along with magnetic nanomaterials, catalysts and quantum dots. It will cover new opportunities built around tandem materials where synthetic biological approaches can be used to extend functionality by co-expressing bionanomaterials and enzymes (e.g. biocatalysts). Wherever possible, the potential use of waste substrates to add financial and economic incentives to drive product development within a circular economy is emphasised.

For new technologies to become market competitors, they must operate substantially cheaper than their competitors or achieve outcomes that are difficult by current methods. Classical life cycle analysis (LCA) focuses on salient ecological impacts but bypasses key economic aspects and does not assign quantifiable benefits. This chapter factors in the benefits of environmental protection, reduced CO2 emissions, and the environmental impacts of oil extraction and fuel production using a well-to-gate (also known as cradle-to-gate) LCA, as well as the economics involving the mitigation of landfill gate fees for waste resources and social cost of carbon. The case histories evaluated involve catalysts bio-refined from wastes for application in cleaner extraction, upgrading, and processing of heavy fossil and pyrolysis bio-oils and comparisons to their commercial counterparts. Each case history material was analysed with a commercial catalyst and a bio-catalyst assessed as an alternative based on oil ratios (%eq. of g : g). Pyrolysis bio-oils from waste wood and algal sources were found to be upgradable successfully using both catalysts. They produce carbon-neutral fuels because of carbon sequestration during photosynthetic biomass growth, and the bacterial components supporting the catalyst become assimilated into the fuel.

Biowastes are continuously generated worldwide in very large quantities per annum, primarily from lignocellulosic and food wastes. Waste disposal is a costly environmental problem, but wastes can serve as renewable resources for the sustainable production of fuels and chemicals. Hot compressed water (HCW), a benign method of biowaste pre-treatment, hydrolyses waste into bioprocess feedstock for onward bioconversion into fuels and chemicals. However it also produces degradation products (DPs) which can affect microbial action if not separated from the fermentable fraction. DPs are wasted resources. Three example biowastes (wheat straw, brewery grain and food waste) were HCW-hydrolysed (200 to 250 °C) to provide substrates for biohydrogen fermentation by Escherichia coli, before and after separation of the DPs using activated carbon. A major DP component, 5-hydroxymethyl furfural (5-HMF), was upgraded to 2,5-dimethyl furan (DMF), a platform chemical and ‘drop-in’ fuel using a novel metallic catalyst made on waste bacteria sourced from the biohydrogen or alternative microbial processes. The technique yielded two potential biofuels per unit of biomass feedstock. The impact of this dual benefit on process economics is discussed within a biorefinery concept.

Natural resource exploitation is accelerating in the face of resource decline, while at the same time people are generating ever growing quantities of wastes. Population and income growth drive up the demand for energy, materials and food. Four planetary boundaries that indicate a safe operating space for humankind may well have been crossed – climate change, land system change, biogeochemical loading and biosphere integrity – all directly linked to resource overexploitation. Resource exploitation has brought welfare to many people, but it is now infringing upon basic human rights such as clean water and a safe living environment. The management of resources needs to change radically from the linear take-make-use-dispose model to a more sustainable, circular model. This chapter introduces the global challenges within which an international movement towards a circular economy has emerged. It critically revisits views on circular economy and proposes a new model that recognises the complex nature of our resource flows. The Resource Recovery from Waste programme is introduced and an overview is provided of the contents of this book.

Biogas-energy is marginally profitable against the “parasitic” energy demands of processing biomass. Biogas involves microbial fermentation of feedstock hydrolyzate generated enzymatically or thermochemically. The latter also produces 5-hydroxymethyl furfural (5-HMF) which can be catalytically upgraded to 2, 5-dimethyl furan (DMF), a “drop in fuel.” An integrated process is proposed with side-stream upgrading into DMF to mitigate the “parasitic” energy demand. 5-HMF was upgraded using bacterially-supported Pd/Ru catalysts. Purpose-growth of bacteria adds additional process costs; Pd/Ru catalysts biofabricated using the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans were compared to those generated from a waste consortium of acidophilic sulfidogens (CAS). Methyl tetrahydrofuran (MTHF) was used as the extraction-reaction solvent to compare the use of bio-metallic Pd/Ru catalysts to upgrade 5-HMF to DMF from starch and cellulose hydrolyzates. MTHF extracted up to 65% of the 5-HMF, delivering solutions, respectively, containing 8.8 and 2.2 g 5-HMF/L MTHF. Commercial 5% (wt/wt) Ru-carbon catalyst upgraded 5-HMF from pure solution but it was ineffective against the hydrolyzates. Both types of bacterial catalyst (5wt%Pd/3-5wt% Ru) achieved this, bio-Pd/Ru on the CAS delivering the highest conversion yields. The yield of 5-HMF from starch-cellulose thermal treatment to 2,5 DMF was 224 and 127 g DMF/kg extracted 5-HMF, respectively, for CAS and D. desulfuricans catalysts, which would provide additional energy of 2.1 and 1.2 kWh/kg extracted 5-HMF. The CAS comprised a mixed population with three patterns of metallic nanoparticle (NP) deposition. Types I and II showed cell surface-localization of the Pd/Ru while type III localized NPs throughout the cell surface and cytoplasm. No metallic patterning in the NPs was shown via elemental mapping using energy dispersive X-ray microanalysis but co-localization with sulfur was observed. Analysis of the cell surfaces of the bulk populations by X-ray photoelectron spectroscopy confirmed the higher S content of the CAS bacteria as compared to D. desulfuricans and also the presence of Pd-S as well as Ru-S compounds and hence a mixed deposit of PdS, Pd(0), and Ru in the form of various +3, +4, and +6 oxidation states. The results are discussed in the context of recently-reported controlled palladium sulfide ensembles for an improved hydrogenation catalyst.

Escherichia coli cells support the nucleation and growth of ruthenium and ruthenium-palladium nanoparticles (Bio-Ru and Bio-Pd/Ru NPs). We report a method for the synthesis of these monometallic and bimetallic NPs and their application in the catalytic upgrading of 5-hydroxymethyl furfural (5-HMF) to 2,5 dimethylfuran (DMF). Examination using high resolution transmission electron microscopy with energy dispersive X-ray microanalysis (EDX) and high angle annular dark field (HAADF) showed Ru NPs located mainly at the cell surface using Ru(III) alone but small intracellular Ru-NPs (size ∼1-2 nm) were visible only in cells that had been pre-"seeded" with Pd(0) (5 wt%) and loaded with equimolar Ru. Pd(0) NPs were distributed between the cytoplasm and cell surface. Cells bearing 5% Pd/5% Ru showed some co-localization of Pd and Ru but chance associations were not ruled out. Cells loaded to 5 wt% Pd/20 wt% Ru showed evidence of core-shell structures (Ru core, Pd shell). Examination of this cell surface material using X-ray photoelectron spectroscopy (XPS) showed Pd(0) and Pd(II) and Ru(IV) and Ru(III), with confirmation by analysis of bulk material using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses. Both Bio-Ru NPs and Bio-Pd/Ru NPs were active in the conversion of 5-HMF into 2,5-DMF but commercial Ru on carbon catalyst outperformed 5 wt% bio-Ru by fourfold. While 5 wt% Pd/20 wt% Ru achieved 20% yield of DMF the performance of the 5 wt% Pd/5 wt% Ru bio-catalyst was higher and comparable to the commercial 5 wt% Ru/C catalyst in a test reaction using commercial 5-HMF (>50% selectivity). 5-HMF was prepared by thermochemical hydrolysis of starch and cellulose with solvent extraction of 5-HMF into methyltetrahydrofuran (MTHF). Here, with MTHF as the reaction solvent the commercial Ru/C catalyst had little activity (100% conversion, negligible selectivity to DMF) whereas the 5 wt% Pd/5 wt% Ru bio-bimetallic gave 100% conversion and 14% selectivity to DMF from material extracted from hydrolyzates. The results indicate a potential green method for realizing increased energy potential from biomass wastes as well as showing a bio-based pathway to manufacturing a scarcely described bimetallic material.

A hydrogen economy powered by fuel cells is emerging as an alternative to the current fossil-fuel based energy system where hydrogen, produced through renewable sources, is used to generate electricity via fuel cells. A commonly investigated fuel cell, the Polymer Electrolyte Fuel Cell (PEMFC), usually uses platinum and other platinum group metal nanomaterials to catalyze the rate limiting Oxygen Reduction Reaction (ORR) of this process. The high prices and durability limitations of these catalysts have prevented their mass commercialization. Biosynthesis of nanomaterials has emerged as a potentially attractive “eco-friendly” alternative to conventional chemical synthesis methods. Various attempts have been made to biosynthesize nanoparticles for use in fuel cells. However, the processing methods used during and post synthesis increase their costs and limit their overall efficacies. We report bimetallic Pt/Pd nanoparticles (NPs) biosynthesized by E. coli [E. coli-Pt/Pd (10 wt%:10 wt%)] that shows promise for direct use as a PEMFC catalyst. This catalyst outperformed single metal versions of the same, i.e., E. coli-Pt (20 wt%) and E. coli-Pd (20 wt%) when tested as an electrocatalyst ex-situ. Direct use of E. coli-synthesized nanoparticles in PEMFCs is limited by the inherent resistances of the bacteria and the internal localization of nanoparticles. Transmission electron microscopy images and impedances (resistivity) tests showed that by initially synthesizing Pd nanoparticles on the E. coli cells, followed by Pt, gave a cell surface-localized metallic shell that improved conductivity of the catalyst. Catalyst Pt synthesis is likely mediated by initially-formed Pd-NPs reducing Pt (IV) under H2 resulting in alloying; this was evidenced by XRD data that showed XRD peaks for E. coli-Pt/Pd (10%:10%) which lie in between XRD peaks for Pt-only and Pd-only nanoparticles on the same planes. Protrusions of agglomerated nanoparticles were seen on the cell surface to form sites for catalytic activity. The catalyst, used in the ORR without optimization, performed significantly worse (~100 times) than a commercial catalyst (extensively developed for purpose) but which contained 5 times as much Pt. This serves as a starting point for a more engineered approach to bio-synthesizing nanoparticles for PEMFC catalysts.

Numerous studies have focused on the bacterial synthesis of palladium nanoparticles (bio-Pd NPs), via uptake of Pd (II) ions and their enzymatically-mediated reduction to Pd (0). Cells of Desulfovibrio desulfuricans (obligate anaerobe) and Escherichia coli (facultative anaerobe, grown anaerobically) were exposed to low-dose radiofrequency (RF) radiation(microwave (MW) energy) and the biosynthesized Pd NPs were compared. Resting cells were exposed to microwave energy before Pd (II)-challenge. MW-injured Pd (II)-treated cells (and non MW-treated controls) were contacted with H-2 to promote Pd(II) reduction. By using scanning transmission electron microscopy (STEM) associated with a high-angle annular dark field (HAADF) detector and energy dispersive X-ray (EDX) spectrometry, the respective Pd NPs were compared with respect to their mean sizes, size distribution, location, composition, and structure. Differences were observed following MWinjury prior to Pd(II) exposure versus uninjured controls. With D. desulfuricans the bio-Pd NPs formed post-injury showed two NP populations with different sizes and morphologies. The first, mainly periplasmically-located, showed polycrystalline Pd nano-branches with different crystal orientations and sizes ranging between 20 and 30 nm. The second NPpopulation, mainly located intracellularly, comprised single crystals with sizes between 1 and 5 nm. Bio-Pd NPs were produced mainly intracellularly by injured cells of E. coli and comprised single crystals with a size distribution between 1 and 3 nm. The polydispersity index was reduced in the bio-Pd made by injured cells of E. coli and D. desulfuricans to 32% and 39%, respectively, of the values of uninjured controls, indicating an increase in NP homogeneity of 30-40% as a result of the prior MWinjury. The observations are discussed with respect to the different locations of Pd(II)-reducing hydrogenases in the two organisms and with respect to potential implications for the catalytic activity of the produced NPs following injury-associated altered NP patterning.

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 RuO 2. 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 (RuO 2 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.

BACKGROUND: The ability of bacterial cells to retain membrane integrity and membrane potential when challenged with palladium (II) solution has not being examined previously, which would provide a platform towards the bio-fabrication of a multifunctional tandem bio-nanoparticles. This study investigates the use of flow cytometry coupled with fluorescent probes to determine membrane integrity and membrane potential of cells of Desulfovibrio desulfuricans and Bacillus benzeovorans challenged with 1 mmol L-1 of sodium tetrachloropalladate (II) (Na2PdCl4) solution at pH 2 followed by reduction of palladium (II) (Pd(II)) with formate to give 1 wt% loading of Pd(0) on the cells. RESULTS: Fluorescently labelled active bacterial cells retained over 80% of membrane potential when challenged with Pd(II) solutions except for Bacillus benzeovorans (Bb) with about 32% retention. Cell viability was also seen to be variable and strain-dependent while dead cells lack any membrane integrity. Since esterase activity is energy independent and unable to confirm the membrane potential of the bacterial cells, the dye 3,3 '-dihexyloxacarbocyanine iodide [DiO(6)(3)] was used to determine and confirm the membrane potential of the bacterial cells. CONCLUSION: The results revealed that since fluorescently labelled bacterial cells containing Pd(0) can retain metabolic activity when analysed with flow cytometry, it provides the potential for combining chemical catalysis with biochemical activity in reactions that require metabolic synergy. (c) 2018 Society of Chemical Industry