H2 Partial Pressure Research Articles

Recovery of methane and acetate during ex-situ biogas upgrading via novel dual-membrane aerated biofilm reactor

Biological biogas upgrading has been well-proven to be a promising approach for renewable bioenergy recovery, but hydrogen (H2)-assisted ex-situ biogas upgrading is hindered by a large solubility discrepancy between H2 and carbon dioxide (CO2). This study established a new dual-membrane aerated biofilm reactor (dMBfR) to improve the upgrading efficiency. Results showed that dMBfR operated at 1.25 atm H2 partial pressure, 1.5 atm biogas partial pressure, and 1.0 d hydraulic retention time could significantly improve the efficiency. The maximum methane purity of 97.6%, acetate production rate of 34.5 mmol L−1d−1, and H2 and CO2 utilization ratios of 96.5% and 96.3% were achieved. Further analysis showed that the improved performances of biogas upgrading and acetate recovery were positively correlated with the total abundances of functional microorganisms. Taken together, these results suggest that the dMBfR, which facilitates the precise CO2 and H2 supply, is an ideal approach for efficient biological biogas upgrading.

Pd/oCNT Monolithic Catalysts for Continuous-Flow Selective Hydrogenation of Cinnamaldehyde

Chemical engineering optimization from a batch process to continuous flow in liquid-phase hydrogenation brings a significant improvement in efficiency. However, its further application is limited due to the severe pressure drop and tube blockage problems in a powder-form catalyst fixed-bed reactor, especially for nanocarbon-supported catalysts. In this work, spherical monoliths containing oxygenated carbon nanotube (oCNT)-supported Pd nanoparticles (ca. average size of 2 mm) are fabricated via an in situ gelation method and applied for cinnamaldehyde (CAL) selective hydrogenation in a continuous-flow system. The simulated results by the computational fluid dynamics–discrete element method (CFD–DEM) coupled method show that the pressure drop of the monolith catalyst bed is maintained within 0.4 Pa. The Pd/oCNT monolithic catalyst exhibits excellent CAL conversion of 85.8% and hydrocinnamaldehyde (HCAL) selectivity of 93.5% within a high weight hourly space velocity (WHSV) of 0.012 s–1 at mild reaction conditions (30 °C, 3 bar). The catalyst maintains robust catalytic activity and HCAL selectivity (>93%) under varied reaction temperatures (30/60 °C), H2 partial pressures (3–10 bar), and WHSVs (0.012–0.184 s–1) and a stable reaction activity for more than 60 h time on stream, revealing the possibility in industrial hydrogenation reactions. The catalytic activity of the monolithic catalyst is determined by the surface properties of the carbon nanotubes and the chemical interactions between Pd nanoparticles and supports. The oxygenated functional groups and surface defects on oCNTs are beneficial for strong chemical interaction with Pd species, which forms abundant electron-deficient Pdδ+ species to facilitate C═C hydrogenation. This study puts forward insights into and perspectives for selective hydrogenation reactions in both electronic structure tuning of the active phase at the atomic scale and fabrication of monolithic catalysts at the macroscopic scale.

Kinetic Investigation on Selective CO<sub>2 </sub>Hydrogenation to Formic Acid over Rhodium Hydrotalcite (Rh-HT) Catalyst

Abstract—A heterogeneous catalyst, rhodium hydrotalcite (Rh-HT), was synthesized, characterized, and explored for kinetic studies for the hydrogenation of CO2 to formic acid using molecular hydrogen in an autoclave. The catalyst was efficient for the selective formation of formic acid at a moderate temperature with up to 5 catalytic cycles without any significant loss in catalytic activity. The detailed kinetic investigations were performed by determining the rate of formic acid formation as a function of time, catalyst amount, total pressure, partial pressure of CO2, partial pressure of H2, reaction volume, v/v ratio of the mixed solvent of methanol and water, agitation speed, and temperature in a wide range of variation. The rates were found to be dependent on all these parameters. The formic acid formation rate followed the first-order kinetics with respect to the partial pressures of CO2 and H2, and catalyst amount. The best reaction conditions obtained from the kinetic parametric optimisation were, 50 bar total pressure (1/1 p/p, CO2 and H2); 60°C temperature; a mixture of methanol:water solvent (5/1 v/v, 60 mL); 24 h time; and 500 rpm agitation speed to get a TON of 15840 for formic acid with no additional base. The thermodynamic performance of the heterogeneous catalyst Rh-HT was appreciably associated with highly negative entropy. The performance of the catalyst was effectively enhanced by the mixture of water and methanol as a solvent. The mechanistic routes for CO2 hydrogenation to formic acid are proposed and discussed based on the kinetic and experimental observations involving the role of the molecular effect of water used in the solvent.

One-pot lower olefins production from CO2 hydrogenation

In this work the one-pot conversion of CO2 into lower olefins is investigated over a physical mixture of a methanol synthesis catalyst and a methanol-to-olefins (MTO) zeolite. First, the feasibility of the single reactions is tested at CO2 to olefins conditions, i.e., high temperature and high H2/CO2 pressure, providing insights on the reaction mechanism and catalyst stability. The effects of the operating conditions are then analyzed over the individual samples, starting from CO2/H2 mixtures in the case of the methanol synthesis catalyst and from methanol in CO2/H2 in the case of the zeolite. The In2O3-ZrO2 catalyst exhibits very good selectivity to methanol and high activity, reaching thermodynamic equilibrium above 380 °C. The zeolite sample showed high activity as well and the presence of high H2 partial pressure consistently increases the zeolite lifetime at high temperatures, but also the paraffin selectivity at the expense of the olefins, especially at low space velocity. It is therefore clear that a trade-off should be identified when testing the bi-functional catalytic samples in order to guarantee high methanol formation and good olefins production in the one-pot process. Finally, a comparison between methanol-mediated and modified Fischer-Tropsch (MFT) routes is presented, highlighting strengths and weaknesses of each reaction pathway. In particular, CO must be reduced in the methanol-mediated route, while methane and C5+ hydrocarbons formation is the main issue for the MFT reaction.

A holobiont approach towards polysaccharide degradation by the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis

BackgroundTermites are among the most successful insects on Earth and can feed on a broad range of organic matter at various stages of decomposition. The termite gut system is often referred to as a micro-reactor and is a complex structure consisting of several components. It includes the host, its gut microbiome and fungal gardens, in the case of fungi-growing higher termites. The digestive tract of soil-feeding higher termites is characterised by radial and axial gradients of physicochemical parameters (e.g. pH, O2 and H2 partial pressure), and also differs in the density and structure of residing microbial communities. Although soil-feeding termites account for 60% of the known termite species, their biomass degradation strategies are far less known compared to their wood-feeding counterparts.ResultsIn this work, we applied an integrative multi-omics approach for the first time at the holobiont level to study the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis. We relied on 16S rRNA gene community profiling, metagenomics and (meta)transcriptomics to uncover the distribution of functional roles, in particular those related to carbohydrate hydrolysis, across different gut compartments and among the members of the bacterial community and the host itself. We showed that the Labiotermes gut was dominated by members of the Firmicutes phylum, whose abundance gradually decreased towards the posterior segments of the hindgut, in favour of Bacteroidetes, Proteobacteria and Verrucomicrobia. Contrary to expectations, we observed that L. labralis gut microbes expressed a high diversity of carbohydrate active enzymes involved in cellulose and hemicelluloses degradation, making the soil-feeding termite gut a unique reservoir of lignocellulolytic enzymes with considerable biotechnological potential. We also evidenced that the host cellulases have different phylogenetic origins and structures, which is possibly translated into their different specificities towards cellulose. From an ecological perspective, we could speculate that the capacity to feed on distinct polymorphs of cellulose retained in soil might have enabled this termite species to widely colonise the different habitats of the Amazon basin.ConclusionsOur study provides interesting insights into the distribution of the hydrolytic potential of the highly compartmentalised higher termite gut. The large number of expressed enzymes targeting the different lignocellulose components make the Labiotermes worker gut a relevant lignocellulose-valorising model to mimic by biomass conversion industries.

Tunable growth of one-dimensional graphitic materials: graphene nanoribbons, carbon nanotubes, and nanoribbon/nanotube junctions

Graphene nanoribbons (GNRs) and carbon nanotubes (CNTs), two representative one-dimensional (1D) graphitic materials, have attracted tremendous research interests due to their promising applications for future high-performance nanoelectronics. Although various methods have been developed for fabrication of GNRs or CNTs, a unified method allowing controllable synthesis of both of them, as well as their heterojunctions, which could largely benefit their nano-electronic applications, is still lacking. Here, we report on a generic growth of 1D carbon using nanoparticles catalyzed chemical vapor deposition (CVD) on atomically flat hexagonal boron nitride (h-BN) substrates. Relative ratio of the yielded GNRs and CNTs is able to be arbitrarily tuned by varying the growth temperature or feeding gas pressures. The tunability of the generic growth is quantitatively explained by a competing nucleation theory: nucleation into either GNRs or CNTs by the catalysts is determined by the free energy of their formation, which is controlled by the growth conditions. Under the guidance of the theory, we further realized growth of GNR/CNT intramolecular junctions through changing H2 partial pressure during a single growth process. Our study provides not only a universal and controllable method for growing 1D carbon nanostructures, but also a deep understanding of their growth mechanism, which would largely benefit future carbon-based electronics and optoelectronics.

Mechanistic Insights into Nonoxidative Ethanol Dehydrogenation on NiCu Single-Atom Alloys

Ethanol dehydrogenation presents a promising pathway toward the production of acetaldehyde, a valuable building block in chemicals production. Under nonoxidative conditions, the reaction is facilitated by supported Cu nanoparticles, which afford reasonable activity and high selectivity. The stability issues associated with Cu nanoparticle sintering can be addressed by the addition of small amounts of Ni, which further boost reactivity while retaining selectivity. Despite the promise of NiCu single-atom alloys for nonoxidative ethanol dehydrogenation, little is known about the role of each component and the pathway of this mechanistically complex process. Herein, kinetic investigations from reactor tests identify C–H bond scission as the rate-limiting step, while 1-hydroxyethyl is detected as the intermediate via IR spectroscopy. Temperature-programmed desorption studies are employed to examine the effect of Ni coverage and to demonstrate that Ni atoms activate ethanol selectively at lower temperatures, resulting in higher acetaldehyde yield than pure Cu. Temperature-programmed desorption experiments also reveal the spillover of intermediates from the Ni atom to neighboring Cu sites as a relevant step in the reaction pathway. Density functional theory calculations are used to investigate the reaction energetics and to confirm that C–H bond scission is the initial reaction step, while a clear effect of H2 partial pressure on the reaction pathway is realized. Further, counter to the expected behavior that all reaction steps take place on the Ni atoms, our degree of rate control analysis reveals that a mechanism involving spillover of the 1-hydroxyethyl intermediate from the Ni atom to the Cu surface, where it will dehydrogenate further, is more likely. Our combined kinetic, spectroscopic, and theoretical approach sheds light on this complex reaction mechanism and represents a promising method for the understanding and designing of highly active, selective, and stable single-atom alloys for other multistep catalytic processes.

Ultra-fast and sensitive magneto-optical hydrogen sensors using a magnetic nano-cap array

Magnetism in curved nano-geometries has opened a new path to design novel characteristics and phenomena that could greatly impact the future fundamental and applied studies of materials. In this report, a hexagonally-packed array of magnetic nano-caps (or nano-patches, NP) exhibiting unique magnetic anisotropy and optimal nanostructure for fast hydrogen kinetics is explored as a sensing element for the spark-free magnetic-circular-dichroism (MCD) H2 sensor. The MCD H2 sensor outperforms the state-of-the-art optical sensors reported to date and satisfies the most challenging performance targets imposed by US Department of Energy. In particular, a Pd67Co33 NP sensor exhibits response time of t90 < 0.9 s, recovery time of t10 < 9.0 s over the 1–100 mbar H2 partial pressure range, and limit of detection (LOD) of ∼1 ppm. The LOD improves to < 700 ppb, when the signal-to-noise ratio is enhanced by stacking three NP arrays. Using a 30-nm TAF (Teflon AF 2400) polymer coating, the sorption kinetics of the Pd67Co33/TAF sensor are significantly accelerated, with t90 < 0.4 s and t10 < 2.8 s over the same pressure range. When the Pd67Co33/TAF sensor is further coated with a 100-nm poly(methyl methacrylate) (PMMA) layer, a rapid sorption time of t90 < 0.5 s, LOD < 1 ppm and excellent sensor accuracy (<2.5% full scale) are maintained, while the sensor obtains strong selectivity against interference gases and moisture, and a negligible aging effect. The MCD nano-cap sensor platform may have a great impact on the future deployment of H2 fuel, environmental monitoring H2 sensors, and fast proton-based magneto-ionic devices.

Selective catalytic deoxygenation of palm oil to produce green diesel over Ni catalysts supported on ZrO2 and CeO2–ZrO2: Experimental and process simulation modelling studies

The selective deoxygenation of palm oil to produce green diesel has been investigated over Ni catalysts supported on ZrO2 (Ni/Zr) and CeO2–ZrO2 (Ni/CeZr) supports. The modification of the support with CeO2 acted to improve the Ni dispersion and oxygen lability of the catalyst, while reducing the overall surface acidity. The Ni/CeZr catalyst exhibited higher triglyceride (TG) conversion and yield for the desirable C15–C18 hydrocarbons, as well as improved stability compared to the unmodified Ni/Zr catalyst, with TG conversion and C15–C18 yield remaining above 85% and 80% respectively during 20 h of continuous operation at 300 oC. The high C17 yields also revealed the dominance of the deCOx (decarbonylation/decarboxylation) pathway. A fully comprehensive process simulation model has been developed to validate the experimental findings in this study, and a very good validation with the experimental data has been demonstrated. The model was then further utilised to investigate the effects of temperature, H2 partial pressure, H2/oil feed ratio and LHSV. The model predicted that maximum triglyceride conversion was attainable at reaction conditions of 300 °C temperature, 30 bar H2 partial pressure, H2/oil of 1000 cm3/cm3 feed ratio and 1.2 h−1 LHSV.

Minimizing the Lag Phase of Cupriavidus necator Growth under Autotrophic, Heterotrophic, and Mixotrophic Conditions.

Cupriavidus necator has the unique metabolic capability to grow under heterotrophic, autotrophic, and mixotrophic conditions. In the current work, we examined the effect of growth conditions on the metabolic responses of C. necator. In our lab-scale experiments, autotrophic growth was rapid, with a short lag phase as the exponential growth stage was initiated in 6 to 12 h. The lag phase extended significantly (>22 h) at elevated O2 and CO2 partial pressures, while the duration of the lag phase was independent of the H2 or N2 partial pressure. Under heterotrophic conditions with acetate as the organic substrate, the lag phase length was short (<12 h), but it increased with increasing acetate concentrations. When glucose and glycerol were provided as the organic substrate, the lag phase was consistently long (>12 h) regardless of the examined substrate concentrations (up to 10.0 g/L). In the transition experiments, C. necator cells showed rapid transitions from autotrophic to heterotrophic growth in less than 12 h and vice versa. Our experimental results indicate that C. necator can rapidly grow with both autotrophic and heterotrophic substrates, while the lag time substantially increases with nonacetate organic substrates (e.g., glucose or glycerol), high acetate concentrations, and high O2 and CO2 partial pressures. IMPORTANCE The current work investigated the inhibition of organic and gaseous substrates on the microbial adaption of Cupriavidus necator under several metabolic conditions commonly employed for commercial polyhydroxyalkanoate production. We also proposed a two-stage cultivation system to minimize the lag time required to change over between the heterotrophic, autotrophic, and mixotrophic pathways.

Repair of aromatic hydrocarbon-based membranes tested under accelerated fuel cell conditions

Hydrocarbon-based materials are of interest as next-generation proton exchange membranes (PEMs) for polymer electrolyte fuel cells (PEFCs). The biggest drawback of aromatic hydrocarbon PEMs is the presence of aromatic groups contained within the polymer, which make these materials susceptible to radical induced degradation reactions. In the fuel cell community antioxidant action is usually equated with scavenging of potent radicals, i.e. HO•, by various additives. In this work, however, we report on the repair of damaged membranes. This is tested by performing in situ accelerated stress tests at open circuit voltage with high H2 and O2 partial pressures. Membranes with aromatic sulfonate groups are synthesized as these are common constituents in hydrocarbon-based membranes. Two different approaches to incorporate the repair agent, cerium(III), are explored: 1) ionic bonding of Ce(III) to sulfonate groups and 2) covalent attachment through stable complexes of crown ether and Ce(III). We report that, during fuel cell operation, polymer degradation can be significantly reduced by Ce(III) when immobilized in the membrane. Ionic attachment did not yield in the desired repair effect as a result of cerium loss from the membrane.

Effect of Ni atomic fraction on active species of graphene growth on Cu-Ni alloy catalysts: a density functional theory study.

Cu-Ni alloys are promising catalysts for precisely controlling the number of graphene layers grown by chemical vapor deposition (CVD). However, the theoretical understanding of the effect of the Ni atomic fraction on the active species, which helps determine the mechanism of graphene growth, is still limited. Here, we examine the energetics, electronic properties, and populations of potential carbon source species (CH3, CH2, CH, C) on Cu-Ni alloy catalysts with various Ni atomic fractions under various CVD growth conditions using density functional theory combined with atomistic thermodynamics. An increased Ni atomic fraction of the Cu-Ni alloy catalyst increases the d-band center and d-orbital delocalization of the Ni atoms. Therefore, the stability of the carbon source adsorbed on the surface and subsurface of the catalyst increases. Relative population analysis shows that the CH and C monomers on the surface are the active species that drive surface-mediated growth on Cu-Ni catalysts with low Ni atomic fractions. The dominance of CH and C species can be further tuned by adjusting the growth temperature and partial pressure of H2. In contrast, in a Cu-Ni catalyst with a high Ni atomic fraction, the C monomer species on the subsurface has high stability and acts as an active species that controls the cooling-induced segregation growth mechanism. This study provides an essential insight into the atomistic mechanism of graphene growth in Cu-Ni alloy catalysts.

Following Cu Microstructure Evolution in CuZnO/Al2O3(−Cs) Catalysts During Activation in H2 using in situ XRD and XRD‐CT

AbstractInvited for this month's cover is the group of Andrew M. Beale at the University College London and at the Research Complex at Harwell (UK). The cover picture demonstrates how X‐rays can be used to obtain spatially resolved chemical imaging insight from within an industrial catalytic reactor. Understanding how the microstructure of the active Cu0 component in the commercially applicable Cu/ZnO/Al2O3(−Cs2O) low‐temperature water‐gas shift catalyst evolves under various H2 partial pressures in the presence/absence of a Cs promoter during thermal activation has been the subject of the present investigation. Read the full text of their Research Article at 10.1002/cmtd.202200015.

PtOx Cly (OH)z (H2 O)n Complexes under Oxidative and Reductive Conditions: Impact of the Level of Theory on Thermodynamic Stabilities.

Platinum-based catalysts with Cl- , OH- , O2- and H2 O ligands, are involved in many industrial processes. Their final chemical properties are impacted by calcination and reduction applied during the preparation and activation steps. We investigate their stability under these reactive conditions with density functional theory (DFT). We benchmark various functionals (PBE-dDsC, optPBE, B3LYP, HSE06, PBE0, TPSS, RTPSS and SCAN) against ACFDT-RPA. PBE-dDsC is well adapted, although hybrid functionals are more accurate for redox reactions. Thermodynamic phase diagrams are determined by computing the chemical potential of the species as a function of temperature and partial pressures of H2 O, HCl, O2 and H2 . The stability and nature of the Pt species are highly sensitive to the activation conditions. Under O2 , high temperatures favour PtO2 while under H2 , platinum is easily reduced to Pt(0). Chlorine modifies the coordination sphere of platinum during calcination by stabilizing PtCl4 and shifts the reduction of platinum to higher temperatures under H2 .

Chemical Stability Enhancement of Aromatic Proton Exchange Membranes Using a Damage Repair Mechanism

Harmful radical species (HO•, HOO•) are formed during fuel cell operation. Out of these species, the highly electrophilic hydroxyl radical is the most reactive (1.8 – 2.7 V vs. NHE). Consequently, the most electron-rich constituents, aromatic rings, are preferentially attacked and undergo rapid degradation. Hydroxyl radical formation rates depend on operating conditions and cell parameters, but even with low formation rates the damage accumulates over time and can lead to thinning or embrittlement of the membrane, and will cause irreversible damage to the cell. Due to these effects, long-term operation becomes challenging. Therefore, membranes with enhanced radical stability are increasingly desirable. In our previous work, we have shown, using kinetics measurements, that it should be possible for Ce(III) to act as a repair agent for formed damaged intermediates (cf. Figure).[1] In our follow-up work we demonstrate that Ce(III) can indeed reduce degradation rates.[2] These experiments were performed in a fuel cell setup using accelerated stress tests at open circuit voltage (OCV), a cell temperature of 80 °C, 100% RH and high H2 and O2 partial pressures of 2 bar. In-situ measurements and post-test analyses unequivocally show that bound Ce(III) can mitigate degradation of poly(α-methylstyrene sulfonate)-based membranes. We believe that this approach could also be applicable for other aromatic-based polymers if a sufficiently long-lived intermediate is formed upon radical attack.

Understanding Gas Permeation during High Pressure Operation of PEM Water Electrolyzers

Governments and industries across the world have initiated implementation of clean hydrogen (H2) to achieve zero emissions, yet significant challenges remain for large scale adoption. With the decreasing renewable electricity cost PEM water electrolyzers (PEMWEs) show significant potential for at scale deployment due to their high faradaic efficiency and high operating current density. To reduce the per kilogram price of hydrogen and increase the overall energy efficiency, PEMWEs need to be operated at high differential pressures (30 to 50 bar) to eliminate the need for compression during storage and transportation1. To achieve high faradaic efficiency, thinner membranes are required to reduce voltage losses within the cell. However, thinner membranes exhibit a higher gas permeation rate which leads to increased crossover of hydrogen from the cathode through the membrane to the anode. Such increased crossover of H2 not only reduces the efficiency but can also result in flammable gas mixtures (lower flammability limit for H2 in O2 is 4 %) as Iridium/Iridium oxide (anode catalyst) is inefficient in oxidizing H2 1. The addition of a gas recombination catalyst (GRC) to the membrane is an useful strategy to oxidize permeating H2 and minimize the H2:O2 ratio at the anode.In this study, a high pressure (up to 30 bar) electrolyzer setup is coupled with online gas chromatography-mass spectrometry to understand the H2 gas permeation in membranes as a function of H2 partial pressure and operating current density (simulated by varying the flow rates) as shown in Figure 1 . Effect of the GRC, its loading, and its location on the H2 permeation will be elucidated. Differences induced by the addition of anode and cathode catalyst layers on H2 permeation rates will also be presented.Figure 1. Ex-situ H2 permeation rate at different cathode operating pressure at 80 °C. The anode was maintained at 1 bar of O2 partial pressure Acknowledgement This research is supported by the U.S. Department of Energy (DOE) through the Hydrogen and Fuel Cell Technologies Office, program manager Dave Peterson Reference Bernt, M., Schröter, J., Möckl, M. & Gasteiger, H. A. Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 167, 124502 (2020). Figure 1

The key factor in High Pressure Hydrogenotrophic Denitrification: Hydrogen partial pressure

In the envisaged hydrogen economy, H2 could be an interesting alternative electron donor for the denitrification of drinking water or wastewater. The main obstacle to engineering the hydrogenotrophic denitrification process is the low solubility of H2 in water under atmospheric pressure, which limits denitrification rate and nitrogen removal efficiency. In this paper, we demonstrated a novel configuration of hydrogenotrophic denitrification, namely High Pressure Hydrogenotrophic Denitrification (HPHD). Elevated H2 partial pressure (pH2) was employed to increase dissolved H2 concentration and concomitantly enhance denitrification rate. Our results showed that the specific denitrification rate increased from 9.6 mg N/(gVSS·h) at 0.5 bars to 51.0 mg N/(gVSS·h) at 9 bars in HPHD. The denitrification effect could be retained with elevated pH2 at a low temperature. The specific denitrification rate at 3 bars and 15 °C was 20.5 mg N/(gVSS·h), approximately 1.5 times that at 1 bar and 30 °C, which was quite beneficial for hydrogenotrophic denitrification under cold conditions. Different from nitrite reduction, less impact was observed on nitrate reduction by low temperature, which explained high nitrite accumulation in HPHD at 15 °C. Overall, our investigations shed light on the role of pH2 in the promising solution for nitrogen removal in HPHD.

Boosting ethanol production rates from carbon dioxide in MES cells under optimal solventogenic conditions

Microbial Electrosynthesis (MES) has been widely applied for acetic acid (HA) production from CO2 and electricity. Ethanol (EtOH) has a higher market value than HA, and wide application in industry and as a biofuel. However, it has only been obtained sporadically and at low concentrations, probably due to sub-optimal operating conditions. This study aimed at enhancing EtOH productivity in MES cells by jointly optimising key operation parameters, including pH, H2 and CO2 partial pressure (pH2 and pCO2), and HA concentration, to promote solventogenesis. Two H-type cells were operated in fed-batch mode at −0.8 V vs. SHE with CO2 as the sole carbon source. A mixed culture, enriched with Clostridium ljungdahlii was used as the biocatalyst. The combination of low pH (<4.5) and pCO2 (<0.3 atm), along with high HA concentration (about 6 g L−1) and pH2 (>3 atm), were mandatory conditions for maintaining an efficient solventogenic culture, dominated by Clostridium sp., capable of high-rate EtOH production. The maximum EtOH production rate was 10.95 g m−2 d−1, and a concentration of 5.28 g L−1 was achieved. Up to 30 % of the electrons and 15.2 % of the carbon provided were directed towards EtOH production, and 28.1 kWh were required for the synthesis of 1 kg of EtOH from CO2. These results highlight that strict conditions are required for a continuous, reliable, EtOH production in MES cells. Future investigation should focus on improving cell configuration to achieve EtOH production at higher current densities while minimizing the electric energy input.

The influence of H2 partial pressure on biogenic palladium nanoparticle production assessed by single-cell ICP-mass spectrometry.

The production of biogenic palladium nanoparticles (bio-Pd NPs) is widely studied due to their high catalytic activity, which depends on the size of nanoparticles (NPs). Smaller NPs (here defined as <100 nm) are more efficient due to their higher surface/volume ratio. In this work, inductively coupled plasma-mass spectrometry (ICP-MS), flow cytometry (FCM) and transmission electron microscopy (TEM) were combined to obtain insight into the formation of these bio-Pd NPs. The precipitation of bio-Pd NPs was evaluated on a cell-per-cell basis using single-cell ICP-MS (SC-ICP-MS) combined with TEM images to assess how homogenously the particles were distributed over the cells. The results provided by SC-ICP-MS were consistent with those provided by "bulk" ICP-MS analysis and FCM. It was observed that heterogeneity in the distribution of palladium over an entire cell population is strongly dependent on the Pd2+ concentration, biomass and partial H2 pressure. The latter three parameters affected the particle size, ranging from 15.6 to 560 nm, and exerted a significant impact on the production of the bio-Pd NPs. The TEM combined with SC-ICP-MS revealed that the mass distribution for bacteria with high Pd content (144 fg Pd cell-1 ) indicated the presence of a large number of very small NPs (D50=15.6nm). These results were obtained at high cell density (1 × 105 ± 3 × 104 cells μl-1 ) and H2 partial pressure (180 ml H2 ). In contrast, very large particles (D50=560 nm) were observed at low cell density (3 × 104 ± 10 × 102 cells μl-1 ) and H2 partial pressure (10-100 ml H2 ). The influence of the H2 partial pressure on the nanoparticle size and the possibility of size-tuned nanoparticles are presented.

Following Cu Microstructure Evolution in CuZnO/Al2O3(−Cs) Catalysts During Activation in H2 using in situ XRD and XRD‐CT

AbstractUnderstanding how the microstructure of the active Cu0 component in the commercially applicable Cu/ZnO/Al2O3(−Cs2O) low‐temperature water‐gas shift catalyst evolves under various H2 partial pressures in the presence/absence of a Cs promoter during thermal activation has been investigated. Time‐resolved XRD and spatially‐resolved XRD‐CT data were measured as a function of H2 concentration along a packed bed reactor to elucidate the importance of the zincite support and the effect of the promoter on Cu sintering mechanisms, dislocation character and stacking fault probability. The rate of Cu reduction showed a dependency on [Cs], [H2] and bed height; lower [Cs] and higher [H2] led to a greater rate of metallic copper nanoparticle formation. A deeper analysis of the XRD line profiles allowed for determining a greater edge character to the dislocations and subsequent stacking fault probability was also observed to depend on higher [H2], smaller Cu0 (and ZnO) crystallite sizes, increased [ZnO] (30 wt.%, sCZA) and lower temperature. The intrinsic activity of Cu/ZnO/Al2O3 methanol synthesis catalysts has been intimately linked to the anisotropic behaviour of copper, and thus the presence of lattice defects; to the best knowledge of the authors, this study is the first instance in which this type of analysis has been applied to LT‐WGS catalysts.