Search

Converting biomass into energy and fuels is considered a promising strategy for replacing the exhaustible fossil fuels. In this study, we report on a tandem process that combines cellulose pyrolysis and plasma-assisted reforming for H-2 production. The hybrid pyrolysis/plasma reforming process was carried out in a two-stage reaction system incorporating a coaxial dielectric barrier discharge (DBD) plasma reactor. The effects of discharge power, steam, reforming temperature, and catalyst on the reaction performance were investigated. The results show that low temperatures are preferred in the non-catalytic plasma reforming process, whereas high temperatures are desired to achieve a high H-2 yield and a high H-2 selectivity in the plasma-catalytic reforming system. The synergistic effect of plasma catalysis was dominant in the plasma-catalytic reforming process at 250 degrees C. In contrast, the catalyst, rather than the plasma, played a dominant role in the plasma-catalytic reforming at higher temperatures (550 degrees C). Using Ni-Co/Al(2)O3 at a reforming temperature of 550 degrees C, a high H-2 yield of 26.6 mmol/g was attainted, which was more than 8 times and about 100% greater than that obtained using plasma alone and catalyst alone, respectively. This work highlights the potential of non-thermal plasmas in lowtemperature biomass conversion., European Union [823745]; Science and Technology Ex-change Project of the Chinese Ministry of Science and Technology [2021-12-2]; Education Cooperation Project between China and Central Eastern European Countries [2021086]; British Council Newton Fund Institutional Links Grant [623389161]; Scientific and Technological Research Council of Turkey (TUBITAK) [219M123]; Chinese Scholarship Council; University of Liverpool, This project has received the funding from the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska Curie Grant Agreement (No. 823745) . C. Quan and N. Gao gratefully acknowledge funding from the Science and Technology Ex-change Project of the Chinese Ministry of Science and Technology (No. 2021-12-2) and the Education Cooperation Project between China and Central Eastern European Countries (No. 2021086) . X. Tu gratefully acknowledges the British Council Newton Fund Institutional Links Grant (No. 623389161) . J. Yanik gratefully acknowledges funding from the Scientific and Technological Research Council of Turkey (TUBITAK Project Contract no. 219M123) . W. Wang thanks the University of Liverpool and the Chinese Scholarship Council for funding this PhD.

Calcium looping integrated with chemical looping combustion (CaL-CLC) process is an efficient and cost-effective CO2 capture technology. In this technique, the heat generated by chemical looping combustion of CuO is used insitu to calcine CaCO3, thus avoiding the implementation of the energy-intensive air separation unit (ASU) in the conventional calcium looping (CaL) process for postcombustion CO2 capture. Many studies, including simulation works and material development, have been carried out on the CaL-CLC process. It is thus imperative to present the recent progress in the CaL-CLC process whilst providing a research prospects framework and direction for future research. First, fundamental understandings of the CaL-CLC process are discussed, including its concept and potential applications. Then, simulation work is reviewed, emphasizing process design and analysis, as well as modeling of the reactor and main reactions involved in the CaL-CLC process. Due to the fast reactivity decay of bifunctional CaO/CuO composites, various strategies have been developed to overcome this issue, which are summarized in detail. Last, future research directions for the CaL-CLC process are proposed.

The simultaneous photocatalytic H2 evolution with environmental remediation over semiconducting metal oxides is a fascinating process for sustainable fuel production. However, most of the previously reported photocatalytic reforming showed nonstoichiometric amounts of the evolved H2 when organic substrates were used. To explain the reasons for this phenomenon, a careful analysis of the products and intermediates in gas and aqueous phases upon the photocatalytic hydrogen evolution from oxalic acid using Pt/TiO2 was performed. A quadrupole mass spectrometer (QMS) was used for the continuous flow monitoring of the evolved gases, while high performance ion chromatography (HPIC), isotopic labeling, and electron paramagnetic resonance (EPR) were employed to understand the reactions in the solution. The entire consumption of oxalic acid led to a ~30% lower H2 amount than theoretically expected. Due to the contribution of the photo-Kolbe reaction mechanism, a tiny amount of formic acid was produced then disappeared shortly after the complete consumption of oxalic acid. Nevertheless, a much lower concentration of formic acid was generated compared to the nonstoichiometric difference between the formed H2 and the consumed oxalic acid. Isotopic labeling measurements showed that the evolved H2, HD, and/or D2 matched those of the solvent; however, using D2O decreased the reaction rate. Interestingly, the presence of KI as an additional hole scavenger with oxalic acid had a considerable impact on the reaction mechanism, and thus the hydrogen yield, as indicated by the QMS and the EPR measurements. The added KI promoted H2 evolution to reach the theoretically predictable amount and inhibited the formation of intermediates without affecting the oxalic acid degradation rate. The proposed mechanism, by which KI boosts the photocatalytic performance, is of great importance in enhancing the overall energy efficiency for hydrogen production via photocatalytic organic reforming.

Transition metal sulfides are an extraordinarily vital class of semiconductors with a wide range of applications in the photocatalytic field. A great number of recent advances in photocatalytic transformations of lignocellulosic biomass, the largest renewable carbon resource, into high-quality fuels and value-added chemicals has been achieved over metal sulfide semiconductors. Herein, the progress and breakthroughs in metal-sulfide-based photocatalytic systems for lignocellulose valorization with an emphasis on selective depolymerization of lignin and oxidative coupling of some important bioplatforms are highligted. The key issues that control reaction pathways and mechanisms are carefully examined. The functions of metal sulfides in the elementary reactions, including CO-bond cleavage, selective oxidations, CC coupling, and CH activation, are discussed to offer insights to guide the rational design of active and selective photocatalysts for sustainable chemistry. The prospects of sulfide photocatalysts in biomass valorization are also analyzed and briefly discussed. ispartof: Advanced Materials vol:33 issue:50 ispartof: location:Germany status: published

Unsteady radiative heat transfer is analyzed numerically in a directly irradiated plane-parallel medium containing a suspension of ceria particles undergoing nonstoichiometric thermal reduction. The micrometer-sized ceria particles are assumed homogenous, nongray, absorbing, emitting, and anisotropically scattering, whereas the overall medium is of nonuniform temperature and composition. The unsteady mass and energy conservation equations are solved using the finite volume method and the Shampine-Gordon time integration scheme. Radiative transport is modeled using the energy-portioning Monte Carlo ray-tracing method with radiative properties obtained from the Mie theory. Increasing the particle volume fraction and decreasing the particle diameter both increase the optical thickness of the particle suspension, resulting in increasing peak temperature and nonstoichiometry at steady state. For 5 mu m-diam particles under 1000 suns irradiation, the peak temperature at steady state ranges from 1855 K for a particle volume fraction of f(v) = 10(-6) to 2092 K for f(v) =10(-4); the temperature nonuniformity ranges from 9 to 622 K. For a fixed volume fraction of f(v) = 10(-6), decreasing the particle diameter from 20 to 1 mu m increases the peak temperature at steady state from 1734 to 2162 K; the temperature nonuniformity increases from 9 to 61 K.

Photocatalytic selective organic transformations provide an efficient synthetic alternative for several industrially relevant chemicals, using solar rather than thermal energy. However, in most cas...

Herein, the catalytic activities of Cu-and Pt-embedded graphene surfaces on the sequential decomposition reaction of NH3 molecule were investigated by density functional theory (DFT). Partial charge changes on the surfaces by embedding Cu and Pt atoms on the bare graphene surface were analyzed by the Bader charge analysis and depicted by the electron density difference maps. Grimme-D2 dispersion correction was employed for weak interactions between adsorbates and both graphene surfaces. The most stable geometries of the adsorption of NHx (x = 0 -> 3) and H species and their fragmented co-adsorption structures on both graphene surfaces were obtained. The internal energy barrier calculations required for the sequential decomposition of NH3 on both graphene surfaces were calculated by the CINEB method and the results obtained for complete decomposition of NH3 were illustrated by relative energy diagram. The findings revealed that the decomposition of NH3 to NH2, NH, and N on the Cu-embedded graphene surface had relatively lower activation barriers of 1.52 eV, 0.72 eV, and 0.64 eV, respectively, compared to the Pt-embedded graphene surface. The Cu-embedded graphene surface was of high selectivity over the NH3 sequential decomposition reaction. This information may paw the way for different strategies for the development of Cu-based catalysts for NH3 decomposition. (C) 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

© 2019 Elsevier B.V. A plasma-assisted chemical looping system for the production of H2 (PCLH) was investigated in this study. This system allows the partial oxidation of CH4 at mild temperatures (573–773 K). Four active oxygen carriers: Fe2O3, NiO-impregnated Fe2O3 (NiO/Fe2O3), SrFeO3−δ and NiO-impregnated SrFeO3−δ (NiO/SrFeO3−δ) were compared, each working both as a packed material for the plasma reactor and an oxygen source for the partial oxidation of CH4. Similar conversions of CH4, and low yields of H2 were obtained in Fe2O3 and SrFeO3−δ. It was concluded that in these cases, H2 was mainly produced from direct cracking of CH4 by plasma. In contrast, when using NiO/Fe2O3 and NiO/SrFeO3−δ, substantial production of H2 was achieved. It is proposed that there is a synergistic effect between the catalyst and the oxygen carrier; the presence of the metallic Ni phase was responsible for catalysing the production of H2, and the oxygen from the support helped prevent the build-up of coke. As a result, the activity of Ni was continuously maintained for H2 production. The chemical loop is closed with the oxygen carriers being regenerated in air with plasma and then used in the next looping cycle. The high H2 production capability in NiO/Fe2O3 was repeatable; whilst, NiO/SrFeO3−δ deactivated in the second and third cycles. Amongst the temperatures studied, NiO/Fe2O3 at 673 K resulted in the best performance for H2-rich gas production. A further increase in the operating temperature led to a total combustion of CH4.

In this study, the usage of biomass-based materials as co-catalysts was tested for simultaneous sugar industry wastewater treatment/hydrogen production by catalytic wet air oxidation and the final product distribution in gas and liquid effluents were investigated. For this purpose, biochar (BC) and graphene oxide-like biomass derivative (BGO) were synthesized from corncob and coupled with LaCoO3 (LC). LaCoO3-Biochar (LC/BC) catalyst was determined as the most compatible one with pure LC in terms of removal efficiencies which were approximately 100% for total saccharide (TSC), 90% of total organic carbon (TOC) and chemical oxygen demand (COD) removal, respectively. This shows that biochar is a promising alternative to replace metal catalysts. The catalyst reusability was examined and the fresh and used catalysts were characterized by SEM-EDX, XRD, and BET analyses. There were slight decreases in catalytic activities of all catalysts including LC which were associated with the chemical and morphological alterations supported by the characterization analyses as a result of formation of acidic intermediates some of which were identified as formic acid and acetic acid in the liquid effluent. The formation of CO2 was determined as proportional with TOC reduction but the behaviour for H-2 production was the opposite as a result of total oxidation in which the final products are CO2 and H2O. Although the amount of H-2 produced was relatively lower for the selected catalyst LC/BC with higher treatment performance, the produced H-2/initial sucrose ratio equal to 0.109 was considered as promising., Ege University Scientific Research Project Coordination [17-MUH-040], This work was supported by Ege University Scientific Research Project Coordination (Grant number: 17-MUH-040). The authors would like to thank for the analyses in characterization studies which were performed in Ege University Central Research Test and Analysis Laboratory Application and Research Center, Middle East Technical University Central Research Laboratory, and Recep Tayyip Erdo.gan University Central Research Laboratory Application and Research Center. The authors would also like to thank to Ege University Chemistry Department for gas product analyses and Ege University Chemical Engineering Department for liquid product analyses which are gratefully acknowledged.

International audience; Despite the report of several structural and functional models of the [NiFe]-hydrogenases, it is still unclear how the succession of electron and proton transfers during H-2 production catalysis are controlled in terms of both sequence (order of the chemical or redox steps) and sites (metal and/or ligand). To address this issue, the structure of the previously described bioinspired [NiFe]-hydrogenase complex [(LNiFII)-Ni-N2S2-F-II Cp(CO)](+) ((LNiFeCp)-Fe-II-Cp-II, with L-N2S2 = 2,2'-(2,2'-bipyridine-6,6'-diy1)bis(1,1'-diphenylethanethiolate) and Cp = cyclopentadienyl) has been fine-tuned by modifying exclusively the Fe site. In [(LNiFeCp)-Ni-N2S2-Fe-II-Cp-II* (CO)](+) ((LNiFeCp)-Fe-II-Cp-II*, with Cp* = pentamethylcyclopentadienyl), the Cp- ligand has been replaced by Cp*- to change both the redox and structural properties of the overall complex as a consequence of the steric hindrance of Cp*-. The (LNiFeCp)-Fe-II-Cp-II* complex acts as an efficient electrocatalyst to produce H-2. Density functional theory (DFT) calculations support a CEEC cycle, following an initial reduction. The initial protonation leads to the cleavage of one thiolate-iron bond and the next reduction to the generation of a bridging Fe-based hydride moiety. Interestingly, the second protonation step generates a species containing a terminal Ni-based thiol and a bridging hydride. In the presence of CO, the electrocatalytic activity of (LNiFeCp)-Fe-II-Cp-II* for H-2 production is markedly inhibited (about 90% of loss), while only a partial inhibition (about 30% of loss) is observed in the case of (LNIFeCp)-I-II-Cp-II. DFT calculations rationalized this effect by predicting that interactions of the one- and two-electron-reduced species for (LNiFeCp)-Fe-II-Cp-II* with CO are thermodynamically more favorable in comparison to those for (LNiFeCp)-Fe-II-Cp-II.

Hydrogen production by the water gas shift reaction (WGS) is equilibrium limited. In the current study, we demonstrate that the overall efficiency of the WGS can be improved by co-feeding methanol and removing CO2 in situ. The thermodynamics of the water gas shift and methanol reforming/WGS (methanol-to-shift, MtoS) reactions for H2 production alone and with simultaneous CO2 adsorption (sorption-enhanced, SEWGS and SEMtoS) were studied using a non-stoichiometric approach based on the minimisation of the Gibbs free energy. A typical composition of the effluent from a steam methane reformer was used for the shift section. The effects of temperature (450–750 K), pressure (5–30 barg), steam and methanol addition, fraction of CO2 adsorption (0–95%) and energy efficiency of the shift systems have been investigated. Adding methanol to the feed facilitates autothermal operation of the shift unit, with and without CO2 removal, and enhances significantly the amount of H2 produced. For a set methanol and CO input, the MtoS and SEMtoS systems show a maximum productivity of H2 between 523 and 593 K due to the increasing limitation of the exothermic shift reaction while the endothermic methanol steam reforming is no longer limited above 593 K. The heat of adsorption of CO2 was found to make only a small difference to the H2 production or the autothermal conditions.

Several species of unicellular microalgae such as the model species Chlamydomonas reinhardtii possess plastid-localized [FeFe]-hydrogenases which, via ferredoxin, can accept electrons from photosynthetic electron transport. Thereby, under specific conditions, these algae light-dependently produce molecular hydrogen (H 2 ), which offers a sustainable way to generate a “green” and efficient fuel. Until today, the most common way to induce sustained H 2 production is to deprive Chlamydomonas of macronutrients such as sulfur (S) which results in a downregulation of photosynthetic production of molecular oxygen (O 2 ) and of assimilatory processes. These acclimation responses allow the O 2 sensitive algal [FeFe]-hydrogenases to become active and serve as an alternative electron sink of photosynthesis. Despite much progress in the field and a general understanding of the underlying mechanisms, many basic and applied aspects of the photosynthetic H 2 metabolism of eukaryotic algae remain to be elucidated. One rarely investigated factor is that microalgae have also been reported to consume H 2 , especially as a response to high H 2 concentrations. Here, we analyzed the H 2 uptake activities of S-deprived Chlamydomonas cells incubated in different PBRs providing different gas phase volumes, either in continuous light or in the dark. We show that H 2 uptake occurs after prolonged incubation in the light as well as in sudden darkness. Dark-induced H 2 uptake can be delayed adding the phosphoribulose kinase inhibitor glycolaldehyde, suggesting a connection to carbohydrate metabolism. The results indicate that PBR setups as well as envisioned outdoor cultivation systems with natural light-dark cycles have to be carefully designed to prevent efficiency losses.

Background: Under low O-2 concentration ( hypoxia) and low light, Chlamydomonas cells can produce H-2 gas in nutrient-replete conditions. This process is hindered by the presence of O-2, which inactivates the [FeFe]-hydrogenase enzyme responsible for H-2 gas production shifting algal cultures back to normal growth. The main pathways accounting for H-2 production in hypoxia are not entirely understood, as much as culture conditions setting the optimal redox state in the chloroplast supporting long-lasting H-2 production. The reducing power for H-2 production can be provided by photosystem II (PSII) and photofermentative processes during which proteins are degraded via yet unknown pathways. In hetero- or mixotrophic conditions, acetate respiration was proposed to indirectly contribute to H-2 evolution, although this pathway has not been described in detail.Main body: Recently, Jurado-Oller et al. (Biotechnol Biofuels 8: 149, 7) proposed that acetate respiration may substantially support H-2 production in nutrient-replete hypoxic conditions. Addition of low amounts of O-2 enhanced acetate respiration rate, particularly in the light, resulting in improved H-2 production. The authors surmised that acetate oxidation through the glyoxylate pathway generates intermediates such as succinate and malate, which would be in turn oxidized in the chloroplast generating FADH(2) and NADH. The latter would enter a PSII-independent pathway at the level of the plastoquinone pool, consistent with the light dependence of H-2 production. The authors concluded that the water-splitting activity of PSII has a minor role in H-2 evolution in nutrient-replete, mixotrophic cultures under hypoxia. However, their results with the PSII inhibitor DCMU also reveal that O-2 or acetate additions promoted acetate respiration over the usually dominant PSII-dependent pathway. The more oxidized state experienced by these cultures in combination with the relatively short experimental time prevented acclimation to hypoxia, thus precluding the PSII-dependent pathway from contributing to H-2 production.Conclusions: In Chlamydomonas, continuous H-2 gas evolution is expected once low O-2 partial pressure and optimal reducing conditions are set. Under nutrient-replete conditions, the electrogenic processes involved in H-2 photoproduction may rely on various electron transport pathways. Understanding how physiological conditions select for specific metabolic routes is key to achieve economic viability of this renewable energy source.

Multi-electron heterogeneous catalysis is a pivotal element in the ( photo) electrochemical generation of solar fuels. However, mechanistic studies of these systems are difficult to elucidate by means of electrochemical methods alone. Here we report a spectro-electrochemical analysis of hydrogen evolution on ruthenium oxide employed as an electrocatalyst and as part of a cuprous oxide-based photocathode. We use optical absorbance spectroscopy to quantify the densities of reduced ruthenium oxide species, and correlate these with current densities resulting from proton reduction. This enables us to compare directly the catalytic function of dark and light electrodes. We find that hydrogen evolution is second order in the density of active, doubly reduced species independent of whether these are generated by applied potential or light irradiation. Our observation of a second order rate law allows us to distinguish between the most common reaction paths and propose a mechanism involving the homolytic reductive elimination of hydrogen.

© 2019 Elsevier B.V. A plasma-assisted chemical looping system for the production of H2 (PCLH) was investigated in this study. This system allows the partial oxidation of CH4 at mild temperatures (573–773 K). Four active oxygen carriers: Fe2O3, NiO-impregnated Fe2O3 (NiO/Fe2O3), SrFeO3−δ and NiO-impregnated SrFeO3−δ (NiO/SrFeO3−δ) were compared, each working both as a packed material for the plasma reactor and an oxygen source for the partial oxidation of CH4. Similar conversions of CH4, and low yields of H2 were obtained in Fe2O3 and SrFeO3−δ. It was concluded that in these cases, H2 was mainly produced from direct cracking of CH4 by plasma. In contrast, when using NiO/Fe2O3 and NiO/SrFeO3−δ, substantial production of H2 was achieved. It is proposed that there is a synergistic effect between the catalyst and the oxygen carrier; the presence of the metallic Ni phase was responsible for catalysing the production of H2, and the oxygen from the support helped prevent the build-up of coke. As a result, the activity of Ni was continuously maintained for H2 production. The chemical loop is closed with the oxygen carriers being regenerated in air with plasma and then used in the next looping cycle. The high H2 production capability in NiO/Fe2O3 was repeatable; whilst, NiO/SrFeO3−δ deactivated in the second and third cycles. Amongst the temperatures studied, NiO/Fe2O3 at 673 K resulted in the best performance for H2-rich gas production. A further increase in the operating temperature led to a total combustion of CH4.

The use of hydrogen as a fuel, when generated from water using semiconductor photocatalysts and driven by sunlight, is a sustainable alternative to fossil fuels. Polymeric photocatalysts are based on Earth-abundant elements and have the advantage over their inorganic counterparts in that their electronic properties are easily tuneable through molecular engineering. Polymeric photocatalysts have developed rapidly over the past decade, resulting in the discovery of many active materials. However, our understanding of the key properties underlying their photoinitiated redox processes has not kept pace, and this impedes further progress to generate cost-competitive technologies. Here, we discuss state-of-the-art polymeric photocatalysts and our microscopic understanding of their activities. We conclude with a discussion of five outstanding challenges in this field: non-standardized reporting of activities, limited photochemical stability, insufficient knowledge of reaction mechanisms, balancing charge carrier lifetimes with catalysis timescales and the use of unsustainable sacrificial reagents. Solar-driven photocatalytic water splitting provides a clean pathway for production of hydrogen fuel. This Review examines both amorphous and crystalline polymeric materials for water splitting, exploring polymer design strategies, theoretical understanding and challenges for the field.

Black TiO2 nanomaterials have recently emerged as promising candidates for solar-driven photocatalytic hydrogen production. Despite the great efforts to synthesize highly reduced TiO2, it is apparent that intermediate degree of reduction (namely, gray titania) brings about the formation of peculiar defective catalytic sites enabling cocatalyst-free hydrogen generation. A precise understanding of the structural and electronic nature of these catalytically active sites is still elusive, as well as the fundamental structure-activity relationships that govern formation of crystal defects, increased light absorption, charge separation, and photocatalytic activity. In this Review, we discuss the basic concepts that underlie an effective design of reduced TiO2 photocatalysts for hydrogen production such as (i) defects formation in reduced TiO2, (ii) analysis of structure deformation and presence of unpaired electrons through electron paramagnetic resonance spectroscopy, (iii) insights from surface science on electronic singularities due to defects, and (iv) the key differences between black and gray titania, that is, photocatalysts that require Pt-modification and cocatalyst-free photocatalytic hydrogen generation. Finally, future directions to improve the performance of reduced TiO2 photocatalysts are outlined.

Several Ni catalysts of supported (on La2O3-&alpha, Al2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts&rsquo, regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500 &deg, C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700 &deg, C. The spent catalysts have been characterized by N2 adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H2 selectivity-stability corresponds to Ni/La2O3-&alpha, Al2O3, due to its smaller Ni0 particle size. Additionally, it is more selective to H2 than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl2O4 spinel catalyst can be completely recovered after regeneration by coke combustion at 850 &deg, C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles.

When scaling up photo-electrochemical processes to larger areas than conventionally studied in the laboratory, substrate performance must be taken into consideration and in this work, a methodology to assess this via an uncomplicated 2 dimensional model is outlined. It highlights that for F-doped SnO2 (FTO), which is ubiquitously used for metal oxide photoanodes, substrate performance becomes significant for moderately sized electrodes (5 cm) under no solar concentration for state of the art Fe2O3 thin films. It is demonstrated that when the process is intensified via solar concentration, current losses become quickly limiting. Methodologies to reduce the impact of substrate ohmic losses are discussed and a new strategy is proposed. Due to the nature of the photo-electrode current-potential relationship, operation at a higher potential where the photo-current saturates (before the dark current is observed) will lead to a minimum in current loss due to substrate performance. Crucially, this work outlines an additional challenge in scaling up photo-electrodes based on low conductivity substrates, and establishes that such challenges are not insurmountable.

Here we report for the first time an H-2-evolving photocathode fabricated by a solution-processed organic inorganic hybrid composed of CdSe and P3HT. The CdSe:P3HT (10:1 (w/w)) hybrid bulk heterojunction treated with 1,2-ethanedithiol (EDT) showed efficient water reduction and hydrogen generation. A photocurrent of -1.24 mA/cm(2) at 0 V versus reversible hydrogen electrode (V-RHE), EQE of 15%, and an unprecedented V-oc of 0.85 V-RHE under illumination of AM1.5G (100 mW/cm(2)) in mild electrolyte were observed. Time-resolved photoluminescence (TRPL), internal quantum efficiency (IQE), and transient photocurrent measurements were carried out to clarify the carrier dynamics of the hybrids. The exciton lifetime of CdSe was reduced by one order of magnitude in the hybrid blend, which is a sign of the fast charge separation upon illumination. By comparing the current magnitude of the solid-state devices and water-splitting devices made with identical active layers, we found that the interfaces of the water-splitting devices limit the device performance. The electron/hole transport properties investigated by comparing IQE spectra upon front- and back-side illumination evidenced balanced electron/hole transport. The Faradaic efficiency is 80-100% for the hybrid photocathodes with Pt catalysts and similar to 70% for the one without Pt catalysts.

Hydrogen evolution by the catalytic decomposition of formic acid in solution is a key reaction for hydrogen storage for which palladium is one of the most efficient catalysts. Based on density functional theory (DFT) computations, we explain why the presence of an anionic promoter renders palladium more active and more selective for formic acid dehydrogenation. The promotion is well-captured by modeling the anion by a negatively charged surface. This promotional effect can be traced back to the modulation of the electric field at the catalyst surface, with a strongly contrasted action on the energy of the various species along the competing pathways through the electrostatic interaction between the electric field and the surface dipole moment. As a result, both the reaction kinetics and selectivity are markedly improved. This opens the door to a rational design of catalytic systems using promoters.

Background: Under low O-2 concentration ( hypoxia) and low light, Chlamydomonas cells can produce H-2 gas in nutrient-replete conditions. This process is hindered by the presence of O-2, which inactivates the [FeFe]-hydrogenase enzyme responsible for H-2 gas production shifting algal cultures back to normal growth. The main pathways accounting for H-2 production in hypoxia are not entirely understood, as much as culture conditions setting the optimal redox state in the chloroplast supporting long-lasting H-2 production. The reducing power for H-2 production can be provided by photosystem II (PSII) and photofermentative processes during which proteins are degraded via yet unknown pathways. In hetero- or mixotrophic conditions, acetate respiration was proposed to indirectly contribute to H-2 evolution, although this pathway has not been described in detail. Main body: Recently, Jurado-Oller et al. (Biotechnol Biofuels 8: 149, 7) proposed that acetate respiration may substantially support H-2 production in nutrient-replete hypoxic conditions. Addition of low amounts of O-2 enhanced acetate respiration rate, particularly in the light, resulting in improved H-2 production. The authors surmised that acetate oxidation through the glyoxylate pathway generates intermediates such as succinate and malate, which would be in turn oxidized in the chloroplast generating FADH(2) and NADH. The latter would enter a PSII-independent pathway at the level of the plastoquinone pool, consistent with the light dependence of H-2 production. The authors concluded that the water-splitting activity of PSII has a minor role in H-2 evolution in nutrient-replete, mixotrophic cultures under hypoxia. However, their results with the PSII inhibitor DCMU also reveal that O-2 or acetate additions promoted acetate respiration over the usually dominant PSII-dependent pathway. The more oxidized state experienced by these cultures in combination with the relatively short experimental time prevented acclimation to hypoxia, thus precluding the PSII-dependent pathway from contributing to H-2 production. Conclusions: In Chlamydomonas, continuous H-2 gas evolution is expected once low O-2 partial pressure and optimal reducing conditions are set. Under nutrient-replete conditions, the electrogenic processes involved in H-2 photoproduction may rely on various electron transport pathways. Understanding how physiological conditions select for specific metabolic routes is key to achieve economic viability of this renewable energy source.

Trace amounts of Pt- and Ru-doped Ni/Mg(Al)O catalysts were prepared by a citrate method and tested in the oxidative reforming of C3H8 under daily start-up and shut-down (DSS) operation. The activity and the sustainability of the catalysts were compared with those of the Pt- and Ru-doped Ni/Mg(Al)O catalysts derived from hydrotalcite (HT) precursor. The DSS operation of C3H8 reforming was carried Out with O-2 gas or O-2/H2O mixed gas between 200 degrees C and 600 degrees C or 700 degrees C under air purging conditions. The catalysts underwent steaming treatment with H-2/H2O mixed gas at 900 degrees C for 10 h. This allowed us to test the effect of Ni sintering on the catalyst deactivation. Coking was significantly suppressed on both HT- and citrate-derived Ni catalysts. Although both preparations produced highly dispersed Ni particles on the catalysts, the HT-derived catalysts exhibited more finely dispersed Ni particles, resulting in higher activity values than those of the citrate-derived catalysts, The regenerative activity due to redispersion of sintered Ni particles was enhanced over the HT-derived catalysts compared with the activity over citrate-derived catalysts. Although a clear redispersion of Ni particles was not observed in the oxidative reforming, i.e., in the absence of steam, the size decrease in Ni particles was more significant over the HT-derived catalysts than over the citrate-derived catalysts. The Mg(Al)O periclase structure derived from Mg-Al HT likely plays an important role in the regenerative activity of Pt- and Ru-Ni/Mg(Al)O catalysts. Pt-doping was more effective than Ru for the catalyst sustainability in the oxidative reforming of C3H8.

Trace amount of Ru-doped Ni/Mg(Al)O catalyst was prepared from hydrotalcite precursor and was tested in the reforming of propane under daily start-up and shut-down (DSS) operation. Mg(Ni,Al)O periclase derived from the hydrotalcite was dispersed in an aqueous solution of Ru nitrate, followed by calcination and reduction. Finely dispersed Ni–Ru was supported on Mg(Al)O periclase particles. The activity as well as the sustainability in the propane reforming was compared with the commercial Al 2 O 3 -supported Ni and Ru catalysts. The DSS operations of partial oxidation, steam reforming and autothermal reforming were carried out under steam or air purging conditions. The Ru doping suppressed the surface oxidation of Ni particles on the Ni/Mg(Al)O catalyst, resulting in the high activity as well as the high sustainability in all reforming reactions except under steam–air combined purging. The deactivation was effectively suppressed by increasing either reaction temperature or Ru doping even under steam–air combined purging. Ni particles also suffered by sintering, but the sintered Ni particles were redispersed and the activity was sustained during DSS operations. Air-purged partial oxidation was the most effective for the redispersion of the sintered Ni particles. This likely indicates that the finely dispersed Ni particles were continuously regenerated by reversible reduction–oxidation between Ni 0 and Ni 2+ via Mg(Ni)Al periclase assisted by hydrogen spillover from Ru or NiRu alloy.

Effects of Ru addition on the activity and the sustainability of Ni/Mg(Al)O catalysts were investigated in the daily start-up and shut-down (DSS) operation of the steam reforming of CH 4 . Mg 2.5 (Ni 0.5 )–Al hydrotalcite was prepared by coprecipitation and calcined to form Mg 2.5 (Al,Ni 0.5 )O periclase. When the powders of the periclase were dipped in an aqueous solution of Ru(III) nitrate, the hydrotalcite was reconstituted on the surface of Mg 2.5 (Al,Ni 0.5 )O particles, resulting in the formation of highly dispersed Ru/Ni bimetal supported catalysts after the calcination, followed by the reduction. The addition of Ru on Ni caused a decrease in the reduction temperature of Ni and an increase in the amount of H 2 uptake on the Ni over the catalyst. Formation of Ru–Ni alloy or strong interaction between Ru and Ni was also suggested. When Ru–Ni 0.5 /Mg 2.5 (Al)O catalysts were tested in the DSS-like operation under steam purging, the deactivation due to the oxidation of Ni metal by steam was effectively suppressed by hydrogen spillover. Moreover, only 0.05 wt% of Ru loading was enough to effectively suppress the deactivation during the DSS-like operation.

A catalytic hollow fibre membrane reactor (CHFMR) was developed in this study for combined steam methane reforming (SMR) and water gas shift (WGS) reaction. This is achieved by incorporating a Ni/SBA-15 catalyst into a plurality of micro-channels with open entrance from inner surface of Al 2 O 3 hollow fibres, followed by coating of a 3.3 µm Pd membrane on the outer surface of the hollow fibre using an electroless plating method. In addition to systematic characterizations of each reactor component, i.e. Ni/SBA-15 catalyst, micro-structured ceramic hollow fibre and Pd separating layer, the effect of how the reactor was assembled or fabricated on the catalytic performance was evaluated. Electroless plating of the Pd membrane impaired the catalytic performance of the deposited Ni/SBA-15 catalyst. Also, the over-removal of hydrogen from the reaction zone was considered as the main reason for the deactivation of the Ni-based catalyst. Instead of mitigating such deactivation using “compensating” hydrogen, starting the reaction at higher temperatures was found more efficient in improving the reactor performance, due to a better match between hydrogen production (from the reaction) and hydrogen removal (from the Pd membrane). An effective methane conversion of approximately 53%, a CO 2 selectivity of 94% and a H 2 recovery of 43% can be achieved at 560 °C. In order for a more significant “shift” phenomenon, alternative methodology of fabricating the reactor and more coke resistant catalysts are recommended.

Microstructured alumina hollow fibers, which contain a plurality of radial microchannels with significant openings on the inner surface, have been fabricated in this study and used to develop an efficient catalytic hollow fiber reactor. Apart from low mass-transfer resistance, a unique structure of this type facilitates the incorporation of Ni-based catalysts, which can be with or without the aged secondary support, SBA-15. In contrast to a fixed bed reactor, the catalytic hollow fiber reactor shows similar methane conversion, with a gas hourly space velocity that is approximately 6.5 times higher, a significantly greater CO2 selectivity, and better productivity rates. These results demonstrate the advantages of dispersing the catalyst inside the microstructured hollow fiber as well as the potential to reduce the required quantity of catalyst.

Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye (RuP) and a nickel bis(diphosphine) electrocatalyst (NiP) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP-NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH 4.5, the efficiency of the system is limited by the poor protonation of NiP, which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP-NiP photocatalytic system, which can be widely applied to other photocatalytic systems.

This paper investigates the scaling-up of cyanobacterial biomass cultivation and biohydrogen production from laboratory to industrial scale. Two main aspects are investigated and presented, which to the best of our knowledge have never been addressed, namely the construction of an accurate dynamic model to simulate cyanobacterial photo-heterotrophic growth and biohydrogen production and the prediction of the maximum biomass and hydrogen production in different scales of photobioreactors. To achieve the current goals, experimental data obtained from a laboratory experimental setup are fitted by a dynamic model. Based on the current model, two key original findings are made in this work. First, it is found that selecting low -chlorophyll mutants is an efficient way to increase both biomass concentration and hydrogen production particularly in a large scale photobioreactor. Second, the current work proposes that the width of industrial scale photobioreactors should not exceed 0.20 m for biomass cultivation and 0.05 m for biohydrogen production, as severe light attenuation can be induced in the reactor beyond this threshold.

Dynamic simulation is a valuable tool to assist the scale-up and transition of biofuel production from laboratory scale to potential industrial implementation. In the present study two dynamic models are constructed, based on the Aiba equation, the improved Lambert–Beer's law and the Arrhenius equation. The aims are to simulate the effects of incident light intensity, light attenuation and temperature upon the photo-autotrophic growth and the hydrogen production of the nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142. The results are based on experimental data derived from an experimental setup using two different geometries of laboratory scale photobioreactors: tubular and flat-plate. All of the model parameters are determined by an advanced parameter estimation methodology and subsequently verified by sensitivity analysis. The optimal temperature and light intensity facilitating biohydrogen production in the absence of light attenuation have been determined computationally to be 34 °C and 247 μmol m− 2 s− 1, respectively, whereas for cyanobacterial biomass production they are 37 °C and 261 μmol m− 2 s− 1, respectively. Biomass concentration higher than 0.8 g L− 1 is also demonstrated to significantly enhance the light attenuation effect, which in turn inducing photolimitation phenomena. At a higher biomass concentration (3.5 g L− 1), cyanobacteria are unable to activate photosynthesis to maintain their lives in a photo-autotrophic growth culture, and biohydrogen production is significantly inhibited due to the severe light attenuation.

Daily startup and shutdown (DSS) operations using several purge gases were applied for Ni-loaded Mg(Al)O periclase catalyst to test the sustainability in steam reforming of CH 4 . Thirteen wt% Ni loaded Mg(Al)O catalysts were prepared by using Mg(Ni)–Al hydrotalcite as the precursor with varying Mg/Al ratios. H 2 O/N 2 (100/25 ml min −1 ), O 2 /N 2 (40/10 ml min −1 ) and CO 2 /H 2 O/N 2 (40/15/25 ml min −1 ) were tested as the purge gas in imitation of steam, air and spent gas, respectively. Use of air as the purge gas resulted in a quick deactivation of all Ni loaded catalysts due to the oxidation of Ni metal on the catalyst surface. Spent gas was the most inert for the DSS operation causing no significant deactivation of Ni loaded catalysts. Steam, the most convenient purge gas for DSS operation of PEFC, revealed evident deactivation depending on the (Mg + Ni)/Al ratio in Ni/Mg(Al)O catalysts; use of the (Mg + Ni)/Al ratio of 3/1 resulted in a quick deactivation with steam purge, although this ratio was the most profitable for the steady state operation with the Ni/Mg(Al)O catalysts. The most stable operation was achieved with the ratio of 6/1 in steam as the purge gas. The deactivation took place mainly by the oxidation of Ni metal by steam as the purge gas during the DSS operation between 200 and 700 °C. It is likely that Mg(Al)O on the Ni/Mg(Al)O catalysts was hydrated by steam to form Mg(OH) 2 on the catalyst surface, resulting in the oxidation of Ni metal finely dispersed on Mg(Al)O periclase.

Effects of the additions of noble metal, i.e. Rh, Pd and Pt, on Ni/Mg(Al)O catalyst have been investigated for the daily start-up and shut-down (DSS) operation under steam purging in the steam reforming of CH 4 . Mg 2.5 (Ni 0.5 )-Al hydrotalcite was prepared by coprecipitation and calcined to form Mg 2.5 (Al,Ni 0.5 )O periclase. When the powders of the periclase were dipped in an aqueous solution of the nitrate of Rh(III), Pd(II) or Pt(II), the hydrotaclite was reconstituted on the surface of Mg 2.5 (Al,Ni 0.5 )O particles due to a “memory effect,” resulting in the formation of highly dispersed noble metal-Ni supported catalysts after the calcination followed by the reduction. The addition of noble metal on Ni resulted in a decrease in the reduction temperature of Ni 2+ in Mg 2.5 (Al,Ni 0.5 )O periclase and an increase in the amount of H 2 uptake on the Ni 0 over the Ni/Mg 2.5 (Al)O catalyst. When Rh-, Pd- and Pt-Ni 0.5 /Mg 2.5 (Al)O catalysts were tested for the DSS-like operation under steam purging, the deactivation due to the Ni metal oxidation by steam was effectively suppressed by hydrogen spillover from noble metal to Ni. Especially, only 0.05 wt% of noble metal loading was enough to suppress effectively the deactivation during the DSS-like operation in the case of using both Rh and Pt.

Photosynthetic organisms developed multiple strategies for balancing light-harvesting versus intracellular energy utilization to survive ever-changing environmental conditions. The light-harvesting complex (LHC) protein family is of paramount importance for this function and can form light-harvesting pigment protein complexes. In this work, we describe detailed analyses of the photosystem II (PSII) LHC protein LHCBM9 of the microalga Chlamydomonas reinhardtii in terms of expression kinetics, localization, and function. In contrast to most LHC members described before, LHCBM9 expression was determined to be very low during standard cell cultivation but strongly increased as a response to specific stress conditions, e.g., when nutrient availability was limited. LHCBM9 was localized as part of PSII supercomplexes but was not found in association with photosystem I complexes. Knockdown cell lines with 50 to 70% reduced amounts of LHCBM9 showed reduced photosynthetic activity upon illumination and severe perturbation of hydrogen production activity. Functional analysis, performed on isolated PSII supercomplexes and recombinant LHCBM9 proteins, demonstrated that presence of LHCBM9 resulted in faster chlorophyll fluorescence decay and reduced production of singlet oxygen, indicating upgraded photoprotection. We conclude that LHCBM9 has a special role within the family of LHCII proteins and serves an important protective function during stress conditions by promoting efficient light energy dissipation and stabilizing PSII supercomplexes.

We report on the development of enzyme-free glucose electrochemical sensors for safety and control application in fermentation industry, manufactured by printing Au/TiO2 composites onto gold based planar electrodes. The electrocatalytic materials were prepared in two steps: firstly, colloidal solutions of Au nanoparticles (NPs) ranging from 2 to 40 nm, were synthesized by reduction of an aqueous solution of HAuCl4; secondly, the Au NPs were deposited on the surface of TiO2 by chemical wet impregnation. The use of different reducing agents allowed to control the size of Au NPs, which plays an important role in their electrocatalytic behaviour. Results showed the high electrocatalytic activity of Au NP-modified gold electrodes towards glucose oxidation in alkaline solution; instead no response was given towards ethanol suggesting the possibility to use these kinds of sensors for fermentation process monitoring in industrial technology. The good sensing properties of Au NP-embedded TiO2 composites may be ascribed to the electrocatalytic activity of Au NPs stabilized on TiO2.

Ethanol steam reforming has been investigated in the low temperature range, focusing not only on H-2 productivity, but also on catalyst stability, very critical parameters under such conditions. Different supports (SiO2 and ZrO2), active phases (Ni, Co, Cu) and reaction temperature (300-500 degrees C) have been employed. Ni confirmed the best performing active phase to promote ethanol decomposition and reforming already at low reaction temperature. However, stability towards coking remains a key problem. The support plays a key role from this point of view. Indeed, the stabilization of the active phase in very dispersed form allowed to reach stable catalyst performance with time-on-stream. SiO2, thanks to no Lewis acidity and sufficiently strong metal-support interaction, demonstrated an interesting support for Ni under the selected operating conditions. (C) 2013 Elsevier B.V. All rights reserved.