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Conventional methods of hydrogen reduction employed for green nickel production face challenges due to the high potentials required for water splitting at room temperature (>1.8 V) and/or the necessity for expensive catalysts. Additionally, the transportation of hydrogen from the production unit to the reduction unit (generally at 900 °C) presents hazards due to potential hydrogen leakage. Our findings address these challenges by proposing an innovative approach that utilises hydrogen generated via electrolysis at high temperatures for the in situ reduction of NiO in molten salt electrolytes. This process involves the hydrolysis of molten salts, generating protons which are then cathodically discharged to produce hydrogen at a low cell voltage, ranging from 1.0 to 1.4 V. Two different setups are investigated, utilising either NiO cathode pellets or NiO powder immersed in the melt to explore the hydrogen evolution and subsequent reduction of the oxide phase. Various parameters, including cell voltage, cell configuration, electrolyte chemical composition and temperature are examined for their impact on the reduction process. It is observed that the composition of the molten salt electrolyte significantly influences the reduction kinetics. The addition of KCl to LiCl electrolyte aids the reduction process by improving the wettability of electrodes, while CaCl2 enhances the hydrolysis of the molten electrolyte. In particular, NiO pellets demonstrate efficient reduction to Ni in LiCl–30 wt% KCl, achieving a remarkable current efficiency of 97.4% with an energy consumption of 1.28 kW h per kilogram of produced Ni. [ABSTRACT FROM AUTHOR]

Herein we report the production of high-pressure (19.3 bar), carbon-negative hydrogen (H2) from glycerol with a purity of 98.2 mol% H2, 1.8 mol% light hydrocarbons (mainly methane), and 400 ppm of CO. Aqueous phase reforming (APR) of 10 wt% glycerol solution was studied with a series of NiPt alumina bimetallic catalysts supported on alumina. The Ni8Pt1-450 catalyst had the highest hydrogen selectivity (95.6%) and the lowest alkanes selectivity (3.7%) of the tested catalysts. The hydrogen selectivity decreased in the order of Ni8Pt1-450 > Ni8Pt1-260 > Ni1Pt1-260 > Pt-260. The CO2 was sequestered with CaO adsorbent which formed CaCO3. We measured the adsorption capacity of the CaO adsorbent at different temperatures. Life cycle analysis showed that the APR of glycerol coupled with CO2 capture has net negative CO2 equivalent greenhouse gas emissions. The CO2 emissions are −9.9 kg CO2 eq./kg H2 and −50.1 kg CO2 eq./kg H2 when grid electricity and renewable electricity are used, respectively, and the CO2 is allocated respectively to the mass of products produced. The cost of this H2 (denoted as "green-emerald") was estimated to be 2.4 USD per kg H2 when grid electricity is used and 2.7 USD per kg H2 when using renewable electricity. The cost of glycerol has the highest contribution of 1.71 USD per kg H2. Participation in the carbon credit markets can further decrease the price of the produced H2. [ABSTRACT FROM AUTHOR]

Carbonic anhydrase (CA) is considered an efficient enzyme for fermentation systems exhibiting a wide range of applications, enhancing both the efficacy and output of the fermentation process. The present study aimed to evaluate the production of acidogenic biohydrogen (bioH2) and volatile fatty acids (VFA) using forest residues as a renewable feedstock. Specifically, the study examined the integration of CA derived from Desulfovibrio vulgaris into the acidogenic fermentation (AF) process. The experimental procedure involved a cascade design conducted in two distinct phases. In phase I, the concentration of CA in the AF was systematically optimized, with glucose serving as the substrate. In phase II, three influential parameters (pH, pressurization with in situ generated gas and organic load) were evaluated on AF in association with optimized CA concentration from phase I. In phase II, glucose was replaced with renewable sugars obtained from forest residues after steam explosion pretreatment followed by enzymatic saccharification. The incorporation of CA in AF was found to be beneficial in steering acidogenic metabolites. Alkaline conditions (pH 8) promoted bioH2, yielding 210.9 mLH2 gCOD -1, while introducing CA further increased output to 266.6 mLH2 gCOD -1. This enzymatic intervention improved the production of bioH2 conversion efficiency (HCE) from 45.3% to 57.2%. Pressurizing the system accelerated VFA production with complete utilization of in situ produced H2 + CO2 compared to non-pressurized systems. Particularly, caproic acid production was improved under pressurized conditions which was accomplished by the targeted enrichment of chain-elongating bacteria in the mixed culture. The microbial diversity analysis showed the dominance of Firmicutes suggesting a significant degree of adaptation to the experimental contexts, leading to an enhanced production of acidogenic metabolites. [ABSTRACT FROM AUTHOR]

A solvent-tuned electrochemical protocol for the selective transfer hydrogenation of imidazopyridines using carbazates as hydrogen donors has been developed. This electrosynthesis strategy provides a more sustainable and greener way to access partially saturated N-heterocycles by avoiding traditionally employed transition metal catalysts and high-pressure hydrogen. Remarkably, the method is scalable and applicable to late-stage functionalization of complex molecules. A possible mechanism has been proposed on the basis of radical-trapping and cyclic voltammetry experiments. [ABSTRACT FROM AUTHOR]

The improper disposal of plastic waste raises significant concerns due to its severe threat to ecosystems and public health. Artificial photosynthesis, compared with the conventional strategies (e.g., pyrolysis) operated under harsh conditions, has emerged as a green and sustainable approach to convert plastic waste into commodity chemicals under ambient conditions. In this study, we have developed a partially oxidized CuIn5S8 nanosheet photocatalyst (O-CuIn5S8) to promote the conversion of polyethylene terephthalate (PET) waste into value-added chemicals while producing hydrogen fuel. After oxygen incorporation, the as-obtained O-CuIn5S8 catalyst demonstrates significantly improved activity, with a hydrogen evolution rate of 2.57 ± 0.02 mmol g−1 h−1, which is 7 times higher than that of the pristine CuIn5S8. Furthermore, O-CuIn5S8 allows an effective transformation of pretreated PET into a range of valuable commodity chemicals, including formate, acetate, and glycolate, via a hole-induced oxidation mechanism. This work paves the way for the rational development of photocatalysts to manage plastic pollution and meanwhile reclaim the carbon source within PET plastic waste. [ABSTRACT FROM AUTHOR]

A new vision of using carbon dioxide (CO2) catalytic processing of oleic acid into C8–C15 alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO2 atmosphere. The yield of C8–C15 ingredients reaches 73.10 mol% in a CO2 atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H2) atmosphere. In the absence of an external H2 source, products which are similar to aviation fuel are generated where aromatization of propene (C3H6) oxidative dehydrogenation (ODH) involving CO2 and propane (C3H8) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO2 atmosphere is significantly different from that in the H2 atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H2 spillover is observed in the H2 atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H2. The CO2 processing of oleic acid described in this paper will significantly contribute to future CO2 utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel. [ABSTRACT FROM AUTHOR]

Tandem catalysis involving simultaneous dihydrogen generation from a hydrogen carrier and substrate reduction on a heterogeneous catalyst provides unique opportunities for green chemistry synthesis under mild reaction conditions. However, in traditional batch conditions for nitro reductions, excess hydrogen is often necessary to achieve full conversion and thermal management on scale-up is a safety issue due to large heats of reaction and adiabatic temperature rise. Herein, we report a continuous-flow strategy to maximize hydrogen utilization efficiency (HUE) and improve reaction safety in tandem nitro-reduction reactions, using stoichiometric amounts of ammonia borane (AB) in methanol as the hydrogen source with Pd/C catalyst. This strategy provides a full conversion of nitrobenzene to highly pure aniline in 15 s, with only air cooling needed. In comparison, a batch reaction with stoichiometric AB only reaches a 42% yield of aniline over Pd/C after 30 min. The space–time yield of aniline in a flow system (92.07 g L−1 min−1) is substantially higher than that in a batch reaction (0.13 g L−1 min−1). The tandem reaction set in a flow configuration was simulated with commercial software (Aspen Plus v8.8) enabling scale-up, safe operation, and optimization of energy use. Our tandem flow system with a full HUE, good thermal management, and excellent catalytic efficiency provides a practical way for the green chemistry synthesis of anilines. [ABSTRACT FROM AUTHOR]

Ultrahigh hydrogen evolution from photocatalytic water splitting using CaTiO3 is difficult due to its low photon-to-electron conversion efficiency. Herein, a facile post-loading strategy was developed for preparing a RuS2@CaTiO3-x heterojunction by anchoring RuS2 on a multi-shelled hollow cube of CaTiO3, which successfully achieved ultrahigh hydrogen evolution through water splitting with the assistance of a photocatalytic biorefinery. After RuS2 anchoring, the utilization of visible light and the separation/migration rate of photo-generated carriers of RuS2@CaTiO3-x enhanced significantly, resulting in a high photon-to-electron conversion efficiency. Correspondingly, the hydrogen evolution rate reached 8140.7 μmol g−1 h−1 in the RuS2@CaTiO3-10 system with the assistance of the photocatalytic selective oxidation of biomass-derived monosaccharides, and it was 45.5- and 4.2-fold greater than those of pristine CaTiO3 and RuS2, respectively. Furthermore, 89.0% yield of lactic acid was obtained in the corresponding system. Electron spin-resonance (ESR) characterization combined with radical capture experiments indicated that ˙OH played a significant role in lactic acid production. Moreover, RuS2@CaTiO3-10 not only exhibits excellent reusability and stability, but also has been successfully used for different biomass-based monosaccharide reforming coupled with water-splitting to co-produce lactic acid and hydrogen. This work sheds light on the development and design of photocatalytic systems. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) is a very promising technology addressing the challenge of carbon dioxide recycling into organic compounds, which might serve as building blocks for the (bio)chemical industry. However, poor process control and understanding of fundamental aspects such as the microbial extracellular electron transfer (EET) currently limit further developments. In the model acetogen Clostridium ljungdahlii, both direct and indirect electron consumption via hydrogen have been proposed. However, without clarification neither targeted development of the microbial catalyst nor process engineering of MES are possible. In this study, cathodic hydrogen is demonstrated to be the dominating electron source for C. ljungdahlii at electroautotrophic MES allowing for superior growth and biosynthesis, compared to previously reported MES using pure cultures. Hydrogen availability distinctly controlled an either planktonic- or biofilm-dominated lifestyle of C. ljungdahlii. The most robust operation yielded higher planktonic cell densities in a hydrogen mediated process, which demonstrated the uncoupling of growth and biofilm formation. This coincided with an increase of metabolic activity, acetate titers, and production rates (up to 6.06 g L−1 at 0.11 g L−1 d−1). For the first time, MES using C. ljungdahlii was also revealed to deliver other products than acetate in significant amounts: here up to 0.39 g L−1 glycine or 0.14 g L−1 ethanolamine. Hence, a deeper comprehension of the electrophysiology of C. ljungdahlii was shown to be key for designing and improving bioprocess strategies in MES research. [ABSTRACT FROM AUTHOR]

In this work, an innovative route for upgrading biomass-derived phenolic monomers by "hydrogen-free" hydrodeoxygenation (HDO) was proposed and evaluated. The HDO process was integrated with the activation of water and aqueous phase reforming of in situ generated methanol over a nano-porous Ni catalyst and finally the one-pot approach was established achieving high selectivity of bio-phenol. DFT calculations confirmed the crucial role of the Ni catalyst in the activation of water and the following HDO process. The study of the reaction pathway and the mechanism showed that the initial hydrogen source came from water splitting on the surface of the Ni catalyst, which triggered the fracture of the aromatic ether bond to afford phenol and methanol. The subsequent aqueous phase reforming of methanol generated more hydrogen and further accelerated the HDO process. Under the optimized conditions the conversion of guaiacol reached 41.5% and the selectivity of phenol can be 100% at 160 °C. On further increasing the temperature to 190 °C, a high conversion of 96.3% could be achieved while maintaining the selectivity of phenol to 77.9%. After a smart design of methanol release during the reaction, the conversion and selectivity could be further improved to 90.5% and 90.3%, respectively. Overall, the proposed method demonstrates the feasibility of upgrading oxygen-containing biological compounds in a neat water system integrating chemo-splitting of water with using endogenous hydrogen for self-hydrolysis inhibiting external hydrogen supply. [ABSTRACT FROM AUTHOR]

Methanol is an important H-carrier and C1 chemical feedstock. In this paper, a direct conversion of methanol to n-C4H10 and H2 was achieved for the first time in a dielectric barrier discharge (DBD) non-thermal plasma reactor. The selective formation of n-C4H10 by limiting COx (x = 1 and 2) generation was obtained by optimizing different plasma processing parameters including the methanol inlet concentration, discharge power, and pre-heating temperature. The results showed that a higher methanol inlet concentration and a higher pre-heating temperature favors the formation of n-C4H10, while a higher methanol inlet concentration and a lower discharge power can effectively limit the formation of CO. The optimal selectivity for n-C4H10 (37.5%), H2 (28.9%) and CO (14%) was achieved, with a methanol conversion of 40.0%, at a methanol inlet concentration of 18 mol%, a discharge power of 30 W and a pre-heating temperature of 140 °C using N2 as a carrier gas. Value-added liquid chemicals (e.g., alcohols, acids, and heavy hydrocarbons) were also obtained from this reaction. Emission spectroscopy diagnostics reveals the formation of various reactive species (e.g., CH, C2, CN, H and metastable N2) in the CH3OH/N2 DBD. Possible reaction pathways for the formation of n-C4H10 were proposed and discussed. [ABSTRACT FROM AUTHOR]

A straightforward protocol involving electrochemical primary amination of imidazopyridines under mild conditions is described. This transformation utilizes TMSN3 as the nitrogen source and a trace amount of H2O as the hydrogen source. A wide range of imidazopyridines were found to be compatible, providing the corresponding C3-amino substituted imidazopyridines in moderate to good yields. [ABSTRACT FROM AUTHOR]

Biomass to hydrogen production has been regarded as a potential approach for green hydrogen synthesis. However, carbon dioxide and bio-tar are inevitably produced, which critically restricts the refinement of biomass-derived syngas. In this study, deoxygenation-enhanced chemical looping biomass gasification (DE-CLBG) is proposed for hydrogen-rich syngas production together with CO2/H2O deoxygenation and catalytic bio-tar removal using the composite Fe/CaO as the deoxidizer. The DE-CLBG process is comprised of a deoxygenated gasification stage and a regeneration stage. During the deoxygenated gasification stage, the deoxidizer is converted under steam gasification via CaO + Fe + O2− → Ca2Fe2O5 with biochar generation; at the regeneration stage, biochar is further gasified with the achievement of deoxidizer reduction via Ca2Fe2O5 + C → CaO + Fe + COx. Experimental results show that the hydrogen production and maximum concentration upon applying 0.300 g of deoxidizer per g of biomass are 6.70 mmol and 89.61 vol%, which was increased by 287% and 27%, respectively, compared with the non-deoxygenated process. Results from the Mössbauer spectrum show that Fe0 is finally transformed into Fe3+ in the form of Ca2Fe2O5 and a small amount of Fe3O4, corresponding to the deoxygenation efficiency of 99.21%. The NMR results imply that aromatic carbon is the main form in biochar whether introducing deoxidizer or not, and deoxygenation can promote the removal of O-alkyl C. [ABSTRACT FROM AUTHOR]

Hydrogen has become widely recognized as a game changer in the era of climate change and stringent carbon reduction targets. For countries with inadequate distributions of renewable energy, a comprehensive evaluation of potential national and international routes for green hydrogen supply networks is imperative. This study examines the economic and environmental aspects of green hydrogen supply routes for hydrogen refueling stations (HRS) in the Republic of Korea. Three supply routes are evaluated in this work: Case (1) hydrogen production via catalytic cracking of imported green ammonia, Case (2) domestic green hydrogen production at a centralized location in Korea, and Case (3) on-site hydrogen production via water electrolysis at HRS powered by solar electricity from the city grid. The levelized costs of hydrogen (LCOH) were calculated as $9.74, $17.32, and $13.97 per kg for Cases 1, 2, and 3, respectively. The results of sensitivity analysis indicate that the capital cost related to the provision of green ammonia (Case 1), solar electricity, and the electrolyzer were the main contributors to LCOH. Based on projected cost reductions, LCOHs would decrease to $8, $11.76, and $10 per kg for Cases 1, 2, and 3, respectively. Life cycle assessment (LCA) shows that Case 3 is the favored environmental alternative owing to reductions in greenhouse gas (GHG) emissions of 44% and 12% compared with Cases 1 and 2, respectively. The results of LCA sensitivity analysis depict that by 2030, with the increase in the distance of transportation, Case 2 can show the highest increase of 58% for GHG emissions, while an increase of about 8% can be expected for Case 1. However, in Case 3, further work on policy design and infrastructure development is required to make solar electricity provisions in the city grid profitable. [ABSTRACT FROM AUTHOR]

A synergistic combination of photoredox and polarity reversal catalysis enabled a hydrogen evolution cross-coupling of silanes with H2O, alcohols, phenols, and silanols, which afforded the corresponding silanols, monosilyl ethers, and disilyl ethers, respectively, in moderate to excellent yields. The dehydrogenative cross-coupling of Si–H and O–H proceeded smoothly with broad substrate scope and good functional group compatibility in the presence of only an organophotocatalyst 4-CzIPN and a thiol HAT catalyst, without the requirement of any metals, external oxidants and proton reductants, which is distinct from the previously reported photocatalytic hydrogen evolution cross-coupling reactions where a proton reduction cocatalyst such as a cobalt complex is generally required. Mechanistically, a silyl cation intermediate is generated to facilitate the cross-coupling reaction, which therefore represents an unprecedented approach for the generation of silyl cation via visible-light photoredox catalysis. [ABSTRACT FROM AUTHOR]

An unprecedented strategy has been developed involving the earth-abundant Cu-catalyzed hydrocarboxylation of alkynes with HCOOH to (E)-acrylic derivatives with high regio- and stereoselectivity via synergistic effects with ppm levels of a Pd catalyst. Both symmetrical and unsymmetrical alkynes bearing various functional groups were successfully hydrocarboxylated with HCOOH, and the modification of a pharmaceutical molecule exemplified the practicability of this process. This protocol employs HCOOH as both a CO surrogate and hydrogen donor with 100% atom economy and it can be viewed as an alternative approach for indirect CO2 utilization. Mechanistic investigations indicate a Cu/ppm Pd cooperative catalysis mechanism via alkenylcopper species as potential intermediates formed from Cu-hydride active catalytic species with HCOOH as a hydrogen source. This bimetallic system involving inexpensive Cu and trace Pd provides a reliable and efficient hydrocarboxylation method to access industrially useful acrylic derivatives with HCOOH as a hydrogen source, and it provides novel clues for optimizing other Cu–H-related co-catalytic systems. [ABSTRACT FROM AUTHOR]

Metal nanocluster-catalyzed hydrogen evolution through water splitting has received substantial interest toward the implementation of hydrogen economy. However, the general and efficient fabrication of well-defined and ligand-free metal nanoclusters (NCs) with precise sizes for efficient hydrogen evolution in various electrolytes remains a formidable challenge. We report herein the synthesis of well-distributed and ligand-free metal (Rh, Ru, Ir) NCs with monodispersity by utilizing nitrogen-doped hollow carbon spheres (NHCSs) as supporting matrices. Due to the spatial confinement of carbon nanopores and the anchoring sites of nitrogen atoms from NHCSs, metal NCs (MNCs) with diameters of sub-2.0 nm (1.97 ± 0.57 nm for Rh NCs, 1.48 ± 0.45 nm for Ru NCs and 1.34 ± 0.69 nm for Ir NCs) are evenly dispersed on NHCSs. Among the catalysts, Rh/NHCSs exhibit not only excellent electrocatalytic activity for the hydrogen evolution reaction (HER) (10 mV in 0.5 M H2SO4, 7 mV in 1.0 M PBS and 6 mV in 1.0 M KOH), but also high stability and long-term durability within the whole pH range, outperforming the commercial Pt/C and most of the previously reported catalysts. Meanwhile, this catalyst can be employed for the HER in natural seawater with high activity, stability and long-term durability. This work proposes a simple and effective method to fabricate highly dispersed MNCs with high performance for pH-universal water/seawater splitting. [ABSTRACT FROM AUTHOR]

Reductive catalytic fractionation (RCF) is an efficient and selective way to produce phenolic monomers from lignin. However, this strategy is difficult to scale up due to its high operating pressure. In this work, we investigated RCF reaction at or near atmospheric pressure and without the use of hydrogen. The atmospheric RCF (ARCF) was conducted in acidified ethylene glycol in glass vessels at 185–195 °C catalyzed by 5% Ru/C. The products mainly include propylguaiacol and propylsyringyl (up to 95.6% among the lignin monomers) and do not contain propanolguaiacol, propanolsyringyl, or H monomers. Although the total yield of lignin monomers in ARCF is about one-quarter less than that of RCF, the operation of ARCF is much easier, milder, safer, and cheaper due to the atmospheric condition and the feasibility of the semi-continuous operation. [ABSTRACT FROM AUTHOR]

Formaldehyde is an essential building block for hundreds of chemicals and a promising liquid organic hydrogen carrier (LOHC), yet its indirect energy-intensive synthesis process prohibits it from playing a more significant role. Here we report a direct CO reduction to formaldehyde (CORTF) process that utilizes hydrogen underpotential deposition to overcome the thermodynamic barrier and the scaling relationship restriction. This is the first time that this reaction has been realized under ambient conditions. Using molybdenum phosphide as a catalyst, formaldehyde was produced with nearly a 100% faradaic efficiency in aqueous KOH solution, with its formation rate being one order of magnitude higher compared with the state-of-the-art thermal catalysis approach. Simultaneous tuning of the current density and reaction temperature led to a more selective and productive formaldehyde synthesis, indicating the electrochemical and thermal duality of this reaction. DFT calculations revealed that the desorption of the *H2CO intermediate likely served as the rate-limiting step, and the participation of H2O made the reaction thermodynamically favorable. Furthermore, a full-cell reaction set-up was demonstrated with CO hydrogenation to HCHO achieved without any energy input, which fully realized the spontaneous potential of the reaction. Our study shows the feasibility of combining thermal and electrochemical approaches for realizing the thermodynamics and for scaling relationship-confined reactions, which could serve as a new strategy in future reaction design. [ABSTRACT FROM AUTHOR]

A novel process for the efficient synthesis of cyclic carbonates from CO2 and epoxides at room temperature in the absence of a solvent has been achieved by using Al-salen complexes as catalysts and imidazolium hydrogen carbonate ionic liquids ([CnCmIm][HCO3]) as cocatalysts. As a halide ion-free cocatalyst, [CnCmIm][HCO3] showed higher catalytic reactivity compared to traditional halogen-containing quaternary ammonium salts (such as (nBu)4NBr) and organic bases. The catalytic system can be used for the cycloaddition of a series of substrates with good to excellent yields at room temperature in the absence of a solvent. Besides, the catalytic system can be easily recycled at least four times without significant loss of catalytic activity. A possible mechanism was proposed, in which Al-salen and carbene activate the epoxides and CO2 respectively. [ABSTRACT FROM AUTHOR]

A mild method of photocatalytic deoxygenation of aromatic ketones to alkyl arenes was developed, which utilized alcohols as green hydrogen donors. No hydrogen evolution during this transformation suggested a mechanism of direct hydrogen transfer from alcohols. Control experiments with additives indicated the role of acid in transfer hydrogenolysis, and catalyst characterization confirmed a larger number of Lewis acidic sites on the optimal Pd/TiO2 photocatalyst. Hence, a combination of hydrogen transfer sites and acidic sites may be responsible for efficient deoxygenation without additives. The photocatalyst showed reusability and achieved selective reduction in a variety of aromatic ketones. [ABSTRACT FROM AUTHOR]

Clean energy and renewable fine chemicals including biofuels, hydrogen, and bicarbonates are critical for a sustainable and green future. In this study, the integrated production of naturally separated high density liquid biofuels (mainly C7 and C14 olefins), hydrogen gas, and fine chemicals is achieved in an electrochemical cell under ambient conditions. Biofuels are obtained by anodic decarboxylation of the carboxylates, hydrogen is obtained by cathodic reduction of water, and fine chemicals are obtained by the reaction between the alkaline aqueous solution and the anodic carbon dioxide products. An environmentally friendly and low-cost aqueous substitution method is employed to prepare self-supporting Pt nanospheres on 3D porous titanium sponge (Pt@TS) composite electrodes for such an integrated electrolysis. A Pt@TS anode with abundant Pt(100) facets exhibits enhanced activity and stability for electrocatalytic biofuel production as compared with commercial Pt anodes. [ABSTRACT FROM AUTHOR]

This work reports the first observation of the reduction of hydrogen carbonate to formate with polyvinyl chloride (PVC) as a hydrogen source in high-temperature water. Results show that NaHCO3 is successfully converted into formate with a 16% yield and nearly 100% selectivity based on hydrogen carbonate, simultaneously achieving the complete dechlorination of PVC at 300 °C. The mechanistic study suggests that CH–OH group formation from the substitution reaction of chlorine in PVC by OH− is an important starting step, and then the CH–OH group and HCO3− react to form formate via a redox reaction. Moreover, the selection of water as the reaction medium played a key role in the reduction of HCO3− to formate using PVC. The present study provides a new and green method for not only hydrogen carbonate/CO2 conversion but also PVC waste dechlorination in a single step. [ABSTRACT FROM AUTHOR]

In order to realize the dream of the practical application of hydrogen energy from solar energy and water, it is necessary to use efficient and earth-abundant cocatalysts for photocatalytic H2 evolution. Compared with a one-component cocatalyst, the multicomponent cocatalysts with a synergistic effect can effectively accelerate the separation of photogenerated electron–hole pairs in photocatalysis. Hence, a novel bicomponent Co3S4/Co@C cocatalyst on a CdS semiconductor photocatalyst is successfully synthesized by a one-step hydrothermal method. The Co3S4/Co-CdS photocatalyst obtained exhibits a highly efficient photocatalytic H2 evolution rate of 15.17 mmol h−1 g−1, which is 2.8 times higher than that of Pt-CdS. Furthermore, the quantum efficiency of Co3S4/Co-CdS reaches a maximum value of 16.80% at 475 nm. The significant improvement in the performance is because of the unique energy level structure of the Co3S4/Co-CdS photocatalyst, which has the maximum efficiency of charge separation and migration. This work not only presents a new protocol for constructing bicomponent cocatalysts on a semiconductor structure, but also proves that the bicomponent Co3S4/Co@C is a promising and low-cost cocatalyst. [ABSTRACT FROM AUTHOR]

A direct route for the synthesis of cyclic carbonates from olefins and CO2 has been achieved by using imidazolium hydrogen carbonate ionic liquids ([CnCmIm][HCO3]) as bifunctional catalysts in the absence of a solvent. [CnCmIm][HCO3] can convert into a carbene–CO2 adduct spontaneously. The HCO3− anion and carbene–CO2 can serve as catalysts for olefin epoxidation and CO2 cycloaddition, respectively, which obviously simplifies the synthesis of cyclic carbonates. The reaction proceeds quite well under mild conditions. This cheap and simple method can be applied to various olefins with good to excellent yields of cyclic carbonates. The catalyst can be easily recycled at least four times without significantly losing its catalytic activity. [ABSTRACT FROM AUTHOR]

Ammonia is well known to be a very important chemical substance for human life. Simultaneously, the conventional ammonia production process needs pure nitrogen and pure hydrogen. Hydrogen has been produced from either liquid natural gas (LNG) or coal. In this study, water is used as a direct hydrogen source for ammonia production, thereby obviating the need for catalysts or water electrolysis. We have studied and developed a plasma/liquid interfacial reaction (P/L reaction) that can be used to produce ammonia from air (nitrogen) and water at ambient temperature and pressure, without any catalysts. In this study, the P/L reaction entails enhanced ultraviolet (UV) irradiation of the surface of the water phase. The nitrogen plasma/water interface reaction locus can produce ammonia. In contrast, the vacuum ultraviolet (VUV) irradiated interface reaction locus produces increased amounts of ammonia. In a spin trap electron spin resonance (st-ESR) experiment, large amounts of atomic H (HṖ) were produced by UV irradiation, especially by VUV irradiation. The derived HṖ effectively enhanced the P/L reaction rate. [ABSTRACT FROM AUTHOR]

Hydrogen is a key industrial product used as a "green energy" carrier and fully compatible co-reagent in many crucial transformations in the chemical industry. Hydrogen production is based on hydrocarbons or water splitting. Both sources are in demand and can find many other uses. Here, calcium carbide residue (CCR) – sludge after acetylene production from calcium carbide – was used for hydrogen generation. The CCR was mixed with various metals, such as zinc, magnesium, iron and calcium, and heated up to 500–700 °C. As a result, hydrogen evolution was observed. According to volumetric data, the yield of hydrogen was up to 99%. The solid residue after hydrogen release was a mixture of the corresponding metal oxides. According to powder XRD, SEM, and EDX analyses of the inorganic residue, when calcium metal was used, only calcium oxide – a starting component in calcium carbide production – was formed. Thus, the waste CCR can be revalorised and used as a hydrogen source followed by re-use in carbide synthesis. The retrieved hydrogen from the CCR was used in the hydrogenation reaction, and the desired products were obtained with up to 99% yields, clearly confirming the nature of the evaluated gas. When calcium carbide was hydrolysed with deuterium oxide, deuterated CCR was obtained. Sintering of CCR-d2 with calcium metal resulted in D2-gas evolution, which was further used in the synthesis of D-labeled compounds with up to 75% deuterium incorporation. [ABSTRACT FROM AUTHOR]

Pentamethylcyclopentadienyl iridium(iii) complexes of bidentate carbene–triazole ligands were found to be excellent homogeneous catalysts for the hydrogen borrowing mediated coupling of alcohols with amines. The reactions are highly efficient, able to reach completion in under 6 h at 100 °C at low catalyst loadings of 0.5 mol%, and are environmentally benign, the only by-product is water. The Ir(iii) catalysts promoted C–N bond formation across a range of alcohol and amine substrates, including biologically relevant motifs. Covalent attachment to a carbon black surface generated a well-defined “hybrid” heterogeneous catalyst which gave good conversion to products in the coupling reaction of aniline with benzyl alcohol, and could be recycled with no catalyst leeching. This represents the first report of a covalently linked heterogeneous iridium catalyst on carbon used for hydrogen borrowing. Turnover numbers (TON) for the heterogeneous were found to be significantly higher than the corresponding homogeneous reaction. To elucidate the homogeneous reaction mechanism, 1H NMR studies inconjuction with deuteration experiments allowed a mechanism to be postulated. [ABSTRACT FROM AUTHOR]

The ketonization of aldehydes joins two molecules, with n carbon atoms each, to a ketone with 2n− 1 carbon atoms. When employing cerium oxide as a catalyst with nano-sized crystals (＜15 nm) the ketone can be obtained in almost 80% yield. In addition, other ketones are observed so that the total ketone selectivity reached almost 90%. Water is consumed during the reaction when the aldehyde is oxidized to the corresponding carboxylic acid, which is established as a reaction intermediate, co-producing hydrogen. Consequently, water has to be co-fed in the reaction to enhance the reaction rate and to improve the catalyst stability with time on stream. In contrast to zirconium oxide which possesses catalytic activity for the aldol condensation liberating water, with cerium oxide water is not abundant on the surface and the reaction kinetics show that the reaction rate depends on the concentration of the water in the gas-phase, in addition to the dependence on the gas-phase concentration of the aldehyde. The liberated hydrogen can be consumed in the hydrodeoxygenation of the ketone product. Doing so, when starting from heptanal, a biomass derived aldehyde, an alkane mixture was obtained with almost 90% diesel content. For the whole cascade reaction with five single steps no reagents are necessary and the only by-product is one molecule of innocuous carbon dioxide (related to two molecules of aldehyde). This shows that cerium oxide possesses a big potential to convert biomass derived aldehydes into biofuels in a very sustainable way. [ABSTRACT FROM AUTHOR]

The reduction of iron ores with hydrogen is considered a promising CO2 breakthrough technology to mitigate CO2 emissions from the iron and steel industry. The state-of-the-art production of iron and steel from mineral iron carbonates (FeCO3) is based on the thermal decomposition of FeCO3 in air to produce hematite (Fe2O3) suitable for iron production. Our approach is to directly reduce FeCO3 with hydrogen to elemental iron, avoiding Fe2O3 formation. As a consequence, CO2 emissions can be decreased by 60% and up to 33% less reducing agent is needed for iron production. The development of environmentally benign production pathways needs to be based on a fundamental understanding of the reaction kinetics and mechanism. Therefore, thermogravimetry was used to determine the kinetics of the formation of iron from mineral iron carbonate and the concomitant decomposition of the accessory matrix carbonates of calcium, magnesium, and manganese. The isoconversional kinetic analysis according to the Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, and Friedman approach confirms the proposed parallel kinetic model. Multi-variate non-linear regression was used to determine the appropriate kinetic parameters. The conversion of iron carbonate to iron can be described with the two-dimensional Avrami-Erofeev model A2. Therefore, a temperature-controlled nucleation and diffusional growth mechanism is suggested for iron formation from mineral iron carbonate and hydrogen. The multi-parameter reaction models Cn-X and Bna can be used to describe the concomitant iron, calcium oxide, magnesium oxide, and manganese oxide formation without applying multi-step kinetics. The multi-parameter reaction models predict a conversion above 95% at 450 °C within less than 60 minutes reaction time. Unavoidably, 1 mole of carbon dioxide is always emitted when 1 mole of FeCO3 is converted into iron. Catalytic carbon dioxide hydrogenation (CCDH) can be applied to diminish inevitable CO2 emissions by chemical conversion into value-added carbon containing chemicals. Therefore, we propose a process that combines the improved iron production via direct FeCO3 reduction with CCDH as a follow-up reaction. [ABSTRACT FROM AUTHOR]

A novel magnetic carbon-based nickel and sodium silicate catalyst (Na2SiO3@Ni/C) was prepared by the precipitation of Ni(OH)2 on bamboo powders, pyrolysis and the loading of Na2SiO3, and was used in the co-production of biodiesel and hydrogen. The catalyst had strong magnetism (magnetic saturation, Ms of 15.7 Am2 kg−1) from the Ni and basicity (3.18 mmol g−1) from the Na2SiO3 for magnetic separation and biodiesel production. In the presence of Na2SiO3@Ni/C, a biodiesel yield of 98.1% was achieved from soybean oil under the best conditions (9/1 methanol/oil molar ratio, 7 wt% catalyst, 65 °C for 100 min), optimized by single-factor experiments. The catalyst was cycled 4 times with biodiesel yields ＞93%, but the yield dropped to 80.9% with a 85.3% catalyst recovery rate in the fifth cycle. The deactivated catalyst, after 5 cycles, catalyzed the hydrothermal gasification of a biodiesel by-product (crude glycerol) at 350 °C for 5 min with a gasification rate of 80.1% and 82.7% H2 purity. The role of Ni is to catalyze the H2 production while the role of Na2SiO3 is to absorb CO2 to achieve high H2 concentrations. After gasification, the structure of the Ni/C changed slightly and can still be cycled to load Na2SiO3 for biodiesel production and subsequent gasification. [ABSTRACT FROM AUTHOR]

Biomass-based ethanol is a potentially promising feedstock and its transformation into value-added chemicals has attracted growing attention. Herein we reported that bi-functional zeolite supported Pd nanoparticle catalysts achieved superior performance in gas-phase selective aerobic oxidation of ethanol to acetaldehyde and ethyl acetate under mild conditions. The selectivity to ethyl acetate and the ethanol conversion remained at 94.7% and 98.6%, respectively, after a long-term reaction for 73 h over the 2Pd/HY catalyst, while acetaldehyde selectivity of 89.0% was obtained on 2PdO/HY at a low temperature of 150 °C. The reaction selectivity can be readily tuned by controlling the oxidation state of the Pd species, the type of zeolite support and the reaction conditions. The coexistence of the Pd0 and Pd2+ species and a moderate oxygen supply played critical roles in following the partial oxidation route to form ethyl acetate rather than formation of acetaldehyde or acetic acid. The specific interaction between metallic Pd nanoparticles and the acidic zeolite surface via the reverse hydrogen spillover process was also speculated to be responsible for the improved catalytic performances. [ABSTRACT FROM AUTHOR]

An all-vanadium dual circuit redox flow battery is an electrochemical energy storage system able to function as a conventional battery, but also to produce hydrogen and perform desulfurization when a surplus of electricity is available by chemical discharge of the battery electrolytes. The hydrogen reactor chemically discharging the negative electrolyte has been designed and scaled up to kW scale, while different options to discharge the positive electrolyte have been evaluated, including oxidation of hydrazine, SO2 and H2S. The system is well suited to convert sulfur dioxide and hydrogen sulfide to harmless compounds while producing hydrogen, with overall system efficiencies from 50 to 70% for hydrogen production. [ABSTRACT FROM AUTHOR]

Via a ruthenium-catalyzed hydrogen transfer strategy, we have demonstrated a one-pot method for efficient synthesis of quinoxalines from 2-nitroanilines and biomass-derived vicinal diols for the first time. In such a synthetic protocol, the diols and the nitro group serve as the hydrogen suppliers and acceptors, respectively. Hence, there is no need for the use of external reducing agents. Moreover, it has the advantages of operational simplicity, broad substrate scope and the use of renewable reactants, offering an important basis for accessing various quinoxaline derivatives. [ABSTRACT FROM AUTHOR]

Correction for 'Mo-Doped/Ni-supported ZnIn2S4-wrapped NiMoO4 S-scheme heterojunction photocatalytic reforming of lignin into hydrogen' by Hang Su et al., Green Chem., 2022, DOI: 10.1039/d1gc04397h. [ABSTRACT FROM AUTHOR]

H2 is an environmentally-friendly fuel that would allow for a circular economy but its sustainable production, e.g. from solar energy and water, remains a challenge. A hybrid CuFexOy‖TiO2-CoHEC (CoHEC = chloro([4,4′-bipyridine]-2,6-dicarboxylic acid)bis(dimethylglyoximato)cobalt(III)) photocathode for hydrogen evolution reaction (HER), with faradaic efficiencies of 54–88%, is described, the preparation of which uses only non-toxic and Earth-abundant elements, avoids etching treatments and limits the use of organic solvents. The semi-conducting CuFexOy light absorber is obtained by sol–gel synthesis followed by calcination at moderate temperature. Grafting the CoHEC cobaloxime catalyst at its surface results in H2 evolution with an onset photocurrent potential of +860 mV; this process being stabilized by the presence of a thin layer of amorphous TiO2 deposited onto CuFexOy. [ABSTRACT FROM AUTHOR]