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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]

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 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]

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]

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]

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]

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]