Sustainable Low-Temperature Hydrogen Production from Lignocellulosic Biomass Passing through Formic Acid: Combination of Biomass Hydrolysis/Oxidation and Formic Acid Dehydrogenation

Microbial mechanisms for higher hydrogen production in anaerobic digestion at constant temperature versus gradient heating

BACKGROUND

Clean energy hydrogen (H2) produced from abundant lignocellulose is an alternative to fossil energy. As an essential influencing factor, there is a lack of comparison between constant temperatures (35, 55 and 65 °C) and gradient heating temperature (35 to 65 °C) on the H2 production regulation potential from lignocellulose-rich straw via high-solid anaerobic digestion (HS-AD). More importantly, the microbial mechanism of temperature regulating H2 accumulation needs to be investigated.

RESULTS

Constant 65 °C led to the lowest lignin residue (1.93%) and the maximum release of cellulose and hemicellulose, and the highest H2 production (26.01 mL/g VS). H2 production at 35 and 55 °C was only 14.56 and 24.13 mL/g VS, respectively. In order to further explore the potential of ultra-high temperature (65 °C), HS-AD was performed by gradient heating conditions (35 to 65 °C). However, compared to constant 65 °C, gradient heating conditions led to higher lignin residue (2.49%) and lower H2 production (13.53 mL/g VS) than gradient heating conditions (47.98%). In addition, metagenomic analysis showed the cellulose/hemicellulose hydrolyzing bacteria and genes (mainly Thermoclostridium, and xynA, xynB, abfA, bglB and xynD), H2-producing bacteria and related genes (mainly Thermoclostridium, and nifD, nifH and nifK), and microbial movement and metabolic functions were enriched at 65 °C. However, the enrichment of two-component systems under gradient heating conditions resulted in a lack of highly-enriched ultra-high-temperature cellulose/hemicellulose hydrolyzing genera and related genes but rather enriched H2 consumption genera and genes (mainly Acetivibrio, and hyaB and hyaA) resulting in a weaker H2 production.

CONCLUSIONS

The lignin degradation process does not directly determine H2 accumulation, which was actually regulated by bacteria/genes contributing to H2 production/consumption. In addition, it is temperature that enhances the hydrolysis process of lignin rather than lignin-degrading enzymes, bacteria and genes by promoting microbial material transfer and metabolism. In terms of temperature, one of the key parameters of HS-AD for H2 production, we developed an important regulatory strategy, enriched the theoretical basis of temperature regulation for H2 production to further expanded the research horizon in this field. Video Abstract.

Enhancing polyol/sugar cascade oxidation to formic acid with defect rich MnO2 catalysts

Oxidation of renewable polyol/sugar into formic acid using molecular O₂ over heterogeneous catalysts is still challenging due to the insufficient activation of both O₂ and organic substrates on coordination-saturated metal oxides. In this study, we develop a defective MnO₂ catalyst through a coordination number reduction strategy to enhance the aerobic oxidation of various polyols/sugars to formic acid. Compared to common MnO₂, the tri-coordinated Mn in the defective MnO₂ catalyst displays the electronic reconstruction of surface oxygen charge state and rich surface oxygen vacancies. These oxygen vacancies create more Mn^δ+ Lewis acid site together with nearby oxygen as Lewis base sites. This combined structure behaves much like Frustrated Lewis pairs, serving to facilitate the activation of O₂, as well as C-C and C-H bonds. As a result, the defective MnO₂ catalyst shows high catalytic activity (turnover frequency: 113.5 h^-1) and formic acid yield (>80%) comparable to noble metal catalysts for glycerol oxidation. The catalytic system is further extended to the oxidation of other polyols/sugars to formic acid with excellent catalytic performance.

Gradient electro-processing strategy for efficient conversion of harmful algal blooms to biohythane with mechanisms insight

Globally eruptive harmful algal blooms (HABs) have caused numerous negative effects on aquatic ecosystem and human health. Conversion of HABs into biohythane via dark fermentation (DF) is a promising approach to simultaneously cope with environmental and energy issues, but low HABs harvesting efficiency and biohythane productivity severely hinder its application. Here we designed a gradient electro-processing strategy for efficient HABs harvesting and disruption, which had intrinsic advantages of no secondary pollution and high economic feasibility. Firstly, low current density (0.888-4.444 mA/cm²) was supplied to HABs suspension to harvest biomass via electro-flocculation, which achieved 98.59% harvesting efficiency. A mathematic model considering coupling effects of multi-influencing factors on HABs harvesting was constructed to guide large-scale application. Then, the harvested HABs biomass was disrupted via electro-oxidation under higher current density (44.44 mA/cm²) to improve bioavailability for DF. As results, hydrogen and methane yields of 64.46 mL/ (g VS) and 171.82 mL/(g VS) were obtained under 6 min electro-oxidation, along with the highest energy yield (50.1 kJ/L) and energy conversion efficiency (44.87%). Mechanisms of HABs harvesting and disruption under gradient electro-processing were revealed, along with the conversion pathways from HABs to biohythane. Together, this work provides a promising strategy for efficient disposal of HABs with extra benefit of biohythane production.

A Review on the Critical Role of H2 Donor in the Selective Hydrogenation of 5-Hydroxymethylfurfural

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) has been of great interest to many scientists and researchers. However, conventional hydrogenation inevitably requires the use of gaseous hydrogen as a reducing agent, which is detrimental to its storage and transport. In this regard, other economical and environmentally friendly strategies, such as catalytic transfer hydrogenation/hydrogenolysis without external molecular H₂ , become more and more attractive. This Review provides the status and insight into the current research of hydrogenating HMF to high-value chemicals, using formic acid, alcohols, polymethylhydrosiloxane, water, and sodium borohydride as hydrogen donors and explains the hydrogenation mechanisms and the related hydrogenation characteristics of different hydrogen donors in the catalytic systems.

Experimental and Theoretical Studies of Ultrafine Pd-Based Biochar Catalyst for Dehydrogenation of Formic Acid and Application of In Situ Hydrogenation

In this work, a novel "foaming" strategy uses sodium bicarbonate (NaHCO₃) and ammonium oxalate ((NH₄)₂C₂O₄) as the foaming agent, turning biomass-derived carboxymethyl cellulose (CMC) into N-doped porous carbon. Highly active palladium nanoparticles (Pd NPs) immobilized on nitrogen-doped porous carbon (Pd@MC(2)-P) are produced through a phosphate-mediation approach. The phosphoric acid (H₃PO₄) becomes the key to the synthesis of highly dispersed ultrafine Pd NPs on active Pd-cluster-edge (the edge of the Pd-cluster-100 and Pd-cluster-111 surfaces). The Pd@MC(2)-P exhibits high activity for formic acid (FA) dehydrogenation with an initial TOF_g of 971 h^-1 at room temperature. The subsequent hydrogenation of phenol using FA as an in situ hydrogen source on Pd@MC(2)-P and the highly efficient hydrogenation of phenol to cyclohexanone reaches more than 90% selectivity and 80% conversion. Density functional theory (DFT) calculations reveal that the reduced H poisoning and more exposed (100) surface over Pd nanoparticles are the keys to the Pd nanoparticles' high activity.

Agricultural waste management strategies for environmental sustainability

Globally, abundant agricultural wastes (AWs) are being generated each day to fulfil the increasing demands of the fast-growing population. The limited and/or improper management of the same has created an urgent need to devise strategies for their timely utilization and valorisation, for agricultural sustainability and human-food and health security. The AWs are generated from different sources including crop residue, agro-industries, livestock, and aquaculture. The main component of the crop residue and agro-industrial waste is cellulose, (the most abundant biopolymer), followed by lignin and hemicellulose (lignocellulosic biomass). The AWs and their processing are a global issue since its vast majority is currently burned or buried in soil, causing pollution of air, water and global warming. Traditionally, some crop residues have been used in combustion, animal fodder, roof thatching, composting, soil mulching, matchsticks and paper production. But, lignocellulosic biomass can also serve as a sustainable source of biofuel (biodiesel, bioethanol, biogas, biohydrogen) and bioenergy in order to mitigate the fossil fuel shortage and climate change issues. Thus, valorisation of lignocellulosic residues has the potential to influence the bioeconomy by producing value-added products including biofertilizers, bio-bricks, bio-coal, bio-plastics, paper, biofuels, industrial enzymes, organic acids etc. This review encompasses circular bioeconomy based various AW management strategies, which involve 'reduction', 'reusing' and 'recycling' of AWs to boost sustainable agriculture and minimise environmental pollution.

Efficient and Controlled H2 Release from Sodium Formate

Sodium formate (SF) has been used for a long time as a technological additive for H2 release from the dehydrogenation of formic acid . Formic acid is often synthesized from...

Hydrophobic Deep Eutectic Solvents for the Recovery of Bio-Based Chemicals: Solid–Liquid Equilibria and Liquid–Liquid Extraction

The solid–liquid equilibrium (SLE) behavior and liquid–liquid extraction (LLX) abilities of deep eutectic solvents (DESs) containing (a) thymol and L-menthol, and (b) trioctylphosphine oxide (TOPO) and L-menthol were evaluated. The distribution coefficients (KD) were determined for the solutes relevant for two biorefinery cases, including formic acid, levulinic acid, furfural, acetic acid, propionic acid, butyric acid, and L-lactic acid. Overall, for both cases, an increasing KD was observed for both DESs for acids increasing in size and thus hydrophobicity. Furfural, being the most hydrophobic, was seen to extract the highest KD (for DES (a) 14.2 ± 2.2 and (b) 4.1 ± 0.3), and the KD of lactic acid was small, independent of the DESs (DES (a) 0.5 ± 0.07 and DES (b) 0.4 ± 0.05). The KD of the acids for the TOPO and L-menthol DES were in similar ranges as for traditional TOPO-containing composite solvents, while for the thymol/L-menthol DES, in the absence of the Lewis base functionality, a smaller KD was observed. The selectivity of formic acid and levulinic acid separation was different for the two DESs investigated because of the acid–base interaction of the phosphine group. The thymol and L-menthol DES was selective towards levulinic acid (Sij = 9.3 ± 0.10, and the TOPO and L-menthol DES was selective towards FA (Sij = 2.1 ± 0.28).

Hydrogen production from cellulose catalyzed by an iridium complex in ionic liquid under mild conditions

A new and simple method for hydrogen production from cellulose using an iridium catalyst and an ionic liquid under mild conditions was developed.

One-pot synthesis of formic acid via hydrolysis-oxidation of potato starch in the presence of cesium salts of heteropoly acid catalysts

Solid bifunctional catalysts based on cesium salts of V-containing heteropoly acids (CsHPA: Cs_3.5H_0.5PW₁₁VO₄₀, Cs_4.5H_0.5SiW₁₁VO₄₀, Cs_3.5H_0.5PMo₁₁VO₄₀) and Cs_2.5H_0.5PMo₁₂O₄₀ were used for studying one-pot hydrolysis–oxidation of potato starch to formic acid at 413–443 K and 2 MPa air mixture. It was shown that the optimum process temperature that prevents formic acid from destruction is 423 K. The studies were focused on the influence of the composition of heteropoly anions on the yield and selectivity of formic acid. Using W–V–P(Si) CsHPA results in the product overoxidation compared to Mo–V-containing CsHPA. The activity of Cs–PMo was significantly lower compared to Cs–PMoV. This may indicate that vanadium plays an important role in the oxidation process. The most promising catalyst was Cs_3.5H_0.5PMo₁₁VO₄₀ which provided the maximum yield of formic acid equal to 51%. Cs_3.5H_0.5PMo₁₁VO₄₀ was tested during nine cycles of starch hydrolysis–oxidation to demonstrate its high stability and efficiency.

Influence of composition of catalysts based on heteropoly acid cesium salts on formic acid production via starch hydrolysis–oxidation was investigated.