METHANOL STEAM REFORMING FOR HYDROGEN PRODUCTION OVER Ni-BASED CATALYSTS: STATE-OF-THE-ART REVIEW AND FUTURE PROSPECTS.

With increasing global emphasis on environmental sustainability, the reliance on traditional energy sources such as coal, natural gas, and oil is encountering significant challenges. H2, known for its high energy content and pollution-free usage, emerges as a promising alternative. However, despite the great potential of H2, approximately 95% of hydrogen production still depends on non-renewable resources. Hence, the shift towards producing H2 from renewable sources, particularly through methods like steam reforming of methanol - a renewable resource - represents a beacon of hope for advancing sustainable energy practices. This review comprehensively examines recent advancements in efficient H2 production using Ni-based catalysts in methanol steam reforming (MSR) and proposes the future prospects. Firstly, the fundamental principles of MSR technology and the significance in clean energy generation are elucidated. Subsequently, the design, synthesis techniques, and optimization strategies for enhancing the catalytic performance of Ni-based catalysts are discussed. Through the analysis of various catalyst compositions, structural adjustments, surface active sites, and modification methods, the review uncovers effective approaches for boosting the activity and durability of MSR reactions. By offering a comprehensive critical analysis, this review serves as a valuable reference to enhance MSR hydrogen production efficiency and catalyst performance.

Cooperative production of monophenolic chemicals and carbon adsorption materials from cascade pyrolysis of acid hydrolysis lignin.

A novel cascade pyrolysis upgrading process for acid hydrolysis lignin (AHL), consisting of pyrolysis, catalytic upgrading of pyrolysis vapors, and pyrolysis char, was developed to improve the yield of value-added products (monophenolic chemicals and carbon materials). Pyrolysis of AHL at 450 °C and subsequent catalytic upgrading of pyrolysis vapors over Ni/H-ZSM-5 boosted the concentration of monophenolic chemicals in pyrolysis liquids by 58%. The carbon material prepared from pyrolysis char using KOH as activating agent exhibited a large specific surface area of 2902.5 m2/g and a large total pore volume of 1.45 cm3/g, thus affording good adsorption capacity for methylene blue (824.87 mg/g) and iodine (2333.17 mg/g). Moreover, the cascade pyrolysis upgrading of AHL achieved a yield of 68.52% desired products, which was much higher than the reported results (single production of monophenols and pyrolysis char). In summary, this work provides a potential reference for efficient utilization of lignin in large-scale applications.

One-Pot Conversion of Cellulose into 2,5-Hexanedione in H2O-Tetrahydrofuran Co-Solvents.

Catalytic conversion of cellulose into the novel platform molecule 2,5-hexanedione (HXD) is regarded as one feasible approach for high-value utilization of biomass resources. Here, we reported one efficient way of one-pot conversion of cellulose into HXD with high yield of 80.3% in H2O and tetrahydrofuran (THF) mixture within Al2(SO4)3 combined with Pd/C as a catalyst. In the catalytic reaction system, Al2(SO4)3 could catalyze the conversion of cellulose into 5-hydroxymethylfurfural (HMF), and Pd/C combined with Al2(SO4)3 could catalyze the hydrogenolysis of HMF into furanic intermediates such as 5-methylfurfuryl alcohol and 2,5-dimethylfuran (DMF) without causing over-hydrogenation of these furanic intermediates. These furanic intermediates were finally transformed into HXD catalyzed by Al2(SO4)3. Besides, the H2O/THF ratio could significantly influence the reactivity of the hydrolytic furanic ring-opening of the furanic intermediates. The catalytic system also showed excellent performance on the conversion of other carbohydrates (glucose and sucrose) into HXD.

Robust Hydrogen Production via Pickering Interfacial Catalytic Photoreforming of n-Octanol-Water Biphasic System.

Pickering emulsion offers a promising platform for conducting interfacial reactions between immiscible reagents; it is particularly suitable for hydrogen production by photoreforming of non-water soluble biomass liquid and water. Herein, Pt-promoted (001)-facet-dominated anatase TiO2 nanosheets were synthesized by a hydrothermal route associated with microfluidic technology for high activity and metal dispersion, and selective surface modification was carried out for preparing Janus particles. Photoreforming hydrogen production through n-octanol and water that formed O/W microemulsion with an average diameter of 540 µm was achieved to obtain amphiphilic catalyst. The as-prepared 2D Janus-type catalysts exhibited remarkably stable emulsification performance as well as photocatalytic activity. This finding indicates that triethoxyfluorosilane had negligible impact on the catalytic performance, yet provided a remarkable benefit to large specific surface area at microemulsion interface, thereby enhancing the H2 yield up to 2003 µmol/g. The cyclic experiments indicate that the decrease in cyclic performance was more likely to be caused by the coalescence of the microemulsion rather than the decrease in catalytic activity, and the microemulsion could be easily recovered by simply hand shaking to more than 96% of the initial performance.

Downstream processing of lignin derived feedstock into end products.

Despite the enormous research efforts in recent years regarding lignin depolymerisation and functionalisation, few commercial products are available. This review provides a summary and viewpoint of extensive research in the lignin-to-product valorisation chain, with an emphasis on downstream processing of lignin derived feedstock into end products. It starts with an introduction of available platform chemicals and polymeric derivatives generated from lignin via existing depolymerisation and functionalisation technologies. Following that, detailed analyses of various strategies for the downstream processing of lignin derived platform chemicals and materials into fuels, valued-added chemicals and functional polymers are provided. A concise techno-economic analysis of various downstream processes is conducted based on the market demand of the end product, economic potential and technological readiness, enabling the identification of processes that are potentially both economically competitive and commercially feasible, and shedding light on processes which deserve further technological development. We wish this review will stimulate further advances in the sustainable production of value-added products from lignin to integrate this invaluable "bio-waste" into the chemical/materials supply chain.

Improving Glycerol Photoreforming Hydrogen Production Over Ag2O-TiO2 Catalysts by Enhanced Colloidal Dispersion Stability.

Solar-driven photocatalytic reforming of biomass-derived resources for hydrogen production offers a sustainable route toward the generation of clean and renewable fuels. However, the dispersion stability of the catalyst particles in the aqueous phase hinders the efficiency of hydrogen production. In this work, a novel method of mixing Ag2O-TiO2 photocatalysts with different morphologies was implemented to promote colloidal dispersion stability, thereby improving hydrogen production performance. A series of Ag2O-TiO2 nanoparticles with different morphologies were synthesized, and their dispersion stabilities in aqueous phase were investigated individually. Two types of Ag2O-TiO2 particles with different morphologies under certain proportions were mixed and suspended in glycerol aqueous solution without adding any dispersant for enhancing dispersion stability while reacting. From the results, photocatalytic hydrogen production was found to be strongly correlated to colloidal dispersion stability. The mixed suspension of Ag2O-TiO2 nanosphere and nanoplate achieved an excellent colloidal dispersion stability without employing any additives or external energy input, and the photoreforming hydrogen production obtained from this binary component system was around 1.1-2.3 times higher than that of the single-component system. From the calculated hydrogen production rate constants between continuous stirring and the binary system, there was only <6% difference, suggesting an efficient mass transfer of the binary system for photoreforming hydrogen production. The proposed method could provide some inspiration to a more energy-efficient heterogeneous catalytic hydrogen production process.

Lignin-first depolymerization of native corn stover with an unsupported MoS2 catalyst.

The lignin-first biorefinery method appears to be an attractive approach to produce phenolic chemicals. Herein, corn stover was employed for the production of phenolic monomers using an unsupported non-noble MoS2 catalyst. The yield of phenolic monomers was enhanced from 6.65% to 18.47% with MoS2 at 250 °C and about 75% lignin was degraded with more than 90% glucan reserved in the solid residues. The Fourier-Transform Infrared (FT-IR) and heteronuclear single quantum coherence-nuclear magnetic resonance (1H-13C HSQC-NMR) characterization suggested that the cleavage of the ß-O-4, γ-ester and benzyl ether linkages were enhanced, promoting the delignification and the depolymerization of lignin. The catalyst performance was relatively effective with 14.30% phenolic monomer yield after the fifth run. The effects of the reaction temperature, the initial hydrogen pressure, the dosage of catalyst, and the reaction time were investigated. The model reactions were also proposed for the potential mechanism study. This work provides some basic information for the improvement of the graminaceous plant lignin-first process with a non-noble metal catalyst.

A novel approach for enhancing hydrogen production from bio-glycerol photoreforming by improving colloidal dispersion stability.

In photocatalytic systems, TiO2 based particles in suspensions tend to aggregate spontaneously, resulting in low efficiency for light utilization and photocatalytic activity. In this study, various TiO2 nanoparticles with different shapes were synthesized and characterized via various analysis. In atmosphere and aqueous environment, the nanoparticles demonstrated different properties in the nature of the agglomerations. Photocatalytic performances of the as-prepared samples were confirmed to be strongly influenced by the dispersion stabilities with TiO2 nanotube exhibited higher colloidal dispersion stability and photocatalytic activity. Mixing binary TiO2 photocatalysts with different shapes as a simple approach was firstly proposed for enhancing photoreforming hydrogen production from bio-glycerol aqueous solution. At a specific mixing ratio, the mixed suspension of TiO2 nanosphere and nanosheet retained excellent colloidal dispersion stability, and photocatalytic hydrogen production was significantly promoted with its maximum H2 production amount as 2.1-2.9 times high as that of TNP and TNS, respectively. This strategy of enhancing colloidal dispersion stability may provide new ideas for the design of efficient and energy-saving photocatalytic system.

Catalytic depolymerization of the hydrolyzed lignin over mesoporous catalysts.

In this work, the mesoporous SBA-15 and a series of modified catalysts based on it, such as Al-SBA-15 and Ni/Al-SBA-15, were synthesized and used for eliminating the char formation during the depolymerization of hydrolyzed lignin. The temperature, time and solvent effects on the lignin depolymerization were also investigated. Results showed that the repolymerization was effectively suppressed over SBA-15 due to its well-ordered pore structure and large pore size. The addition of Al and Ni elements in SBA-15 could improve the lignin depolymerization performance and saturate the instable intermediates. Ethanol was found to be more effective in suppressing repolymerization than other solvents. 81.4% liquefaction degree and 21.90wt% monomer yield was achieved, and no obvious char was observed after the depolymerization of hydrolyzed lignin in ethanol solvent at 300°C for 4h over Ni/Al-SBA-15(20) catalyst.

Insight into the solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin.

The aim of this study is to explore the reaction mediums and conditions for producing high yield of valuable monomers from concentrated sulfuric acid hydrolyzed lignin. The solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin were investigated under the catalysis of Pd/C and CrCl3. Supercritical methanol exhibits the best depolymerization performance, because of its unique diffusion, dissolution and acid-base properties. Afterwards, the influence of reaction temperature and time on depolymerization, repolymerization and coking during hydrogenolysis was examined in methanol. The high temperature is found to favor the depolymerization, with the ß-O-4 linkages cleaved significantly. However, the repolymerization is promoted simultaneously, and a high amount of ß-ß groups form. These reactions are in constant competition with each other and the repolymerization is preferred at excessive high temperature, producing bulk char residues, that is coking. This study will provide a beneficial reference for the maximization of lignin waste valorization.

Investigation on the structural effect of lignin during the hydrogenolysis process.

Structure has a significant effect on the lignin degradation, so the investigation of structural effect on the lignin depolymerization is important and imperative. In this study, hydrogenolysis of three typical lignins with different structures, dealkaline lignin, sodium lignosulfonate and organosolv lignin, was intensively compared over the synergistic catalyst of CrCl3 and Pd/C. The effects of reaction temperature, time, hydrogen pressure and catalyst dosage on the catalytic performance of lignin species were investigated. The structure evolution of lignins during the hydrogenolysis process was also compared. The results showed that organosolv lignin was more sensitive for hydrogenolysis than others due to its high unsaturation degree and low molecular weight. Further analysis indicated that the hydrogenolysis, hydrodeoxygenation and repolymerization reactions took place and competed intensely. Wherein, the depolymerization products with unsaturated carbonyl groups were prone to repolymerize. And the methylation was helpful to stabilize the depolymerization products and suppress the further repolymerization.

Efficient and product-controlled depolymerization of lignin oriented by metal chloride cooperated with Pd/C.

An efficient lignin depolymerization process with highly controllable product distribution was presented using metal chloride (MClx) cooperated with Pd/C. The catalytic performances of MClx were investigated. The effect of reaction conditions on the lignin depolymerization and products distribution were also studied. Results showed that more than 35.4% yield of phenolic monomer including 7.8% phenols and 1.1% guaiacols could be obtained under optimized condition. And the product distribution can be efficiently controlled by the modification of the metal cation through different pathway of Lewis acid catalysis and coordination catalysis. Furthermore, the Pd/C catalyst showed an excellent recyclability, where no significant loss of the catalytic activity was exhibited after 3 runs. Moreover, the product control mechanism was proposed.