Highest H2 Yield Research Articles

Effect of Fe-loading in iron-based catalysts for the CH4 decomposition to H2 and nanocarbons

The catalytic CH4 decomposition (CMD) over Fe-based catalyst is an economical and environmentally friendly way to produce Cox-free H2 and carbon nanotubes (CNTs). The Fe-loading was varied to study its influence on the catalytic performance. The highest H2 yield (82.25%) was obtained with a 12% Fe content where the activity of the catalyst did not decrease for 3 h on-stream. A higher Fe content causes the Fe dispersion to decrease, resulting in a reduced available surface area of active sites. Different techniques were used to characterise the fresh and spent catalysts i.e., ICP-AES, XRD, H2-TPR, SEM, TEM, and Raman spectroscopy. Plotting kinetic results as a function of 1/T, defines two different conversion ranges, being reaction rate controlled at low temperature and diffusion rate controlled at high temperature. For the reaction rate controlled regime, the Arrhenius equation provides an activation energy of 101.26 kJ/mol (Ea) and a pre-exponential factor of 393 kmol/s (A).

Catalytic ammonia decomposition to produce hydrogen: A mini-review

Hydrogen (H2) is considered one of the most promising alternative energy resources instead of fossil fuels, serving as a clean energy carrier. Ammonia (NH3) is regarded as a high percentage hydrogen carrier and utilized as an initial material for H2 production. As for the H2 production through NH3 decomposition, there are various catalytic processes particularly using Ru- and Pd-based catalysts. The Ru- and Ni-based NH3 decomposition catalysts have been studied due to synergetic effect of active metal phase in stabilizing unstable nitrogen intermediate species during NH3 decomposition reaction. The Pd catalyst-based membrane reactors were developed to enhance H2 separation from the product stream of NH3 decomposition. Integrated systems combining Ru catalyst and Pd-based membrane were also explored to achieve a high yield of H2 from NH3. This review summarizes recent literatures on catalytic NH3 decomposition to produce H2. It probably provides useful insights into designing large-scale H2 production processes.

Advancement in steam reforming of methanol to produce hydrogen: A review

The main deliberation of this review paper is on metallic catalysts, including Cu-based catalysts, with distinct formulations and compositions, utilized for steam reforming of methanol (SRM). The review critically examines the performance of these catalysts, considering the active components, supports, promoters, and their interactions. Additionally, the review identifies and elucidates the various kinds of reaction mechanisms and routes involved in SRM. This comprehensive analysis provides valuable insights into the progress of well-organized and effective catalysts for SRM. To achieve high yields of H2, it is crucial to conduct a fundamental study of the role of copper as a component in both mono and multimetallic systems, as well as the nature of support. These factors are essential to understand the catalytic mechanisms involved in the steam reforming of methanol and to develop effective strategies for optimizing hydrogen production. Therefore, a thorough investigation of copper-based catalysts and their interaction with the support material is essential for the development of highly efficient steam reforming processes.

Defects influence photocatalytic NOCM product selectivity by controlling photogenerative carriers

Photocatalytic Non-oxidative coupling of methane (NOCM) is a green method to convert methane into high value-added products such as ethane and ethylene by using photogenerated electron-holes. Compared with oxidative coupling of methane (OCM), besides C2 products, H2 is also produced in NOCM process. However, the effect of the photogenerative carriers on the yield and selectivity of photocatalytic NOCM products is still unclear. We tested Au1-ZnO/TiO2 synthesized by NaBH4 reduction and photodeposition in a flowing gas reactor at atmospheric pressure without external heat source. The Au1-ZnO/TiO2-N sample showed a superior C2H6 yield of 0.015 mmol/h accompanied by a small amount of H2 production (1.32 μmol/h). Meanwhile, Au1-ZnO/TiO2-p120 sample shows much higher H2 yield (0.012 mmol/h) and a lower C2H6 yield (4.96 μmol/h). Through varies characterizations, we demonstrated that the selectivity of C2H6 and H2 are highly related to photogenerative carriers. We propose that defects affect the degree of peroxidation in photocatalytic NOCM by controlling the concentration of photogenerated holes.

Effect of zero-valent iron nanoparticles on taxonomic composition and hydrogen production from kitchen waste

This study investigated the effects of varying zero-valent iron (ZVI) (0 to 5,000 mg/L) on fermentative hydrogen (H2) production, metabolic pattern, and taxonomic profile by using kitchen waste as substrate. The study demonstrated that the supplementation of 500 mg ZVI/L resulted in the highest H2 yield (219.68 ± 11.19 mL H2/g-volatile solids (VS)added), which was 19% higher than the control. The metabolic pattern analysis showed that acetic and butyric acid production primarily drove the H2 production. The taxonomic analysis further revealed that Firmicutes (relative abundance (RA): 80–96%) and Clostridium sensu stricto 1 (RA: 68–88%) were the dominant phyla and genera, respectively, during the exponential gas production phase, supporting the observation of accumulation of acetic and butyric acids. These findings suggest that supplementation of ZVI can enhance H2 production from organic waste and significantly influence the metabolic pattern and taxonomic profile, including the metalloenzymes.

Integrated biohydrogen production and dairy manure wastewater treatment via a microalgae platform

The present study aimed to investigate the feasibility of sustainable biohydrogen production from dairy manure wastewater using a microalgae platform to achieve simultaneous wastewater treatment and clean energy production. Compared to single-stage microalgae cultivation, two-stage cultivation of indigenous wastewater bacteria and carbohydrate-rich microalgae Chlorella vulgaris ESP-6 achieved satisfactory removal of nutrients and chemical oxygen demand. The resulting biomass, with high carbohydrate content (48.8 ± 2.3%), was used as alternative feedstock for biohydrogen production by Clostridium butyricum CGS5 via dark fermentation after thermal acid pretreatment. The implementation of an automatic pH control strategy significantly promoted H2 generation, resulting in a hydrogen yield of 211 mL/g VS and a maximum productivity of 391.1 mL/L/h. To the best of our knowledge, this is the first integrated study of dairy manure wastewater treatment and biohydrogen production with high H2 yield and productivity comparable to those reported in the literature.

Constructing bifunctional porous nanosheets for efficient conversion of waste plastics into valuable hydrogen and carbons

Metal oxides as promoting materials can convert waste plastics into hydrogen (H2) fuel by microwave pyrolysis, solving ecological pollution worldwide, but their tendency of agglomeration and poor porosity limit further applications. Herein, we reported a two-dimensional (2D) metal oxide nanosheets with porous network for recycling high-purity hydrogen and carbon nanotubes from waste plastics in microwave-induced reaction. The 2D porous structure significantly improves the growing space of CNTs and enhances the ability of wave absorption, thereby exhibiting a remarkable H2 selectivity of 87.5% and high H2 yield of 60.2 mmol g−1 LDPE, as well as producing high-value CNTs. Moreover, the reaction mechanism for microwave-induced catalytic pyrolysis is proposed, where the Fe2O3 particles on composites facilitated the breakage of C-H bonds, contributing to the generation of H2. The current work provides new insights into the recovery of waste plastics by metal oxides through microwave pyrolysis.

Magnetic nitrogen-doped activated carbon improved biohydrogen production.

Low biological hydrogen (bioH2) production due to non-optimal metabolic pathways occurs frequently. In this work, magnetic nitrogen-doped activated carbon (MNAC) was prepared and added into the inoculated sludge with glucose as substrate to enhance hydrogen (H2) yield by mesophilic dark fermentation (DF). The highest H2 yield appeared in 400 mg/L AC (252.8 mL/g glucose) and 600 mg/L MNAC group (304.8 mL/g glucose), which were 26.02% and 51.94% higher than that of 0 mg/L MNAC group (200.6 mL/g glucose). The addition of MNAC allowed for efficient enrichment of Firmicutes and Clostridium-sensu-stricto-1, accelerating the metabolic pathway shifted towards butyrate type. The Fe ions released by MNAC facilitated electron transfer and favored the reduction of ferredoxin (Fd), thereby obtaining more bioH2. Finally, the generation of [Fe-Fe] hydrogenase and cellular components of H2-producing microbes (HPM) during homeostasis was discussed to understand on the use of MNAC in DF system.

Triphenylphosphine ruthenium (RuP) complex anchored with exfoliated g-C3N4 (ECN) with an externally reflected solar photoreactor system for highly efficient solar H2 production

Designing an efficient photocatalytic system capable of higher photocatalytic efficiency for hydrogen production is extremely challenging. In the current study, a triphenylphosphine ruthenium (RuP) complex as a cocatalyst with exfoliated g-C3N4 nanosheets (ECN) and an externally reflected solar photoreactor has been investigated for photocatalytic H2 production. With the alternate morphology of g-C3N4, both the specific surface area and charge separation efficiency were enhanced. The ruthenium (RuP) complex attached to ECN (RuP/ECN) enables efficient visible light absorption due to works as a photosensitizer to yield more hydrogen. The 3% RuP/ECN exhibited excellent photocatalytic efficiency, and optimal H2 yield reached up to 1705 µmol g−1 with QY 2.85 %, 23.4 and 334 folds more than attained with pure ECN and bulk g-C3N4, respectively. Due to the exfoliated structure with photosensitization and oxygen vacancies, the photoactivity was greatly increased for visible light assisted H2 evolution. Furthermore, using an externally reflected solar photoreactor system, H2 yield was significantly improved due to concentrating more light irradiations inside the slurry system even at lower light intensity. Using the traditional and externally reflected solar systems, the critical operational parameters, including sacrificial reagents, feed concentration, and catalyst loading, were further explored. Mass transfer, charge transfer, and amount of photoinduced charges were greatly dependent on the operating parameters. The highest H2 yield with lower catalyst loading and feed concentration was obtained with an externally reflected solar system. This study introduces a new technique to manufacturing porous materials and creating an effective photoreactor system that might be advantageous to boost performance in other solar energy-related applications.

Energy recovery from agro-forest wastes through hydrothermal carbonization coupled with hydrothermal co-gasification: Effects of succinic acid on hydrochars and H2 production

Aiming to upgrade agro-forest wastes into value-added solid and gaseous fuels in the present investigation, hydrothermal carbonization (HTC) of spruce (SP), canola hull (CH), and canola meal (CM) was optimized in terms of operating conditions, maximizing the higher heating value of hydrochars. The optimal operating conditions were achieved at HTC temperature, reaction time, and solid-to-liquid ratio of 260 °C, 60 min, and 0.2 g mL−1, respectively. At the optimum condition, succinic acid (0.05–0.1 M) was used as HTC reaction medium to investigate the effects of acidic medium on the fuel characteristics of hydrochars. The succinic acid assisted HTC was found to eliminate ash-forming minerals e.g., K, Mg, and Ca from hydrochar backbones. The calorific values, H/C and O/C atomic ratios of hydrochars were in the range of 27.6–29.8 MJ kg−1, 0.8–1.1, and 0.1–0.2, respectively, indicating the biomass upgrading into coal-like solid fuels. Finally, hydrothermal gasification of hydrochars with their corresponding HTC aqueous phase (HTC-AP) was assessed. Gasification of CM resulted in a relatively high H2 yield of 4.9–5.5 mol kg−1 followed by that for SP with 4.0–4.6 mol H2 per kg of hydrochars. Results suggest that hydrochars and HTC-AP have a great potential for H2 production via hydrothermal co-gasification, while suggesting HTC-AP reuse.

Comparison of Hydrogen Production Efficiency by Rhodopseudomonas palustris MP3 and Rhodopseudomonas harwoodiae SP6 Using an Iron Complex as an Enhancement Factor

In the present study, an iron(II)-nanoscale organic complex (Fe-NO) was used as an enhancement factor by two different Rhodopseudomonas species of purple non-sulphur bacteria (PNSB) to produce hydrogen (H2). The Fe-NO complex was synthesised using FeSO4·7H2O and Eucalyptus viminalis—a native Australian plant leaf extract—in a 1:2 and 2:1 concentration ratio. Besides, FeSO4·7H2O was also used as a source of iron(II) for comparison with the Fe-NO complex. The photo-fermentative bacterial cultures were isolated from a fishpond, and only two strains, MP3 and SP6, were found viable after several attempts of quadrate streaking. After phylogenetic analysis, these strains were designated as R. palustris MP3 and R. harwoodiae SP6. After comparison with the control, the results showed that the PNSBs manifested an approximately 50% higher H2 yield when the 1:2 Fe-NO complex was used in the fermentation broth at 10 mg/L concentration, where 10.7 ± 0.54 and 10.0 ± 0.49 mL H2/L were obtained by R. palustris MP3 and R. harwoodiae SP6, respectively. The study revealed that the 1:2 Fe-NO complex could be an important material for efficient H2 production.

Catalytic Steam-Reforming of Glycerol over LDHs-Derived Ni-Al Nanosheet Array Catalysts for Stable Hydrogen Production

In the present work, LDHs–derived Ni–Al nanosheet arrays (NiAl/NA) were successfully synthesized via a one–step hydrothermal method, and applied in the steam-reforming of glycerol reaction for enhanced and stable hydrogen production. The physicochemical properties of catalysts were characterized using various techniques, including XRD, SEM–EDS, XPS, N2–physisorption, Raman, and TG–DTG. The results indicate that smooth and cross–linked Ni–Al mixed metal oxide nanosheets were orderly and perpendicularly grown on the Ni foam substrate. The SEM line scan characterization reveals the metal concentration gradient from the bottom to the top of nanosheet, which leads to distinctly optimized Ni valence states and an optimized binding strength to oxygen species. Owing to the improved reducibility and more exposed active sites afforded by its array structures, the NiAl/NA catalyst shows enhanced glycerol conversion (83.1%) and a higher H2 yield (85.4%), as well as longer stability (1000 min), compared to the traditional Ni–Al nanosheet powder. According to the characterization results of spent catalysts and to density functional theory (DFT) calculations, coke deposition is effectively suppressed via array construction, with only 1.25 wt.% of amorphous carbons formed on NiAl/NA catalyst via CO disproportionation.

Iron-promoted zirconia-alumina supported Ni catalyst for highly efficient and cost-effective hydrogen production via dry reforming of methane

Developing cost-effective and high-performance catalyst systems for dry reforming of methane (DRM) is crucial for producing hydrogen (H2) sustainably. Herein, we investigate using iron (Fe) as a promoter and major alumina support in Ni-based catalysts to improve their DRM performance. The addition of iron as a promotor was found to add reducible iron species along with reducible NiO species, enhance the basicity and induce the deposition of oxidizable carbon. By incorporating 1 wt.% Fe into a 5Ni/10ZrAl catalyst, a higher CO2 interaction and formation of reducible "NiO-species having strong interaction with support" was observed, which led to an ∼80% H2 yield in 420 min of Time on Stream (TOS). Further increasing the Fe content to 2wt% led to the formation of additional reducible iron oxide species and a noticeable rise in H2 yield up to 84%. Despite the severe weight loss on Fe-promoted catalysts, high H2 yield was maintained due to the proper balance between the rate of CH4 decomposition and the rate of carbon deposit diffusion. Finally, incorporating 3 wt.% Fe into the 5Ni/10ZrAl catalyst resulted in the highest CO2 interaction, wide presence of reducible NiO-species, minimum graphitic deposit and an 87% H2 yield. Our findings suggest that iron-promoted zirconia-alumina-supported Ni catalysts can be a cheap and excellent catalytic system for H2 production via DRM.

Porous Carbon Aerogel Decorated with TiO2 Quantum Dots for Highly Improved Photocatalytic H2 Evolution

The design of photocatalysts plays a central role in determining the photocatalytic H2 yield. Here, we used a design strategy that is different from conventional methods to prepare our photocatalytic systems. Large porous carbon aerogels (CA) with rich surface areas were used to receive photogenerated electrons. TiO2 quantum dots were used as photocatalysts and anchored on large porous CAs to form CA@TiO2 systems. The H2 yield of the optimized CA@TiO2 composite is ∼2.1 mmol/g, ∼11 times higher than that of pure TiO2 quantum dots. High-resolution X-ray photoelectron spectroscopy and high-angle annular dark-field scanning transmission electron microscopy demonstrate that the photogenerated electrons can be easily transferred from TiO2 quantum dots to porous CAs. Thus, efficient charge separation can be realized for the succeeding highly efficient H2 evolution. Our results here provide a different way from conventional methods to design photocatalytic systems with high H2 yield.

Electric double layer-mediated polarization field for optimizing photogenerated carrier dynamics and thermodynamics

Photocatalytic hydrogen evolution efficiency is limited due to unfavorable carrier dynamics and thermodynamic performance. Here, we propose to introduce electronegative molecules to build an electric double layer (EDL) to generate a polarization field instead of the traditional built-in electric field to improve carrier dynamics, and optimize the thermodynamics by regulating the chemical coordination of surface atoms. Based on theoretical simulation, we designed CuNi@EDL and applied it as the cocatalyst of semiconductor photocatalysts, finally achieved a hydrogen evolution rate of 249.6 mmol h−1 g−1 and remained stable after storing under environmental conditions for more than 300 days. The high H2 yield is mainly due to the perfect work function, Fermi level and Gibbs free energy of hydrogen adsorption, improved light absorption ability, enhanced electron transfer dynamics, decreased HER overpotential and effective carrier transfer channel arose by EDL. Here, our work opens up new perspectives for the design and optimization of photosystems.

Synthesis of a composite Fe–CaO-based sorbent/catalyst by mechanical mixing for CO2 capture and H2 production: An examination on CaO carbonation and tar reforming performance

A composite CaO-based sorbent/catalyst (Fe/CaO-CA, CA stands for Ca12Al14O33) with good cyclic CO2 uptake characteristics, mechanical stability and tar reforming performance for the carbon-negative biomass calcium looping gasification (CLG) technology is prepared by mechanical mixing method. Different synthesis parameters regarding cyclic CO2 capture and Fe/CaO-CA's mechanical strength have been investigated. Different reaction conditions, such as low carbonation temperature, high calcination temperature, long cycles, and large particle size, were also investigated using a thermogravimetric analyzer. Results showed Fe/CaO-CA performed better in mechanical strength and carbonation when it was prepared by calcination at 750 °C for 4 h. In the carbonation temperature range from 650 °C to 850 °C, 750 °C was more favourable to promote CO2 capture during cyclic reactions. Fe/CaO-CA still exhibited promising CO2 uptake characteristics under severe calcination conditions, including high CO2 partial pressure, high temperature and long-term response up to 40 cycles. Additionally, the effect of Fe/CaO-CA on tar removal enhancement was also studied via the reforming of 1-methyl naphthalene (1-MN) by using a self-designed fixed-bed reactor. Fe/CaO-CA presented the maximum 1-MN conversion and the highest H2 yield (0.15 mol h−1 g−1) compared to the other three candidate samples (CaO, CaO-CA and Fe/CaO). Furthermore, Fe/CaO-CA showed the largest CO2 uptake capacity and the least amount of coke deposition during tar reforming.

Advanced application of a geometry-enhanced 3D-printed catalytic reformer for syngas production

Catalyst research on reforming processes for syngas production has mainly focused on the active metals and support materials, while the effect of the catalyst’s geometry on the reforming reactions has been poorly studied. The application of 3D-printed materials with enhanced geometries has recently started to be studied in heterogeneous catalysis and is of interest to be implemented for reforming biomass and plastic waste to produce H2-rich syngas. In this study, a geometry-enhanced 3D-printed Ni/Al2O3/FeCrAl-based monolithic catalyst with a periodic open cellular structure (POCS) was designed and fabricated. The catalyst was used for batch steam reforming biomass pyrolysis volatiles for syngas production at different parameters (temperature and steam-to-carbon ratio). The results showed complete reforming of pyrolysis volatiles in all experimental cases, a high H2 yield of ≈ 7.6 wt% of biomass was obtained at the optimized steam-to-carbon ratio of 8 and a reforming temperature of 800 °C, which is a higher yield compared to other batch reforming tests reported in the literature. Moreover, CFD simulation results in COMSOL Multiphysics demonstrated that the POCS configuration improves the reforming of pyrolysis volatiles for tar/bio-oil reforming and H2 production thanks to enhanced mass and heat transfer properties compared to the regular monolithic single-channel configuration.

Clean treatment and resource utilization of oilfield wastewater using supercritical water gasification

Unconventional oil and gas resources are expected to be recovered efficiently by multi-component supercritical thermal fluid (MCSCTF) which is generated based on supercritical water gasification (SCWG) of oilfield wastewater and hydrogen oxidation technology. In this paper, SCWG experiments of oilfield wastewater were performed under 550–750 °C, 2–15 min, 21–29 MPa, and feedstock concentration of 2–10 wt%. High temperatures, extended residence times, and low concentrations encouraged the production of gases. There was no significant change in SCWG as the pressure changed. The highest H2 yields and carbon gasification efficiency (CE) were 52.31 mol/kg and 97.59%, respectively. The SCWG mechanism was summarized to describe the conversion details. The SCWG of oilfield wastewater has the fastest initial rate to present a trend of deceleration and the activation energy of CE was calculated as 135.7 kJ/mol. The reason for gasification deceleration was explained by the proposed gaseous product kinetics. Small molecules and saturated hydrocarbons etc. (Int 1) can be quickly decomposed while the decomposition of phenols and aromatic hydrocarbons etc. (Int 2) is slower. Inhibition of Int 2 generation and enhanced Int 2 decomposition is the key to total gasification. This work is useful for reactor design and process intensification.

Ruthenium/nickel ex-solved perovskite catalyst for renewable hydrogen production by autothermal reforming of ethanol

Ruthenium/nickel ex-solved perovskite catalysts have been synthesized by incipient impregnation. As-synthesized and spent catalysts have been characterized by XRD, TPR-H2, SEM-EDX and TEM analyses. Reduced catalysts have been tested in the autothermal reforming of ethanol, in the temperature range of 600–800 °C. All tested catalysts gave the total conversion of ethanol in the range of investigated temperatures, confirming the oxidative ability and oxygen storage capacity of perovskite, that promotes the catalyst activation. The highest hydrogen yield (83%) is obtained by ruthenium/nickel ex-solved perovskite containing the 0.5 wt% of Ru (SFMN/0.5Ru catalyst) at 600 °C. Increasing the amount of Ru in the catalyst an inhibiting effect is observed: high Ru content modifies the metal species and their reducibility. H2 yield strongly decreases (lower than the 50%) for the catalyst containing the 1 wt% of ruthenium (SFMN/1Ru catalyst), at all the reaction temperatures tested. At 600 °C, were the highest H2 yield is registered, the coke deposition increases with this order: SFMN/1Ru< SFMN/0.5Ru< SFMN, confirming the positive role of noble catalyst toward the inhibition of carbon species formation. By comparison of all catalytic aspects (ethanol conversion, hydrogen yield, coke deposition and stability) the catalyst showing the best performance is ruthenium/nickel ex-solved perovskite with 0.5 wt% of Ru content (SFMN/0.5Ru).

Effect of the photosynthesis inhibitors on hydrogen production by non-heterocyst cyanobacterial strains

The energy of cyanobacterial hydrogen (H2) produced via bio-photolysis is being investigated as a potential solution to early-century environmental challenges. The main limiting factors of cyanobacterial H2 photoproduction are the availability of electrons for [NiFe]-hydrogenase (H2ase) and the suppression of bidirectional H2ase activity induced by O2 acquired from water molecules splitting in photosystem II. The current study investigated how photosynthetic inhibitors (PIs) affected H2 production in non-N2-fixing cyanobacteria. Study findings revealed a rather high H2 yield in Synechocystis sp. PSU 1262, as well as a beneficial (14.2-fold) influence of 500 μmol KCN on the H2 production by the aforesaid strain. A 12/6-h light/dark cycle increased H2 production by 80.3% in cells supplemented with 500 μmol KCN. Under the optimised conditions, the photobiological H2 production of Synechocystis sp. PSU 1262 increased from 49.6 to 1552 nmol H2 mg−1Chl a h−1. PIs suppressed chlorophyll a concentration under illumination, lowering the O2 levels, which enhanced bidirectional H2ase activity in Synechocystis sp. PSU 1262 cells. Applying varied light modes, preceded by the incorporation of PIs at optimal concentrations in H2 production by research cyanobacterial strains, improved the H2 yield and contributed significantly to the research originality.