Catalyst For H2 Production Research Articles

ZnO with Different Morphologies Sensitized by Metalloporphyrins as Catalysts for H2 Production by Water Splitting Under Sunlight.

In this work, zinc oxide with different morphologies and textural properties were prepared and sensitized with metalloporphyrins (MPs) aiming to improve its solar energy harvesting capability for H2 production by water splitting under sunlight (a 300 W Xe/Hg lamp). An anionic iron(III)porphyrin and a cationic manganese(III)porphyrin were immobilized on different ZnO solids predominantly by electrostatic interactions. In general, the prepared MP-free ZnO solid yielded modest catalytic results which had apparently no direct correlation with their textural properties or morphology. On the other hand, when these ZnO solids had iron or manganese porphyrin sensitizing them, their catalytic performances changed and a superior yield towards H2 production was observed in comparison to the pure ZnO solids, making evident the synergy achieved between these two components (ZnO and metalloporphyrins) for the prepared solids. It was also observed that the metalloporphyrins and the respective free-base ligand suffered redox reactions when used as homogenous catalyst in this reaction, which could influence their performances as catalysts. The same was not observed in the solids containing immobilized MP, suggesting some protective effect of the ZnO solids on the MP complexes upon immobilization probably due to interaction of the complexes with the ZnO matrix.

The catalytic decomposition of CH4 using Ce-doped Fe/CaO-Ca12Al14O33 catalyst and its regeneration performance for H2 production

The catalytic decomposition of CH4 using low cost and non-toxicity Fe-based catalysts is a prospective method for H2 production. The regeneration process of iron-based catalysts involves CO2 emission and incomplete conversion of carbon deposition. In this work, a novel catalytic decomposition of CH4/regeneration process was proposed using the Ce-doped Fe/CaO-Ca12Al14O33 catalyst for H2 production. To remove the carbon deposition in the catalyst, the regeneration stage includes four steps: solid carbon production by vibratory separation, steam gasification of residual carbon deposition to produce H2 where CO2 is captured by CaO to form CaCO3, calcination of CaCO3 to produce CaO and pure CO2, methanol production by CO2 and H2 from carbon deposition gasification. The effects of Ce doping on the catalysis/regeneration performance of Fe/CaO-Ca12Al14O33 catalysts were studied, and the Ce-doped Fe/CaO-Ca12Al14O33 catalyst was compared with Cu-, Zn-, and Mn- doped Fe/CaO-Ca12Al14O33 catalysts. The solid carbon obtained from the catalytic decomposition of CH4/regeneration cycles was characterized. The Ce-doped Fe/CaO-Ca12Al14O33 catalyst shows excellent catalysis, CO2 capture, and stability performance in the catalytic decomposition of CH4/regeneration cycles. The average CH4 conversion is 90.02% in the first cycle, which decreases to 80.01% after 8 cycles. Carbon nanotubes are the main forms of obtained solid carbon with the favorable pore structure. The doping of Ce improves the effective adsorption sites for CH4 and CO2. Carbon deposition in the catalyst is efficiently removed by steam gasification. In addition, CeO2 promotes the electron transfer, oxygen vacancy generation, and Fe3C decomposition, which leads to superior catalytic performance and resistance to deactivation of the catalyst. The CeO2-doped Fe/CaO-Ca12Al14O33 catalyst is promising for H2 production via catalysis/regeneration cycles.

CoMo/g-C3N4 as a highly effective, reusable, non-noble metal-based catalyst for H2 production via NaBH4 hydrolysis focused on stationary application under mild conditions: A kinetic study

Among hydrogen storage chemicals for proton exchange membrane fuel cells (PEMFCs), sodium borohydride stands out for yielding exceptionally pure hydrogen. This study synthesized cobalt-molybdenum catalysts supported on g-C3N4 using an ultrasonic-assisted impregnation method. Various CoMo/g-C3N4 catalysts with different CoMo mass ratios were created, all showing high hydrogen production and complete NaBH4 conversion under mild conditions. Catalytic activity depends on the cobalt-molybdenum mass ratio, with optimal performance at a 1:1 ratio (w/w), maintaining up to 83% activity over 5 cycles. The effect of operating conditions on hydrogen release was explored, resulting in the rate law: rH2 = 1.708 × 10-3 [NaBH4]1.25 [Catalyst dosage]1.39 [NaOH]0.44 at 298 K, with a low activation energy of 22.9 kJ mol−1. Molybdenum's promoting effect prevented significant deactivation of the cobalt catalyst, ensuring complete NaBH4 conversion to H2 and good stability over multiple cycles.

In-situ prepared co exsolution nano catalyst for efficient hydrogen generation via ammonia decomposition

Active and durable catalytic material for ammonia (NH3) decomposition reaction is attracting attentions for utilization of NH3 as an innovative hydrogen carrier. In this study, diverse single metal and alloy nano catalysts are prepared via in-situ exsolution method and their NH3 decomposition properties are evaluated. Transition metal cations (Ni, Co, Fe ions) are doped into the La0.43Ca0.37MxNyTi1-(x+y)O3-δ (LCMNT) perovskite oxide structure and exsolved on its surface as supported nano particles under reduction condition. The maximum doping level and chemical composition of exsolution catalysts are investigated to optimize their NH3 decomposition activity. The exsolution catalyst demonstrates improved NH3 decomposition characteristics compared to conventionally prepared infiltration catalysts, indicating higher conversion efficiency and H2 production rate. The exsolved nano catalysts also exhibit great thermochemical stability against catalyst agglomeration or surface nitriding. The results obtained in this study suggest the potential utilization of exsolution catalysts for on-site production of H2 through NH3 decomposition catalysis.

Expedited Proton Relay in Enzyme-Inspired Cobaloximes Facilitate Organic Transformations.

Developing a water-soluble, oxygen-tolerant, and acid-stable synthetic H2 production catalyst is vital for renewable energy infrastructure. To access such an effective catalyst, we strategically incorporated enzyme-inspired, multicomponent outer coordination sphere elements around the cobaloxime (Cl-Co-X) core with suitable axial coordination (X). Our cobaloximes with axial imidazole or L-histidine coordination in photocatalytic HAT including the construction of anilines via a non-canonical cross-coupling approach is found superior compared to commonly used cobaloxime catalysts. The reversible Co(II)/Co(I) process is influenced by the axial N ligand's nature. Imidazole/L-histidine with a higher pKa promptly produces H2 upon irradiation, leading to the improved reactivity compared to previously employed axial (di)chloride or pyridine analogue.

Double-Ligand [Fe/PNP/PP3] and Their Hybrids [Fe/SiO2@PNP/PP3] as Catalysts for H2-Production from HCOOH

Two types of iron-based catalysts, [Fe/SiO2@iProPNP/PP3] and [Fe/SiO2@tBuPNP/PP3], for the dehydrogenation of formic acid (FADH), were synthesized. These catalysts were developed using a double-ligand approach combining a PNP ligand and a PP3 ligand, demonstrating functionality without the need for additional cocatalysts or additives. Furthermore, hybrid catalysts [Fe/SiO2@iProPNP/PP3] and [Fe/SiO2@tBuPNP/PP3] were created by covalently grafting PNP ligands onto SiO2 particles. The hybrid [Fe/SiO2@iProPNP/PP3] exhibited enhanced recyclability, with turnover numbers (TONs) exceeding 74,000. In situ ATR-FTIR and UV-Vis spectroscopies were used to monitor the structure and dynamics of the catalysts under catalytic conditions, revealing the formation of active catalysts through the involvement of all components: [Fe (metal)/PNP (first ligand)/PP3 (second ligand)/FA (substrate)], which are crucial to FADH catalysis. An Arrhenius study revealed that the hybrid [Fe/SiO2@iProPNP/PP3] had a lower activation energy (Ea = 42.5 kJ/mol) compared to its homogeneous counterpart (Ea = 48.2 kJ/mol), indicating superior catalytic performance. Conversely, [Fe/SiO2@tBuPNP/PP3] showed an increased activation energy (Ea = 48.3 kJ/mol) compared to its homogeneous form (Ea = 46.4 kJ/mol). This study discusses the differing roles of tBuPNP and iProPNP in catalyst configuration, highlighting the potential of double-ligand catalysts to enhance the performance and recyclability of PNP ligands in FADH, offering significant implications for the development of efficient and reusable catalytic systems.

Oxygen vacancy engineering in ZnO/ZrO2 composite catalysts for highly enhanced hydrogen production by methanol steam reforming

The ZnO/ZrO2 binary catalyst system has been an emerging and promising catalyst for efficient production of H2 through methanol steam reforming (MSR). Herein, ZrO2 supports with different crystalline phases were prepared by the oxygen vacancy engineering strategy of Li doping, and then ZnO/ZrO2 catalysts were prepared by the isovolumic impregnation method. The different quantities of doped Li have been found to have a significant impact on dominant crystal phase of ZrO2 supports, which dictates the interaction between ZnO and ZrO2 and the number of oxygen vacancies. In comparison with ZnO/ZrO2-20Li and ZnO/ZrO2-40Li catalysts with predominate tetragonal and monoclinic crystal phase, ZnO/ZrO2-3Li with a mixed crystalline phase exhibits higher catalytic activity for methanol conversion (XCH3OH) and CO selectivity (SCO). Complete methanol conversion of the best performing ZnO/ZrO2-3Li catalyst was observed at a very low CO selectivity of 3.1 % at 375 ℃. The XRD, UV, and XPS characterization results indicate that the strong interaction between ZrO2 and ZnO leads to the appearance of large amount of oxygen vacancies at the ZnO/ZrO2 interface, which greatly improves the performance of the catalyst. ZnO/ZrO2 catalyst showed remarkable stability without obvious deactivation after 32 hours of continuous testing. This work highlights the effectiveness of oxygen vacancy engineering of the ZnO/ZrO2 catalysts for applications in methanol steam reforming and other heterogeneous catalytic systems.

Stable Pt/MgAl2O4 catalysts for efficient production of H2 from cyclohexane dehydrogenation

Cyclohexane as liquid organic hydrogen carriers has attracted considerable interest in the field of hydrogen storage technology. However, the innovation of efficient catalyst for producing H2 through cyclohexane dehydrogenation remains a substantial challenge. In this study, we have successfully developed Pt/MgAl2O4 catalysts exhibiting outstanding catalytic performance in cyclohexane dehydrogenation. Notably, the optimal catalyst Pt/MgAl2O4-700 achieves cyclohexane conversion of 89.1 % and benzene selectivity of over 99 % at 345 °C, resulting in a high hydrogen evolution rate of 933 mmol/gPt/min. Moreover, this catalyst exhibits remarkable long-term stability, with no evident loss of activity in 225-hour dehydrogenation reaction. The catalyst was characterized by XRD, N2 adsorption–desorption, STEM, XPS, NH3-TPD, CO-FTIR and H2-TPR techniques, which provides detailed structure information for elucidation of structure–activity relationship. The spinel structure and moderate acid density of the support enable highly dispersed Pt species at the surface of MgAl2O4. This results in the formation of ultra-small and sintering-resistant Pt particles that exhibit exceptional activity in cyclohexane dehydrogenation. Additionally, the presence of positively charged Ptδ+ species in Pt/MgAl2O4 facilitates the rapid desorption of benzene product. This effectively prevents the formation of coke arising from benzene dehydrogenation, which ensures to achieve high stability. These findings provide valuable knowledge for the rational design of efficient metal-based catalysts for liquid organic hydrogen carriers in hydrogen storage systems.

Experimental study on Finding stable catalytic methane decomposition for hydrogen production

This study attempts to find active and stable catalysts for H2 production from catalytic methane decomposition (CMD). Experimental results show that metal-based (Ni, Fe, and Ni–Fe alloy) and carbon-based (biochar and activated carbon) catalysts are gradually deactivated due to carbon deposition during the CMD reaction. Although the CMD performance can be enhanced using bimetallic catalysts supported by either metal oxide (Al2O3) or activated carbon, deactivation due to carbon deposition is still inevitable. It was also found the carbon-based carbon catalyst has lower activity as compared with the metal-based catalysts. When using commercially available nickel foams with pore per inch (PPI) higher than 90 as the catalysts, stable H2 production can be obtained. The reasons for obtaining the stable CMD are attributed to high surface area and catalyst active sites, better heat transfer characteristics, and enhanced Ni dispersion of Ni. For the reaction temperature of 900 °C and the nickel foam with a PPI of 110, the stable methane conversion of 90% can be obtained without COx production.

Palladium‐Silver Alloys Deposited on Different Carriers for Dehydrogenation of Formic Acid

AbstractHydrogen (H2) is recognized as a clean energy carrier with great potential for the future energy systems. Given the existing challenges in direct H2 storage and delivery, the current option for utilizing hydrogen energy is to produce hydrogen from its storage carriers on‐site, and the development of a highly active, highly selective, and highly stable catalyst for H2 production is an important part of this. Herein, PdAg alloy was deposited on mesoporous carbon nitride (mpg‐C3N4) as a catalyst for the dehydrogenation of the formic acid (FA). The synergistic effect of Pd and Ag metals for catalysis was explored. The role of the supports on the catalytic performance was also demonstrated by depositing PdAg alloy on several carriers of Silica@Resorcinol‐Formaldehyde Spheres, Carbon Flower Particles and SBA‐15. Pd1Ag1/2/mpg‐C3N4 showed a considerable activity during FA dehydrogenation with a turnover frequency (TOF) value of 887 h−1 at 333 K, demonstrating that carbon nitride as a carrier has a significant enhancement on the catalytic hydrogen production from formic acid.

Replacing a Cysteine Ligand by Selenocysteine in a [NiFe]-Hydrogenase Unlocks Hydrogen Production Activity and Addresses the Role of Concerted Proton-Coupled Electron Transfer in Electrocatalytic Reversibility.

Hydrogenases catalyze hydrogen/proton interconversion that is normally electrochemically reversible (having minimal overpotential requirement), a special property otherwise almost exclusive to platinum metals. The mechanism of [NiFe]-hydrogenases includes a long-range proton-coupled electron-transfer process involving a specific Ni-coordinated cysteine and the carboxylate of a nearby glutamate. A variant in which this cysteine has been exchanged for selenocysteine displays two distinct changes in electrocatalytic properties, as determined by protein film voltammetry. First, proton reduction, even in the presence of H2 (a strong product inhibitor), is greatly enhanced relative to H2 oxidation: this result parallels a characteristic of natural [NiFeSe]-hydrogenases which are superior H2 production catalysts. Second, an inflection (an S-shaped "twist" in the trace) appears around the formal potential, the small overpotentials introduced in each direction (oxidation and reduction) signaling a departure from electrocatalytic reversibility. Concerted proton-electron transfer offers a lower energy pathway compared to stepwise transfers. Given the much lower proton affinity of Se compared to that of S, the inflection provides compelling evidence that concerted proton-electron transfer is important in determining why [NiFe]-hydrogenases are reversible electrocatalysts.

Controlled dispersion of Ni catalyst on N-doped carbon support for stable and selective hydrogen production from formic acid

Formic acid is a liquid organic hydrogen carrier from which hydrogen can be released together with CO2 by catalytic decomposition. The development of supported Ni catalysts for H2 production is important. Here, the effects of Ni state/dispersion are considered. For this purpose, three samples were prepared with about 3 wt% Ni deposited on porous N-doped carbon. The first sample contained predominantly Ni nanoparticles (∼2 nm), the second contained Ni clusters (<1 nm), and the third – single-atom Ni sites. The catalysts showed close activity in the gas-phase reaction. However, a minimum apparent activation energy of 105 kJ/mol and a maximum selectivity towards H2 production of 99% were achieved for the single-atom Ni catalyst. The nature of its single-atom sites was established to correspond to Ni-N4 and Ni-O4, which showed greater stability under the conditions of the catalytic reaction.

A novel high-entropy spinel ferrites (CoNiCuZnMg)Fe2O4 catalyst for H2 production via steam reforming of derived volatiles from polypropylene and waste cooking oil

Municipal organic waste conversion to high-value products is a vital carbon–neutral way to simultaneously tackle the energy crisis and environmental contamination. This study aims to develop and evaluate a novel high-entropy spinel ferrites (Co0.2Ni0.2Cu0.2Zn0.2Mg0.2)Fe2O4 catalyst (HEO) toward H2 production from co-pyrolysis volatiles of polypropylene (PP) and waste cooking oil (WCO) in an integrated two-stage reactor system. In the 1st stage of medium temperature reforming, the optimal 3:7 PP/WCO blend mass ratio facilitated H2 production. Under a catalytic reforming at high temperature of 750 °C in the 2nd stage, the HEO catalyst demonstrated remarkable efficiency, yielding 58.43 mmol·g−1 of H2 with a composition of 65.17 %, a notable 22.3 times higher than that without HEO. The catalyst exhibited a prolonged service life of 540 min without compromising H2 selectivity, maintaining a high yield of 510.2 mmol·gcat.−1·s−1. The exceptional performance of HEO arises from the synergistic effects of multiple elements, augments oxygen vacancy, enhances reducibility, and promotes structural stability in the high-entropy system, which causes the strong C–C breaking ability and the excellent C–H breaking abilities of Fe, Ni, Co, Cu, and Zn species. The analysis of tar, gaseous products, and deactivated HEO catalyst characterization results provides a comprehensive understanding of the co-pyrolysis route and volatiles catalytic reforming process. This study developed a high-entropy ferrite catalyst that not only achieves efficient and stable H2 production but also lays the foundation for a new high-entropy catalyst design concept, fostering the development of efficient reforming catalysts for H2 production.

Tailoring Second Coordination Sphere for Tunable Solid–Liquid Interfacial Charge Transfer toward Enhanced Photoelectrochemical H2 Production

AbstractThe recombination of photogenerated charge carriers severely limits the performance of photoelectrochemical (PEC) H2 production. Here, we demonstrate that this limitation can be overcome by optimizing the charge transfer dynamics at the solid–liquid interface via molecular catalyst design. Specifically, the surface of a p‐Si photocathode is modulated using molecular catalysts with different metal atoms and organic ligands to improve H2 production performance. Co(pda‐SO3H)2 is identified as an efficient and durable catalyst for H2 production through the rational design of metal centers and first/second coordination spheres. The modulation with Co(pda‐SO3H)2, which contains an electron‐withdrawing −SO3H group in the second coordination sphere, elevates the flat‐band potential of the polished p‐Si photocathode and nanoporous p‐Si photocathode by 81 mV and 124 mV, respectively, leading to the maximized energy band bending and the minimized interfacial carrier transport resistance. Consequently, both the two photocathodes achieve the Faradaic efficiency of more than 95 % for H2 production, which is well maintained during 18 h and 21 h reaction, respectively. This work highlights that the band‐edge engineering by molecular catalysts could be an important design consideration for semiconductor–catalyst hybrids toward PEC H2 production.

Tailoring Second Coordination Sphere for Tunable Solid-Liquid Interfacial Charge Transfer toward Enhanced Photoelectrochemical H2 Production.

The recombination of photogenerated charge carriers severely limits the performance of photoelectrochemical (PEC) H2 production. Here, we demonstrate that this limitation can be overcome by optimizing the charge transfer dynamics at the solid-liquid interface via molecular catalyst design. Specifically, the surface of a p-Si photocathode is modulated using molecular catalysts with different metal atoms and organic ligands to improve H2 production performance. Co(pda-SO3H)2 is identified as an efficient and durable catalyst for H2 production through the rational design of metal centers and first/second coordination spheres. The modulation with Co(pda-SO3H)2, which contains an electron-withdrawing -SO3H group in the second coordination sphere, elevates the flat-band potential of the polished p-Si photocathode and nanoporous p-Si photocathode by 81 mV and 124 mV, respectively, leading to the maximized energy band bending and the minimized interfacial carrier transport resistance. Consequently, both the two photocathodes achieve the Faradaic efficiency of more than 95 % for H2 production, which is well maintained during 18 h and 21 h reaction, respectively. This work highlights that the band-edge engineering by molecular catalysts could be an important design consideration for semiconductor-catalyst hybrids toward PEC H2 production.

Fabrication of graphene-incorporated tin-niobate-doped zinc oxide for highly enhanced photocatalytic hydrogen evolution and degradation

This study focuses on designing, synthesizing, and characterizing an innovative graphene-based Sn2Nb2O7-ZnO. Ternary Sn2Nb2O7-ZnO with graphene is added to a catalyst, enhancing the efficiency of visible-light photocatalytic hydrogen (H2) evolution and ciprofloxacin (CIP) degradation in an aqueous solution. It also facilitates easier charge transfer and control over electron-hole recombination between light-harvesting processes. Additionally, the UV–vis shows that rGO doping can be used to tune significant visible light absorption in addition to the effective charge transmission channel of Sn2Nb2O7-rGO-ZnO nanorods. Under visible light, Sn2Nb2O7-rGO-ZnO nanorods demonstrate expected photocatalytic hydrogen evolution and CIP degradation of 1240 μmol·h−1·g−1, a 96% increase over pure catalysts. Photocatalytic H2 production over Sn2Nb2O7-rGO-ZnO is assessed using transient photocurrent response, suggesting a possible mechanism. Owing to the type II process ability, more electrons can participate in the H2 evolution reduction and CIP degradation. Furthermore, it has the potential to completely replace the present base metal as an incredibly powerful and long-standing light radiation-based photocatalyst. In this study, we prepared catalysts that are more stable and highly efficient up to a six-cycle test, non-toxic, low-cost catalysts for H2 production and CIP degradation.

The synthesis and characterization of carbon nanotube-supported CuBi catalyst for H2 production from NaBH4 methanolysis

In this study, carbon nanotube (CNT) supported bimetallic CuBi catalysts are synthesized by sodium borohydride (SBH, NaBH4) reduction method at different atomic molar ratios. X-ray diffraction (XRD), scanning electron microscopy and X-ray energy dispersion (SEM-EDX), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD) analytical techniques have been characterized for the synthesized catalysts. The effects of temperature and catalyst, methanol, and NaBH4 amounts on the initial hydrogen production rate (HGR) are investigated. The initial HGR of CuBi(80:20)/CNT catalyst is calculated as 37545.6 mL/min.gcat at 25 mg catalyst, 1.5% NaBH4, 10 mL methanol (metOH), and 60 °C temperature (optimum parameters). Furthermore, the activation energy (Ea) calculated from the Arrhenius equation is calculated as 34.72 kJ/mol. As a result, CuBi(80:20)/CNT catalyst is promising as a catalyst for NaBH4 methanolysis.

Cost-Effective Single-Step Synthesis of Metal Oxide-Supported Ni Catalyst for H2-Production Through Dry Reforming of Methane

AbstractPreparing catalysts from cheap metal precursors in a single pot are an appealing method for reducing catalytic preparation costs, minimizing chemical waste, and saving time. With regards to the catalytic conversion of dry reforming of methane, it offers the prospect of significantly reducing the cost of H2 production. Herein, NiO-stabilized metal oxides like Ni/TiO2, Ni/MgO, Ni/ZrO2, and Ni/Al2O3 are prepared at two different calcination temperatures (600 °C and 800 °C). Catalysts are characterized by X-ray diffraction, Raman spectroscopy, surface area-porosity analysis, Temperature program experiments, infrared spectroscopy, and thermogravimetry analysis. The MgO-supported Ni catalyst (Ni/MgO-600), ZrO2-supported Ni catalyst (Ni/ZrO2-600), and Al2O3-supported Ni (Ni/Al2O3-600) catalyst calcined at 600 °C show initial equal H2 yields (~ 55%). The population of CH4 decomposition sites over ZrO2-supported Ni catalyst remains highest, but H2-yield drops to 45% against high coke deposition. The catalytic activity remains constant over the Ni/MgO-600 catalyst due to the enrichment of “surface interacted CO2-species”. MgO-supported Ni catalyst calcined at 800 °C undergoes weak interactions of NiO-M′ (M′ = support), serious loss of CH4 decomposition sites and potential consumption of H2 by reverse water gas shift reaction, resulting in inferior H2 yield. H2-yield remains unaffected over an Al2O3-supported Ni catalyst even against the highest coke deposition due to the formation of stable Ni (which exsolves from NiAl2O4) and proper matching between carbon formation and rate of carbon diffusion.

Feeble Single-Atom Pd Catalysts for H2 Production from Formic Acid.

Single-atom catalysts are thought to be the pinnacle of catalysis. However, for many reactions, their suitability has yet to be unequivocally proven. Here, we demonstrate why single Pd atoms (PdSA) are not catalytically ideal for generating H2 from formic acid as a H2 carrier. We loaded PdSA on three silica substrates, mesoporous silicas functionalized with thiol, amine, and dithiocarbamate functional groups. The Pd catalytic activity on amino-functionalized silica (SiO2-NH2/PdSA) was far higher than that of the thiol-based catalysts (SiO2-S-PdSA and SiO2-NHCS2-PdSA), while the single-atom stability of SiO2-NH2/PdSA against aggregation after the first catalytic cycle was the weakest. In this case, Pd aggregation boosted the reaction yield. Our experiments and calculations demonstrate that PdSA in SiO2-NH2/PdSA loosely binds with amine groups. This leads to a limited charge transfer from Pd to the amine groups and causes high aggregability and catalytic activity. According to the density functional calculations, the loose binding between Pd and N causes most of Pd's 4d electrons in amino-functionalized SiO2 to remain close to the Fermi level and labile for catalysis. However, PdSA chemically binds to the thiol group, resulting in strong hybridization between Pd and S, pulling Pd's 4d states deeper into the conduction band and away from the Fermi level. Consequently, fewer 4d electrons were available for catalysis.

Hydrolysis of NaBH4 using carbonized melamine foam-supported cobalt borate composite catalyst for H2 production

Catalysts are crucial for the hydrolysis of NaBH4, and noble metal catalysts cannot be used in large-scale NaBH4 hydrolysis because of their high cost. Therefore, developing low-cost, high-activity, non-precious metal catalysts is the focus of current research. In this study, a composite catalyst with a coral rod-like structure was synthesized by loading CoB particles on the surface of a carbonized melamine foam (CMF)-CoO composite carrier. For preparing CMF-CoO, thick flakes of Co-MOF precursors were grown on CMF and calcined in an inert atmosphere. Then, CoB particles were loaded using a chemical reduction method to obtain the CMF-CoO-CoB catalyst. The morphology and microstructure of the CMF-CoO-CoB catalyst were characterized through scanning electron microscopy and X-ray photoelectron spectroscopy. The catalyst efficiently catalyzes the hydrolysis of NaBH4, providing a hydrogen release rate of 6974 mL∙min−1∙g−1. The activation energy is 35.05 kJ∙mol−1 at 30 °C. In addition, 80.4% of the catalytic activity of CMF-CoO-CoB was retained after five catalytic cycles. The CMF-CoO-CoB catalyst has a significantly higher activity and better cycling stability than the catalyst using a single carrier. Thus, the CMF-CoO-CoB composite catalyst with excellent performance has high potential for application in the hydrolysis of NaBH4.