In-situ hydrodeoxygenation of phenol by supported Ni catalyst – explanation for catalyst performance

In-situ hydrodeoxygenation of phenol with aqueous hydrogen donor over supported Ni catalyst was investigated. The supported Ni catalysts exerted very poor performance, if formic acid was used as the hydrogen donor. Catalyst modification by loading K, Na, Mg or La salt could not make the catalyst performance improved. If gaseous hydrogen was used as the hydrogen source the activity of Ni/Al₂O₃ was pretty high. CO₂ was found poisonous to the catalysis, due to the competitive adoption of phenol with CO₂. If formic acid was replaced by methanol, the catalyst performance improved remarkably, with major products of cyclohexanone and cyclohexanol. The better effect of methanol enlightened the application of the supported Ni catalyst in in-situ hydrodeoxygenation of phenol.     

Photocatalytic hydrogen generation over alkaline-earth titanates in the presence of electron donors

The efficiency of alkaline-earth titanate-based compounds (Ca, Sr, Ba) for catalysts in photocatalytic hydrogen generation has been investigated. In this report, we have shown that the addition of organic donors (such as formic acid, acetic acid, methanol, 2-propanol and formaldehyde) enhanced the efficiency of the studied process. The systematic study has shown that the most efficient organic donor in regards to its hydrogen generation efficiency is formic acid. Of the catalysts explored, the highest photocatalytic activity was shown by SrTiO₃:TiO₂. Additionally, the effects of photocatalyst quantity and formic acid concentration on hydrogen evolution have been investigated.     

Fast hydrogen evolution by formic acid decomposition over AuPd/TiO2-NC with enhanced stability

Well-dispersed AuPd nanoparticles were immobilized on TiO₂-NC supports derived from NH₂-MIL-125(Ti) and used as highly active, stable catalysts for hydrogen production from formic acid under mild conditions. The highest total turnover frequency, i.e., 3207 h⁻¹, for formic acid dehydrogenation was achieved with Au₂Pd₈/TiO₂-NC-800 as the catalyst at 60 °C; this is 1.4 times that achieved with Au₂Pd₈/TiO₂–C-800 under the same conditions. The excellent performance of the Au₂Pd₈/TiO₂-NC-800 catalyst originates from the high anatase TiO₂ content, pyridinic N and oxygen vacancies in the support, the small size and alloying effect of the AuPd nanoparticles, and the metal–support synergistic effect. Doping the support with N improves the catalyst stability because N prevents metal particle aggregation to some extent. These results provide guidelines for the future development and applications of catalysts based on TiO₂ and metal–organic-framework-derived carbon-based materials.     

Facile synthesis of NiS2 nanowires and its efficient electrocatalytic performance for hydrogen evolution reaction

Recently, the first-row transition metal dichalcogenides MX₂ (M = Fe, Co, Ni; X = S, Se) have been widely reported as promising catalysts for hydrogen evolution reaction (HER) because of its excellent catalytic activity and earth-abundance. The rational nanostructure designs have been proved as an effective way to improve their catalytic performance. However, the reported one dimension (1D) NiS₂ nanowires for HER suffer from a large Tafel slope. Here, we report a facile synthesis of 1D NiS₂ nanowires and its high efficient catalytic activity in HER. This nanowire structure with large surface area and active sites enables highly efficient electrocatalytic performance in HER with a much smaller Tafel slope (83.5 mV/dec) compared to that of bulk NiS₂ (136 mV/dec) as well as long-term stability. Our work builds up a structure–performance relationship and enriches the synthetic strategy to other efficient catalysts such as first-row transition metal dichalcogenides or transition metal phosphide.     

A perspective on the production of hydrogen from solar-driven thermal decomposition of methane

In addition to “green” hydrogen from electrolysis of the water molecule with solar-photovoltaic or wind electricity, and “white” hydrogen, based on solar-thermal driven thermochemical splitting of the water molecule, there is another emerging opportunity to produce CO2 free hydrogen at a reduced cost. The perspective advocates in favor of “aquamarine” hydrogen, based on the solar-thermal driven thermal decomposition of methane. This pathway has an energy requirement that is much less than white and green hydrogen, and even if based on hydrocarbon fuel, has no direct production of CO₂ as a by-product, but rather carbon particles of commercial interest. Catalytic methane decomposition can be based on self-standing/supported metal-based catalysts such as Fe, Ni, Co, and Cu, metal oxide supports such as SiO₂, Al₂O₃, and TiO₂, and carbon-based catalysts such as carbon blacks, carbon nanotubes, and activated carbons, the pathway of higher technology readiness level (TRL). Thus, catalytic methane decomposition appears to be a highly promising approach, with undoubtedly many challenges, but also huge opportunities following pathways to be further refined through research and development (R&D).     

A DFT study on production of hydrogen from biomass-derived formic acid catalyzed by Pt–TiO2

Production and storage of hydrogen from biomass component by using efficient catalysts, it can finely maintain the future energy of the world and reduce human dependence on fossil fuels. Hydrogen production mechanism via formic acid decomposition on the TiO₂ anatase (101) and Pt–TiO₂ surfaces in the solvent (water) and gaseous conditions performed by density functional theory (DFT) calculation. Regarding to the proposed routes, decomposition reaction of formic acid on TiO₂ surface incline to be followed by second route in the water which is acceptable in terms of energy. Decomposition reaction of formic acid on Pt–TiO₂ surface prefers to do it via first route (rotation around CO bond of formic acid) in solvent conditions. Furthermore, adsorption energy and geometric changes of formic acid on TiO₂ anatase (101) and Pt–TiO₂ surface in gaseous and solvent conditions were clearly studied.     

Ammonia decomposition on a highly-dispersed carbon-embedded iron catalyst derived from Fe-BTC: Stable and high performance at relatively low temperatures

Fe-BTC (iron 1,3,5-benzenetricarboxylic acid), a commercially available metal organic framework (MOF), was used as a sacrificial template to produce a series of carbon-embedded Fe catalysts upon its pyrolysis at different temperatures. The catalyst prepared by pyrolyzing Fe-BTC at 400 °C under flowing N₂ provided a high graphitic degree on the carbon support hosting highly dispersed Fe species at a Fe loading of 34 wt%. Performance measurements on ammonia decomposition to produce CO_x-free hydrogen showed that this catalyst provided an ammonia conversion of 73.8% at a space velocity of 6000 cm³ NH₃ h⁻¹ g_cat⁻¹ and at 500 °C for at least 120 h. This stable performance, exceeding that of some of the best non-noble metal catalysts, was associated with the presence of highly-dispersed Fe species at a significantly high Fe loading, embedded in a carbonaceous shell. The presence of the carbonaceous shell not only protected the active species against sintering, but also made them electron rich owing to its high level of graphitization.     

Catalytic supercritical water gasification of black liquor along with lignocellulosic biomass

Supercritical water gasification (SCWG) is a novel technology for environmental pollution management and hydrogen production from biomass and wastes. In this study, the SCWG of black liquor (BL) which is high-potential biomass and rich in alkalis was investigated. The experiments were conducted in a batch reactor at 350–400 °C, reaction time of 1–60 min, and constant concentration of 9 wt% of BL in the absence and presence of heterogeneous catalysts (3–5 wt%), lignocellulosic biomass, and formic acid (5 and 7 wt %) in three parts. First, the SCWG of BL was performed without any additive. The experimental results showed that the maximum production of H₂, CO₂, and CH₄ was obtained at the highest temperature and reaction time; 400 °C and 60 min. The hydrogen yield was also enhanced by increasing the temperature, and reached 3.51 mol H₂/kg dry ash free-black liquor (DAF-BL) at 400 °C. Reaction time increment improved the gas product and gasification efficiency up to 28.03 mmol and 21.73%, respectively. Subsequently, three heterogeneous catalysts (MnO₂, CuO, and TiO₂) were used, however 5 wt% of MnO₂ was the best catalyst, significantly improving the hydrogen yield compared to the same condition of BL gasification without a catalyst. Hydrogen yield reached 5.09 mol H₂/kg (DAF-BL) at 400 °C and the reaction time of 10 min. Finally, BL with poplar wood residue as a lignocellulosic biomass and formic acid was gasified separately and the highest hydrogen yield was obtained in the case of 5 wt% of formic acid (10.79 mol H₂/kg (DAF-BL)). Overally, SCWG dramatically reduced the chemical oxygen demand of BL to 76% using 5 wt% of formic acid.     

Hydrogen production from low temperature supercritical water Co-Gasification of low rank lignites with biomass

Co–gasification of low rank lignite (Çan) with sorghum energy crop was investigated under low temperature conditions with supercritical water (773 K, 26.9 MPa). The effects of the water volume in the reactor, blending ratios of the coal/sorghum mixtures, the use of different catalysts, and the variation of feedstock concentrations on the gasification efficiency, product distribution, and hydrogen yields were evaluated. Synergistic effects were observed for both the gasification efficiency and the hydrogen yield with a coal content of 25 wt% in the coal/biomass mixture. Increasing the initial water volume, decreasing the feedstock concentration, and using the alkali metal catalysts Na₂CO₃ and K₂CO₃ significantly increased the gasification efficiency and the hydrogen yield. In experiments with CaO, almost all the carbon dioxide formed was isolated from the gas product during gasification, and the hydrogen yield was more than 70%. The liquid products were mainly composed of alkylphenols and their derivatives.     

Hydrogen production by ethanol steam reforming over M-Ni/sepiolite (M = La,Mg or Ca) catalysts

Ethanol steam reforming (ESR) is a technology of great promise for hydrogen production but designing highly efficient, green and inexpensive Ni-based catalysts for inhibiting metal sinter and carbon deposition and increasing catalyst activity and stability is still a key challenge. In this paper, the M-Ni/Sepiolite catalysts (M-Ni/SEP, M = La, Mg or Ca) were synthesized using a hydrothermal-assisted impregnation method. The results from characterizations such as N₂ adsorption-desorption, XRD, H₂-TPR, XPS, HRTEM and NH₃/CO₂-TPD showed that La, Mg and Ca promoters can facilitate the dispersion and exposure of Ni⁰ active sites, enhance the metal-support interaction and modify surface acid/alkaline sites. Furthermore, the results of catalyst activity tests in ESR demonstrated that the Ca–Ni/SEP catalyst exhibited the highest carbon conversion of 95% and hydrogen yield of 65%, attributed to the small mean Ni particle size, strong metal-support interaction, abundant surface Ni⁰ active sites and modified surface alkaline/acid sites. According to the carbon deposition analyses, it was observed in Ca–Ni/SEP that the carbon deposition amount was evidently decreased, and the graphitic degree of coke was increased due to the increased metal site amount.     

Hydrogen production from dairy wastewater using catalytic supercritical water gasification: Mechanism and reaction pathway

The supercritical water gasification (SCWG) of real dairy wastewater (cheese-based or whey) was performed in a batch reactor in presence of two catalysts (MnO₂, MgO) and one additive (formic acid). The operational conditions of this work were at a temperature range of 350–400 C and the residence time of 30–60 min. The catalysts and formic acid were applied in 1 wt%, 3 wt%, and 5 wt% to determine their effect on hydrogen production. The concentrations of catalysts and formic acid were calculated based on the weight of feedstock without ash. The results showed that increased temperature and prolonged residence time contributed to the hydrogen production (HP) and gasification efficiency (GE). The gas yield of hydrogen in the optimum condition (400 C and 60 min) was achieved as 1.36 mmol/gr DAF (dry ash free). Formic acid addition was favored towards enhancing hydrogen content while the addition of metal oxides (MnO₂ and MgO) had an apex in their hydrogen production and they reached the highest hydrogen in 1 wt% concentration then ebbed. Moreover, GE was increased by the addition of the catalysts and formic acid concentrations. The highest hydrogen content (35.4%) was obtained in 1 wt% MnO₂ and the highest GE (32.22%) was attained in the 5 wt% formic acid concentration. A reaction pathway was proposed based on the GC-MS data of feedstock and produced liquid phase at different condition as well as similar studies.     

NiCoP nanoparticles anchored on CdS nanorods for enhanced hydrogen production by visible light-driven formic acid dehydrogenation

Photocatalytic dehydrogenation of formic acid (FA), HCOOH→H₂+CO₂, is a promising strategy for hydrogen production. Although tremendous efforts have been made, developing efficient and robust system driven by visible light without noble metal still remains a huge challenge. Herein, we report for the first time the use of NiCoP nanoparticles anchored on CdS nanorods (NiCoP@CdS NRs) as a highly efficient and robust catalyst for photocatalytic FA dehydrogenation. NiCoP nanoparticles as cocatalyst can effectively separate the electron-hole pairs generated by CdS NRs. The H₂ production rate of the NiCoP@CdS nanorods reached ~354 μmol mg⁻¹ h⁻¹ under visible light irradiation (λ > 420 nm) and the apparent quantum yield (AQY) was ~45.5 % at 420 nm which are among the best values ever reported in photocatalytic FA dehydrogenation systems. This work provides a prospective strategy for developing noble-metal-free photocatalytic FA dehydrogenation systems and hydrogen-based energy applications.     

An effective low Pd-loading catalyst for hydrogen generation from formic acid

As an interesting hydrogen carrier, formic acid is bio-renewable, non-toxic and available in the liquid state at room temperature. The development of active and low-cost catalyst is of significance for hydrogen generation from formic acid. In this study, both a relatively cheap metal (Ag) and a functional support (nitrogen modified reduced graphene oxide, N-rGO) were applied to prepare Pd catalyst. It was found that the Ag atoms facilitated the formation of Pd-rich surface in the preparation strategy, in which the reductive N-rGO and a two-step feeding process of metal precursors played important roles. In addition, Ag additive was found to benefit catalyst stability. Most interestingly, the obtained low Pd-loading Pd₁Ag₆/N-rGO catalyst showed a specific Pd loading turnover frequency of 171 mol Pd^?1 h^?1 and a specific metal cost turnover frequency of 64.2 $^?1 h^?1, which were predominant among currently available Pd-based catalysts towards formic acid decomposition without any additive under room temperature.     

Highly efficient ternary hierarchical NiV2S4 nanosphere as hydrogen evolving electrocatalyst

Hydrogen is undoubtedly considered as clean energy fuel and hence the importance of hydrogen production at a larger scale is a major concern in front of the scientific community. The development of highly efficient, low cost metal-based electro-catalysts for hydrogen evolution reaction and oxygen evolution reaction during water electrolysis is necessary. Novel materials such as ternary metal sulphides are being projected as good candidates for hydrogen generation from water splitting due to the difference in electronic structures from the two metal components. Furthermore, morphological alteration to such ternary sulphides is expected make them much more efficient. The present work describes the synthesis of highly efficient ternary NiV₂S₄ nanosphere (NPs) with two different morphological structures and their electro-catalytic performance for water electrolysis by employing the polymer electrolyte membrane water electrolyzer system. The characterization and morphological study of the synthesized NPs were carried out using Raman spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and BET surface area analysis. The results of electrochemical measurement suggested that due to higher surface area in hierarchical structures of the ternary metal sulphide NiV₂S₄, its efficiency for producing hydrogen is higher in comparison to the solid NiV₂S₄ NPs containing smooth surfaces leading to the reduced surface area. This work will help in evaluating the ternary metal sulphides as electro-catalysts for hydrogen production with the help of electrochemical techniques.     

Dehydrogenation of formic acid mediated by a Phosphorus–Nitrogen PN3P-manganese pincer complex: Catalytic performance and mechanistic insights

The utilization of formic acid as a liquid organic hydrogen carrier has taken a vast interest lately because of several desirable properties. The state-of-the-art homogenous catalysts known for formic acid dehydrogenation are mainly based on noble metals such as iridium or ruthenium. 3d metals are considered to be an attractive alternative due to their abundance and low toxicity. Exploration of 3d metals has achieved exciting results mainly with iron-based catalysts; however, manganese has not received much attention, and only a few examples are available. Here we report a manganese complex [Mn(PN³P)(CO)₂]Br containing a pincer backbone, as an efficient catalyst for formic acid dehydrogenation. Under the optimized condition, the complex afforded a TON of 15,200. To the best of our knowledge, this is considered one of the best TON achieved using a manganese-based complex with excellent selectivity. Mechanistic studies suggested that the imine arm participates in the formic acid activation/deprotonation step, emphasizing the importance of metal-ligand cooperativity during substrate activation to promote catalytic efficacy.     

Fe-doped NiCo2S4 catalyst derived from ZIF – 67 towards efficient hydrogen evolution reaction

The development of economical, efficient and stable non-noble metal catalysts plays a key role in electrocatalytic hydrogen evolution. NiCo₂S₄ has been proved to be an efficient non-noble catalyst, to further improve its electrocatalytic performance is a meaningful work. In this paper, the effects of Fe doping on electrochemical performance of NiCo₂S₄ is investigated. The Fe-doped NiCo₂S₄ catalyst is prepared by a facile solvothermal method with metal-organic-framework (MOF, ZIF-67) as template, and it exhibits an improved hydrogen evolution reaction (HER) performance with an overpotential of 181 mV at 10 mA cm^?2, a Tafel slope of 125 mV dec^?1 compared with that of NiCo₂S₄ (252 mV overpotential and 149 mV dec^?1 Tafel slope). The combination of improved conductivity, mesopores architecture retained with the ZIF-67 template, which result the reduced internal resistance, enhanced charge transportation as well as large electrochemical double-layer capacitance. This work provides an effective and synergistic strategy for fabricating NiCo₂S₄-based catalysts toward electrochemical water splitting.     

Engineering of the N-doped carbon support for improved performance of supported Pd catalysts in hydrogen production from gas-phase formic acid

Development of N-doped Pd/C catalysts for hydrogen production from gas-phase formic acid is a challenge. To elucidate the efficient routes of nitrogen insertion on the surface of a mesoporous carbon support, the latter was treated with melamine (Mel), dicyandiamide or NH₃ at 673 and 823 K. Pyrolysis of the melamine/carbon mixture taken in a 1:2 ratio provides an increase in the reaction rate by a factor of 5. The inserted N-sites strongly interact with Pd leading to the formation of highly dispersed Pd nanoparticles (∼1.6 nm) and active atomically dispersed Pd²⁺ species. With a further increase of the Mel/C ratio, the number of surface N-sites decreases due to occupation of carbon support pores with a g–C₃N₄–type residue. This provides a decrease in the Pd dispersion leading to lower reaction rates. Therefore, melamine is an efficient N precursor. The considered synthesis of N-doped catalysts could be scaled.     

A review on the catalysts used for hydrogen production from ammonia borane

Boron compounds have recently attracted attention in hydrogen production since they contain many hydrogen atoms. Among these compounds, ammonia borane, which has high hydrogen density (in weight basis), can be used to produce hydrogen through a hydrolysis reaction. However, since the ammonia borane solution is highly resistant to hydrolysis under ambient conditions, there is a need for active and stable catalysts to accelerate the reaction. In this review paper, unsupported and carbon-based supported metal catalysts used for hydrogen production through the hydrolysis of ammonia borane are presented. Noble metal catalysts (Ru, Rh, Pd, Pt and their binary and ternary alloys) and non-noble metal catalysts (Co, Ni, Fe, Cu and their binary and ternary alloys) were examined. The activation energy of reaction and turnover frequency (TOF) values were compared for these catalysts. Among the unsupported catalysts, it was concluded that the multi-metal catalyst systems (binary, ternary and quaternary) have higher catalytic activity than a single use of the same metals. In addition, the comparison showed that the supported catalysts are more resistant to catalytic cycles and suitable for long-term use. It was observed that CNT supported Rh (TOF = 706 mol H₂ mol cat⁻¹ min⁻¹) and graphene supported Ru (TOF = 600 mol H₂ mol cat⁻¹ min⁻¹) catalysts are the most active catalysts for the hydrogen generation from the ammonia borane at room temperature.     

In-situ nitrogen and Cr2O3 co-doped MOF-derived porous carbon supported palladium nanoparticles: A highly effective catalyst towards formic acid dehydrogenation

Fast and high selective dehydrogenation of formic acid (FA) is regarded as one of the most promising pathways to obtain the clean energy carrier: hydrogen. In this work, a nitrogen and Cr₂O₃ co-doped hierarchical carbon material has been successfully synthesized by in-situ pyrolysis of NH₂-MIL-101(Cr) in one step, followed by boiling in hot NaOH solution for surface etching. The activated carbon material is used to anchor the ultrafine Pd nanoparticles (2.18 nm) for formic acid dehydrogenation (FAD). As a result, the 5 wt% Pd@Cr₂O₃-NPCB-850 exhibits an excellent catalytic activity towards FAD: the turnover frequency (TOF) value is as high as 11 241 h⁻¹ at 333 K, and the selectivity of H₂ is up to 100%. The excellent catalytic performance is mainly attributed to the existence of N species and Cr₂O₃, which plays an important role of electron transfer and anti-aggregation. Our studies open a new methodology for convenient and fast syntheses of nitrogen and metal oxide co-doped activated carbon material, which also provides potential access for producing more highly effective catalysts for other catalytic reactions.     

MgFe and Mg–Co–Fe mixed oxides derived from hydrotalcites: Highly efficient catalysts for COx free hydrogen production from NH3

Mg–Fe Layered Double Hydroxide (LDH) with M²⁺: M³⁺ 3:1 stoichiometric ratio was synthesized and employed as catalyst precursor for CO_x-free hydrogen production from ammonia. The resulting catalyst showed good catalytic activity. A series of Mg/Co–Fe layered double hydroxides were synthesized by replacing Mg²⁺ with Co²⁺ without disturbing M²⁺:M³⁺ ratio. The influence of nature and extent of Co(II) substitution on structure, morphology and surface properties were studied. A systematic study was carried out using these materials as catalyst precursors for ammonia decomposition. BET, XRD, TPR, XPS, CO₂-TPD and TEM techniques were used to characterize the synthesized catalysts. These Fe-based catalysts are highly active, highly stable and not promoting any stable surface nitridation during the ammonia decomposition reaction. Among all catalysts, the Mg₃Co₃Fe₂ catalyst showed the highest activity i.e. 100% conversion at 6,000 h⁻¹ and 60% at 50,000 h⁻¹ space velocities at 550 °C. The registered superior catalytic activity was result of the formed specific catalyst's properties like high surface area, high surface Co and Fe atomic concentration and suitable basicity. These Fe-based materials are, cost-effective, easily synthesize and highly stable, thus attractive for large-scale operation.