Non-noble Metal-based Catalysts Research Articles

Air-stable and reusable porous silica-supported ultrafine Nix-NiO nanoparticles for semi-hydrogenation of alkynes

The practical application of non-noble metal-based hydrogenation catalysts is limited because of their low activity and easy oxidation in air. Here, porous silica-supported ultrafine nickel oxide (NiO) was prepared by calcining an organic–inorganic hybrid 3D nanomaterial that was formed via the Michael addition/Schiff’s base reaction, and hydrolyzation of triethoxysilane. NiO nanoparticles with ca. 2.6 nm diameter was uniformly dispersed and confined in the cogenerated mesoporous SiO2 skeleton, thanks to the coordination between pyrogallol/amino units and Ni2+ ions, and the isolation effect of Si-O-Si network. The as-prepared catalyst featured mesoporous structure and high specific surface area (715 m2/g), and exhibited excellent activity, selectivity and reusability in the semi-hydrogenation of alkynes. Small amount of metallic nickel (Nix-NiO) that formed on the surface of NiO nanoparticles during the semi-hydrogenation acted as the active species, and the moderate adsorption/desorption energies on Nix-NiO facilitated the activity enhancement. Most importantly, it showed constant catalytic activity and selectivity after a long-term storage in air. This work provides a green and feasible strategy, as an alternative to the traditional impregnation method, for the preparation of ultrafine metal-supported catalysts with air-stability and reusability.

A self-supported porous NiMo electrocatalyst to boost the catalytic activity in the hydrogen evolution reaction.

To develop hydrogen energy production and address the issues of global warming, inexpensive, effective, and long-lasting transition metal-based electrocatalysts for the synthesis of hydrogen are crucial. Herein, a porous electrocatalyst NiMo/Ni/NF was successfully constructed by a two-step electrodeposition process, and was used in the hydrogen evolution reaction (HER) of electrocatalytic water decomposition. NiMo nanoparticles were coated on porous Ni/NF grown on nickel foam (NF), leading to a resilient porous structure with enhanced conductivity for efficient charge transfer, as well as distinctive three-dimensional channels for quick electrolyte diffusion and gas release. Notably, the low overpotential (42 mV) and fast kinetics (Tafel slope of 44 mV dec-1) at a current density of 10 mA cm-2 in 1.0 M KOH solution demonstrate the excellent HER activity of the electrode, which was superior to that of recently reported non-noble metal-based catalysts. Additionally, NiMo/Ni/NF showed extraordinary catalytic durability in stability tests at a current density of 10 mA cm-2 for 70 h. The porous structure catalyst and the electrodeposition-electrocatalysis technique examined in this study offer new approaches for the advancement of the electrocatalysis field because of these benefits.

A manganese-based catalyst system for general oxidation of unactivated olefins, alkanes, and alcohols.

Non-noble metal-based catalyst systems consisting of inexpensive manganese salts, picolinic acid and various heterocycles enable epoxidation of the challenging (terminal) unactivated olefins, selective C-H oxidation of unactivated alkanes, and O-H oxidation of secondary alcohols with aqueous hydrogen peroxide. In the presence of the in situ generated optimal manganese catalyst, epoxides are generated with up to 81% yield from alkenes and ketone products with up to 51% yield from unactivated alkanes. This convenient protocol allows the formation of the desired products under ambient conditions (room temperature, 1 bar) by employing only a slight excess of hydrogen peroxide with 2,3-butadione as a sub-stoichiometric additive.

Polyoxometalate-derived electrocatalysts enabling progress in hydrogen evolution reactions.

Platinum-based catalysts exhibit outstanding electrocatalytic performance in the hydrogen evolution reaction (HER). However, platinum-based catalysts face significant challenges due to their rarity and high cost. This paper endeavors to shed light on a promising alternative: polyoxometalate (POM)-based catalysts, which possess significant potential for the synthesis of non-noble metal-based catalysts for the HER. Utilizing POMs as raw materials to assemble POM-derived materials, including POM-derived crystalline materials, metal sulfides, phosphides, carbides, nitrides, and so on, has emerged as an effective approach for the synthesis of hydrogen evolution electrocatalysts. This approach offers advantages in both stability and electrocatalytic performance. This comprehensive review navigates through latest progress in the assembly strategy and HER performance of POM-based crystal materials, alongside discussion on transition metal compounds derived from POMs, such as carbides, phosphides, and sulfides. Besides, future developments in POM-derived electrocatalyst regulation of the electrochemical HER are prospected.

Influence of the catalyst precursor for cobalt on activated carbon applied in ammonia decomposition

Ammonia is a key compound for storing and transporting green hydrogen. However, the efficient release of stored hydrogen through thermocatalytic ammonia decomposition is achievable only at temperatures around 600 °C, particularly with non-noble metal-based catalysts, which prove to be both ecologically and economically more feasible. In this study, electrically conductive activated carbon was selected as the catalyst support, chosen specifically for its suitability in achieving more energy-efficient direct reactor heating through the ohmic resistance of the catalysts. Cobalt salts were wet impregnated on activated carbon investigating the influence of different precursors (cobalt nitrate and cobalt acetate) and pyrolysis temperatures (400 °C and 600 °C) under N2 flow on the cobalt particle size and the incorporation of cobalt into the carbon matrix. TEM imaging and CO-chemisorption revealed well dispersed cobalt particles with sizes below 10 nm for the catalysts synthesized from the cobalt nitrate precursor. On the other hand, cobalt acetate led to about nine times larger Co agglomerates, which were partially detached from the carbon matrix. Moreover, this substantial difference in the Co particle size results in a significantly higher ammonia conversion for cobalt nitrate-based catalysts, achieving 94 % of ammonia conversion at 600 °C. Furthermore, the long-term stability test of the cobalt nitrate-based catalyst resulted in a slight deactivation of only 2 % ammonia conversion at 500 °C.

Heterogeneous Catalysts for Carbon Dioxide Methanation: A View on Catalytic Performance

CO2 methanation offers a promising route for converting CO2 into valuable chemicals and energy fuels at the same time as hydrogen is stored in methane, so the development of suitable catalysts is crucial. In this review, the performance of catalysts for CO2 methanation is presented and discussed, including noble metal-based catalysts and non-noble metal-based catalysts. Among the noble metal-based catalysts (Ru, Rh, and Pd), Ru-based catalysts show the best catalytic performance. In the non-noble metal catalysts, Ni-based catalysts are the best among Ni-, Co-, and Fe-based catalysts. The factors predominantly affecting catalytic performance are the dispersion of the active metal; the synergy of the active metal with support; and the addition of dopants. Further comprehensive investigations into (i) catalytic performance under industrial conditions, (ii) stability over a much longer period and (iii) activity enhancement at low reaction temperatures are anticipated to meet the industrial applications of CO2 methanation.

A general and robust Ni-based nanocatalyst for selective hydrogenation reactions at low temperature and pressure.

Catalytic hydrogenations are important and widely applied processes for the reduction of organic compounds both in academic laboratories and in industry. To perform these reactions in sustainable and practical manner, the development and applicability of non-noble metal-based heterogeneous catalysts is crucial. Here, we report highly active and air-stable nickel nanoparticles supported on mesoporous silica (MCM-41) as a general and selective hydrogenation catalyst. This catalytic system allows for the hydrogenation of carbonyl compounds, nitroarenes, N-heterocycles, and unsaturated carbon─carbon bonds in good to excellent selectivity under very mild conditions (room temperature to 80°C, 2 to 10 bar H2). Furthermore, the optimal nickel/meso-silicon dioxide catalyst is reusable (4 cycles) without loss of its catalytic activity.

Multi-metal catalysts for selective furfural hydrogenation: Toward biomass valorisation

The research presented here focuses on the design of non-noble transition metal-based bimetallic catalysts, prepared via a green sol-gel process (the urea-glass route), which leads to well-defined (in composition and size) and crystalline nanoparticles, with high surface area. The potential of these tailor-made catalysts for biomass-related model reactions is also presented. In particular, carbon supported Ni, Ni3Fe, Ni0.5Fe0.5, Ni0.5Fe0.5/Fe3C and Ni0.35Fe0.65/NiFe2O4 nanoparticles were synthesized and tested as-prepared, with no need for post-synthesis purification, activation, or co-catalysts addition. Results showed that these catalysts are active in the liquid-phase hydrogenation of furfural (FUR), with almost full conversion with Ni° catalyst, at 170 °C after 22 h, under 4 MPa hydrogen pressure, obtaining the highest yield towards tetrahydrofurfuryl alcohol (THFA) of 85%. More interesting, the incorporation of Fe, to form NiFe alloys, modifies the hydrogenating capacity of the catalyst, provoking a change in the selectivity pattern, from tetrahydrofurfuryl alcohol (THFA), obtained as the only product with Ni° nanoparticles, to furfuryl alcohol (FFA). Thus, high FFA and THFA yields can be obtained by modifying the nature of the metallic phase of samples synthesized with the urea-glass route, demonstrating the potential of this methodology for the preparation of active and selective catalysts for liquid-phase FUR hydrogenation.

Edge-rich molybdenum disulfide tailors carbon-chain growth for selective hydrogenation of carbon monoxide to higher alcohols

Selective hydrogenation of carbon monoxide (CO) to higher alcohols (C2+OH) is a promising non-petroleum route for producing high-value chemicals, in which precise regulations of both C-O cleavage and C-C coupling are highly essential but remain great challenges. Herein, we report that highly selective CO hydrogenation to C2-4OH is achieved over a potassium-modified edge-rich molybdenum disulfide (MoS2) catalyst, which delivers a high CO conversion of 17% with a superior C2-4OH selectivity of 45.2% in hydrogenated products at 240 °C and 50 bar, outperforming previously reported non-noble metal-based catalysts under similar conditions. By regulating the relative abundance of edge to basal plane, C2-4OH to methanol selectivity ratio can be overturned from 0.4 to 2.2. Mechanistic studies reveal that sulfur vacancies at MoS2 edges boost carbon-chain growth by facilitating not only C-O cleavage but also C-C coupling, while potassium promotes the desorption of alcohols via electrostatic interaction with hydroxyls, thereby enabling preferential formation of C2-4OH.

Electronic optimization of heterostructured MoS2/Ni3S2 by P doping as bifunctional electrocatalysts for water splitting

MoS2 is an excellent catalyst for hydrogen evolution reaction (HER) because of its close proximity to the optimum hydrogen adsorption free energy (ΔGH*). However, poor oxygen evolution reaction (OER) intrinsic activity, insufficient active sites, and poor conductivity hinder its application as a bifunctional electrocatalyst. Here, Ni3S2 is combined with MoS2 forming MoS2/Ni3S2 heterostructure due to its intrinsic OER activity and P is chosen as an anion dopant to optimize ΔGH* due to its near-thermoneutral H adsorption to explore the bifunctional performance of MoS2 based nanocomposites. The electronic configurations of Mo, Ni, and S on the interface are modulated by P doping, which optimizes their adsorption/desorption ability of intermediates. The synergistic effect of anion doping and heterostructure induces excellent catalytic activity in P40-MoS2/Ni3S2–5 (Mo to S molar ratio of 1:5 and 40 mg P dopants) with overpotentials of 142 mV for HER and 278 mV for OER at 100 mA cm−2 in 1.0 M KOH solution. The voltage of overall water splitting is 1.76 V using P40-MoS2/Ni3S2–5 as the anode and cathode. This work elucidates a method of optimizing the electronic structure by doping P anion in heterointerface, providing an avenue to boost the catalytic activity of non-noble metal-based catalysts.

In-situ fabrication of bimetallic FeCo2O4-FeCo2S4 heterostructure for high-efficient alkaline freshwater/seawater electrolysis

Rational construction of bifunctional electrocatalysts with long-term stability and high electrocatalytic activity is of great importance, but it is challenging to obtain highly efficient non-precious metal-based catalysts for overall seawater electrolysis. Herein, a nickel foam (NF) self-supporting CoFe-layered double hydroxide (CoFe-LDH/NF) was directly converted into FeCo2O4-FeCo2S4 heterostructure via hydrothermal method in 50 mM Na2S solution, instead of FeCo2O4@FeCo2S4 core-shell structure. The FeCo2O4-FeCo2S4 heterojunction shows nanosheets structure with rough surface (the thickness of ∼ 198.9 nm), which provides rich oxide/sulfide interfaces, high electrochemical active area, a large number of active sites, as well as fast charge and mass transfer. In 1.0 M KOH solution, 1.0 M KOH + 0.5 M NaCl, and alkaline natural seawater, the FeCo2O4-FeCo2S4 heterojunction exhibits eminently electrocatalytic performance, with overpotentials of η-100 = 225 mV, η-100 = 233 mV, and η-100 = 238 mV for OER, as well as η-100 = 271 mV, η-100 = 273 mV, and η-100 = 277 mV for HER, respectively. Furthermore, self-supporting FeCo2O4-FeCo2S4 electrode (FeCo2O4-FeCo2S4/NF) as the cathode and anode of an electrolyzer exhibits a lower cell voltage of E-100 = 1.75 V in alkaline seawater than those of FeCo2S4/NF (1.77 V), CoFe-LDH/NF (1.87 V), and FeCo2O4/NF (1.91 V). Specifically, FeCo2O4-FeCo2S4 electrolyzer can stably produce hydrogen for over 48 h in alkaline freshwater/seawater electrolyte. These outstanding electrocatalytic performances and corrosion resistance to salty-water can be attributed to the surface reconstruction behavior of the FeCo2O4-FeCo2S4/NF catalyst during OER, which leads to the in-situ formation of metal oxyhydroxides. In particular, the FeCo2O4-FeCo2S4 heterojunction is also very competitive among most state-of-the-art non-noble metal-based catalysts, whether in KOH or alkaline salty-water electrolytes.

Improving the Sulfurophobicity of the NiS-Doping CoS Electrocatalyst Boosts the Low-Energy-Consumption Sulfide Oxidation Reaction Process.

Producing sulfur from a sulfide oxidation reaction (SOR)-based technique using sulfide aqueous solution has attracted considerable attention due to its ecofriendliness. This study demonstrates that NiS-doped cobalt sulfide NiS-CoS-supported NiCo alloy foam can deliver the SOR with superior electrocatalytic activity and robust stability compared to reported non-noble metal-based catalysts. Only 0.34 V vs RHE is required to drive a current density of 100 mA cm-2 for the SOR. According to the experiment, the catalyst exhibits a unique sulfurophobicity feature because of the weak interaction between sulfur and the transition metal sulfide (low affinity for elemental sulfur), preventing electrode corrosion during the SOR process. More impressively, the chain-growth mechanism of the SOR from short- to long-chain polysulfides was revealed by combining electrochemical and spectroscopic in situ methods, such as in situ ultraviolet-visible and Raman. It is also demonstrated that electrons can transfer straight from the sulfion (S2-) to the active site on the anode surface during the low-energy-consumption SOR process. This work provides new insight into simultaneous energy-saving hydrogen production and high-value-added S recovery from sulfide-containing wastewater.

TiO2 supported non-noble Ni-Fe catalysts for the high yield production of 2,5-dimethylfuran biofuel

The establishment of the future biorefinery schemes requires the sustainable conversion and valorisation of renewable bioresources into eco-friendly fuels and chemicals. To this end, 2,5-dimethylfuran (DMF) is a promising biofuel competitive to benchmarks like ethanol due to high-value intrinsic properties. It can be produced by the catalytic hydrogenation of the 5-hydroxymethylfurfural (HMF) platform molecule, one of the biobased intermediate chemicals derived from the abundant lignocellulosic biomass. We evidenced that bimetallic NiFe alloys supported on TiO2 are earth-abundant non-noble metal-based catalysts allowing the high yield production of DMF to be achieved. We showed that the preparation method and the reduction temperature of the catalyst are of prime importance, and are directly influencing the structure of the supported NiFe bimetallic particles and in consequence the catalyst behaviour. The highest yield to DMF is obtained on a catalyst prepared by co-impregnation and reduced at 500 °C, that features an unperfect core/shell structure of the NiFe alloy, with a partial Fe shell surrounding an Fe-enriched Ni core. The key-feature necessary for achieving high performance lies on the surface structure of the NiFe alloy that allows for an optimum availability of highly active Ni domains. The Ni atoms were maintained highly dispersed by the presence of Fe-containing surface phases. The specific surface structure is proposed to promote the HMF adsorption through the carbonyl group, while preventing from the hydrogenation of the aromatic furan ring to maintain high selectivity.

Direct-Fed Ethanol Metal-Supported Solid Oxide Fuel Cell System with Regeneration Process by Air Pulsing

Metal-Supported-SOFC (MS-SOFC) can handle rapid start-up and cool-down without cracking, making it more suitable for mobile applications than a conventional cermet-based SOFC, which is more susceptible to cracking when experiencing thermal shock due to its ceramic component. Despite having more robust mechanical properties, the MS-SOFC still relies on Ni as its anode catalyst, where it can be deactivated due to coking formation if the cell is operated under liquid logistics or hydrocarbon fuels. One of the most effective solutions is introducing a micro-reforming catalyst layer on the anode layer. The micro-reforming catalyst will reform the fuel into H2 and CO mixture called syngas, and then the anode will use the reformatted syngas to run the electrochemical reaction to produce electricity. This method will effectively improve the cell power output, stability, and coking resistance.In this work, we integrated the MS-SOFC with a reforming catalyst through the precursor infiltration method. We infiltrated a non-noble metal-based catalyst with a ceria-zirconia (CZ) into the MS-SOFC. The cell is then operated under direct ethanol fuel at 700 °C with the S/C ratio of 2. The non-noble metal catalyst is less expensive than noble but it also has lower catalytic activity and coking resistance during the cell operation in ethanol. Therefore, a regeneration cycle is necessary to maintain the cell performance and the catalytic activity of the cell. The regeneration cycle is performed by air pulsing directly into the cell’s anode surface to burn off the coking generated during the cell operation. The regeneration process involves a redox cycle that is only possible for a mechanically stable structure like MS-SOFC.Our experimental data showed that the MS-SOFC with infiltrated micro-reforming catalyst was gradually deactivated during the operation under ethanol fuel, indicated by the cell voltage drops due to coking. After the regeneration procedure with air pulsing, the cell voltage was recovered to its original performance. At the same time, the gas chromatograph detects a significant CO2 signal from the effluent gas, suggesting that the carbon removal process was successfully performed. Additionally, we observed an improvement in the cell’s performance under H2 and ethanol fuel. After a long-term constant current stability test, the cell shows up to ~20% and ~25% maximum current density drops under H2 and ethanol fuel, respectively, compared to its initial performance. Upon the cell regeneration with air pulse, the cell’s maximum current density was recovered to its initial performance and showed an improvement up to ~21 and 13% under H2 and ethanol, respectively, compared to its initial performance before the long-term test. This result suggests that some of the carbons might remain within the cell’s functional layer and help improve its conductivity and electrochemical performances. These data clearly show that the air pulsing regeneration process in the MS-SOFC can improve the cell’s lifetime by removing the coking deposit within the anode and enhancing its electrochemical and catalytic activity.-------Figure Caption: Fig 1.(A) The IV pot of the MS-SOFC with reforming catalyst under H2 and (B) ethanol solution (S/C=2) at 700 °C of the MS-SOFC. The IV measurements were taken during its initial screening, after both constant current stability tests, and after both regeneration procedures. (C) Long-term stability test of the cell in ethanol solution under the constant current density of 125 mA/cm2. Figure 1

Defect engineered efficient catalytic transfer hydrogenation of furfural to furfuryl alcohol in ethanol by Co-doped LaMnO3

As energy and CO2 concerns have become important aspects of scientific research, researchers are focusing on the development of alternative and green energies. Biomass is a significant energy source due to its cyclic utilization process and ability to renew CO2. The catalytic transfer hydrogenation (CTH) of sugar-derived furfural (FF) into furfuryl alcohol (FA) has attracted increasing attention; however, designing and synthesizing efficient nonnoble catalysts remains challenging. In this work, an oxygen defect-abundant LaMnO3 perovskite (R-LM4C-3h) was synthesized by combining the advantages of both Co heteroatom doping and H2 reduction. Raman, O2 temperature programmed desorption (O2-TPD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS) characterizations revealed that R-LM4C-3h exhibited abundant oxygen defects that improved its electronic properties. As a result, adsorption ability for FF was enhanced, the reaction energy barrier was decreased, and CTH catalytic activity was promoted. A 93.6 mol% FA yield with 100 % FF conversion was achieved using ethanol as the hydrogen source. The oxygen defect-mediated catalyst also exhibited excellent stability with almost no activity reduction after 5 cycles. This surface reconstruction strategy for obtaining perovskites by fabricating abundant oxygen defects provides a superior opportunity to better explore the structure–function relationship of catalysts and develop efficient nonnoble metal-based catalysts.

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries.

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

Facile Synthesis of Nitrogen-Rich Porous Carbon/NiMn Hybrids Using Efficient Water-Splitting Reaction.

Proper design of multifunctional electrocatalyst that are abundantly available on earth, cost-effective and possess excellent activity and electrochemical stability towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required for effective hydrogen generation from water-splitting reaction. In this context, the work herein reports the fabrication of nitrogen-rich porous carbon (NRPC) along with the inclusion of non-noble metal-based catalyst, adopting a simple and scalable methodology. NRPC containing nitrogen and oxygen atoms were synthesized from polybenzoxazine (Pbz) source, and non-noble metal(s) are inserted into the porous carbon surface using hydrothermal process. The structure formation and electrocatalytic activity of neat NRPC and monometallic and bimetallic inclusions (NRPC/Mn, NRPC/Ni and NRPC/NiMn) were analyzed using XRD, Raman, XPS, BET, SEM, TEM and electrochemical measurements. The formation of hierarchical 3D flower-like morphology for NRPC/NiMn was observed in SEM and TEM analyses. Especially, NRPC/NiMn proves to be an efficient electrocatalyst providing an overpotential of 370 mV towards OER and an overpotential of 136 mV towards HER. Moreover, it also shows a lowest Tafel slope of 64 mV dec-1 and exhibits excellent electrochemical stability up to 20 h. The synergistic effect produced by NRPC and bimetallic compounds increases the number of active sites at the electrode/electrolyte interface and thus speeds up the OER process.

Al-Doped Core-Shell-Structured Ni@Mesoporous Silica for Highly Selective Hydrodeoxygenation of Lignin-Derived Aldehydes.

Selective deoxygenation of chemicals using non-noble metal-based catalysts poses a significant challenge toward upgrading biomass-derived oxygenates into advanced fuels and fine chemicals. Herein, we report a bifunctional core-shell catalyst (Ni@Al3-mSiO2) consisting of Ni nanoparticles closely encapsulated by the Al-doped mesoporous silica shell that achieves 100% vanillin conversion and >99% yield of 2-methoxy-4-methylphenol under 1 MPa H2 at 130 °C in water. Due to the unique mesoporous core-shell structure, no significant decrease in catalytic activity was observed after 10 recycles. Furthermore, incorporating Al atoms into the silica shell significantly increased the number of acidic sites. Density functional theory calculations reveal the reaction pathway of the vanillin hydrodeoxygenation process and uncover the intrinsic influence of the Al sites. This work not only provides an efficient and cost-effective bifunctional hydrodeoxygenation catalyst but also offers a new synthetic protocol to rationally design promising non-noble metal catalysts for biomass valorization or other widespread applications.

Direct solvent-free selective hydrogenation of levulinic acid to valeric acid over multi-metal [NixCoyMnzAlw]-doped mesoporous silica catalysts

Valeric acid (VA) and valeric esters (VEs) are among the essential platform chemicals derived from bio-levulinic acid (LA). However, synthesizing VA from LA is still challenging due to solvent consumption, precious metals utilization, and catalyst deactivation. Thus, this study developed an efficient direct solvent-free selective hydrogenation reaction of LA to VA using non-noble metal-based catalysts. NixCoyMnzAlw-doped mesoporous silica (NMCAS) catalysts were synthesized using a facile one-pot procedure, with 100% LA conversion and 96.3% VA yield obtained at 200 °C and 3 MPa (H2) over the NMCAS catalyst. Ni-based catalysts provided 100% LA conversion, whereas the Mn-Co-based catalyst exhibited a 79.8% LA conversion. The increase in the selectivity for VA observed with the doping of Mn and Al into the catalysts can be explained by the generation of Brønsted and Lewis acid sites, which facilitated the ring-opening of GVL to form VA. The effects of reaction time, temperature, pressure, and solvent were considered. At elevated temperatures and pressures, the formation of 1,4-PDO, resulting from the CO bond breakage of O-C–O in the GVL ring-opening and the subsequent dehydration-cyclization to 2-methyltetrahydrofuran (MTHF), including the over-hydrogenation of VA to pentanol, was detected. An increase in the partial pressure of hydrogen enhanced the hydrogenation activity, thus producing 2-MTHF and pentanols. The NMCAS catalyst has also been applied with various solvents to study the reaction pathway and produce VEs. This work is the primary example of the direct solvent-free, selective, and high-yield production of VA from LA over non-noble heterogeneous catalysts.

Ni-based nanocatalyst protected by ultrathin mesoporous nitrogen-doped carbon layer with hollow structure for the efficient transfer hydrogenation of halogenated nitrobenzenes

It is of great scientific and industrial value to develop cheap and efficient supported non-noble metal-based catalysts for the selective hydrogenation of halogenated nitrobenzenes. In this work, hollow-structured Ni-based nano-catalysts coated with ultrathin nitrogen-doped carbon layers (H-Ni@NC) have been prepared. The etching of SiO2 template before calcination and decomposition of residual Ni3Si2O5(OH)4 shell into SiO2 leads to the resulting catalysts could maintain good mechanical property and stability. The H-Ni@NC catalyst prepared at 600 °C exhibits the optimal catalytic performance for the catalytic selective hydrogenation of halogenated nitrobenzenes under mild conditions (60 °C) when using hydrazine hydrate (N2H4·H2O) as the reducing agent, and could maintain its catalytic properties even after 5 consecutive runs. The contrast experiments confirm that the combination of hollow structure with N-doped carbon protective layer make the catalyst show the best catalytic effect, and the synergistic effects are further discussed in detail combined with characterization analysis. In addition, this work further reveals the mechanism of Ni-based catalysts for the transfer hydrogenation of halogenated nitrobenzenes, which may provide a reference idea for the preparation of other Ni-based catalysts.