Efficient and Reusable Pb(II) Metal–Organic Framework for Knoevenagel Condensation

A microporous lead–organic framework {[Pb₄(µ₈-MTB)₂(H₂O)₄]·5DMF·H₂O}_n (MTB?=?methanetetrabenzoate, DMF?=?N,N′-dimethylformamide) was synthesized and studied as a catalyst in Knoevenagel condensation reactions. The framework is built from tetranuclear [Pb₄(µ₃-COO)(µ₂-COO)₆(COO)(H₂O)₄] clusters and exhibits a 3D structure, with repeated 1D jar-like cavities with sizes about 14.98?×?7.88 and 14.98?×?13.17 Å² and BET specific surface area of 980 m² g^?1. To obtain open framework with unsaturated Pb(II) sites needed for catalysis, the thermal activation of the solvent exchanged sample was performed (DMF was exchanged by EtOH). The activated compound was tested in Knoevenagel condensation of bulky aldehydes and active methylene compounds at different temperatures. Excellent catalytic conversion and selectivity in condensation of small-sized aldehydes with malononitrile was observed, which indicates that the opened Pb(II) sites play a significant role in the heterogeneous catalytic process. Leaching test confirmed the stability of the catalyst in catalytic reactions. Moreover, the compound displayed good recyclability after several reuses without significant decrease in the original catalytic activity.

Graphical Abstract

Novel Pb(II) metal–organic framework was tested in Knoevenagel condensation. The catalyst showed excellent catalytic conversion, selectivity and recyclability. Aldehydes with lower kinetic diameter demonstrated high conversions and yields. Catalyst is less efficient for condensation of larger aromatic aldehydes.

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Zr-Modified SBA-15 Supported Ni Catalysts with Excellent Catalytic Performance of CO Selective Methanation in H<Subscript>2</Subscript>-Rich Fuels

CO selective methanation is a promising route for the purification of CO in H₂-rich gas for on-board H₂-based fuel cells. Herein, we synthesized a Zr-modified SBA-15 supported Ni catalyst, which exhibits both high catalytic performance, deep-removing CO concentration to below 10 ppm with a selectivity higher than 50% in a very low-temperature range (170–220 °C), and long-term stability. The results of XRD, XPS, TPR, TPD and TEM characterizations reveal that the doping of Zr not only improves the dispersion of Ni species, enhances the CO adsorption, but also suppresses the CO₂ adsorption, resulting in the prominent catalytic performance.

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Electrocatalytic H<Subscript>2</Subscript> Evolution of Bis(3,5-di-methylpyrazol-1-yl)acetate Anchored Hexa-coordinated Co(II) Derivative

A mononuclear Co(II) derivative, (1) is afforded by employing a ‘scorpionate’ type precursor, bdtbpza [bdtbpza?=?bis(3,5-di-t-butylpyrazol-1-yl)acetate]. Single crystal X-ray structure reveals that the Co^II ion exhibits an octahedral geometry possessing on a O₆ coordination environment. Detailed EPR interpretation and electrocatalytic hydrogen evolution study are reported. Electrochemical and catalytic study of 1 in DMSO with the presence of acetic acid as weak proton source shows an observed rate constant of 3.7?×?10³ s^?1 and hydrogen evolution Faradaic efficiency of 74.7%. The catalytic process requires two-electron reduction of the catalyst and formation of a cobalt(II)-hydride species as reactive intermediate.

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Tuning the Core–Shell Structure of Au<Subscript>144</Subscript>@Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> for Optimal Catalytic Activity for CO Oxidation

Core–shell heterostructures have been utilized as a catalyst that is thermally stable and exhibits a synergistic effect between core and shell, resulting in increased catalytic activity. Here we report on the synthetic procedure involving a Au₁₄₄ core with an iron oxide shell which can be varied in thickness. The Au₁₄₄@Fe₂O₃ particles with Au:Fe mass ratios of 1:2, 1:4, and 1:6 were synthesized and then deposited onto silica via colloidal deposition. Using CO oxidation, each Au₁₄₄@Fe₂O₃/SiO₂ catalyst gave varying degrees of full CO conversion depending on the thickness of the iron oxide layer. The 1:4 Au₁₄₄@Fe₂O₃/SiO₂ catalyst produced the best catalytic activity and was further investigated via thermal treatments, where calcination at 300 °C presented the best results, and the 1:4 ratio was still active at 100 °C after thermal treatments.

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Embedding Noble-Metal-Free Ni<Subscript>2</Subscript>P Cocatalyst on g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> for Enhanced Photocatalytic H<Subscript>2</Subscript> Evolution in Water Under Visible Light

Photocatalytic hydrogen evolution is considered as one of the promising pathways to settle the energy crises and environmental issues by utilizing solar energy. In this paper, noble-metal-free Ni₂P was used as cocatalyst to enhance g-C₃N₄ for photocatalytic hydrogen production under visible light irradiation (λ?>?420 nm). Characterization results indicated that Ni₂P nanoparticles were successfully loaded onto g-C₃N₄, which can significantly contribute to accelerate the separation and transfer of photogenerated electron. The hydrogen evolution rate reached ～?270 µmol h^?1 g^?1 and the apparent quantum yield (AQY) was ～?2.85% at 420 nm. Meanwhile, there is no obviously decrease of the hydrogen production rate even after 36 h under visible light illumination. In addition, the mechanism of photocatalytic hydrogen evolution was also elaborated in detail.

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Agarose Hydrogel Beads: An Effective Approach to Improve the Catalytic Activity,Stability and Reusability of Fungal Amyloglucosidase of GH15 Family

This study deals with the immobilization of amyloglucosidase within agarose using method of entrapment. Enzyme was produced from Aspergillus fumigatus KIBGE-IB33 and then partially purified using 40% ammonium sulphate saturation. Using 40 gl^?1 concentration of agarose and adjusting 3.0 mm size of hydrogels, maximum entrapment yield (78%) was obtained. The kinetic behavior was slightly changed after immobilization as reaction time and reaction temperature increases from 5.0 min (soluble) to 10.0 min (immobilized) and 60 °C (soluble) to 65 °C (immobilized), respectively while, pH optima remained same (pH 5.0). Substrate saturation kinetics revealed that K_m was increased from 1.47 to 4.215 mg ml^?1 while, the value of V_max decreased from 947 to 611 kU mg^?1 for soluble and entrapped amyloglucosidase, respectively. The stability profile of amyloglucosidase also significantly improved after entrapment in agarose hydrogels at 50, 60 and 70 °C for 120 min with retention of 77, 59 and 25% residual activity, respectively. Furthermore, the t_1/2 of soluble and immobilized amyloglucosidase at 60 °C was 167 and 375 min respectively. Due to increase in reusability for various subsequent cycles of entrapped amyloglucosidase, about 8.73 mg ml^?1 increase in glucose production was observed as compared to soluble enzyme.

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Facile Synthesis of Ag–γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Superior Nanocomposite for Catalytic Reduction of Nitroaromatic Compounds and Catalytic Degradation of Methyl Orange

A facile synthetic route for preparing silver-doped maghemite (Ag–γ-Fe₂O₃) nanocomposite via a modified co-precipitation method was developed. The prepared magnetic nanocomposite was characterized by means of thermal analysis, transmission electron microscope, X-Ray diffraction, vibrating sample magnetometer and Fourier transform infrared techniques. The characterization results showed that the prepared Ag–γ-Fe₂O₃ nanocomposite is nanocrystalline and 6–8 nm in size with superparamagnetic behavior. The synthesized Ag–γ-Fe₂O₃ nanocomposite showed exceptional catalytic activities towards reduction of nitroaromatic compounds with specific activities parameters of 1441.7 and 904.2 s^??1 g_Ag^?1 for both 4-nitrophenol and 2-nitroaniline, respectively. Besides, it shows a superior activity for catalytic degradation of methyl orange. All the three catalytic reactions were carried out in aqueous medium at room temperature and in the presence of reducing agent NaBH₄. The magnetic behavior of the synthesized Ag–γ-Fe₂O₃ enables the ease of separation of the nanocomposite from the reaction medium for further reuse.

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Effect of Potassium on the Physiochemical and Catalytic Characteristics of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> Catalysts in <Emphasis Type="Italic">o</Emphasis>-Xylene Partial Oxidation to Phthalic Anhydride

Abstract

Vanadia species formed on the surface depend on the K/V atomic ratio. At small K/V ratios, Raman spectra show the formation of the K-doped and K-perturbed monomeric species. At K/V?=?1, kristalline KVO₃ is mainly present on the surface. In situ high temperature XRD-results exhibit a promoting effect on the anatase to rutile phase transformation in the presence of 0.03 and 0.21 wt% potassium. Large amount of K (3 wt%) provides thermal stability of V/Ti/O catalyst and no transformation is found up to 600?°C. Reduction of vanadia K-doped vanadia catalysts is moved to higher temperatures than for the catalyst without potassium. The catalyst having 0.21 wt% K possesses the highest activity in o-xylene oxidation. Furthermore, the K-doped monomeric vanadia species in this catalyst leads to a promoted adsorption or a prevented desorption of phthalide, resulting in a decreased selectivity towards phthalide and CO_x and a increased PA selecticity.

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Strontium Doped MCM-41: A Highly Efficient,Recyclable and Heterogeneous Catalyst for the Synthesis of Phenoxy Pyrazolyl Pyrazolines

Strontium doped MCM-41 (Sr-MCM-41) has been synthesized as an efficient, heterogeneous and recyclable catalyst. The catalyst, Sr-MCM-41 is characterized by various techniques such as FTIR, SEM, EDX, elemental Mapping, TEM, TGA, BET, XRD, XPS and ICP-AES analyses. The catalytic activity of the catalyst (Sr-MCM-41) has been explored by synthesizing a library of phenoxy pyrazolyl pyrazoline derivatives in excellent yield (96–98%) under microwave irradiation (3–5 min) using ethanol as solvent. The catalyst could be recycled upto five cycles.

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Switching from Ethylene Trimerization to Ethylene Polymerization by Chromium Catalysts Bearing SNS Tridentate Ligands: Process Optimization Using Response Surface Methodology

Two types of chromium catalysts bearing pyridine and amine based SNS ligands under the title of (pyridine-SNS-alkyl/CrCl₃) and (amine-SNS-alkyl/CrCl₃) were synthesized. Different thiolates such as octyl, pentyl, butyl, cyclohexyl and cyclopentyl thiolates were reacted with 2,6-pyridine-dimethylene-ditosylate (PMT)/THF solution at room temperature. Then, the purified pyridine-based SNS ligands (1–5) were reacted with CrCl₃ (THF)₃ to obtain the pyridine-SNS-alkyl/CrCl₃ catalysts (6–10) in 50–70% yields. MMAO-activated pyridine-SNS-alkyl/CrCl₃ catalysts were capable of oligomerizing ethylene. Statistical experimental design was conducted using the central composite design method and surface methodology to study of the effect of important parameters such as ethylene pressure, Al/Cr ratio, catalyst concentration and the reaction temperature on 1-C₆ productivity of catalyst (7). A quadratic polynomial equation was developed to predict the 1-C₆ productivity. Ethylene oligomerization using the catalyst (7) was lead to a optimized reaction conditions, including the ethylene pressure of 19.5 bar, the temperature of 58.2 °C, the MMAO co-catalyst, Al/Cr?=?841 and the catalyst concentration of 8.7 µmol. The catalytic properties for ethylene oligomerization are strongly affected by reaction temperature. The experimental results indicated the reasonable agreement with the predicted values. The transformation from ethylene trimerization to ethylenev polymerization of catalyst system (7) was occurred by exchanging the reaction pressure. Influence of ligand structure with different substitutions on sulphur atom on productivity and selectivity was investigated. 1-C₆ with the high selectivity and productivity 4318 (g 1-C₆/g Cr h) was obtained for catalyst (7). In the second part, 1-C₆ was obtained with high selectivity and productivity around 141?×?10³ (g 1-C₆/g Cr h) for amine-based catalyst. All amine-based catalysts (14–16) showed considerably higher catalytic activities compared to pyridine-based catalysts. According to the TGA analysis the thermal stability of pyridine-based catalysts was found to be higher than the amine-based catalysts.

Graphical Abstract

Chromium complexes bearing pyridine and amine based SNS ligands have been synthesized and their catalytic performance in ethylene oligomerization has been investigated. A switching from ethylene trimerization to ethylene polymerization of the catalyst (7) was obtained utilizing exchanging of the ethylene pressure.

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Catalytic cracking of rubber seed oil using basic mesoporous molecular sieves K<Subscript>2</Subscript>O/MeO-SBA-15 (Me = Ca,Mg or Ba) as heterogeneous catalysts for the production of liquid hydrocarbon fuels

Liquid hydrocarbon fuels obtained from the catalytic cracking animal fats and plant oils have become one kinds of the attractive fuels because of their possible environment benefits and the current concern over the depletion of fossil fuel sources. In this work, using the combined methods of one-pot synthesis and wetness-impregnation, some basic mesoporous molecular sieves K₂O/MeO-SBA-15 (Me?=?Ca, Mg or Ba) were prepared, characterized and used in the catalytic cracking of rubber seed oil (RSO). The results indicated that the catalysts K₂O/MeO-SBA-15 had better catalytic performances than MeO-SBA-15, assigning to their stronger basicity. The catalyst K₂O/MgO-SBA-15 obtained with 15 wt% KNO₃ impregnation concentration showed the excellent catalytic performance with about 93.2% conversion and 78.3% yield of liquid hydrocarbon biofuel. The obtained liquid biofuel had similar chemical composition to diesel-based fuels and showed good cold flow property, high calorific and low acid value. Importantly, the catalyst K₂O/MgO-SBA-15 was of excellent reusability, and it was reused with negligible loss in its catalytic performance for five times, attributing to the MgO layer between silicon skeleton and potassium species which prevents the reaction between silicon in the framework and potassium species.

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Controllable Synthesis of MoS<Subscript>2</Subscript>/h-CdS/c-CdS Nanocomposites with Enhanced Photocatalytic Hydrogen Evolution Under Visible Light Irradiation

Firstly, h-CdS/c-CdS homojunction was prepared by solvothermal method with controlling the Cd-to-S molar ratio. Then, the MoS₂/h-CdS/c-CdS nanocomposites were constructed by ultrasonic method with different MoS₂ amount. The experimental results showed that when the molar ratio of Cd and S was 1:1 and the amount of MoS₂ was 1.5 wt%, the MoS₂/h-CdS/c-CdS nanocomposites exhibited excellent photocatalytic performance for hydrogen evolution under visible light. The total amount of hydrogen evolution was 3753.12 µmol for 5 h, and its average hydrogen evolution rate was 40.79 mmol h^?1 g^?1 with an apparent quantum efficiency of 38.16% irradiated at 420 nm, which was about 7.3 times when compared with the h-CdS/c-CdS homojunction (Cd:S?=?1:8). The enhanced photocatalytic performance of MoS₂/h-CdS/c-CdS could be attributed to the improved specific surface area and formation of well bonded interface structure, which not only enhanced the response to visible light but also decreased the recombination rates of photogenerated charge carriers.

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Syntheses and Characterization of Zinc Oxide Nanoparticles on Graphene Sheets: Adsorption-Reaction In Situ DRIFTS of Methane and CO<Subscript>2</Subscript>

Zinc oxide and graphene support as catalyst were synthesized and characterized using different techniques. Results showed that graphene presented thermal stability, and maintained its structure under heat treatment at temperatures of 500 °C. TPD He experiments showed decomposition of residual compounds, releasing oxygenated compounds after functionalization of the graphene oxide. The catalyst performance was evaluated for the reaction of CH₄?+?CO₂ and O₂ by surface reaction at programmed temperature. We observed the formation of CO, H₂ and H₂O. However, TPSR and DRIFTS coupled to a mass spectrometer evidenced methane activation on ZnO/rGO-T, due to the evolution of H₂ and CO₂ traces of water and hydrocarbons, such as ethane (C₂H₆). Less sensitive but present was the signal 60, which can be assigned to the formation of acetic acid (CH₃COOH) at 300 °C.

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A Comparative Study of Supported and Bulk Cu–Mn–Ce Composite Oxide Catalysts for Low-Temperature CO Oxidation

A series of supported and bulk Cu–Mn–Ce ternary oxide catalysts was synthesized by wet-impregnation (IM), deposition–precipitation (DP), traditional co-precipitation (CP), co-precipitation with cetyltrimethyl ammonium bromide (CC), and sol–gel (SG) methods. The supported catalysts (CuMn/Ce-IM, CuMn/Ce-DP) exhibited significantly higher activity for CO oxidation than the bulk catalysts (CuMnCe-CP, CuMnCe-CC and CuMnCe-SG). The improved performance could be attributed to the presence of more isolated CuO and MnO_x entities on the surface of supported catalysts, which contributed to the efficient utilization of both lattice oxygen from CeO₂ and spillover oxygen from surface MnO_x. For bulk catalysts, major Cu–Mn species were doped to form \({\text{C}}{{\text{u}}_{\text{x}}}{\text{M}}{{\text{n}}_{\text{y}}}{\text{C}}{{\text{e}}_{1 - {\text{x}} - {\text{y}}}}{{\text{O}}_{2 - {\text{z}}}}\) solid solutions and a part of them were coated by ceria mechanically. Lowest 50% CO conversion temperature were achieved at 76.9 °C for CuMn/Ce-IM catalyst. Low-temperature CO oxidation activities of all catalysts were in the sequence of CuMn/Ce-IM?>?CuMn/Ce-DP?>?CuMnCe-SG?>?CuMnCe-CC?>?CuMnCe-CP.

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Direct Synthesis of Amides from Oxidative Coupling of Benzyl Alcohols and <Emphasis Type="Italic">N</Emphasis>-substituted Formamides Using a Co–Al Based Heterogeneous Catalyst

Present work reports the direct synthesis of amides from oxidative coupling of benzyl alcohols with various N-substituted formamides using a cobalt-hydrotalcite (Co-HT) derived catalyst. The Co-HT derived catalysts (Co-HT-2, Co-HT-3 and Co-HT-4 having Co²⁺/Al³⁺ molar ratio in the catalyst preparation mixture as 1/1, 2/1 and 3/1 respectively) were prepare following a co-precipitation method and characterized well by powder XRD, XPS, FEG-SEM, EDS, DTG–TGA, FT-IR and N₂ physisorption measurements. A range of functional amides were obtained in good yields from oxidative coupling of various substituted benzyl alcohols and a range of N-substituted formamides using Co-HT-3 catalyst and oxidant TBHP. Mechanistic investigation suggests that the amidation reaction is associated with the formation and coupling of radical species. Furthermore, the Co-HT derived catalyst was easily recoverable and recyclable with retained high catalytic activity towards the oxidative coupling of benzyl alcohol with DMF.

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Impact of Chain Length on the Catalytic Performance in Hydroisomerization of <Emphasis Type="Italic">n</Emphasis>-Alkanes Over Commercial and Alkaline Treated *BEA Zeolites

The present paper highlights the influence of desilication of nanocrystal *BEA zeolites (CP811 and CP814E) by different alkaline treatments in presence of NaOH alone, NaOH?+?TPABr and NaOH?+?TBAOH, on the catalytic performance in the hydroisomerization reactions of n-alkanes (n-C₁₀, n-C₁₂ and n-C₁₄). The well-balanced catalyst was reached after impregnation of 1.5 wt% of Pt, where the activity and isomers selectivity was seen to be the maximum, knowing that the Pt content effect was studied on the CP811 zeolite catalyst. All the other catalysts were after impregnated by approximately 1.5 wt% of Pt. The improvement of the textural properties by means of desilication was not always accounting for the influence of the catalytic performance of the catalysts, but rather it may be the bifunctional characteristics in charge. The impact of chain length was investigated on the catalysts to study if the presence of the inter- and intracrystalline mesopores would account for better diffusion of larger molecules as, n-C₁₂ and n-C₁₄. It was found on the majority of the catalysts that the activity was high whether the chain length was, but the isomers selectivity was decreasing with chain length except on one catalyst that possesses high textural and bifunctional characteristics. Among the three n-alkanes studied, n-C₁₂ have marked the highest TOF values and lowest selectivity to isomers, a phenomenon attributed to the confinement effect that seems to increase the interaction of n-C₁₂ molecules with the acidic sites of the zeolites, apparently causing their strength to be higher. This effect was pronounced more with n-C₁₂ than the other two n-alkanes.

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Synthesis and Characterization of Platinum Impregnated Zn-ZSM5 Nanocatalysts for Xylene Isomerization Reactions

The influence of zinc to the synthesis of ZSM-5 nanocatalysts (Si/Al?=?24) was investigated in xylene isomerization reactions. Pt was doped through partial vacuum impregnation method on both the parent and Zn-ZSM-5. The synthesized nanocatalyst were characterized by ICP, BET, XRD, FE-SEM, XPS, ²⁷Al MAS NMR, FTIR, NH₃-TPD, and TG analysis. The concentration of weak acid sites of ZSM-5 nanocatalyst slightly decreased while that of strong acid sites increased with the addition of Zn to the nano zeolite structure. Reducing weak acidity resulted in lower coke formation and remarkable catalytic stability in Zn-ZSM-5 nanocatalysts. The precence of Pt on the Zn-containing ZSM-5 illustrated simultaneous high PX yield and high catalytic stability. (0.1 wt%)Pt/(0.8 wt%) Zn-ZSM-5 as an active and stable nanocatalyst for xylene isomerization reactions demonstrated high PX yield (32.6 wt%), high level of EB conversion (68%) and low xylene loss (2.1%).

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Application of Mesoporous Metal Oxide Immobilized Gold–Palladium Nanoalloys as Catalysts for Ethanol Oxidation

Gold–palladium nanoalloys (AuPd) were synthesized by a dendrimer templating method and the as-prepared nanoalloys were immobilized on several reducible mesoporous metal oxides (MMOs). The MMOs of MnO₂, Co₃O₄ and CeO₂ exhibited low catalytic activity in gas-phase oxidation of ethanol. Upon immobilization of the AuPd nanoalloys the activity increased significantly, with high acetaldehyde selectivity at 120 °C. However, this activity increase from pure MMOs to AuPd/MMOs was accompanied by decrease in selectivity to acetaldehyde. One other interesting observation lies on the amount of gold in the nanoalloy. Increasing the ratio of Au:Pd in the nanoalloy from 1:1 to 10:1 lowered the activity by a factor of six but had a positive effect on selectivity. From this, we postulate dissociation absorption of molecular oxygen to the reactive oxides occurs more effectively on the Pd metal surface. With higher Au loading, the acetaldehyde selectivity remained above 90% even at higher reaction temperatures of 160 °C. This led to a postulation of quick desorption of acetaldehyde from the Au surface more than it does on the Pd surface.

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Nickel–Tungsten Supported on Thin Carbon Coated SiO<Subscript>2</Subscript> Nanosphere for Cellulose Conversion to Lower Polyols

Production of polyols and other chemicals from cellulose was important for sustainable society, and it had long relied on the design of suitable catalysts to achieve high yield of lower polyols. Herein, we reported a new preparing strategy for nickel–tungsten catalyst to fabricate Ni–W/SiO₂@C catalysts coated by thin carbon. The crystal carbon demonstrated the recommendable confinement effect to obtain the well dispersed metallic particles on SiO₂. The prepared composites were characterized by means of XRD, N₂ physisorption, thermogravimetry, XPS, TEM, element mapping and atomic force microscope. These characterizations confirmed that more phases including WO₃, Ni, NiW alloys and NiC were formed by incorporation of porous crystal carbon. Moreover, the metallic particles were dispersed in size range of 2–8 nm influenced by coating carbon and ethanediamine (dispersant). The activities of catalysts were evaluated in hydrogenolysis of cellulose to lower polyols at 240 °C under 5.0 MPa H₂ pressure in the presence of water. Results showed that catalyst Ni–W/SiO₂@C-12 was more favorable for EG production, with the highest EG yield of 60.7% and 100% cellulose conversion after reaction for 60 min.

Graphical Abstract

The series of high efficient nickel–tungsten catalysts Ni–W/SiO₂@C were fabricated and coated by thin carbon. The thin coating carbon demonstrated the recommendable confinement effect to obtain the well dispersed metallic particles on SiO₂.

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Morphology-Controlled Synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> Materials and its Electrochemical Catalytic Properties Towards Oxygen Evolution Reaction

In the present study, we present a facile strategy to synthesis Co₃O₄ materials with different morphology. Experimental results show that Co₃O₄ materials with flower-like, fiber, sheet-like and rod morphologies have been successfully prepared by hydrothermal synthesis in different solvent. The effect of the morphology on the electrochemical catalytic properties were also studied. It is found that sheet-like Co₃O₄ exhibits the best activity towards oxygen evolution reaction (η₁₀?=?390 mV) in 1 M KOH, which can be attribute to its short electrolyte infiltration diffusion path lengths and low charge transfer resistant.

Graphical Abstract

LSV curves measured at 5 mV/s in 1 M KOH solution for OER, the inset image is FE-SEM image of prepared Co₃O₄ materials. a Flower, b fiber, c sheet and d rod.

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