Efficient Heterogeneous Catalyst Research Articles

Pd Nanoparticle Supported on N‐Doped Carbon Derived from Sodium Alginate/Melamine Blends as Efficient Heterogeneous Catalyst for Heck Reactions

AbstractN‐doped porous carbon shows great potential in the field of heterogenous supports due to its high porosity, large surface area, rich active sites, and strong chelation with catalytic active metals species. Herein, we successfully prepared a novel N‐doped porous carbon derived from sodium alginate/melamine blends (SAMNC) with different mass ratio through a simple carbonization and activation process. Hierarchical porous structure of the derived N‐doped carbon has been confirmed with the SEM, TEM, and N2 adsorption characterization. After Na2PdCl4 solution impregnation and further reduction process, Pd0 nanoparticles have been uniformly immobilized on the SAMNC support to produce novel Pd@SAMNC catalyst. The optimal Pd@SAMNC‐0.6 possesses a high N content (5.13%), Pd content (5.90%), large BET specific surface area of 1884.5 m2·g−1. Positron annihilation lifetime spectroscopy (PALS) investigation of the porous carbon materials provided the sub‐nano level microporous information proofs of Pd@SAMNC‐0.6 had the capability to provide more active sites for reactions than commercial Pd supported on activated carbon (Pd@AC). Pd@SAMNC‐0.6 catalyst showed superior catalytic efficiency in Heck coupling reaction between aromatic halides and alkenes and can be recycled for 17 runs without significant decrease in catalytic efficiency.

Sustainable Production of Biofuels from Biomass Feedstocks Using Modified Montmorillonite Catalysts.

The rampant exploitation of fossil fuels has led to the significant energy scarcity and environmental disruption, affecting the sound momentum of development and progress of human civilization. To build a closed-loop anthropogenic carbon cycle, development of biofuels employing sustainable biomass feedstocks stands at the forefront of advancing carbon neutrality, yet its widespread adoption is mainly hampered by the high production costs. Montmorillonite, however, has garnered considerable attention serving as an efficient heterogeneous catalyst of ideal economic feasibility for biofuel production, primarily due to its affordability, accessibility, stability, and excellent plasticity. Up to now, nevertheless, it has merely received finite concerns and interests in production of various biofuels using montmorillonite-based catalysts. There is no timely and comprehensive review that addresses this latest relevant progress. This review fills the gap by providing a systematically review and summary in controllable synthesis, performance enhancement, and applications related to different kinds of biofuels including biodiesel, biohydrogenated diesel, levulinate, γ-valerolactone, 5-ethoxymethylfurfural, gaseous biofuels (CO, H2), and cycloalkane, by using montmorillonite catalysts and its modified forms. Particularly, this review critically depicts the design strategies for montmorillonite, illustrates the relevant reaction mechanisms, and assesses their economic viability, realizing sustainable biofuels production via efficient biomass valorization.

Electrochemical sensing for simultaneous determination of dopamine and acetaminophen based on ZIF-8@ZIF-67 derived Co/Mo2C embedded in N-doped carbon hollow nanocages

The exploration of an economical and efficient noble metal-free heterogeneous catalyst is of great significance for the construction of an electrochemical method for the simultaneous detection of Dopamine (DA) and acetaminophen (AC). In this paper, we employed a facile strategy to obtain Co/Mo2C nanoparticles embedded in nitrogen-doped carbon hollow nanocages (Co/Mo2C@N-C HNCs) heterogeneous structure by pyrolyzing ZIF-8@ZIF-67 precursor. The unique hollow structure ensures a fast electron transport channel, N doping regulates the local electronic structure of the catalyst, and the synergistic effect with Mo2C and Co nanoparticles provides more electrocatalytic active sites. The Co/Mo2C@N-C HNCs electrode separates the overlapping voltammetry peaks of DA and AC into two distinct voltammetry peaks (△E=200 mV), thereby selectively determining DA in the presence of AC and vice versa. The transfer coefficient (α) and electron transfer number (n) of DA and AC electrocatalytic oxidation were also studied. Using Co/Mo2C@N-C HNCs as electrode, an electrochemical sensor platform for the simultaneous detection of acetaminophen (AC) and dopamine (DA) was first constructed with linear range of 1–185 μM, and 1–100 μM and low detection limit of 0.35 μM and 0.46 μM for AC and DA, respectively. Satisfactory results have been obtained in the determination of human serum and acetaminophen tablets samples. DFT calculation reveals the molecular mechanisms for DA and AC interacting with the Co/Mo2C@N-C HNCs catalysts. This strategy provides a new idea for the selective determination of several analytes in complex substrates.

Using In situ Transmission Electron Microscopy to Study Strong Metal‐Support Interactions in Heterogeneous Catalysis

AbstractPrecisely controlling the microstructure of supported metal catalysts and regulating metal‐support interactions at the atomic level are essential for achieving highly efficient heterogeneous catalysts. Strong metal‐support interaction (SMSI) not only stabilizes metal nanoparticles and improves their resistance to sintering but also modulates the electrical interaction between metal species and the support, optimizing the catalytic activity and selectivity. Therefore, understating the formation mechanism of SMSI and its dynamic evolution during the chemical reaction at the atomic scale is crucial for guiding the structural design and performance optimization of supported metal catalysts. Recent advancements in in situ transmission electron microscopy (TEM) have shed new light on these complex phenomena, providing deeper insights into the SMSI dynamics. Here, the research progress of in situ TEM investigation on SMSI in heterogeneous catalysis is systematically reviewed, focusing on the formation dynamics, structural evolution during the catalytic reactions, and regulation methods of SMSI. The significant advantages of in situ TEM technologies for SMSI research are also highlighted. Moreover, the challenges and probable development paths of in situ TEM studies on the SMSI are also provided.

Oxygen vacancies promoted hydrogen production from methanol aqueous phase reforming over MgAl−LDHs supported plasmonic Ru nanoparticles catalyst

Catalytic aqueous phase reforming of methanol is a promising process for the sustainable hydrogen production. The search for highly efficient heterogeneous catalyst is a topic of interest. Herein, we report oxygen vacancies enriched MgAl−LDHs supported plasmonic Ru nanoparticles catalyst exhibit excellent photocatalytic performance for efficient hydrogen production at 150 ºC under light irradiation. Characterizations demonstrate abundant oxygen vacancies are introduced into MgAl−LDHs via “memory effect”. The local electron transfer from oxygen vacancies of the MgAl−LDHs to the Ru nanoparticles leading the formation of electron-rich Ru species, which promote the dehydrogenation of methanol under light irradiation. In situ DRIFTS demonstrated a redox mechanism of water-gas shift reaction due to the existence of oxygen vacancies, which resulted a faster hydrogen production rate. This work displays a facile strategy for synthesis of oxygen vacancies rich LDH supported metal nanoparticles catalysts and deep understanding into the pathway and mechanism toward the effective hydrogen production.

Regulating RuxMoy Nanoalloys Anchored on Porous Nitrogen-Doped Carbon via Domain-Confined Etching Strategy for Neutral Efficient Ammonia Electrosynthesis.

Neutral electrochemical nitrate (NO3-) reduction to ammonia involves sluggish and complex kinetics, so developing efficient electrocatalysts at low potential remains challenging. Here, we report a domain-confined etching strategy to construct RuxMoy nanoalloys on porous nitrogen-doped carbon by optimizing the Ru-to-Mo ratio, achieving efficient neutral NH3 electrosynthesis. Combining in situ spectroscopy and theoretical simulations demonstrated a rational synergic effect between Ru and Mo in nanoalloys that reinforces *H adsorption and lowers the energy barrier of NO3- hydrodeoxygenation for NH3 production. The resultant Ru5Mo5-NC surpasses 92.8% for NH3 selectivity at the potential range from -0.25 to -0.45 V vs RHE under neutral electrolyte, particularly achieving a high NH3 selectivity of 98.3% and a corresponding yield rate of 1.3 mg h-1 mgcat-1 at -0.4 V vs RHE. This work provides a synergic strategy that sheds light on a new avenue for developing efficient multicomponent heterogeneous catalysts.

An efficient, green and solvent-free three-component synthesis of 2,4,6-triarylpyridines utilizing ZSM-5 as a heterogeneous catalyst

ZSM-5, an efficient and reusable heterogeneous catalyst, is employed for the one-pot, three-component synthesis of 2,4,6-triarylpyridines from substituted benzaldehydes, acetophenones and ammonium acetate using a simple, efficient, and green method. Both electron-releasing and withdrawing aldehydes and ketones went smoothly into substituted 2,4,6-triarylpyridines. Notably, the present reaction was carried out in the solvent-fee condition. The key merits of the present protocol are the milder reaction condition, easy workup protocol, high yield of desired pyridines and recyclability and reusability of the catalyst. The developed protocol offers a broad scope of substrate applicability and good sustainability.

An economic, and environmentally benign Psidium guajava L. leaves catalyst for biodiesel production at room temperature: Process optimization, and life cycle cost analysis

Biodiesel has emerged as a popular alternative to conventional fossil fuel in transportation sector and thus producing low-cost biodiesel is a topic of interest for a large community of researchers. This study reports the preparation of an efficient and robust heterogeneous catalyst from dried Psidium guajava L. (Guava) leaves and its application towards generation of biodiesel from soybean oil at room temperature. The biomass material was calcinated at variable temperature and the efficiency of each of the catalyst prepared was studied. The catalyst generated as well as the product biodiesel was thoroughly characterized using sophisticated analytical techniques. The catalyst was found to have mesoporous structure with active basic sites which contributed towards accelerating the transesterification process. Detailed characterization unveiled the occurrence of Ca as oxide and carbonate, in addition to a certain quantity of K in oxide and carbonate form, which contribute to the catalyst’s activity. Maximum biodiesel yield of 95.8 % was observed for reaction performed under optimum experimental conditions i.e., 1:17 oil-to-methanol ratio, 6 wt% loading of GL-850 (catalyst prepared by calcination at 850°C), and 15 % n-Hexane loading for 3 h at room temperature. GL-850 demonstrated exceptional recyclability for up to the fifth cycle exhibiting a mere 3.7 % decline in yield. The calculated expense for 1 kg catalyst was found to be $0.478, whereas the production cost of 1 kg biodiesel was found to be merely $1.120, indicating a strong economic feasibility of the process.

A Chemically Robust 2D Ni-MOF as an Efficient Heterogeneous Catalyst for One-Pot Synthesis of Therapeutic and Bioactive 2-Amino-3-Cyano-4H-Pyran Derivatives.

Despite possessing numerous catalytic advantages of MOFs, developing 2D frameworks having excellent chemical stability along with new catalytic properties, remains a grand challenge. Herein, by employing a mixed ligand synthetic approach, we have constructed a 2D Ni-MOF, IITKGP-52, which exhibits excellent framework robustness in open air, water, as well as over a wide range of pH solutions (2-12). Benefitting from its robustness and abundant Lewis acidic open metal sites, IITKGP-52 is explored in catalyzing the heterogeneous three-component condensation reaction for the tandem synthesis of bioactive 2-amino-3-cyano-4H-pyran derivatives with low catalytic loading, greater compatibility for a wide range of substrates, excellent recyclability and superior catalytic efficiency than the previously employed homo and heterogeneous systems. IITKGP-52inaugurates the employment of MOF-based catalysts for one-pot synthesis of therapeutic and bioactive 2-amino-3-cyano-4H-pyran derivatives.

Corncob waste derived carbon with sulfonic acid group: An efficient heterogeneous catalyst for production of ethyl levulinate as biodiesel additives

Alkyl levulinate is a biomass-based chemical compound used as a fuel additive. This research aims to produce ethyl levulinate from levulinic acid and ethanol using esterification with the assistance of a heterogeneous sulfonated carbon catalyst. The carbon sulfonate catalyst is obtained from corncob waste that has undergone carbonization at 300 °C and sulfonation using sulfuric acid at a temperature of 150 °C for 8 h. The catalyst is used for esterification with predetermined operating variables using Box-Behnken Design (BBD) on the response surface methodology (RSM). The result shows significant variables for ethyl levulinate esterification are catalyst loading and esterification time. The FTIR analysis indicates the presence of S=O bonds in the sulfonated carbon catalyst. The XRD and SEM analysis shows that the sulfonated carbon catalyst is in amorphous and mesoporous form. Catalyst reusability demonstrates that the corncob-derived carbon sulfonate catalyst can be used up to 3 times. The optimum condition for esterification is 9 h of reaction, 10 % catalyst loading, and a molar ratio of levulinic acid to ethanol of 1:10, which has 83.15 % conversion. These results present the optimum parameter conditions for an efficient heterogeneous catalyst from corncob for producing ethyl levulinate.

Copper immobilized onto the polyvinyl imidazole coated magnetic graphene oxide as an efficient heterogeneous catalyst for A3 and C–X cross-coupling reactions

Copper immobilized onto the polyvinyl imidazole coated magnetic graphene oxide as an efficient heterogeneous catalyst for A3 and C–X cross-coupling reactions

Review on polyaniline-based nanocomposite heterogeneous catalysts for catalytic reduction of hazardous water pollutants.

Water contamination by highly toxic substances has generated serious ecological disturbances and health problems for humans. Hence, decontamination of toxic pollutants using advanced, inexpensive, and eco-friendly approaches is the current demand. Heterogeneous catalyst-based catalytic reduction processes have offered the opportunity to transform hazardous water pollutants into non-hazardous products via sustainable, eco-friendly, and efficient routes and might be a competitive substitute for existing traditional water purification techniques. However, the key challenges linked with pure heterogeneous catalysts include agglomeration and poor dispersion, stability, recovery, and reusability, which result in poor activity and efficiency. Thus, it is essential to produce multipurpose polymer-based composite catalysts using conducting polymers, which are exceptionally good supportive and matrix materials. The blending of metal-based nanomaterials with polyaniline conducting polymers produces highly stable and efficient heterogeneous nanocomposite catalysts with amazing catalytic activity against a wide range of water pollutants. The heterogeneous catalytic reductive degradation of immensely toxic pollutant water has gained substantial curiosity because of its excellent physicochemical and surface characteristics, porous structure, recoverability, and recyclability. Therefore, this review presents the latest efforts to generate various polyaniline-based nanocomposite catalysts using a polyaniline matrix and various nanofiller materials and their potential applications in heterogeneous catalytic reduction degradation of water pollutants.

Exploring enhanced syngas production via the catalytic performance of metal‐doped X‐Ni/CeO2 (X = Zr, La, Sr) in the dry reforming of methane

AbstractBackgroundThe quest to manufacture large amounts of syngas to bridge fossil fuels and the renewable energy ecosystem stimulates the creation of efficient and stable heterogeneous catalysts. The NiCeO2 catalysts, synthesized via ultrasonic‐assisted citric acid complexation, are highly efficient for the dry reforming of methane (DRM) reaction. Different promoter metals (Zr, La and Sr) were tested for catalytic performance and syngas production. A range of analyses, including X‐ray diffraction (XRD), N2 physisorption, H2 temperature‐programmed reduction, CO2 temperature‐programmed desorption, field emission scanning electron microscopy (FESEM), transmission electron microscopy and X‐ray photoelectron spectroscopy, were employed to characterize the physicochemical properties of the catalysts.ResultsXRD results indicated the formation of NiO, CeO2, solid solution ceria–zirconia, perovskite LaNiO3 and SrNiO3 crystalline phases. FESEM results showed the promoted catalysts (Zr, La, Sr) produce large pores to facilitate reactant diffusion, with zirconia specifically creating a spiderweb morphology. At 800 °C, the CH4 and CO2 conversions follow the sequence of NiCeO2 catalyst (CH4 = 54%, CO2 = 45%) < Sr/NiCeO2 (CH4 = 60%, CO2 = 67%) < La/NiCeO2 (CH4 = 85%, CO2 = 84%) < Zr/NiCeO2 (CH4 = 95%, CO2 = 87%). The integration of promoters in DRM catalysts has notably improved carbon formation resistance, as evidenced by the following ranking: Zr/NiCeO2 (5.1 wt%) < commercial catalyst (6.0 wt%) < La/NiCeO2 (7.85 wt%) < Sr/NiCeO2 (10.9 wt%) < NiCeO2 (11.3 wt%).ConclusionThis study demonstrates that incorporating promoters, particularly Zr, in NiCeO2 significantly enhances resistance to carbon formation. It offers valuable insights into selecting metal catalyst promoters for excellent catalytic performance in DRM. © 2024 Society of Chemical Industry (SCI).

Functionalized Phosphorus‐Doped Porous Organic Polymers (FPPOPs)‐Promoted Pd‐Catalyzed Arylation of Hydrosilanes

The development of novel catalyst systems, especially as highly efficient heterogeneous catalysts for Si‐C bond ‐forming arylation reaction of hydrosilanes is highly desirable. Herein, we developed a simple and eco‐friendly methodology for construction of functionalized phosphorus‐doped porous organic polymers (FPPOPs) and its heterogeneous palladium catalyst through anchoring on FPPOPs bearing a phosphine ligand, in which the fabrication of FPPOPs was completed through the vinyl‐substituted triphenylphosphine (ViPPh3) and vinyl‐substituted polyhedral oligomeric silsequioxane (ViPOSS) as well as functional olefins via radical co‐polymerization. All these FPPOPs could act as a phosphine ligand for Pd‐catalyzed arylation of hydrosilanes have been characterized by SEM, FTIR, and X‐RAD. Moreover, the POSS‐based functionalized phosphorus‐doped porous organic polymers (POSS‐PPOPs) proved to be a high efficiency catalyst system for Si‐C bond ‐forming arylation of hydrosilanes with aryl iodides and with good yields as well as excellent chemoselectivity with low amount of catalyst under mild conditions. The mechanistic studies supported the effect of functional group on the catalytic activity of Pd/FPPOPs catalyst, which revealed that the weak coordination as well as non‐covalent interaction between porous organic polymers and substrate played important role in the enhancement of chemoselectivity.

Impact of Synthetic Variables on the Structural Diversity of TbIII-Carboxylate Frameworks: Gas Adsorption, Magnetism, and Organocatalysis Investigations.

In this work, three unique TbIII-carboxylate frameworks with the formula {[Tb2(OH)2(H2O)2(abtc)]·2H2O}n (1), {[Tb2(abtc)1.5(H2O)3(DMA)]·H2O}n (2) and {[Tb3(abtc)2.5(H2O)4]·H3O}n (3), each displaying structural variations, have been successfully synthesized by the solvothermal reactions of Tb(NO3)3·6H2O with the azo-containing ligand 3,3',5,5'-azobenzene tetracarboxylic acid (H4abtc) under varying conditions. Detailed single-crystal X-ray diffraction (SC-XRD) analysis manifested a remarkable diversity in these structures, demonstrating various coordination patterns of TbIII-metal nodes with the carboxylate groups of the organic linker, which contributed to the generation of intricate three-dimensional (3D) coordination networks with remarkable chemical resistance. Furthermore, frameworks 2 and 3, characterized by porous networks containing two and three independent TbIII-metal nodes, respectively, were both demonstrated to be efficient heterogeneous catalysts toward the cyanosilylation of imines under mild conditions with excellent reusability. In addition, direct current (Dc) magnetic susceptibility measurements conducted on frameworks 1, 2, and 3 indicated that there were obvious antiferromagnetic interactions among the TbIII-metal nodes, which suggests the involvement of intricate intra- and intertrimer exchange channels, adding another fascinating dimension to their physical properties.

Immobilization of tetrabromidozincate(Ⅱ) anions on ion exchange resin for efficiently catalytic conversion of CO2 to cyclic carbonates

Integrating reactive Lewis acid sites and nucleophilic anions into porous materials is a promising approach to develop efficient heterogeneous catalysts for the cycloaddition of CO2 to epoxides (CCE) into cyclic carbonates. In this work, ZnBr42− coordination anions consisting of Zn2+ ions as Lewis acid sites and Br− ions as nucleophiles were immobilized on the poly (styrene–divinylbenzene) anion-exchange resin D201 containing quaternary ammonium cationic groups through a simple ion-exchange method. The obtained catalyst, named ZnBr4-D201, was characterized by X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM) and thermo-gravimetry (TG). Under the condition of solvent and co-catalyst free, ZnBr4-D201 exhibited efficient catalytic activity for CCE reaction. Take the cycloaddition of CO2 to 1,2-epoxybutane (BO) as an example, ZnBr4-D201 gave a BO conversion rate of 97 % and a selectivity of 98 % for cyclic carbonate with a high TOF value at 1 MPa CO2 and 80 °C for 6 h, which is superior to most of heterogeneous catalysts ever reported. Furthermore, ZnBr4-D201 showed good recoverability, and the yield of cyclic carbonate was still up to 82 %. The excellent catalytic performance and convenient preparation process make ZnBr4-D201 have great potential for CCE reaction in practical production.

Ceria nanocatalyst-supported oxidative organic transformations of aromatic alcohols and p-nitrotoluene

Hydrothermally derived nanocubes of CeO2(10 nm) were explored as an efficient heterogeneous catalyst in the partial oxidation of aromatic alcohols to the corresponding aldehydes and aerobic oxidation ofp-nitrotoluene top-nitrobenzoic acid. The CeO2nanocatalyst was characterized by x-ray diffraction, transmission electron microscopy (TEM), energy dispersive spectroscopy, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy, thermal gravimetric analysis and ultraviolet-visible spectroscopy. TEM/high-resolution TEM micrographs reveal a morphology of mostly cubic nanostructures with exposed highly active {100} and {110} facets. The surface area of nanoceria was determined by BET analysis and found to be 33.8 m2g-1. To demonstrate the universality of the catalytic system, the selective oxidation of different substrates of benzylic alcohol and complete oxidation ofp-nitrotoluene was investigated under mild conditions. Absolute selectivity towards their respective aldehydes was found to be 99.50% (benzaldehyde), 90.18% (p-chlorobenzaldehyde), 99.71% (p-nitrobenzaldehyde), 98.10% (p-fluorobenzaldehyde), 94.66% (p-anisaldehyde) and 86.14% (cinnamaldehyde). Moreover, the catalytic oxidative transformation of nitrotoluene results in 100% conversion with 99.29% selectivity towards nitrobenzoic acid.

Hollow porous silica nanoreactors encapsulating VOx-decorated Pt nanoparticles for the reverse water–gas shift reaction

Reverse water–gas shift (RWGS) reaction is a desirable strategy for achieving CO2 utilization and enhancing CO production. Due to the endothermic nature and the chemical equilibrium of this reaction, the reaction is typically conducted at high temperatures (300 ∼ 1000 °C); however, high temperature conditions lead to the sintering of the catalyst, resulting in a catalyst deactivation. Herein we report the synthesis of a metal oxide (V or Mo oxide)-decorated Pt nanoparticles encapsulated in hollow porous silica nanoreactors (HPSNs) by a W/O micro-emulsion system using branched poly(ethyleneimine) (PEI) as a sacrificial metal–ligand. The HPSNs encapsulating VOx-decorated Pt nanoparticles (Pt-VOx@HPSNs) afforded a 1.8-fold increased activity in RWGS reaction at 500 °C compared with Pt@HPSNs with a net CO production rate of 1140.3 mmol/gcat/h and with nearly 100 % CO selectivity. In situ XAFS measurement and reaction kinetic analysis reveal that the interplay of Pt nanoparticles and the decorated V oxide, which simultaneously activate H2 and CO2, respectively, leads to a lowering of the activation energy and a faster CO production rate. Furthermore, the Pt-VOx@HPSNs catalyst retains over 92 % activity after 50 h of continuous operation at 500 °C with the aid of a protective silica shell. This work offers a strategy for the design and development of an efficient and stable heterogeneous catalyst for RWGS reactions.

Two nickel-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24via WO4/Sb2O bridges and Ni-O-W linkages with efficient hydrogen evolution activity.

Two Ni-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24 units via WO4/Sb2O bridges and Ni-O-W linkages, Na4H8[Ni(enMe)2][(Sb2O)2(NiW6O24)-{Ni12O2(OH)4(enMe)4(H2O)3(WO4)2(B-α-PW9O34)2}2]·39H2O (1) and H9[Ni(en)2(H2O)][Ni0.5(en)2(H2O)][Ni-(enMe)2(H2O)][(Sb2O)2(NiW6O24){Ni12O2(OH)4(en)2(enMe)2(H2O)3(WO4)2}-{Ni12O2(OH)4(en)4(H2O)3(WO4)2}(B-α-PW9O34)4]·45H2O (2), have been hydrothermally synthesized and characterized, in which the {Ni12(WO4)2(PW9)2} subunit was obtained by the synergistic directing effect of 2 lacunary PW9O34 (PW9) fragments and further linked by a central Anderson-type (Sb2O)2(NiW6O24) bridge. Both compounds represent the first example of Ni-added polyoxometalates (POMs) simultaneously based on Keggin-type and Anderson-type POM components. Photocatalytic studies revealed that 2 can work as an efficient heterogeneous catalyst towards a light-driven H2 evolution reaction, achieving a hydrogen evolution rate of as high as 19 214 μmol g-1 h-1 (TON = 1500), which is superior to most of the reported POM-based heterogeneous catalysts.

Transformation of by-product silicon tetrachloride to an efficient and stable heterogeneous base catalyst: Valorization of glycerol into valuable glycerol carbonate

The by-product silicon tetrachloride (SiCl4) from the polysilicon industry was recycled to fabricate a highly efficient and stable lithium silicate (LS) catalyst for upgrading of oversupplied biodiesel by-product glycerol to valuable glycerol carbonate (GC). The characteristics of the LS catalyst were systematically investigated by various experimental characterization techniques and density functional theory (DFT) calculations. The experimental results showed that the hydrolysis of SiCl4 in the lithium nitrate solution helping to the solid phase synthesis of the LS catalyst as lithium could be uniformly dispersed in the silica gel. The as-synthesized LS catalyst mainly consists of lithium orthosilicate with strong basic sties, favoring the catalytic conversion of glycerol. The LS catalyst exhibited an appreciably high catalytic efficiency (turnover frequency of 2.72 min−1) and glycerol conversion (99.8±1.8 %) compared to other reported solid base catalysts. The apparent activation energy (Ea) of this reaction was calculated to be 39.51 kJ/mol. Further, benefiting from the stable silicate structure, the LS catalyst showed an enhanced catalytic stability as the glycerol conversion declined less than 5 % after five times reuse without regeneration. The LS catalyst also revealed marked resistance to the solid base catalyst poisons like water and methanol compare to that of commercial calcium-based catalyst. The temperature-programmed desorption of CO2 (CO2-TPD) and DFT results affirmed that the low-coordination lattice oxygen of the isolated SiO4 tetrahedron on the surface of the LS catalyst acting as a strong basic electron donor promoted the transesterification reaction between DMC and glycerol. As a result, the SiCl4-derived LS catalyst possessed remarkable catalytic efficiency and reusability, which could be an ideal candidate to meet the requirements for industrial application and highlight the potential application of the by-product SiCl4.