Combination Of Catalyst Research Articles

Solvent-free multi-component synthesis of unsymmetrical bis(indolyl)alkanes with Lewis acid-surfactant-SiO2 as nanocatalyst

Herein we report the multicomponent synthesis of the bis(indolyl)methane derivatives in a ball mill. The reaction was carried out under solvent-free conditions using only the Lewis acid-surfactant-SiO2 composite nanocatalyst (LASSC) prepared in situ. The unsymmetrical bis(indolyl) methane derivatives containing nitro or fluorine substitution with a yield of 72%–92% were obtained in a short reaction time. Within we verified that under the action of the combined catalyst of AlCl3·6H2O + SDS + SiO2, the method of preparing unsymmetrical bis(indolyl)methane by mechanical grinding without solvent has obvious advantages. Finally, we inspected that the catalysis system can be used eight times without a significant decrease in activity.

Facial synthesis of ferric molybdate (Fe2(MoO4)3) nanoparticle and its efficiency for biodiesel synthesis via oleic acid esterification

Catalytic esterification of fatty acids, such as oleic acid, is one of the most important chemical pathways for producing biofuels, and attention is now focused on looking for heterogeneous catalysts to avoid the defects of homogeneous catalysts. With this approach, an efficient Lewis acidic catalyst, Fe 2 (MoO 4 ) 3 , was successfully prepared with definite crystalline morphology to catalyze the esterification reaction of oleic acid together with ethanol. Under optimum conditions (70 °C, 9 alcohol: 1 oleic molar ratio and 3% catalyst amount), the catalytic conversion of oleic acid to biodiesel was 90.5% and 92.5 in case of 5% catalyst, indicating that the combined catalyst has good catalytic activity. The kinetic study of ethanol–oleic acid esterification was conducted, as the kinetic study follows first-order kinetics with the calculated activation energy E a = 25.21 kJ mol − 1 and pre-exponential factor A 0 = 2449.16 min − 1 . Thermodynamic showed a positive value of Δ H, Δ S, and Δ G (endothermic reaction). • The iron–molybdate catalysts Fe 2 (MoO 4 ) 3 was prepared using a sol–gel process. • The esterification reaction of oleic acid and ethanol using Fe 2 (MoO 4 ) 3 . • The catalyst showed high catalytic activity at 70 C with O/E molar ratio is 1:9. • The catalyst exhibited high efficiency and reusability up to six times.

Dehydrogenative Coupling of Alkanes and Benzene Enhanced by Slurry-Phase Interparticle Hydrogen Transfer.

The dehydrogenative coupling reaction of alkanes and benzene has attracted attention as a method of direct conversion of alkanes to raw materials for useful chemical products. Here, we report the first combined catalyst system composed of hydrotalcite-supported palladium and solid acid aluminum-exchanged montmorillonite for the direct alkylation of benzene promoted by slurry-phase interparticle hydrogen transfer at 150 °C. The combination of the two catalytic particles showed excellent activity and achieved the maximum benzene conversion of 21% and target product selectivity of 84% in the reaction of n-heptane and benzene. Our results, thus, provide a feasible strategy to design efficient liquid-phase reaction systems employing simple physical mixing of two catalytic particles.

Photocatalytic (Het)arylation of C(sp3)–H Bonds with Carbon Nitride

Graphitic carbon nitride materials have attracted significant interest in recent years and found applications in diverse light-to-energy conversions such as artificial photosynthesis, CO2 reduction, or degradation of organic pollutants. However, their utilization in synthetic photocatalysis, especially in the direct functionalization of C(sp3)–H bonds, remains underexplored. Herein, we report mesoporous graphitic carbon nitride (mpg-CN) as a heterogeneous organic semiconductor photocatalyst for direct arylation of C(sp3)–H bonds in combination with nickel catalysis. Our protocol has a broad synthetic scope (>70 examples including late-stage functionalization of drugs and agrochemicals), is operationally simple, and shows high chemo- and regioselectivities. Facile separation and recycling of the mpg-CN catalyst in combination with its low preparation cost, innate photochemical stability, and low toxicity are beneficial features overcoming typical shortcomings of homogeneous photocatalysis. Detailed mechanistic investigations and kinetic studies indicate that an unprecedented energy-transfer process (EnT) from the organic semiconductor to the nickel complex is operating.

Direct C2-arylation of N-acyl pyrroles with aryl halides under palladium catalysis

C2-arylation of N-acyl pyrroles with aryl halides is developed for the first time using Pd(PPh3)4 as a catalyst in combination with Ag2CO3 under air, which allowed the application of a good compatibility catalytic system. This protocol provides a straightforward method for the preparation of valuable arylated pyrroles in moderate to good yields under the standard conditions with good substrate tolerance. Interestingly, while N-benzoyl pyrroles reacted well, the use of substrates with a thiophene or furan ring indicated that the thiophene and furan rings are more reactive than pyrrole for the present catalytic system.

Surfactant-mediated thioglycosylation of 1-hydroxy sugars in water.

Thioglycosides are an important class of sugars, since they can be used as non-ionic biosurfactants, biomimetic glycosides, and building blocks for carbohydrate synthesis. Previously, Brønsted- or Lewis-acid-catalyzed dehydrative glycosylations between a 1-hydroxy sugar and a thiol have been reported to yield open-chain dithioacetal sugars as the major products instead of the desired thioglycosides. These dithioacetal sugars are by-products derived from the endocyclic bond cleavage of the thioglycosides. Herein, we report dehydrative glycosylation in water mediated by a Brønsted acid-surfactant combined catalyst (BASC). Glycosylations between 1-hydroxy furanosyl/pyranosyl sugars and primary, secondary, and tertiary aliphatic/aromatic thiols in the presence of dodecyl benzenesulfonic acid (DBSA) provided the thioglycoside products in moderate to good yields. Microwave irradiation led to improvements in the yields and a shortening of the reaction time. Remarkably, open-chain dithioacetal sugars were not detected in the DBSA-mediated glycosylations in water. This method is a simple, convenient, and rapid approach to produce a library of thioglycosides without the requirement of anhydrous conditions. Moreover, this work also provides an excellent example of complementary reactivity profiles of glycosylation in organic solvents and water.

Development of bamboo charcoal and fragaria vesca powder photocatalysts in hydrogen production via water splitting

Hydrogen has become the subject of attention as an environmentally friendly and effective source in recent years. The photocatalysis method with biomass-photocatalyst is an alternative step for hydrogen production via water splitting. In this study, bamboo charcoal (BC) and Fragaria Vesca Powder (FVP) are biomass materials used to develop photocatalysts in hydrogen production. The light source for photocatalysis was a halogen lamp with a wavelength of 560 nm. The hydrogen gas produced is measured using the MQ-8 sensor which is capable of measuring hydrogen gas in 100–10,000 ppm. Hydrogen production is significantly increased with the combination of the BC and FVP photocatalysts. Based on scanning electron microscope (SEM) image analysis by Image J software, BC and FVP have a negative and positive charge, respectively. The aromatic carbon ring in BC has an energy gap of 2.48 eV whereas that in FVP has a lower energy gap, 2.32 eV due to functional groups energizing electron in the FVP aromatic ring. The interaction between positive and negative charges when BC and FVP are combined generates the second lower energy gap in the combined catalyst, 1.66 eV that tends to increase electron density on the catalyst surface. The more dense electrons destabilize more hydrogen and covalent bonds in water increasing hydrogen production by 20 times from that with BC only or by 4 times from that with FVP only. When aluminum foil (AF) was added to the bottom of the reactor tube, the photocatalyst's performance was strengthened. The AF material was an 8011 aluminum alloy with a thickness of 0.02 mm and a diameter of 80 mm. AF has two important roles, that is, accelerates reduction reaction and facilitates the breaking of the hydrogen and covalent bonds in water

Synthesis of Spirocyclic Piperidines by Radical Hydroarylation.

Reported here are conditions for the construction of spirocyclic piperidines from linear aryl halide precursors. These conditions employ a strongly reducing organic photoredox catalyst in combination with a trialkylamine reductant to achieve formation of aryl radical species. Regioselective cyclization followed by hydrogen-atom transfer affords a range of complex spiropiperidines. This system operates efficiently under mild conditions without the need for toxic reagents or precious metals.

Polyoxometalates as catalysts for fluorescence amplification in rapid and sensitive detection of artemisinin

The combination therapy based on artemisinin is the most effective method to treat malaria. Sensitive, rapid and accurate detection of artemisinin is very important to monitor clinical pharmaceutical effect as well as the drug quality control. In this work, catalytic performance of polyoxometalates (POMs), vanadomolybdophosphoric heteropoly acid (H5PMo10V2O40, PMoV2) and tungstophosphoric heteropoly acid (Na5PW11O39Cu, PW11Cu), are investigated. It is indicated that the POMs exhibit peroxidase-like activity, which efficiently catalyze the artemisinin/thiamine reaction to produce fluorescent product thiochrome. With the usage of the POMs as the catalyst in combination with fluorescent probes, we propose a method for highly sensitive and rapid determination of artemisinin. When PMoV2 and PW11Cu are used as catalysts, the linear ranges are 1.0 × 10−6-1.0 × 10−1 mM and 5.0 × 10−6-9.0 × 10−1 mM, and the detection limits are as low as 0.5 nM and 1 nM, respectively. The method is successfully applied to determine artemisinin in human plasma and Artemisia annua. L leaves with good accuracy.

Developing single-site Pt catalysts for the preferential oxidation of CO: A surface science and first principles-guided approach

We report a comprehensive study combining surface science, Density Functional Theory (DFT) calculations, and catalyst synthesis, characterization, and testing to investigate the preferential oxidation of CO in the presence of H2 over single-site Pt1/CuxO catalysts. Surface science studies show that while Pt1/CuxO model surfaces enable low-temperature CO oxidation via a Mars-van Krevelen mechanism, there was no evidence for H2 activation or oxidation. DFT-based calculations explain these results and demonstrate that the H2 oxidation barrier is high as compared to H2 desorption from Pt1/CuxO. Inspired by these model catalyst studies, nanoporous Pt1/CuxO catalysts were synthesized and demonstrated to be active and highly selective for the preferential oxidation of CO. This work highlights the potential of combined surface science, theory, and catalyst studies for identifying new catalytic materials, which in this case led to the development of a promising single-site Pt1/CuxO catalyst for the preferential oxidation of CO.

Carbonization mechanism of polypropylene catalyzed by Co compounds combined with phosphorus-doped graphene to improve its fire safety performance

Polypropylene (PP), as a non-charring polymer, is highly flammable without obvious char residue after combustion. Catalyzing carbonization of the polymer during combustion has become a valid method for improving its flame retardancy. In this work, two novel combined catalysts were designed and their effects on the thermal stability and flame retardancy of PP were researched. Thermogravimetric analysis results indicated that the combination of Co compounds and P atom-doped reduced graphene oxide (PRGO) markedly improved the thermal stability of PP. Besides, the char residue of PP was increased with the addition of combined catalysts. The char yield was enhanced from 1.09 wt % for pure PP to 7.10 wt % for PP/Co-MOF/PRGO. Combustion behaviors of PP and its composites were investigated by the cone calorimeter test. The incorporation of combined catalyst resulted in the reductions of peak heat release rate, total heat release, CO and CO2 releases of PP during combustion. The presence of carbon spheres in the residual char has been confirmed by X-ray diffraction and scanning electron microscope. The flame-retardant mechanism was summarized based on the results of gas chromatography-mass spectrometry and char analysis. This research extends the method of catalyzing the formation of high-quality carbonaceous protection layers to improve the flame-retardant performance of polymers.

Making an Anode of a Hydrogen–Air Fuel Cell More Tolerant to CO: PtRuCo/C Catalyst and Synergistic Effect of PtRu/C and Oxygen Additives

Methods for making platinum-based catalytic systems (Pt/C, PtRu/С) in an anode for a low-temperature hydrogen–air fuel cell with a Nafion membrane more tolerant to CO were suggested and implemented. A PtRuCo/C trimetallic catalyst was synthesized, and the influence of the modification of the binary catalyst with cobalt on the current characteristics of the fuel cell was evaluated in a model of a hydrogen–air fuel cell. The fuel cell models had higher operation characteristics in oxidation of pure and technical-grade hydrogen, compared to those with the monoplatinum and binary catalysts. The influence of the air injection into hydrogen containing CO impurities was analyzed. The contribution of the air injection is manifested more strongly for the binary system than for the monoplatinum system. The trimetallic catalyst in combination with the air injection into hydrogen fuel can be used for optimizing the operation of the membrane–electrode unit of a fuel cell operating on technical-grade hydrogen.

Multifaceted Substrate–Ligand Interactions Promote the Copper-Catalyzed Hydroboration of Benzylidenecyclobutanes and Related Compounds

A unified synthetic strategy to access tertiary four-membered carbo/heterocyclic boronic esters is reported. Use of a Cu(I) catalyst in combination with a modified dppbz ligand enables regioselective hydroboration of various trisubstituted benzylidenecyclobutanes and carbo/heterocyclic analogs. The reaction conditions are mild, and the method tolerates a wide range of medicinally relevant heteroarenes. The protocol can be conveniently conducted on gram-scale, and the tertiary boronic ester products undergo facile diversification into valuable targets. Reaction kinetics and computational studies indicate that the migratory insertion step is turnover-limiting and accelerated by electron-withdrawing groups on the dppbz ligand. Energy decomposition analysis (EDA) calculations reveal that electron-deficient P-aryl groups on the dppbz ligand enhance the T-shaped π/π interactions with the substrate and stabilize the migratory insertion transition state.

Efficient production of 5-hydroxymethylfurfural from glucose over silica-tin oxide composite catalysts

In this study, silica-tin oxide composites (xSiSnO) and a H3PO4 modified 20SiSnO (SiSnPO) have been synthesized via a simple procedure and evaluated for the catalytic dehydration of glucose to 5-hydroxymethylfurfural (HMF). FTIR, XPS, UV–vis, NH3-TPD, and Py-FTIR characterizations revealed that Sn species were possibly inserted into the framework structure of silica to generate weak-to-medium Lewis acid sites; besides, calcining H3PO4 impregnated 20SiSnO obviously improved the Brønsted acid sites. When the 20SiSnO/HCl combined catalysts were used, a high HMF yield of 75.5% was achieved in DMSO/H2O at 160 °C for 60 min, and the 20SiSnO showed relatively high stability even under thermal acidic environment. By utilizing the multifunctional SiSnPO as catalyst, an inspiringly high HMF yield was also reached (70.3%), and the SiSnPO exhibited reasonable recyclability for glucose dehydration. Furthermore, the possible reaction pathway of glucose dehydration over SiSnPO catalyst has been discussed.

Oriented Hydrocracking of Naphthalene into High-Value Light Aromatics over Difunctional Catalysts: Effect of Hydrogen Spillover and Utilization of Hydroreaction Characteristics for Different Active Metals

Serial difunctional catalysts supported on γ-Al2O3 and HY zeolite were synthesized and characterized systemically. The characterization results disclosed that hydrogen spillover existed in the NiMo and CoMo catalysts, and decreasing Ni/Mo and Co/Mo ratios could reduce hydrogen spillover. Meanwhile, the naphthalene hydrocracking behaviors over different catalysts were investigated and compared. The higher yield of cyclane for CoMo/AY catalysts demonstrated that hydrogen spillover could deeply hydrogenate naphthalene into cyclane. The combined catalysts of Ni/[email protected]/A, Ni/[email protected]/A and Ni/[email protected]/A showed relatively lower conversions of naphthalene but higher yields of valued <C10 aromatics. The combined catalyst Ni/[email protected]/A presented the highest yield of light aromatics due to the appropriate reduction of hydrogen spillover and rational utilization of hydro-reaction characteristics for different active metals. Moreover, the stability of CoMo catalyst was higher than NiMo catalyst. The catalysts containing Co and Mo active metals presented low content of carbon deposition.

Highly efficient conversion of waste plastic into thin carbon nanosheets for superior capacitive energy storage

The wide application of carbon nanosheets (CNS) is still restricted by low production. Meanwhile, the accumulation of waste plastic generates serious environmental pollution. Nowadays, the conversion of waste plastic into two-dimensional CNS is regarded as a promising way to address these issues due to the high carbon content of waste plastic. However, this conversion process is still impeded by low-efficient catalysts so far. Herein, the highly efficient carbonization of waste polypropylene (PP) into CNS is achieved using a combined catalyst of ferrocene and sulfur. The carbonization process in sealed space ensures an ultrahigh carbon yield (62.8%) and a thin thickness (4–4.5 nm) of as-prepared CNS, even though little catalyst is used. After activation, the activated carbon nanosheets (ACNS) show a well-defined hierarchical porous structure with a large specific surface area (3200 m2 g−1) and a big pore volume (3.71 cm3 g−1). The ACNS based electrode delivers a high specific capacitance of 349 F g−1 at 0.5 A g−1. The fabricated symmetric supercapacitor manifests a high energy density of 23 Wh kg−1 at 225 W kg−1. These findings provide a reference for the efficient conversion of waste plastic into energy storage materials.

Catalytic and photocatalytic epoxidation over microporous titanosilicates with nanosheet or layered structure

Bulky epoxides are industrially produced by organic synthesis in multistep procedures, generating significant amounts of waste products in the process. Efficient catalyst in combination with a simple oxidant (H2O2 or O2) would significantly reduce the waste production. Four types of microporous titanosilicates with extra-large pores (Ti-UTL), and shortened diffusion pathways (L-TS, Ti-MCM-22, and Ti-SPP) were prepared and investigated in the epoxidation of cyclooctene with H2O2 and photocatalytic oxidation using O2. Ti-UTL is a zeolite possessing 14−12-ring channel system. l-TS-1 and Ti-MCM-22 are composed of aggregates of titanosilicate nanosheets with the thickness of ca. 2 nm and hexagonal thin platelets, respectively. Ti-SPP is composed of olive-like aggregates with approximately length of 0.88–1.12 μm and width of 0.44−0.68 μm consisting of intergrown (self-pillared) nanosheets having 13−70 nm in size. In the epoxidation with H2O2 as an oxidant, Ti-MCM-22 showed the highest catalytic activity due to the wide interlayer space, which enhanced the accessibility of cyclooctene to active titanium site. While, in the photocatalytic epoxidation in the presence of O2 instead of H2O2, Ti-UTL showed the highest activity. The incorporated germanium atoms, which is indispensable component for the construction of extra-large pores, may affect the electronic properties of active titanium species, leading to high photocatalytic activity.

Understanding the active sites of boron nitride for CWPO: An experimental and computational approach

Hexagonal boron nitride (h-BN) has been explored as a catalyst for degrading persistent organic pollutants in wastewater by Catalytic Wet Peroxide Oxidation (CWPO). Herein, the superior activity of the h-BN on the phenol degradation (model pollutant) compared to other metal-free catalysts, such as carbon-based ones, and the lower selectivity to CO encourage the potential application of h-BN catalysts in CWPO processes. Through a combined density functional theory calculations, experimental reactions and catalyst characterization approach, a comprehensive study on the reaction mechanism has been conducted. According to this, only defected B atoms in the h-BN layer, protonated as B-(OH2)+, decompose the hydrogen peroxide into highly reactive hydroxyl radicals. The radical species diffuse towards inner h-BN regions and react with the phenol adsorbed by π-π interaction on the h-BN surface. Oxidation by-products cause carbonaceous deposits and progressive deactivation of the h-BN catalyst that can be directly regenerated by burning off in air.

NNC-Scorpionate Zirconium-Based Bicomponent Systems for the Efficient CO2 Fixation into a Variety of Cyclic Carbonates.

Two new derivatives of the bis(3,5-dimethylpyrazol-1-yl)methane modified by introduction of organosilyl groups on the central carbon atom, one of which bearing a chiral fragment, have been easily prepared. We verified the potential utility of these compounds through the reaction with [Zr(NMe2)4] for the preparation of novel zirconium complexes in which an ancillary bis(pyrazol-1-yl)methanide acts as a robust monoanionic tridentate scorpionate in a κ3-NNC chelating mode, forming strained four-membered heterometallacycles. These κ3-NNC-scorpionate zirconium amides were investigated as catalysts in combination with tetra-n-butylammonium bromide as cocatalyst for CO2 fixation into five-membered cyclic carbonate products. The study has led to the development of an efficient zirconium-based bicomponent system for the selective cycloaddition reaction of CO2 with epoxides. Kinetics investigations confirmed apparent first-order dependence on the catalyst and cocatalyst concentrations. In addition, this system displays very broad substrate scope, including mono- and disubstituted substrates, as well as the challenging biorenewable terpene derived limonene oxide, under mild and solvent-free conditions.

Advances in solid catalysts for selective hydrogenolysis of glycerol to 1,3-propanediol

ABSTRACT Glycerol is one of the top 12 platform chemicals obtained from biomass. Its surplus availability as a by-product of biodiesel, fat-splitting and soap manufacturing industries and affordable price lends significant opportunity for its valorization, using solid catalysts, into propanediols (PDOs), particularly to 1,3-propanediol (1,3-PDO), by selective hydrogenolysis. 1,3-PDO is an important chemical with wide applications including that as a precursor in polymers manufacturing. However, the synthesis of 1,3-PDO by selective cleavage of the secondary C-O bond of glycerol in the presence of hydrogen (instead of the primary C-O bond yielding 1,2-PDO) is highly challenging. Of late, supported Pt and Ir catalysts in combination with a reducible oxide (WOx or ReOx) were found selective for 1,3-PDO formation. Support, metals composition and additives (co-added metals) affect the performance of these catalysts. Detailed investigations revealed that metal dispersion, electronic connectivity between metal and metal oxide/support, hydrogen activation/spillover and Brönsted acidity are some parameters that influence the activity and selectivity of these bi-functional, metal-metal oxide catalysts. This review summarizes the latest advances in these solid catalysts for selective hydrogenolysis of glycerol to 1,3-PDO, a monomer for advanced polymers.