Mixed Catalyst System Research Articles

Bottom-Up Construction of Ni(II)-Incorporated Covalent Organic Framework for Metallaphotoredox Catalysis.

The construction of an all-in-one catalyst, in which the photosensitizer and the transition metal site are close to each other, is important for improving the efficiency of metallaphotoredox catalysis. However, the development of convenient synthetic strategies for the precise construction of an all-in-one catalyst remains a challenging task due to the requirement of precise installation of the catalytic sites. Herein, we have successfully established a facile bottom-up strategy for the direct synthesis of Ni(II)-incorporated covalent organic framework (COF), named LZU-713@Ni, as a versatile all-in-one metallaphotoredox catalyst. LZU-713@Ni showed excellent activity and recyclability in the photoredox/nickel-catalyzed C-O, C-S, and C-P cross-coupling reactions. Notably, this catalyst displayed a better catalytic activity than its homogeneous analogues, physically mixed dual catalyst system, and, especially, LZU-713/Ni which was prepared through post-synthetic modification. The improved catalytic efficiency of LZU-713@Ni should be attributed to the implementation of bottom-up strategy, which incorporated the fixed, ordered, and abundant catalytic sites into its framework. This work sheds new light on the exploration of concise and effective strategies for the construction of multifunctional COF-based photocatalysts.

Fast Catalyst Ratio Estimate in Gas Phase Polyethylene Dual Catalyst System

AbstractOne approach used in the industry to improve the properties of polyethylene is to use multi‐reactor with a single catalyst or multiple catalysts in a single reactor. In the latter case, two catalysts with distinct kinetics are selected to achieve the desired product properties. Such mixed catalyst systems enable tailored and advantageous properties at the cost of more challenging process control, because the ratio of the two catalysts serves as an additional manipulated variable. A fast method to estimate the ratio of active catalysts using headspace gas chromatography measurements is proposed here. In this method, a small perturbation in the feed rate is introduced to induce transient responses in the gas phase concentration. Ideally, with known responses from each individual catalyst, the active catalyst ratio can be estimated. To demonstrate this concept, a process model is developed in Aspen Plus. A set of dynamic simulation is performed to understand the responses of each catalyst and the mixed catalyst system, to changes in feed comonomer concentration. The results demonstrate that this method has significantly faster responses compared to feedback from bulk polymer properties and induces minimal process upset or product off‐spec due to small perturbations in a short period of time.

One-pot conversion of wheat straw into biobased chemicals in methanol/water medium using cheap mixed acid catalyst.

Environmental concerns and the diminishing availability of unrenewable resources have spurred research into the use of agricultural waste as a feedstock for industrial applications. Efficient conversion of wheat straw into biobased chemicals is an important way to realize the potential value of renewable agricultural biomass. This study investigated one-pot conversion of wheat straw into two notable platform chemicals, levulinic acid (LA) and methyl levulinate (ML). A mixed acid catalyst system, including 1% H2 SO4 and 0.015mol L-1 Al2 (SO4 )3 , was an efficient catalyst for the conversion of wheat straw due to the combination of Brønsted acid and Lewis acid. A ratio of wheat straw to methanol of 5g/50 mL was identified as the preferred solid/liquid ratio, and a methanol/H2 O medium with 25% water content aided the simultaneous production of LA and ML from wheat straw. Under optimum conditions, the maximum total yield of LA and ML reached 23.01% at 220 °C and 3h. The kinetics of biobased chemical formation and the reaction pathways in methanol/water were investigated. The presence of water in the methanol/H2 O medium affected the distribution of products and promoted hydrolysis reactions. The methanol/H2 O medium not only inhibited the side reactions but also promoted the degradation of wheat straw and increased the total yield of LA and ML. This study provides a feasible method for the conversion of wheat straw to prepare biobased chemicals. © 2021 Society of Chemical Industry.

Two-stage ex-situ catalytic pyrolysis of lignocellulose for the production of gasoline-range chemicals

The appropriate system is needed to produce a scalable and economically viable renewable energy from biomass. The objective of this study is to improve the quality of bio-oil, in terms of Organic Liquid Product (OLP), water content, acidity, favourable fractions, as well as gasoline-range chemicals. The influence of a staged layered catalyst system consists of a mesoporous catalyst, Al-MCM-41, and a microporous catalyst, HZSM-5, on the bio-oil quality was investigated. Additionally, the effect of reaction temperatures in the range of 400–600 °C with the optimum staged catalyst system on the catalytic pyrolysis product was analysed. The experiments of lignocellulosic biomass pyrolysis and catalytic pyrolysis were performed using a fixed bed reactor equipped with oil condensers and a gas collection sample bag. The quality of bio-oil produced from the thermal pyrolysis of lignocellulosic biomass, catalytic pyrolysis with single catalysts, catalytic pyrolysis with the staged catalyst system, as well as catalytic pyrolysis with mixed catalyst system was studied. The results show that Al-MCM-41 with HZSM-5 in the staged catalyst system enhanced the production of favourable compounds: hydrocarbons, phenols, furans, and alcohols. The favourable compounds yield that boosted 5.25–6.43% of that with single HZSM-5 catalyst was produced with HZSM-5:Al-MCM-41 mass ratio of 3:1 and 7:1. The pyrolysis and catalysis temperature of 500 °C with HZSM-5:Al-MCM-41 ratio of 3:1 obtained the optimum quality of bio-oil with 11.08 wt.% of OLP, 76.20% of favourable fractions, 41.97 wt.% of water content, low TAN of 43.01 mg-KOH/g, high deoxygenation, as well as high gasoline-range production of 97.89%.

Catalytic Direct-Type Addition Reactions of Alkylarenes with Imines and Alkenes.

Catalytic addition reactions of very weakly acidic nonactivated alkylarenes such as toluene and its derivatives were developed by using a strongly basic mixed catalyst system under mild reaction conditions. The addition reactions with imines and alkenes proceeded smoothly under proton-transfer conditions to afford the desired products in good to high yields, and high levels of regio- and stereoselectivity were achieved. It was also revealed that the asymmetric addition reaction of an alkylarene was possible.

Catalytic Direct‐Type Addition Reactions of Alkylarenes with Imines and Alkenes

AbstractCatalytic addition reactions of very weakly acidic nonactivated alkylarenes such as toluene and its derivatives were developed by using a strongly basic mixed catalyst system under mild reaction conditions. The addition reactions with imines and alkenes proceeded smoothly under proton‐transfer conditions to afford the desired products in good to high yields, and high levels of regio‐ and stereoselectivity were achieved. It was also revealed that the asymmetric addition reaction of an alkylarene was possible.

Fuel-Borne Catalyst와 Perovskite로 구성된 복합촉매 시스템에 의한 디젤 탄소입자상 물질의 연소반응: 반응성능과 Perovskite 촉매조성 (La1-x A′xBO3: A′ = K, Sr; 0 ≤ x ≤ 1; B = Fe, Cr, Mn)의 상관관계

최근 선진국을 중심으로 고연비-저배출 내연기관 (디젤) 자동차 보급의 필요성이 대두되면서 기존 촉매후처리 장치의 저온성능 강화를 위한 기술적 방안들이 시급히 요구되고 있다. 본 논문에서는 디젤엔진 배출 탄소입자상 물질의 연소반응에 있어 연료함유 촉매(Fuel-Borne Catalyst)와 페로브스카이트(Perovskite)의 복합촉매 시스템이 보이는 상용모델촉매 대비 우수한 저온 연소성능과 이의 Perovskite 촉매 조성에 대한 의존성에 관해 논하였다. Fe/Ce 계열 연료함유 촉매가 A-site 원소(La)에 K이 부분치환되고, B-site 금속이 Fe인 Perovskite 촉매와 복합화될 때 상대적으로 우수한 저온 연소성능 개선효과가 관찰되었다. 이를 관찰하기 위해 연료함유 촉매가 함유되거나 함유하지 않은 탄소 입자상 물질과 다양한 조성의 La 계열 Perovskite 촉매를 혼합한 고정층에 대한 온도상승 산화반응 실험(Temperature-Programmed Oxidation)을 수행하였으며, 이산화탄소 생성과 질소산화물 농도 저하 패턴의 연동특성을 통해 두 촉매의 상호 연계작용을 유추하였다.

Synthesis, characterization and correlation with the catalytic activity of efficient mesoporous niobia and mesoporous niobia–zirconia mixed oxide catalyst system

Mesoporous mixed oxide has always remained as a subject of interest due to diffusion relaxation and generation of new surface potential and acidity by mixing of different stoichiometries of metal oxide. To deliver more insight on niobia based catalyst, herein, we have synthesized mesoporous niobia and five different mole ratios of niobia–zirconia mixed oxide. The catalysts were characterized by XRD, N2-physisorption, FTIR, UV–Vis and NH3-TPD techniques. Less distorted NbO6 octahedra and NbOH or Nb–OH–Zr are found to act as Bronsted center responsible for reaction. The results established the role of Kung model to generate acidic sites in mesoporous mixed oxide.

A practical and efficient synthesis of methyl levulinate from cellulosic biomass catalyzed by an aluminum-based mixed acid catalyst system

A combination of aluminum compounds and organic sulfonic acids was an efficient catalyst system for direct methyl levulinate synthesis from both microcrystalline cellulose and wood powder.

ChemInform Abstract: Calcium‐Catalyzed Formal [2 + 2 + 2] Cycloaddition.

AbstractA formal [2 + 2 + 2] cycloaddition of enynes (I) and (IV) with aliphatic and aromatic aldehydes is achieved in the presence of Ca(NTf2)2 and Bu4NPF6 or Bu4NBF4 as mixed catalyst system resulting in the formation of dihydropyran derivatives (III) and (V).

Niobia-alumina as methanol dehydration component in mixed catalyst systems for dimethyl ether production from syngas

Pure or niobia-modified aluminas containing from 5.9 to 20wt% Nb2O5 were used as the dehydration component in the direct synthesis gas conversion to dimethylether (DME), in combination with a conventional CuO-ZnO-Al2O3 methanol synthesis catalyst, modified or not with niobia.A in situ DRIFTS study with the pure and one niobia-modified alumina under a CO/H2 stream at the same temperature used in the catalytic experiments (538K) showed irreversible formation of surface formate on the alumina surface, which occurred reversibly and to a smaller extent on the niobia-modified alumina.Modification with niobia caused a strong decrease on the alumina surface basicity and had little effect on its acidity. With the methanol synthesis catalyst, niobia addition had little effect on crystallite size and reducibility, but caused a decrease in surface basicity and a strong increase in surface acidity.The mixed catalyst systems were tested in the direct syngas to DME conversion in a liquid-phase CSTR, using n-hexadecane as the catalyst suspension medium, at 538K and 5MPa. It was found that the mixed-catalyst system displayed higher overall activity when the methanol dehydration catalyst was a niobia-modified alumina, rather than the pure alumina. The highest activity was obtained for the smallest niobia addition to alumina (5.9wt%niobia). This effect was ascribed to the decrease in the alumina surface basicity due to deposition of niobia, which causes improved tolerance of the methanol dehydration catalyst to large concentrations of carbon monoxide and carbon dioxide in the reaction medium. The opposite effect was found when the methanol synthesis catalyst was modified with niobia.

Synthesis and characterization of iPP‐sPP stereoblock produced by a binary metallocene system

ABSTRACTStereoblock polypropylenes comprising of iPP and sPP segments are synthesized by polymerization of the following binary system of metallocenes: the Cs‐symmetric [2,7‐t‐Bu2(Flu)2Ph2C(Cp)ZrCl2] and the C2‐symmetric rac‐Me2Si(2‐Me‐4‐Ph‐Ind)2ZrCl2. Blends of samples made either by each catalyst individually (solution blend) with materials obtained with the mixed catalyst system (reactor blend) are compared. The simultaneous presence of MAO and DEZ, enhancing fast and reversible transfer of the growing chains between the two active centers, leads to the formation of a stereoblock microstructure. In this case, low molecular weight polymers are obtained. The junction between the blocks is qualitatively observed in 13C NMR. When made in toluene, the stereoblock material consists of a majority of syndiotactic sequences, whereas the ratio is more equilibrated when the polymerization was conducted in the more polar chlorobenzene. This is confirmed by the results obtained with 13C NMR, CRYSTAF, HT HPLC, DSC, SSA, WAXD, and optical microscopy. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1422–1434

알루미늄 화합물 혼합촉매계의 L-lactide 용액중합 특성 연구

Solution polymerization behaviors of L-lactide using single and mixed aluminium catalyst systems were studied. Triisobutylaluminium (TIBA) was a reference catalyst for mixing. For the /TIBA catalytic systems, the molecular weight of the resulting polylactide (PLA) decreased as the composition of increased. The higher molecular weight shoulder was revealed in their GPC curve. At TIBA of 80 mol% a bimodal GPC curve was shown. The conversion in the trimethylaluminium (TMA)/TIBA catalysts system decreased as the composition of TMA in the mixed catalyst increased. The conversion in the trioctylaluminium (TOA)/TIBA catalysts system decreased as the composition of TOA in the mixed catalyst increased. The unimodal molecular weight distribution was observed with the TOA/TIBA catalyst systems. The Al compounds-mixed catalyst could produce a higher molecular weight shoulder in the GPC curve.

Niobia-modified aluminas prepared by impregnation with niobium peroxo complexes for dimethyl ether production

Use of a water-soluble niobium peroxo complex allowed the preparation of niobium-modified aluminas containing up to 90% of the theoretical niobia monolayer in one impregnation step. There was a maximum in the density of surface Lewis acid sites at 45% of the theoretical monolayer. FTIR of adsorbed pyridine and adsorbed CO2 suggest the vertical growth of the Nb2O5 layer for the largest niobium contents. The addition of 22.5% of the theoretical monolayer eliminated about 80% of the basic surface hydroxyls, inhibiting the adsorption of gas phase CO2 by the samples. The niobia/alumina catalysts suffered less inhibition by CO2 than the pure alumina in the methanol dehydration reaction, confirming that Nb2O5 is mainly deposited on sites where the CO2 adsorption is stronger, leaving free sites that are active in catalytic dehydration and less inhibited by CO2, however none of the niobia/aluminas was more active than the pure alumina. Nevertheless, in the direct syngas to DME conversion using a mixed catalyst system comprised of a CuZnAl methanol synthesis catalyst and a methanol dehydration component, the activity was significantly larger with a niobia/alumina as a dehydrating component than with the pure alumina.

Microwave-assisted microemulsion synthesis of carbon supported Pt-WO3 nanoparticles as an electrocatalyst for methanol oxidation

A microwave-assisted microemulsion synthesis of carbon supported Pt-WO3 nanoparticles is presented. Amorphous WO3 nanoparticles of 1.0nm in size were first deposited onto carbon from an alkaline tungstate containing microemulsion via mixing with an acid containing microemulsion under controlled microwave exposure. Platinum was subsequently deposited onto the carbon supported WO3 nanoparticles by reducing H2PtCl6 in a microemulsion under controlled microwave exposure forming nanoparticles with an average size of 2.5nm. This method produced a homogeneous distribution of nanoparticles on the carbon support with a uniform Pt:W ratio. The Pt:W can be well controlled by varying the metal precursors’ Pt:W ratio. Hydrogen adsorption, CO-stripping and Cu-UPD stripping method were used to estimate the electrochemical surface area of Pt in the Pt-WO3 mixed catalyst system. Cyclic voltammetry and chronopotentiometry experiments demonstrate that a 1:1 ratio of Pt:W has the highest electrocatalytic activity based on Pt mass for methanol oxidation in sulfuric acid. The enhanced electrocatalytic activity is attributed to both physical and chemical influence of the WO3 component.

Factors influencing recyclability of Co(III)-salen catalysts in the hydrolytic kinetic resolution of epichlorohydrin

The recyclability of Co(III)-salen catalysts, where salen is defined by ( R, R)- N, N′-bis(3,5-di- tert-butylsalicylidene)-1,2-cyclohexanediamine, for the hydrolytic kinetic resolution (HKR) of racemic epichlorohydrin is a strong function of the counterion of the Co(III)-salen catalyst. The nature of the counterion determines whether the HKR reaction follows primarily a bimetallic or monometallic reaction path, which significantly affects catalyst recyclability. For example, Co(III)-salen initially containing the nucleophilic Cl − counterion catalyzes the HKR of epichlorohydrin according to a bimetallic reaction path but loses activity upon recycle, as Cl − is replaced with OH − during the reaction. In contrast, a Co(III)-salen catalyst containing non-nucleophilic SbF 6 − counterion catalyzes the reaction according to a monometallic reaction path and is quite stable during multiple recycles, albeit at a low rate with less selectivity. A mixed catalyst system with Co(III)-salen initially containing Cl − to which Co(III)-salen with SbF 6 − is later added demonstrates high activity and high stability to recycling. Additional experiments with Co(III)-salen initially containing the acetate counterion reveal a progressive decline in activity with multiple recycles even after regeneration with acetic acid between runs, suggesting a destructive role of the regeneration process.

ChemInform Abstract: Acceleration of the Morita—Baylis—Hillman Reaction by a Simple Mixed Catalyst System.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Effect of preparation conditions on selective oxidation of propane to acrylic acid

The effects of chemical composition and preparation conditions, especially calcination atmosphere and water content on the catalytic performances of MoVTeNbO mixed oxide catalyst system for the selective oxidation of propane to acrylic acid were investigated. Among the catalysts studied, Mo 1.0V 0.3Te 0.23Nb 0.12O x catalyst calcined in inert atmosphere at 600 °C shows the best performance in terms of propane conversion and selectivity to acrylic acid. The results reveal that proper chemical composition, calcination atmosphere and water content affect greatly the catalysts in many ways including structure, chemical composition, which are related to their catalytic performances; and 51.0% propane conversion and 30.5% one-pass yield to acrylic acid can be achieved at the same time.

Synthesis and Stille Cross-Coupling Reactions of 2-(Tributylstannyl)- and 2,5-Bis(trimethylstannyl)tellurophene

Herein, we describe the synthesis and Stille cross-coupling reactions of 2-(tributylstannyl)- and 2,5-bis(trimethylstannyl)tellurophene. The reactions were most optimal when using aryl iodides as coupling partners, and a mixed catalyst system consisting of tetrakis(triphenylphosphine)palladium(0) and copper(I) iodide, together with cesium fluoride as additive, in N,N-dimethylform­amide. This is the first reported synthesis and use of stannylated tellurophenes for cross-coupling reactions.

Acceleration of the Morita−Baylis−Hillman Reaction by a Simple Mixed Catalyst System

By using a catalytic amount of 4-dimethylaminopyridine (DMAP) as a nucleophile in the presence of an equal amount of tetramethylethylenediamine (TMEDA) and MgI(2), Morita-Baylis-Hillman adducts can be obtained in good to excellent yields from various aromatic and aliphatic aldehydes and cyclic enones/enoates at room temperature after convenient reaction times.