Synthesis of isoamyl acetate usin NaX and NaY zeolites as catalysts

A liquid phase esterification reaction between glacial acetic acid and isoamyl alcohol has been studied using NaX and NaY zeolites as catalysts. The influence of calcination temperature, the amount of catalysts, reaction temperature, time of esterification and the molar ratio of the reactants has been investigated. Water insoluble products have been isolated from the reaction mixture and analyzed for the ester. Both NaX and NaY are found to be active as catalysts in the reaction. However, their catalytic activity varies with the reaction conditions and their calcination temperature. The reaction has been found to be 100% selective to ester formation. Catalytic activity of the zeolites has been correlated with their surface acidity.     

Morphological and heterojunctional engineering of two-dimensional porous Mo-Ni based catalysts for highly effective catalytic reduction of aromatic nitro compounds

Hydrogenation reactions play crucial roles on chemical synthesis and pollutant elimination. The improvement of the ability to activate reactants and increase of the contact probability between the catalysts and reactants are positive to improve the catalytic performance. Herein, we have reported the design of two-dimensional porous Ni-Ni₃N-Ni Mo N heterojunction sheets(2D Mo-Ni based nanosheets) for efficient catalytic hydrogenation of the aromatic nitro-compounds. The heterojunction ...     

Reduction of Carbonyl Compounds with Chiral Oxazaborolidine Catalysts: A New Paradigm for Enantioselective Catalysis and a Powerful New Synthetic Method

High enantioselectivity can be achieved when chiral oxazaborolidines are used as catalysts in the reduction of ketones by borane. In the transition state on the way to the complex chiral compounds, the two reactants are activated and held in close proximity by the catalyst, as shown below.     

New catalysts for the oxidation of carbon monoxide

Catalytic activity of binary and multicomponent semiconductors of the ZnSe-CdTe system prepared in a form of powders and nanofilms in CO oxidation was studied by pulsed flow and circulation flow methods. The conditions of maximal CO conversion were determined from the results of investigation of individual and joint adsorption of the reactants in a broad temperature range, and the specific activity of the catalysts was determined by the specific reaction rate at the specified temperature and composition of the reaction mixture. A noticeable catalytic transformation of CO on the semiconductors under study (up to 78.5%) was noted as low as room temperature. It was concluded that the oxidation of CO and adsorption of the CO + O₂ mixture proceeds mainly by the collisional mechanism. It was noted that the high activity of studied catalysts already at room temperature (the (ZnSe)_0.05(CdTe)_0.95 solid solution possessed the highest activity) and the absence of high-cost metals in their composition allow us to recommend them as low-temperature, relatively low-cost catalysts for the neutralization of CO (carbon monoxide).     

Alumina and silica oxides as catalysts for the oxidation of benzoins to benzils under solvent-free conditions

Alumina or silica gel are used as catalysts for a solvent-free oxidation of benzoins to the corresponding benzils. These catalysts are easily recovered after completion of the reactions, which are carried out either by heating in a sand bath or using microwave irradiation. Comparison of the results obtained with both catalysts indicates that all the reactants examined were oxidized faster on alumina than on silica under these conditions.     

Simplified data processing for the simultaneous determination of catalysts by catalytic kinetics

An approximate equation for data processing is proposed for the simultaneous determination of catalysts by catalytic kinetics. On applying the equation to the reaction between two reactants catalysed by two catalysts, the calculation is simplified to that of only one reactant, simplifying the experiment and data processing. The equation was used to treat the simultaneous determination of ruthenium and osmium with Ce(IV)As(III) as the indicator reaction, with the results in good agreement with those using the exact equation.     

密度泛函理论计算研究表面应力对钯催化乙炔选择性加氢活性与选择性的影响（英文）

在石油催化裂解过程中,除了生成乙烯、丙烯及丁烯等烯烃,还会产生部分炔烃.目前工业上通常采用炔烃选择性加氢转化为对应的单烯烃,以除去其中炔烃.由于产品烯烃中的炔烃等杂质含量需极低,这就对用于加氢催化剂的活性和选择性提出了很高的要求,即催化剂需要选择性吸附炔烃并加氢,而不损失其中的烯烃.经过前期大量的基础研究工作,目前工业中炔烃选择性加氢应用最广泛的催化剂是负载型钯基催化剂.然而,单独的钯金属选择性并不理想,因而对其选择性以及活性进行调控成为了当前关注的研究课题.本文采用密度泛函理论计算结合微观反应动力学模拟手段,研究了钯金属表面应力存在条件下的活性与选择性,以及形成次表层物种的可能性和形成后的活性与选择性.研究发现,改变钯金属的晶格参数与表面应力,反应物、表面反应中间体和产物的吸附能都会产生相应的变化,且吸附能与晶格参数的变化存在线性关系,晶格参数越大,吸附越强.利用表面反应过渡态能量与初始态能量之间的线性关系,相应的乙炔加氢生成乙烯的反应速率可以通过微观反应动力学模拟得到.结果显示,不同晶格参数的钯催化剂催化乙炔加氢生成乙烯的反应活性位于相应火山型曲线的强吸附侧,即减弱乙炔和氢的吸附强度可提高乙烯的生成速率.在此基础上,本文研究了不同表面应力的钯催化剂在次表面吸附不同覆盖度碳原子和氢原子的情况,发现晶格参数越大越有利于碳原子和氢原子在次表面的吸附.同时,研究发现在次表面碳掺杂的条件下,不同表面应力条件下的钯催化剂的活性均有所增强.此外,由于乙烯在所有研究的钯催化剂表面脱附比进一步加氢容易,因而乙烯都可以选择性生成.     

过渡金属硫化物催化剂催化加氢作用机理

负载型过渡金属(Co、Mo、Ni、W)硫化物催化剂广泛应用于石油炼制催化加氢过程。为了开发高性能的加氢催化剂,过渡金属硫化物催化剂催化活性相的结构与加氢脱硫性能的关系一直以来是催化研究的热点之一。本文从过渡金属硫化物催化剂的活性相结构和反应物在催化剂表面活性位上的吸附-催化反应机理两个方面阐述了过渡金属硫化物催化剂的催化作用研究进展,并对过渡金属硫化物催化剂催化机理研究存在的争议和未来的研究方向进行了分析。     

Continuous biphasic catalysis: palladium catalyzed cross coupling reactions

The immobilisation of polymer tagged catalysts in a stationary solvent in a reactor and the flow of reactants dissolved in another immiscible solvent through it, allows the conversion of a continuous feed of reactants into a product stream, as exemplified by the Sonogashira coupling of aryl halides and acetylenes.     

水对SBA-15负载的钴基费-托合成催化剂催化性能的影响

以SBA-15分子筛为载体,采用等体积浸渍法制备了负载量为20%的钴基催化剂,采用TEM、XRD、H2-TPR和N2物理吸附-脱附等方法对催化剂进行了表征,并在浆态床反应器中考察了水的加入对费-托合成反应性能的影响.结果表明,金属钴物种进入到SBA-15载体的孔道中;产物在孔道中的滞留以及水促进的金属钴物种的团聚,引起了催化剂活性的降低;水的加入有利于反应物和产物在孔道中的传输,增加CO的转化率;在SBA-15负载的钴基催化剂中,产物在孔道中的滞留对催化剂活性影响较大,引起的扩散限制是催化剂活性降低的重要原因.     

Axial coordination of NHC ligands on dirhodium(II) complexes: generation of a new family of catalysts

An efficient new methodology for the arylation of aldehydes is disclosed which uses dirhodium(II) catalysts and N-heterocyclic carbene (NHC) ligands. Complexes of Rh 2(OAc) 4 with one and two NHCs attached on the axial positions were successfully isolated, fully characterized, and used as catalysts in the reaction. The saturated monocomplex ((NHC 5)Rh 2(OAc) 4) 31 was shown to be the most active catalyst and was particularly efficient in the arylation of alkyl aldehydes. DFT calculations support participation of complexes with one axial NHC in the reaction as the catalysts active species and indicate that hydrogen bonds involving dirhodium unit, reactants, and solvent (alcohol) play an important role on the reaction mechanism.     

Highly Efficient Esterification of an Equimolar Amount of Carboxylic Acids and Alcohols Catalyzed by ZrOCl_2·8H_2O

Esterification of carboxylic acids with alcohols is one of the most fundamental and useful transformations in organic synthesis. The most common catalysts are H2SO4 and TsOH. However, H2SO4 or TsOH-catalyzed esterification procedure has some problems such as corrosion, side reactions, difficulty in separation. Hence, recently, various solid acid catalysts such as ion-exchanged resins, molecular sieve, and heteropoly acids etc. have been employed for esterification reaction. However, the s…     

Cooperation of catalytic species for the selective reduction of nitrogen monoxide with hydrocarbons

Studies on the cooperation effect of catalytic species for the selective reduction of NO with hydrocarbons under oxidizing con-ditions have been reviewed. Based on the catalyst form, the effect can be classified into multiple-stage catalysts, mechanical or physi-cal mixture catalysts, and uniform catalysts with two or more catalytic components. Broadening of the temperature window for NO reduction by using two or more catalysts with different windows in series is an example for the first case. For the other two cases, bifunctionality of catalytic species is expected since the reaction is considered to proceed via a series of sequential and parallel steps. Actually, the promotion of NO reduction activity has been reported by the addition of catalysts or catalytic species having NO oxi-dation activity, where the NO oxidation step was slow. Another example is the combination of acidity and metal species to create NO reduction activity.     

Polydimethylsiloxane Coating for a Palladium/MOF Composite: Highly Improved Catalytic Performance by Surface Hydrophobization

Surface wettability of active sites plays a crucial role in the activity and selectivity of catalysts. This report describes modification of surface hydrophobicity of Pd/UiO‐66, a composite comprising a metal–organic framework (MOF) and stabilized palladium nanoparticles (NPs), using a simple polydimethylsiloxane (PDMS) coating. The modified catalyst demonstrated significantly improved catalytic efficiency. The approach can be extended to various Pd nanoparticulate catalysts for enhanced activity in reactions involving hydrophobic reactants, as the hydrophobic surface facilitates the enrichment of hydrophobic substrates around the catalytic site. PDMS encapsulation of Pd NPs prevents aggregation of NPs and thus results in superior catalytic recyclability. Additionally, PDMS coating is applicable to a diverse range of catalysts, endowing them with additional selectivity in sieving reactants with different wettability.     

Fullerene-coated beads as reusable catalysts

New heterogeneous catalysts that use oxygen and light to generate singlet oxygen ((1)O2) have been prepared. The catalysts facilitate various types of singlet oxygenation reactions including the Ene reaction, the Diels-Alder reaction, and others. The catalysts are made by stirring a heterogeneous mixture of fullerene-C(60) (dissolved in toluene) with aminomethylated poly(styrene-co-divinylbenzene) beads. Also, catalysts for aqueous photooxidations are made by reacting the initial catalysts with poly(allylamine) to create an outer layer that is more hydrophilic.     

Copolymerization of propene-nonconjugated dienes: Derivatization through hydroboration and epoxydation

Copolymerization of propylene and nonconjugated dienes such as 1–9 decadiene (α–ω symmetric) and 7-methyl-1,6 octadiene (asymmetric) is carried out in the presence of highly active isospecific catalysts for propene polymerization. The incorporation of the diene is random and does not affect the isospecificity of the catalytic system. For a low amount of diene, whatever its structure, an activation effect is observed. For the symmetric diene, the reactivity of the second double bond gives rise to crosslinking. Derivatization through hydroboration or epoxydation is carried out in suspension, using a toluenetetrahydrofuran solvent mixture that is able to swell the polypropylene and dissolve the reactants. After hydroboration the copolymer is transformed into hydroxylated polymer through oxidation in a phase transfer condition. The epoxydized copolymer shows excellent adhesive properties on anodized stainless steel.     

Supramolecular catalysts for the gas-phase synthesis of single-walled carbon nanotubes

Reversed micelles containing metallic ions have been used as precursors of novel catalysts for the gas-phase synthesis of single-walled carbon nanotubes (SWNTs). This technique possesses the following advantages: (i) excellent solubility in organic solvents, which are used as reactants and (ii) facile preparation of multicomponent catalysts enabling systematic screening of catalyst compositions for the synthesis of SWNTs. In this study, we report the results of the screening study on the catalytic behavior of Fe-Mo binary catalysts during the synthesis of SWNTs. The results suggested that the catalytic ability was closely related to the strain of the crystal structure of Fe-Mo catalysts formed in the reaction and/or the phase transition caused by dissolution of the Mo atoms. The addition of lithium to the Fe-Mo binary catalysts has revealed an increase in the yield of SWNTs.     

Shock-induced chemical reactions in nickel-aluminum powder mixtures: Radiation pyrometer measurements

Time-resolved emission of visible and near-infrared thermal radiation has been measured from powders of pure nickel and mixed nickel-aluminum shocked to peak pressures of 14 GPa. Temperatures determined from the measurements indicate that the Ni-Al mixture has a source of heat in addition to that supplied by shock compression. The extra heat, produced on a time scale of 100 ns, is inferred to come from an exothermic reaction between the two metals forming a binary alloy. If the alloy is Ni₃Al, the measured temperatures are consistent with prompt shock-induced reaction of at least 45% of the reactants.     

Kinetic Influences on Enantioselectivity for Non-Diastereopure Catalyst Mixtures

Different kinetic rate laws were observed for two diastereomeric catalysts which separately gave opposite enantioselectivities in the asymmetric hydrogenation of the dimethyl ester of itaconic acid. In reactions carried out using an equal mixture of the two catalysts, a conversion-dependent enantioselectivity was predicted from the separate reaction-rate data, in agreement with the experimentally observed final enantioselectivity of 54.8 % ee (see diagram).