Comparative studies of gold catalysts prepared via solvated metal atom impregnation and conventional impregnation: characterization and low-temperature co oxidation

Supported Au catalysts for low-temperature CO oxidation were prepared by solvated metal atom impregnation (SMAI) and conventional impregnation (CI). X-ray photoelectron spectroscopy investigations indicated that gold in all the samples was in the metallic state. TEM and XRD measurements showed that the mean diameter of Au particles prepared by SMAI was smaller than that of those prepared by CI with the same gold content. Catalytic tests showed that SMAI catalysts had higher CO oxidation activity than CI catalysts with the same compositions. Both SMAI and CI Au/TiO₂catalysts exhibited high activities in low temperature CO oxidation. Full CO conversion was obtained at 323 K for 3.1 wt.% Au/TiO₂ (SMAI) catalyst, which displayed higher activity than the 3.1 wt.% Au/D-72(SMAI) and 3.1 wt.% Au/TiO₂(CI). Although the sizes of gold particles prepared by the same method and supported on both TiO₂ and resin were comparable, the Au/TiO₂ catalysts showed significantly higher activities than the Au/resin catalysts with the same Au contents under the same reaction conditions. These results prove that not only the gold particle size, but also the support plays a key role in CO oxidation. This revised version was published online in June 2006 with corrections to the Cover Date.     

新形态全氟磺酸树脂催化剂研究进展

全氟磺酸树脂是绿色固体酸催化剂，对许多反应有较好的催化活性和选择性。但由于全氟磺酸树脂比表面较低，埋没在氟碳基体中的酸性中心不易被反应物所接近，质量比活性低。本文对近年来新形态全氟磺酸树脂，如多孔、负载化、纳米复合物及其改性的全氟磺酸树脂的催化作用进行了综述，文献结果表明全氟磺酸树脂纳米复合物对很多有机合成反应具有很高的催化活性。     

Grubbs Catalysts Immobilized on Merrifield Resin for Metathesis of Leaf Alcohols by using a Convenient Recycling Approach

Three new types of heterogeneous catalysts were prepared using a facile approach by the immobilization of Grubbs catalysts on PEGylated Merrifield resin. One of the immobilized catalysts was more efficient than the free catalyst for the metathesis of leaf alcohols in conversion and selectivity and was reused repeatedly (up to 5 cycles) with only a slight loss of activity (10.5 %). The long-chain PEGylated linker provided an appropriate distance between the resin and the catalytic center so that the ruthenium catalysts acted as the free catalyst.     

Polymer‐ and Silica‐Supported Iron BPMEN‐Inspired Catalysts for CH Bond Functionalization Reactions

Direct catalytic C? H bond functionalization is a key challenge in synthetic chemistry, with many popular C? H activation methodologies involving precious‐metal catalysts. In recent years, iron catalysts have emerged as a possible alternative to the more common precious‐metal catalysts, owing to its high abundance, low cost, and low toxicity. However, iron catalysts are plagued by two key factors: the ligand cost and the low turnover numbers (TONs) typically achieved. In this work, two approaches are presented to functionalize the popular N¹,N²‐dimethyl‐N¹,N²‐bis(pyridin‐2‐ylmethyl)ethane‐1,2‐diamine (BPMEN) ligand, so that it can be supported on porous silica or polymer resin supports. Four new catalysts are prepared and evaluated in an array of catalytic C? H functionalization reactions by using cyclohexane, cyclohexene, cyclooctane, adamantane, benzyl alcohol, and cumene with aqueous hydrogen peroxide. Catalyst recovery and recycling is demonstrated by using supported catalysts, which allows for a modest increase in the TON achieved with these catalysts.     

Synthesis,characterization and applications of coordination polymers of Ln(III)

The resin was synthesized by condensation of 2‐hydroxy‐4‐ethoxybenzophenone with 1,4‐butane diol in presence of polyphosphoric acid as a catalyst at 155 °C for 10 h. The synthesized resin was used to get polychelates of 4f‐block elements. The resin and its polychelates were characterized on the basis of elemental analyses, electronic spectra, magnetic susceptibilities, FTIR, NMR and thermogravimetric analyses. Morphological study of resin and polychelates were carried out by scanning electron microscope. The number average molecular weight (M?_n) was determined using a vapor pressure osmometry method. The catalytic activity of selected polychelates was examined for organic synthesis. It is observed from the study that polychelates give excellent results. They were found to be efficient and effective catalysts and antimicrobial agents. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of tetrabutyltin on the acidity and reducibility of platinum-tin alumina supported sol-gel catalysts

Tin precursor effect in Pt−Sn/Al₂O₃ sol-gel catalysts has been studied. It is shown that catalysts prepared with tetrabutyltin allow a better reduction of platinum than catalysts prepared with tin tetrachloride and with tin tetra-tert-amyloxide. The solids prepared with tetrabutyltin are catalysts showing a high activity in isopropanol decomposition and cyclohexane dehydrogenation.     

Studies on epoxy resins cured by cationic latent thermal catalysts: The effect of the catalysts on the thermal,rheological, and mechanical properties

To investigate the effect of catalysts on the thermal, rheological, and mechanical properties of an epoxy system, a resin based on diglycidyl ether of bisphenol‐A (DGEBA) was cured by two cationic latent thermal catalysts, N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH). Differential scanning calorimetry was used for the thermal characterization of the epoxy systems. Near‐infrared spectroscopy was employed to examine the cure reaction between the DGEBA and the latent thermal catalysts used. The rheological properties of the blend systems were investigated under an isothermal condition with a rheometer. To characterize the mechanical properties of the systems, flexure, fracture toughness (K_IC), and impact tests were performed. The phase morphology was studied with scanning electron microscopy of the fractured surfaces of mechanical test samples. The conversion and cure activation energy of the DGEBA/BQH system were higher than those of the DGEBA/BPH system. The crosslinking activation energy showed a result similar to that obtained from the cure kinetics of the blend systems. The flexure strength, K_IC, and impact properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system. This was a result of the substituted benzene group of the BQH catalyst, which increased the crosslink density and structural stability of the epoxy system studied. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 187–195, 2001     

Dehydration-dehydrogenation of 1-phenylethanol over acid-basic catalysts

1-Phenylethanol transformation over several oxide catalysts (MgO, MgO-B₂O₃, ZrO₂, AlPO₄-SiO₂ and a Spanish sepiolite of Vallecas) was used as test reaction to determine their acid-basic properties. Different kinds of surface sites are proposed for dehydration and dehydrogenation processes. Thus, strong basic sites are related to the dehydrogenation process while both weak acid and basic sites are responsible for that of dehydration.     

Pd/NbOPO4 Multifunctional Catalyst for the Direct Production of Liquid Alkanes from Aldol Adducts of Furans

Great efforts have been made to convert renewable biomass into transportation fuels. Herein, we report the novel properties of NbO_x‐based catalysts in the hydrodeoxygenation of furan‐derived adducts to liquid alkanes. Excellent activity and stability were observed with almost no decrease in octane yield (>90 % throughout) in a 256 h time‐on‐stream test. Experimental and theoretical studies showed that NbO_x species play the key role in C? O bond cleavage. As a multifunctional catalyst, Pd/NbOPO₄ plays three roles in the conversion of aldol adducts into alkanes: 1) The noble metal (in this case Pd) is the active center for hydrogenation; 2) NbO_x species help to cleave the C? O bond, especially of the tetrahydrofuran ring; and 3) a niobium‐based solid acid catalyzes the dehydration, thus enabling the quantitative conversion of furan‐derived adducts into alkanes under mild conditions.     

Copolymers of poly-{acrylamide-co-[3- (acryloylamino)propyltrimethylammoniumchloride]} as carriers for platinum species and their use as catalysts in heterogeneous gas phase reactions

In the following, the binding of PtCl₆²⁻ to quarternary ammonium groups of the copolymers followed by reduction of platinum to a zerovalent state is described. At temperatures between 60 and 180°C the supported catalysts were effective in isomerization and hydrogenation of hexene(1). The dependence of catalytic activity and selectivity on copolymer composition and the average molecular weight (M_w) of the polymer have been analyzed. Copolymers of the composition 90% acrylamide/10% quarternary compound and average molecular weights of about one million were found to be the most active ones. Thermal and chemical stability of the catalysts were studied by differential thermal analyses, thermal gravimetric analyses, and elemental analyses. Morphology and structure were analyzed by raster electron microscopy, x-ray photon spectroscopy, far infrared spectroscopy, and Fourier transform infrared spectroscopy. Several particle properties of the new catalysts, such as pore volume and surface area, were also investigated. © 1996 John Wiley & Sons, Inc.     

Synthesis of Supported Bimetal Catalysts using Galvanic Deposition Method

Supported bimetallic catalysts have been studied because of their enhanced catalytic properties due to metal‐metal interactions compared with monometallic catalysts. We focused on galvanic deposition (GD) as a bimetallization method, which achieves well‐defined metal‐metal interfaces by exchanging heterogeneous metals with different ionisation tendencies. We have developed Ni@Ag/SiO₂ catalysts for CO oxidation, Co@Ru/Al₂O₃ catalysts for automotive three‐way reactions and Pd−Co/Al₂O₃ catalysts for methane combustion by using the GD method. In all cases, the catalysts prepared by the GD method showed higher catalytic activity than the corresponding monometallic and bimetallic catalysts prepared by the conventional co‐impregnation method. The GD method provides contact between noble and base metals to improve the electronic state, surface structure and reducibility of noble metals.     

New palladium catalyst immobilized on epoxy resin: synthesis,characterization and catalytic activity

A new thiol‐functionalized epoxy resin as a support for palladium(II) complexes has been synthesized in good yields. A palladium catalyst was ‘heterogenized’ by anchoring [PdCl₂(PhCN)₂] complexes to these thiol‐functionalized polymers via ligand exchange reaction. These new palladium catalysts were tested in Mizoroki–Heck coupling and hydrogenation reactions. The activity of the complexes in terms of yield is comparable to that of homogeneous PdCl₂(PhCN)₂. The stability and a good recycling efficiency of these catalysts make them useful for prolonged use. The constant and good selectivity of the supported catalysts during recycling experiments indicate that they could be useful for practical application in many organic reactions. To characterize the heterogeneous complexes before and after use, X‐ray photoelectron spectroscopy, infrared spectroscopy, scanning electron microscopy, energy dispersive X‐ray microscopy, atomic absorption spectroscopy and time‐of‐flight secondary ion mass spectrometry were applied. Density functional theory calculations were also used to better understand the structures of the obtained palladium complexes. Polythiourethanes contain three atoms, oxygen, nitrogen and sulfur, capable of coordinating to transition metals. We examined the possibility of intra‐ and intermolecular binding for both cis and trans palladium complexes. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalysis Studies of Macroreticular Polystyrene Cation‐exchange Resin with Terminal Perfluoroalkanesulfonic Acids

Macroreticular p‐(ω‐sulfonic‐perfluoroalkylated) polystyrene (FPS) resin with the advantages of both sulfonic polystyrene (such as macroreticular Amberlyst‐15) and perfluoroalkanesulfonic resin (such as superacidic Nafion NR50) has exhibited excellent catalytic selectivity and activity in cyclization of pseudoionone and condensation of indole. In this paper, FPS was characterized by XPS, nitrogen sorption technique, FESEM and Hammett indicator method, and employed as the solid acid catalyst in the esterification, acylation and alkylation reactions. The FPS resin showed better activity than commercial solid acid catalysts (Amberlyst‐15 and Nafion NR50) owing to its high surface area and strong acidity close to superacidity.     

Structural and electronic trends in ortho-metalated dirhodium(II) complexes

Properties of chiral dirhodium catalysts with ortho-metalated aryl phosphine ligands have been studied by a computational quantum chemical density functional theory method. The main aim in the current work was to systematically modify the ligand core of the Rh₂(O₂C R)₂(PC)₂ catalysts (PC is ortho-metalated aryl phosphine) in order to find structural and electronic trends involved with the modifications. The strongest impact on the properties of the active rhodium site was found when electron-withdrawing groups were introduced in the ligand core. The computational approach offers a possibility for a stepwise study of the properties of the catalysts and therefore a tool for further design of the most effective structures.     

Reactions of organic exhausts and the thermal stability of catalysts

The catalytic combustion of various organic compounds has been investigated over noble and non-noble metal catalysts using a fixed bed. It was concluded that the activity order of different organic compounds on a noble metal catalyst, is toluene > 2-butanone > benzene >n-heptane≈isopropyl alcohol > acrylonitrile > cyclohexane. On non-noble metal catalyst, it is isopropyl alcohol > 2-butanone > acrylonitrile > toluene >n-heptane > cyclohexane > benzene. In order to compare the thermal stability of catalysts, the catalytic reaction of toluene has been studied over noble and non-noble metal catalysts which were calcined at various temperatures up to 900°C for 3 h.     

微波条件下固体酸催化剂催化酯化生物油的研究

以乙醇和乙酸的酯化作为反应模型,考察固体酸催化剂阳离子交换树脂、SO₄²-/ZrO₂和分子筛在微波加热条件下的酯化活性。结果表明,三类固体酸催化剂的活性顺序为Amberlite树脂﹥SO₄²-/ZrO₂﹥HZSM-5,催化剂活性与酸度一致;酯化反应中水的含量对催化剂的活性有不同程度的影响,水含量较高时催化剂SO₄²-/ZrO₂酯化活性明显变差,而阳离子交换树脂仍具有较高的酯化活性。采用阳离子交换树脂对生物油进行微波催化酯化提质后,原生物油中含有的大量不同种类的羧酸被有效地转化成各种酯类,酯类化合物由原油中的4种增加到13种。与传统加热条件下生物油催化提质比较,生物油微波提质具有明显优势,提质后生物油组分得到优化。     

Metallosilicates as supports of Co catalysts for the synthesis of liquid hydrocarbons from CO and H2

The effect of the nature of the silicate support on the activity and selectivity of 10%. Co/M silicate catalysts (where M=Cu, Zn, Ce, Ti, Hf, La, Al, Zr, Co, Mg) in the synthesis of hydrocarbons from CO and H₂ has been established. Co and Zr catalysts have been shown to provide the highest catalytic efficiency. The yield of liquid hydrocarbons in their presence exceeds 120 g m^–3.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 480–482, March, 1993.     

ansa-Zirconocenium catalysis of syndiospecific polymerization of propylene: Theory and experiment

The syndiospecific propylene polymerizations catalyzed by isopropylidene(cyclopentadienyl)(fluorenyl)- and (2,2-dimethylpropylidene)(cyclopentadienyl)(fluorenyl)-zirconocenium ( 1 ⁺ and 2 ⁺) have been investigated theoretically and compared with experimental observations. With the ab initio calculated structures for the transition state (TS) of 1 ⁺(M)P and 2 ⁺(M)P (M = propylene, P = 2-methylpentyl), their steric energies (E°) have been computed using MM2 force-field. The difference between steric energies E°(m) and E°(r) for the meso and racemic enchainment of propylene, respectively, is defined as the stereocontrol energy [δE°(m ? r)] for syndiotactic propagation. The δE°(m ? r) for the TS of 1 ⁺ (M)P is about 2.1 kcal/mol, the value is 1 kcal/mol greater for 2 ⁺(M)P. The observed steric pentad distributions of the syndiotactic poly(propylene) obtained by these catalysts are consistent with smaller effective stereocontrol energy, which is about two-third as large as δE°(m ? r) values calculated for the MM2 optimized structure. Syndiotactic enchainment is favored over isotactic enchainment for all combinations of site configurations in the catalyst. α-Agostic interaction seems to enhance syndioselectivity, whereas γ-agostic interaction changes the stereoselectivity to meso enchainment. The mirror plane symmetry of the syndiotactic propagating species renders the stereoselectivity of the polymerization insensitive to reaction conditions. These catalysts are also highly regiospecific. © 1995 John Wiley & Sons, Inc.     

Co3+-Rich Na1.95CoP2O7 Phosphates as Efficient Bifunctional Catalysts for Oxygen Evolution and Reduction Reactions in Alkaline Solution

Implementing sustainable energy conversion and storage technologies is highly reliant on crucial oxygen electrocatalysis, such as the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, the pursuit of low cost, energetic efficient and robust bifunctional catalysts for OER and ORR remains a great challenge. Herein, the novel Na-ion-deficient Na_2−xCoP₂O₇ catalysts are proposed to efficiently electrocatalyze OER and ORR in alkaline solution. The engineering of Na-ion deficiency can tune the electronic structure of Co, and thus tailor the intrinsically electrocatalytic performance. Among the sodium cobalt phosphate catalysts, the Na_1.95CoP₂O₇ (NCPO5) catalyst exhibits the lowest ΔE (E_J10,OER−E_J−1,ORR) of only 0.86 V, which favorably outperforms most of the reported non-noble metal catalysts. Moreover, the Na-ion deficiency can stabilize the phase structure and morphology of NCPO5 during the OER and ORR processes. This study highlights the Na-ion deficient Na_2−xCoP₂O₇ as a promising class of low-cost, highly active and robust bifunctional catalysts for OER and ORR.     

Amine groups functionalized gel-type resin supported Pd catalysts: Physicochemical and catalytic properties in hydrogenation of alkynes

Palladium catalysts (0.125–0.5 wt.% Pd) supported by amine groups—functionalized gel-type resin (FCN) were studied in the hydrogenation of alkynes reagents, 2-butyne-1,4-diol and phenylacetylene. The catalysts were prepared by two routes. The first, “OAc” is based on the immobilization of Pd-precursor in the pre-swollen resin from THF solution of Pd(OAc)₂, followed by chemical reduction of the Pd-centers. This method produces Pd particles of size in nano-scale. The second procedure, “aq” implies the deposition of Pd-species on dry resin beads using aqueous solution of PdCl₂. Reduction of these Pd-species gives relatively large Pd particles, dominating are 30–50 nm in size. The SEM studies performed over the cross-section of catalysts grains showed location of Pd in outer shell of polymer beads in both “OAc” and “aq” catalysts; however, thinner layer of Pd appears in “aq” series catalysts. In the presence of all catalysts, prepared by “OAc” and “aq” methods the selectivity towards alkenes is high, above 90%. The catalysts of “aq’ series are much more active and more selective than “OAc” analogues giving selectivity to alkene ca. 94% at almost complete conversion of alkynes. Moreover, catalytic performance of “aq’ series catalyst is unchanged under recycling use. The catalyst was recovered and reused 4 times, maintaining its catalytic efficiency.