[4+2] Annulation - Convenient Synthesis of Substituted Dihydropyranones in Aqueous Media

A facile and convenient synthesis of dihydropyranones has been developed by a formal [4+2] annulation of readily available alpha-acetyl ketene S,S-acetals with various aldehydes, involving a tandem aldol reaction and conjugate addition-elimination reaction, in the presence of NaOH in water.

Low-Temperature Selective Catalytic Reduction (SCR) of NOx with n-Octane Using Solvent-Free Mechanochemically Prepared Ag/Al2O3 Catalysts

Low-temperature (<200 degrees C) hydrocarbon selective catalytic reduction of NOx has been achieved for the first time in the absence of hydrogen using a solvent-free mechanochemically prepared Ag/Al2O3 catalyst. Catalysts prepared by this ball-milling method show a remarkable increase in activity for the reduction of nitrogen oxides with octane by lowering the light-off temperature by up to 150 degrees C compared with a state-of-the-art 2 wt %Ag/Al2O3 catalyst prepared by wet impregnation. The best catalyst prepared from silver oxide showed 50% NOx conversion at 240 degrees C and 99%, at 302 degrees C. The increased activity is not due to an increased surface area of the support, but may be associated with a change in.the'defeet structure of the alumina surface, leading to the formation of the small silver clusters necessary for the activation of the octane without leading to total combustion. On the other hand, since one possible role of hydrogen is to remove inhibiting species from the silver, we cannot exclude some change in the chemical properties of the silver as a result of the ball-milling treatment.

Syndiotactically enriched 1,2-selective polymerization of 1,3-butadiene initiated by iron catalysts based on a new class of donors

A series of phosphoryl (P=O) contained compounds: triethylphosphate (a), diethyl phenyl phosphate (b), ethyldiphenylphosphate (c) triarylphosphates (d and h-m), triphenylphosphine oxide (e), phenyl diphenylphosphinate (f) and diphenyl phenylphosphonate (g) have been prepared. Iron catalysts, which are generated in situ by mixing the compounds with Fe(2-EHA)(3) and (AlBu3)-Bu-i in hexane, are tested for butadiene polymerization at 50 degrees C. Phosphates donated catalysts have been, unprecedently, found to conduct extremely high syndiotactically (pentad, rrrr=46.1-94.5%) enriched 1,2-selective (1,2-structure content=56.2-94.3%) polymerization of butadiene.

Ethylene Polymerization by the New Chromium Catalysts Based on Amino-Pyrrolide Ligands

A series of amino-pyrrolide ligands (1-4a) and their derivatives aminothiophene ligand (5a), amino-indole ligand (6a) were prepared. Chromium catalysts, which were generated in situ by mixing the ligands with CrCl3(thf)(3) in toluene, were tested for ethylene polymerization. The preliminary screening results revealed that the tridentate amino-pyrrolide ligands containing soft pendant donor, 3a, 4a/CrCl3(thf)(3) systems displayed high catalytic activities towards ethylene polymerization in the presence of modified methyaluminoxane. The electronic and steric factors attached to the ligand backbone significantly affected both the catalyst activity and the polymer molecular weight. Complex 4b was obtained by the reaction of CrCl3(thf)(3) with one equivalent of the lithium salts of 4a, which was the most efficient ligand among the tested ones. The effect of polymerization parameters such as cocatalyst concentration, ethylene pressure, reaction temperature, and time on polymerization behavior were investigated in detail. The resulting polymer obtained by 4b display wax-like and possess linear structure, low molecular weight, and unimodal distribution.

Studies on the elimination of NO over the La-Ba-Cu mixed oxide catalysts with perovskite structure

The mixed oxides, including YBa2Cu3O7, LaBa2Cu3O7, LaBaCu2O5, La2BaCu3O7, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, TPD and TPR method. It was found that they were the active catalysts for the NO decomposition and NO reduction by CO. The existance of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

Ring-opening polymerization of epsilon-caprolactone and L-lactide using organic amino calcium catalyst

Poly (6-caprolactone) (PCL) and poly (L-lactide) (PLA) were prepared by ring-opening Polymerization catalyzed by organic amino calcium catalysts (Ca/PO and Ca/EO) which were prepared by reacting calcium ammoniate Ca(NH3)(6) with propylene oxide and ethylene oxide, respectively. The catalysts exhibited high activity and the ring-opening polymerization behaved a quasi-living characteristic. Based on the Fr-IR spectra and the calcium contents of the catalysts, and based on the H-1 NMR end-group analysis of the low molecular weight PCL prepared using catalysts Ca/PO and Ca/EO, it was proposed that the catalysts have the structure of NH2-Ca-O-CH(CH3)(2) and NH2-CaO-CH2CH3 for Ca/PO and Ca/EO, respectively. The ring-opening polymerization of CL and LA follows a coordination-insertion mechanism and the active site is the Ca-O bond.

Layered La-Ba-Cu mixed oxides with perovskite structure as catalyst for NO reduction by CO

The mixed oxides, including LaBa2Cu3O7, LaBaCu2O5, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, H-2-TPR. It was found that their structures were layered ABO(3) perovskite structure and they were the active catalysts for the NO reduction by CO. The existence of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

Preparação e caracterização de catalisadores à base de titânio suportado em MCM-41 para produção de compostos oxigenados através da pirólise catalítica do capim elefante

In recent years, the area of advanced materials has been considerably, especially when it comes to materials for industrial use, such as is the case with structured porosity of catalysts suitable for catalytic processes. The use of catalysts combined with the fast pyrolysis process is an alternative to the oxygenate production of high added value, because, in addition to increasing the yield and quality of products, allows you to manipulate the selectivity to a product of interest, and therefore allows greater control over the characteristics of the final product. Based on these arguments, in this work were prepared titanium catalysts supported on MCM-41 for use in catalytic pyrolysis of biomass, called elephant grass. The reactions of pyrolysis of biomass were performed in a micro pyrolyzer, Py-5200, coupled to GC / MS, the company CDS Corporation, headquartered in the United States. The catalysts Ti-MCM-41 in different molar ratios were characterized by XRD, TG / DTG, FT-IR, SEM, XRF, UV-visible adsorption of nitrogen and the distribution of particle diameter and specific surface area measurement by the BET method. From the catalytic tests it was observed that the catalysts synthesized showed good results for the pyrolysis reaction.The main products were obtained a higher yield of aldehydes, ketones and furan. It was observed that the best reactivity is a direct function of the ratio Si/Ti, nature and concentration of the active species on mesoporous supports. Among the catalysts Ti-MCM-41 (molar ratio Si / Ti = 25 and 50), the ratio Si / Ti = 25 (400 ° C and 600 ° C) favored the cracking of oxygenates such as acids , aldehydes, ketones, furans and esters. Already the sample ratio Si / Ti = 50 had the highest yield of aromatic oxygenates

Electrocatalytic Activity of Platinum-Niobium Nanoparticles for Ethanol Oxidation

Three nanostructured platinum-niobium supported on Vulcan XC-72R carbon black materials were prepared as catalysts for the ethanol electroxidation: (i) deposition of platinum and niobium on Vulcan XC-72R carbon black, (ii) platinum decorated on a mixture of commercial amorphous Nb2O5/carbon black, and (iii) the same than ii but using crystalline Nb2O5, by reduction of the precursors with sodium borohydride in ethanol. All the catalysts showed platinum crystal sizes in the range of 3-4 nm, with no or little modification of the lattice parameter. The analyses of the electronic structure from the XANES region of the XAS spectra displayed some interactions between platinum and niobium, despite the niobium was primarily in the form of pentoxide in all the catalysts. CO stripping exhibited a promising low onset potential and a large current density, especially in the case of the deposited catalyst. Ethanol electroxidation experiments revealed that the Pt-Nb(2)O(5)crystalline/C generated the largest current. However it was not effective to completely oxidize ethanol, leading to acetic acid as the main product. In this sense, the highest efficiency for the complete oxidation of ethanol was obtained for the deposited catalyst. These results were interpreted in terms of the physico-chemical characteristic displayed by the different catalysts. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.040210jes] All rights reserved.

Non-covalent immobilization of RhDuphos on carbon nanotubes and carbon xerogels

The immobilization of the chiral complex RhDuphos, by electrostatic or π–π (adsorption) interactions, on carbon nanotubes and carbon xerogels is investigated. To promote such interactions, the supports were either oxidized or heat treated to create carboxylic type surface groups or an apolar surface, respectively. The catalysts were tested in the hydrogenation of methyl 2-acetamidoacrylate. The prepared hybrid catalysts are less active than the homogeneous RhDuphos, but most of them show a high enantioselectivity and the one prepared with the oxidized carbon xerogel is also reusable, being able to give a high substrate conversion, keeping as well a high enantioselectivity. The anchorage by electrostatic interactions is more interesting than the anchorage by π–π interactions, as the π–π adsorption method produces a modification of the metal complex structure leading to an active hybrid catalyst but without enantioselectivity. The creation of carboxylic groups on the support surface has led to some hindering of the complex leaching.

Preparação e caracterização de catalisadores à base de titânio suportado em MCM-41 para produção de compostos oxigenados através da pirólise catalítica do capim elefante

In recent years, the area of advanced materials has been considerably, especially when it comes to materials for industrial use, such as is the case with structured porosity of catalysts suitable for catalytic processes. The use of catalysts combined with the fast pyrolysis process is an alternative to the oxygenate production of high added value, because, in addition to increasing the yield and quality of products, allows you to manipulate the selectivity to a product of interest, and therefore allows greater control over the characteristics of the final product. Based on these arguments, in this work were prepared titanium catalysts supported on MCM-41 for use in catalytic pyrolysis of biomass, called elephant grass. The reactions of pyrolysis of biomass were performed in a micro pyrolyzer, Py-5200, coupled to GC / MS, the company CDS Corporation, headquartered in the United States. The catalysts Ti-MCM-41 in different molar ratios were characterized by XRD, TG / DTG, FT-IR, SEM, XRF, UV-visible adsorption of nitrogen and the distribution of particle diameter and specific surface area measurement by the BET method. From the catalytic tests it was observed that the catalysts synthesized showed good results for the pyrolysis reaction.The main products were obtained a higher yield of aldehydes, ketones and furan. It was observed that the best reactivity is a direct function of the ratio Si/Ti, nature and concentration of the active species on mesoporous supports. Among the catalysts Ti-MCM-41 (molar ratio Si / Ti = 25 and 50), the ratio Si / Ti = 25 (400 ° C and 600 ° C) favored the cracking of oxygenates such as acids , aldehydes, ketones, furans and esters. Already the sample ratio Si / Ti = 50 had the highest yield of aromatic oxygenates

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure.

Enhancement of the electrooxidation of ethanol on Pt-Sn-P/C catalysts prepared by chemical deposition process

In this paper, five Pt3Sn1/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt3Sn1P2/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt3Sn1/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm(-2) that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.