Showing papers in "Topics in Catalysis in 2010"
TL;DR: In this article, the concept of using formic acid as a hydrogen storage material is presented, and the main part the historic development and recent examples of homogeneously catalyzed hydrogen generation from Formic acid are covered in detail.
Abstract: In this account the concept of using formic acid as a hydrogen storage material is presented. Catalytic reduction of carbon dioxide and heterogeneously catalyzed decomposition of formic acid to hydrogen and carbon dioxide are briefly discussed. In the main part the historic development and recent examples of homogeneously catalyzed hydrogen generation from formic acid are covered in detail.
377 citations
TL;DR: In this article, a new mode of metal-ligand cooperation based on aromatization-dearomatization of pyridine-based pincer-type ligands was developed, and demonstrated it in the activation of H2 and C-H bonds by PNP Ir complexes.
Abstract: We have developed a new mode of metal–ligand cooperation, based on aromatization–dearomatization of pyridine-based pincer-type ligands, and have demonstrated it in the activation of H2 and C–H bonds by PNP Ir complexes. This type of metal–ligand cooperation plays a key role in the recently discovered environmentally benign reactions of alcohols, catalyzed by PNP and PNN pincer complexes of ruthenium, including (a) dehydrogenation of secondary alcohols to ketones (b) dehydrogenative coupling of primary alcohols to form esters and H2 (c) hydrogenation of esters to alcohols under mild conditions (d) unprecedented amide synthesis: catalytic coupling of amines with alcohols, with liberation of H2. Ligand modification in the latter reaction has led to unprecedented synthesis of imines with H2 liberation. These reactions are very efficient, proceed under neutral conditions and produce no waste.
270 citations
TL;DR: In this article, a recent overview of mesoporous molecular sieves as catalysts and catalysts supports is presented, including metathesis, acylation reactions, C-C coupling reactions of Heck and Suzuki types, base-catalyzed reactions (Knoevenagel and Michael additions, Claisen-Schmidt condensation, Tischenko reaction) and last but not least immobilization of organometallic complexes for different catalytic applications including chiral catalysts.
Abstract: This overview covers the recent achievements in the application of mesoporous molecular sieves as catalysts and catalyst supports. Main structural and textural features are outlined in relation to the novel synthesis approaches of mesoporous molecular sieves and understanding of their properties. For application of mesoporous molecular sieves as catalysts different ways of introduction of active sites on their surfaces are provided. The main part describes selected catalytic reactions catalyzed by mesoporous molecular sieves focused on very recent papers. The examples include metathesis, acylation reactions, C–C coupling reactions of Heck and Suzuki types, base-catalyzed reactions (Knoevenagel and Michael additions, Claisen-Schmidt condensation, Tischenko reaction) and last but not least immobilization of organometallic complexes for different catalytic applications including chiral catalysts.
231 citations
TL;DR: In this paper, trends in the reactivity of transition metals are discussed on the basis of density functional theory (DFT) calculations using Volcano type relations between the catalytic rate and adsorption energies of important intermediates and the effect of adsorbate-adsorbate interaction on the trends is discussed.
Abstract: Using high temperature CO oxidation as the example, trends in the reactivity of transition metals are discussed on the basis of density functional theory (DFT) calculations. Volcano type relations between the catalytic rate and adsorption energies of important intermediates are introduced and the effect of adsorbate–adsorbate interaction on the trends is discussed. We find that adsorbate–adsorbate interactions significantly increase the activity of strong binding metals (left side of the volcano) but the interactions do not change the relative activity of different metals and have a very small influence on the position of the top of the volcano, that is, on which metal is the best catalyst.
196 citations
TL;DR: In this paper, the deoxygenation of triglycerides (tristearin, triolein and soybean oil) under nitrogen atmosphere was investigated over 20 wt% Ni/C, 5 t% Pd/C and 1 tt% Pt/C catalysts.
Abstract: The deoxygenation of triglycerides (tristearin, triolein and soybean oil) under nitrogen atmosphere was investigated over 20 wt% Ni/C, 5 wt% Pd/C and 1 wt% Pt/C catalysts. Use of the Ni catalyst resulted in near quantitative conversion of the triglyceride in each case, high yields of linear C5 to C17 alkanes and alkenes being obtained. Oxygen was rejected as CO and CO2, while small amounts of light alkanes (C1–C4) and H2 were also formed. 13C NMR spectroscopic analysis of the liquid product from soybean oil deoxygenation at intermediate reaction times suggested that one pathway for triglyceride deoxygenation involves liberation of fatty acids via C–O bond scission and concomitant H transfer, followed by elimination of CO2 from the acids in a later step. Compared to Ni, catalysts containing Pd or Pt supported on activated carbon showed lower activity for both triglyceride deoxygenation and for cracking of the fatty acid chains.
196 citations
TL;DR: In this paper, the authors classified the solid catalysts into two categories based on their catalytic temperature, i.e. high temperature catalysts and low temperature catalyst, and provided a review of three aspects, catalyst activity, catalyst life and oil flexibility.
Abstract: Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel and have been studied intensively over the last decade. Unlike the homogeneous catalysts, heterogeneous catalysts can be easily separated from reaction mixture and reused for many times. They are environmentally benign and could be easily operated in continuous processes. This review classifies the solid catalysts into two categories based on their catalytic temperature, i.e. high temperature catalysts and low temperature catalysts. The nature of the catalysts can be specified into solid bases and solid acids. Three aspects, catalyst activity, catalyst life and oil flexibility, will be reviewed. Two kinds of heterogeneous catalysts, reported by IFP Inc. and by WSU, respectively, show a high catalytic activity, long catalyst life and low leaching of catalyst components. These two catalysts also show ability to simultaneously catalyze esterification and transesterification, and can be used in half-refined or crude oil system which provide a potential for greatly decrease the feedstock cost.
177 citations
TL;DR: The use of inorganic salts as catalysts for the reactions of d-glucose in aqueous solutions in a batch reactor is reported in this article, where the type of salt and effect of reaction time were examined in detail at a fixed salt (5 mM) and d-Glucose concentration (0.1 M) and at a temperature of 140 °C.
Abstract: The use of inorganic salts as catalysts for the reactions of d-glucose in aqueous solutions in a batch reactor is reported. The type of salt and effect of reaction time were examined in detail at a fixed salt (5 mM) and d-glucose concentration (0.1 M) and at a temperature of 140 °C. Al(III) and Cr(II) salts gave the highest conversion of d-glucose. Typical reaction products were organic acids like lactic acid, levulinic acid, furanics like hydroxymethylfurfural and insoluble products (humins). The chemo-selectivity is a clear function of the type of inorganic salt. For Al(III), the major water soluble product was lactic acid, for Zn(II) HMF was formed in the highest yields. A reaction scheme is proposed to explain the observed product compositions.
163 citations
TL;DR: In this paper, the feasibility of producing these species in a flow reactor was demonstrated, and the results showed that the selectivities to these products depended on oxidant, pH, catalyst, and reactor operating conditions.
Abstract: 5-Hydroxymethylfurfural (HMF) was catalytically converted in a bench-scale flow reactor to the oxidized derivatives 2,5-furandicarboxylic acid (FDCA), 5-formyl-2-furancarboxylic acid (FFCA), and 2,5-diformylfuran (DFF). Conversions and selectivities to these products depended on oxidant, pH, catalyst, and reactor operating conditions. The feasibility of producing these species in a flow reactor was demonstrated.
147 citations
TL;DR: A solid Bronsted acid of amorphous carbon bearing SO3H, COOH and phenolic OH groups has been studied as a catalyst for biodiesel production as discussed by the authors, and the results suggest that this catalyst can directly convert crude vegetable oils composed of triglycerides, free higher fatty acids and water into biodiesel with minimal energy consumption.
Abstract: A solid Bronsted acid of amorphous carbon bearing SO3H, COOH and phenolic OH groups has been studied as a catalyst for biodiesel production. The carbon material functions as a stable and efficient catalyst for the formation of biodiesel from oleic acid at 353 K; the catalytic performance is 70–80% that of sulfuric acid. The carbon material also exhibits remarkable catalytic performance for transesterification of triolein at 403 K, maintaining high catalytic activity even in the presence of water. These results suggest that this catalyst can directly convert crude vegetable oils composed of triglycerides, free higher fatty acids and water into biodiesel with minimal energy consumption.
137 citations
TL;DR: In this article, preliminary stability and deactivation studies of supported enantioselective Co-salen epoxide ring-opening catalysts and enanti-lective Ru-Salen olefin cyclopropanation catalysts are summarized.
Abstract: Research on heterogenized metal complex catalysts has been carried out for 40 years. Despite thousands of published catalysts, there are only two significant commercial processes that utilize supported metal complex catalysts. Most academic papers are simply “demonstration of concept” studies reporting myriad ways to support various metal complex catalysts. Too few papers focus on rigorous studies of reaction kinetics, catalyst recycle, catalyst stability and deactivation pathways. Here, preliminary stability and deactivation studies of supported enantioselective Co-salen epoxide ring-opening catalysts and enantioselective Ru-salen olefin cyclopropanation catalysts are summarized. Insights with regard to catalyst deactivation suggest methodologies for catalyst stabilization, allowing for more effective catalyst recycle and enhanced catalyst turnover. Further examples where supported metal complex catalysts are applied in commercial processes will require the field to shift focus from “demonstration of concept” studies to more detailed investigations of catalyst stability and recyclability.
134 citations
TL;DR: In this article, a two-liquid-phase (aqueous-toluene) plug-flow reactor at 260 °C and 55 atm with 98% conversion rate, 98% furfural molar yield, and 98% selectivity was used.
Abstract: Xylose was dehydrated over (H+) mordenite, using a continuous two-liquid-phase (aqueous-toluene) plug-flow reactor at 260 °C and 55 atm, with 98% conversion rate, 98% furfural molar yield, and 98% furfural selectivity (results from the first pass). Furfural in toluene was hydrogenated over a Cu/Fe catalyst, at 252 °C (gas-phase), in a 99% conversion rate to give 2-methylfuran in a 98% yield (same activity maintained for a 20-h operation).
TL;DR: In this paper, the effect of Re to activated carbon-supported Ru and Pd catalysts in the hydrogenation of 15-wt% succinic acid aqueous solutions to 1,4-butanediol (BDO) was examined.
Abstract: The effect of addition of Re to activated carbon-supported Ru and Pd catalysts in the hydrogenation of 15 wt% succinic acid aqueous solutions to 1,4-butanediol (BDO) was examined. The yield and selectivity were in the range 62–66% at 160 °C and 150 bar over the Re promoted catalysts. Bio-succinic acid from a fermentation process could be efficiently hydrogenated on 4 wt%Re–2 wt%Pd/C without significant loss of selectivity.
TL;DR: In this paper, the authors investigated the deoxygenation of triglycerides over Co and Mo sulfides supported on a series of mesoporous molecular sieves (MCM-41) with varying Si/Al ratio.
Abstract: Deoxygenation of triglycerides over Co and Mo sulfides supported on a series of mesoporous molecular sieves (MCM-41) with varying Si/Al ratio has been investigated in this contribution. The catalysts were tested in a flow reactor at reaction temperatures 300 and 320 °C, hydrogen pressures 2–11 MPa and space velocities 1–4 h−1 using refined rapeseed oil as a feedstock. Incorporation of Al into the framework of MCM-41 led to an increase of both conversion of triglycerides and selectivity to hydrocarbons, namely n-heptadecane and n-octadecane. However, the conversion of triglycerides was lower than that achieved over alumina supported CoMo. Moreover, the rather high selectivity to oxygenated products, as compared with alumina supports, has made possible a detailed description of the reaction intermediates and their dependence on the reaction conditions.
TL;DR: In this article, a personal account summarizes recent developments of catalytic hydrosilylations and hydrogenations of carboxylic amides and nitriles to selectively give amines.
Abstract: This personal account summarizes our recent developments of catalytic hydrosilylations and hydrogenations of carboxylic amides and nitriles to selectively give amines. Special focus is given to highly chemoselective iron- and zinc-catalyzed reductions of amides.
TL;DR: In this article, a mesoporous catalysts based on SBA-15 silica were designed for the conversion of fructose to 5-hydroxymethylfurfural (HMF).
Abstract: Solid catalysts based on SBA-15 silica were designed for the conversion of fructose to 5-hydroxymethylfurfural (HMF). The catalysts incorporate thioether groups that may promote the tautomerization of fructose to its furanose form, as well as sulfonic acid groups to catalyze its dehydration. The materials were characterized by elemental analysis, X-ray diffraction, N2 adsorption/desorption, and solid-state 13C and 29Si CP/MAS NMR spectroscopy. Functional groups incorporated into mesoporous silica by co-condensation are more robust under the reaction conditions (water at 180 °C) than those grafted onto a non-porous silica. The bifunctional mesoporous catalyst achieved a selectivity for HMF of 74% at 66% fructose conversion.
TL;DR: In this article, the size and shape of the silicoaluminophosphate molecular sieve SAPO-34 have been effectively controlled in the reaction system of Al2O3-P2O5-SiO2-TEAOH-H2O under microwave radiations.
Abstract: The crystal size and shape of the silicoaluminophosphate molecular sieve SAPO-34 have been effectively controlled in the reaction system of Al2O3–P2O5–SiO2–TEAOH–H2O under microwave radiations. Nano sheet-like SAPO-34 crystals are obtained when using colloidal silica as the silica source. When TEOS is used as the source of silica, homogeneous SAPO-34 crystals with a particle size of about 100 nm are formed, and the morphology of the crystals changes from uniform nano particles (~100 nm) to microspheres (~1.5 μm) by varying the H2O/Al2O3 molar ratio. To further investigate the morphology control of SAPO-34, the synthetic factors, such as the silica source, water content, crystallization time and aging time have been studied in detail.
TL;DR: In this paper, high-resolution scanning tunneling microscopy (STM) studies and density functional theory (DFT) investigations of the interaction of water with the rutile TiO2 (110) surface are summarized.
Abstract: Scanning Tunneling Microscopy (STM) studies and Density Functional Theory (DFT) investigations of the interaction of water with the rutile TiO2 (110) surface are summarized. From high-resolution STM the following reactions have been revealed: water adsorption and diffusion in the Ti troughs, water dissociation in bridging oxygen vacancies, assembly of adsorbed water monomers into rapidly diffusing water dimers, and formation of water dimers by reduction of oxygen molecules. The STM results are rationalized based on DFT calculations, revealing the bonding geometries and reaction pathways of the water species on the TiO2 (110) surface.
TL;DR: In this paper, the role of new feedstocks in meeting increased demand for biodiesel and circumventing the food versus fuel issue, biodiesel production, as well as fuel properties and their improvement are discussed.
Abstract: Biodiesel, an alternative to petroleum-derived diesel fuel, is defined as the mono-alkyl esters of vegetable oils and animal fats. Several current issues affecting biodiesel that are briefly discussed include the role of new feedstocks in meeting increased demand for biodiesel and circumventing the food versus fuel issue, biodiesel production, as well as fuel properties and their improvement.
TL;DR: In this article, the authors have developed supported metal hydroxide catalysts based on the information of the catalytically active sites with polyoxometalates (POMs).
Abstract: This article summarizes our recent developments for H2O2- and O2-based green oxidation reactions by polyoxometalates (POMs) and related compounds. POM-based structurally controlled molecular catalysts exhibit high catalytic performance for epoxidation and sulfoxidation with H2O2. These molecular catalysts can be immobilized on the organic–inorganic hybrid support with covalently anchoring N-octyldihydroimidazolium cation fragments via the anion exchange. In addition, we have developed supported metal hydroxide catalysts such as Ru(OH)x/Al2O3 and Cu(OH)x/TiO2 on the basis of the information of the catalytically active sites with POMs. By using these supported metal hydroxide catalysts, novel aerobic oxidative synthesis of nitriles and amides, and efficient aerobic oxidative homocoupling of alkynes can be realized.
TL;DR: In this paper, 2-methyl-1-propanol (isobutanol) is used directly as a biofuel or can be catalytically dehydrated to isobutylene, a platform molecule for synthesizing other fuels or chemicals.
Abstract: Fermented 2-methyl-1-propanol (isobutanol) can be used directly as a biofuel or can be catalytically dehydrated to 2-methylpropene (isobutylene), which serves as a platform molecule for synthesizing other fuels or chemicals. The dehydration reaction was studied over alumina catalysts to determine the impact of process conditions and model compound impurities from fermentation. No significant impurity effects were observed over short (8 h) timescales and dehydration was demonstrated at high conversion and with high selectivity to isobutylene.
TL;DR: In this article, the combination of density functional theory (DFT) calculations and kinetic analyses is a very useful approach to study surface reactions in heterogeneous catalysis, and some recent work applies this approach to Fischer-Tropsch (FT) synthesis.
Abstract: The combination of density functional theory (DFT) calculations and kinetic analyses is a very useful approach to study surface reactions in heterogeneous catalysis The present paper reviews some recent work applying this approach to Fischer–Tropsch (FT) synthesis Emphasis is placed on the following fundamental issues in FT synthesis: (i) reactive sites for both hydrogenation and C–C coupling reactions; (ii) reaction mechanisms including carbene mechanism, CO-insertion mechanism and hydroxyl-carbene mechanism; (iii) selectivity with a focus on CH4 selectivity, α-olefin selectivity and chain growth probability; and (iv) activity
TL;DR: In this article, a highly efficient and stable solid adsorbent invoking a direct incorporation of tetraethylenepentamine (TEPA) onto the as-synthesized mesocelullar silica foam (MSF) has been developed for CO2 capture.
Abstract: A highly efficient and stable solid adsorbent invoking a direct incorporation of tetraethylenepentamine (TEPA) onto the as-synthesized mesocelullar silica foam (MSF) has been developed for CO2 capture. Unlike most amine-functionalized silicas, which typically exhibit CO2 adsorption capacities less than 2.0 mmol/g, such organic template occluded mesoporous silica-amine composites exhibited remarkably high CO2 uptake as high as 4.5 mmol/g at 348 K and 1 atm. Moreover, notable increases in CO2 adsorption capacities of the composite materials were observed when in the presence of humidity. Durability test performed by cyclic adsorption–desorption revealed that such adsorbents also possess excellent stability, even though a slight decrease in adsorption capacity over time was observed.
TL;DR: A brief overview of recent progress in the design and synthesis of chiral metal-organic frameworks (CMOFs) and their applications in heterogeneous asymmetric catalysis can be found in this article.
Abstract: This paper provides a brief overview of recent progress in the design and synthesis of chiral metal–organic frameworks (CMOFs) and their applications in heterogeneous asymmetric catalysis. Catalytically active CMOFs can be synthesized using two distinct strategies, either by post-synthetic activation of pre-synthesized porous MOFs or by directly linking well-designed catalytically competent bridging ligands with metal ion or metal cluster nodes. Heterogeneous asymmetric catalysis with very high activity and enantioselectivity has been achieved with CMOFs. The intrinsic tunability of CMOFs promises to lead to the design and synthesis of a variety of practically useful heterogeneous asymmetric catalysts for many organic transformations.
TL;DR: In this article, simultaneous transesterification and esterification of rapeseed oil with methanol in the presence of myristic acid was investigated, and the effect of reaction temperature (120, 150 and 170 °C) and the initial free fatty acid content in oil (0, 10 and 20 wt%) on reaction rate were studied.
Abstract: Simultaneous transesterification and esterification of rapeseed oil with methanol in the presence of myristic acid was investigated. The effect of reaction temperature (120, 150 and 170 °C) and the effect of initial free fatty acid content in oil (0, 10 and 20 wt%) on reaction rate were studied. The catalysts were found to increase the rate of all reactions. Sulfated zirconia prepared by a solvent-free method exhibited higher activity in simultaneous reaction than the conventional method. The presence of 10 wt% free fatty acids in the triglyceride increased the reaction rate and the final total fatty acid methyl esters content, and suggests that a “non-catalytic” reaction may be feasible.
TL;DR: In this article, tall oil fatty acids (TOFA) was demonstrated over palladium catalysts supported on mesoporous carbon at 300 °C using dodecane as a solvent.
Abstract: Catalytic deoxygenation of tall oil fatty acids (TOFA) was demonstrated over palladium catalysts supported on mesoporous carbon at 300 °C using dodecane as a solvent. Maximally 95% selectivity to linear C17 hydrocarbons was achieved. The effects of reaction atmosphere and initial TOFA concentration were investigated.
TL;DR: In this paper, the catalytic dehydration of glycerol to acrolein is investigated over silica-supported niobia catalysts in a continuous fixed-bed gas-phase reactor.
Abstract: The catalytic dehydration of glycerol to acrolein is investigated over silica-supported niobia catalysts in a continuous fixed-bed gas-phase reactor. Various supported niobia catalysts are prepared and characterized using surface analysis and spectroscopic methods (XRD, UV-Vis, XPS, N2 adsorption), as well as with ammonia adsorption microcalorimetry. Good results are obtained with initial glycerol conversions of over 70% and with 50-70% selectivity to acrolein. We investigate the influence of changing the catalyst acid strength by varying the niobia content and catalyst calcination temperature. Glycerol conversion and acrolein selectivity depend on the surface acid strength. Catalyst deactivation by coking is also observed, but simple oxidative treatment in air restores the activity of the catalysts completely.
TL;DR: The photocatalytic oxidation of benzyl alcohol into benzaldehyde proceeded with high conversion and selectivity on a TiO2 photocatalyst by O2 under visible light irradiation as mentioned in this paper.
Abstract: The photocatalytic oxidation of benzyl alcohol into benzaldehyde proceeded with high conversion and selectivity on a TiO2 photocatalyst by O2 under visible light irradiation Surface complex formed by the interaction of benzyl alcohol with the Ti sites and/or surface OH groups of TiO2 play an important role in the absorption of visible light and unique selective photocatalytic reaction
TL;DR: In this paper, the impact of alloying on the local electronic structure of different sites in alloys and on their local chemical reactivity is predicted using quantum chemical DFT calculations.
Abstract: While it is fairly straightforward to predict the relative chemical reactivity of pure metals, obtaining similar structure-performance relationships for alloys is more challenging. In this contribution we present experimental analysis supported with quantum chemical DFT calculations which allowed us to propose a simple, physically transparent model to predict the impact of alloying on the local electronic structure of different sites in alloys and on the local chemical reactivity. The model was developed through studies of a number of Pt alloys. The central feature of the model is that hybridization of d-orbitals in alloys does not lead to significant charge transfer between the constituent elements in the alloy, and therefore the width of the local density of d-states projected on a site, which is easily calculated from tabulated parameters, is an excellent descriptor of the chemical reactivity of the site.
TL;DR: In this paper, a method for palladium catalyzed cross-coupling reactions under environmentally benign conditions (in water and/or at room temperature) has been developed, which involves in situ activation of carbon-halogen or carbon-hydrogen bonds using zinc metal, or cationic palladium, respectively.
Abstract: New methodologies that enable palladium catalyzed cross-coupling reactions to be performed under environmentally benign conditions (in water and/or at room temperature) have been developed. Described approaches involve in situ activation of carbon–halogen or carbon–hydrogen bonds using zinc metal, or cationic palladium, respectively.
TL;DR: The metal organic framework (MOF) as mentioned in this paper is a hybrid of organic and inorganic structures, which offers an unprecedented flexibility in the possibility to incorporate both organic and metallic functional groups into the ordered crystalline lattice and thereby opening up for a much greater possibility to copy structural motifs known from enzymes into much simpler but also more stable open structures.
Abstract: Everyone who works within the field of catalysis draws inspiration from the amazing functionality of nature’s catalysts, the enzymes. It is particularly the mild conditions that these catalysts are able to operate at and the selectivity that they demonstrate that make these materials dream targets for scientists involved in the art of synthesizing homogeneous and heterogeneous industrial catalysts. But enzymes also have their weak points; in particular their low thermal stability and their often too slow reaction rates for an economical industrial process are problems that have to be overcome. The obvious solution would be to copy the catalytic active center into a robust open framework. A key property of an enzyme is its selectivity; this property is partly regulated by steric constraints surrounding the catalytically active site. The microporous zeolite based catalysts in some cases show impressive selectivity based on the geometrical constraints imposed by the size and shape of the regular channels in these crystalline silicate and alumino-phosphate based structures, and enzyme-like properties have been claimed but the pure inorganic nature of the selective internal surface in these materials makes it impossible to mimic many important enzymatic properties. The new generation of microporous materials, Metal Organic Frameworks (MOFs) are hybrids of organic and inorganic structures. This dualistic nature offers an unprecedented flexibility in the possibility to incorporate both organic and metallic functional groups into the ordered crystalline lattice and thereby opening up for a much greater possibility to copy structural motifs known from enzymes into much simpler but also more stable open structures. Several groups are working on development of new catalysts by this approach. Here we will illustrate this approach with structures that mimic anhydrase and C–H activation.