Showing papers in "Catalysis Letters in 2011"

Hydrodeoxygenation of Furfural Over Supported Metal Catalysts: A Comparative Study of Cu, Pd and Ni

Abstract: The hydrodeoxygenation of furfural has been investigated over three different metal catalysts, Cu, Pd and Ni supported on SiO2, on a continuous-flow reactor under atmospheric pressure of hydrogen in the 210–290 °C temperature range. The distribution of products is a strong function of the metal catalyst used. High selectivity to furfuryl alcohol is obtained over Cu/SiO2, with the formation of only small amounts of 2-methyl furan at the highest reaction temperature studied. In contrast to Cu catalyst, the conversion of furfural over Pd/SiO2 mainly produces furan by decarbonylation. Furan can further react with hydrogen to form tetrahydrofuran (THF). Finally, on Ni/SiO2 catalysts ring opening products (butanal, butanol and butane) can be obtained in significant amounts. The different product distributions are explained in terms of the strength of interaction of the furan ring with the metal surface and the type of surface intermediates that each metal is able to stabilize.

Universal Brønsted-Evans-Polanyi Relations for C–C, C–O, C–N, N–O, N–N, and O–O Dissociation Reactions

Abstract: It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.

Finite Size Effects in Chemical Bonding: From Small Clusters to Solids

Abstract: We address the fundamental question of which size a metallic nano-particle needs to have before its surface chemical properties can be considered to be those of a solid, rather than those of a large molecule. Calculations of adsorption energies for carbon monoxide and oxygen on a series of gold nanoparticles ranging from 13 to 1,415 atoms, or 0.8–3.7 nm, have been made possible by exploiting massively parallel computing on up to 32,768 cores on the Blue Gene/P computer at Argonne National Laboratory. We show that bulk surface properties are obtained for clusters larger than ca. 560 atoms (2.7 nm). Below that critical size, finite-size effects can be observed, and we show those to be related to variations in the local atomic structure augmented by quantum size effects for the smallest clusters.

Atomic-Scale Modeling of Particle Size Effects for the Oxygen Reduction Reaction on Pt

Abstract: We estimate the activity of the oxygen reduction reaction on platinum nanoparticles of sizes of practical importance. The proposed model explicitly accounts for surface irregularities and their effect on the activity of neighboring sites. The model reproduces the experimentally observed trends in both the specific and mass activities for particle sizes in the range between 2 and 30 nm. The mass activity is calculated to be maximized for particles of a diameter between 2 and 4 nm. Our study demonstrates how an atomic-scale description of the surface microstructure is a key component in understanding particle size effects on the activity of catalytic nanoparticles.

Alumina Over-coating on Pd Nanoparticle Catalysts by Atomic Layer Deposition: Enhanced Stability and Reactivity

Abstract: ALD Alumina was utilized as a protective layer to inhibit the sintering of supported nano-sized ALD Pd catalysts in the methanol decomposition reaction carried out at elevated temperatures. The protective ALD alumina layers were synthesized on Pd nanoparticles (1-2 nm) supported on high surface area alumina substrates. Up to a certain over-coat thickness, the alumina protective layers preserved or even slightly enhanced the catalytic activity and prevented sintering of the Pd nanoparticles up to 500 C.

Selective N-Alkylation of Aromatic Primary Amines Catalyzed by Bio-catalyst or Deep Eutectic Solvent

Abstract: Biocatalysts or deep eutectic solvents (DES) are effective for selective N-alkylation of various aromatic primary amines. These methods avoided complexity of multiple alkylations giving products in good yields. Both DES and lipase can be recycled and re-used at least five times. In addition, these catalysts are biodegradable, non-toxic and cost-effective.

Cluster Structure and Reactions: Gaining Insights into Catalytic Processes

Abstract: To many researchers outside the field of cluster science it may come as a surprise that much can be learned of its relevance to catalysis, even restricting the discussion to ionized systems. This perspective is largely focused on catalytic oxidation reactions in which oxygen radical centers on transition metal oxides play a dominant role. The objective is to present how fundamental insights into reaction mechanisms can be gained through employing alternative approaches that complement rather than supersede more conventional methods in t he field of catalysis. In view of the well acknowledged role of defect centers in effecting reactivity, and the preponderance of recent papers presenting evidence of the importance of charged sites, the need/desire to conduct repetitive experiments is clear. Presented herein are approaches using clusters to accomplish this in order to unravel fundamental catalytic reaction mechanisms, and to use identified superatoms and the concepts of element mimics to tailor catalysts with desired functionality.

CeO2–WO3 Mixed Oxides for the Selective Catalytic Reduction of NOx by NH3 Over a Wide Temperature Range

Abstract: A series of cerium-tungsten oxide catalysts was prepared by the co-precipitation method and was evaluated for the selective catalytic reduction of NO x by ammonia (NH3-SCR) over a wide temperature range. These catalysts were characterized by BET, XRD, XPS and H2-TPR analyses. The experimental studies demonstrated that, among cerium-tungsten oxides, CeO2–WO3 with a Ce/W molar ratio of 3/2 exhibited the best activity toward NH3-SCR reactions, N2 selectivity and SO2 durability over a broad temperature range of 175–500 °C at a space velocity of 47,000 h−1. The strong interaction between Ce and W could be the main factor leading to the high activity of the CeO2–WO3 mixed oxide catalyst. A series of cerium-tungsten oxide catalysts was prepared by the co-precipitation method and was evaluated for the selective catalytic reduction of NO x by ammonia (NH3-SCR) over a wide temperature range. These catalysts were characterized by BET, XRD, XPS and H2-TPR analyses. The experimental studies demonstrated that, among cerium-tungsten oxides, CeO2–WO3 with a Ce/W molar ratio of 3/2 exhibited the best activity toward NH3-SCR reactions, N2 selectivity and SO2 durability over a broad temperature range of 175–500 °C at a space velocity of 47,000 h−1. The strong interaction between Ce and W could be the main factor leading to the high activity of the CeO2–WO3 mixed oxide catalyst.

Catalytic Reactions of Guaiacol: Reaction Network and Evidence of Oxygen Removal in Reactions with Hydrogen

Abstract: The conversion of guaiacol, a prototypical compound representative of lignin-derived pyrolysis bio-oils, was catalyzed by Pt/Al2O3 in the presence of H2 at 573 K. The conversion took place with a high selectivity for aromatic carbon–oxygen bond cleavage relative to the accompanying methyl group transfer reactions. This oxygen removal was not observed in the absence of H2 as a co-reactant. Products that were formed by methyl-group transfer match those produced in the conversion catalyzed by zeolite HY, which was not active for oxygen removal reactions. .

Photoreduction of Carbon Dioxide Over NaNbO3 Nanostructured Photocatalysts

Abstract: NaNbO3 had been successfully developed as a new photocatalyst for CO2 reduction. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet–visible spectroscopy (UV–Vis). The DFT calculations revealed that the top of VB consisted of the hybridized O 2p orbital, while the bottom of CB was constructed by Nb 3d orbital, respectively. In addition, the photocatalytic activities of the NaNbO3 samples for reduction of CO2 into methanol under UV light irradiation were investigated systematically. Compared with the bulk NaNbO3 prepared by a solid state reaction method, the present NaNbO3 nanowires exhibited a much higher photocatalytic activity for CH4 production. This is the first example that CO2 conversion into CH4 proceeded on the semiconductor nanowire photocatalyst. NaNbO3 had been successfully developed as a new photocatalyst for CO2 reduction. It was noted that NaNbO3 nanowires showed a much higher activity for CH4 production compared with bulk counterpart (SSR NNO).

(100) facets of γ-Al2O3: The Active Surfaces for Alcohol Dehydration Reactions

Abstract: Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523–533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Bronsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding –OH groups (Bronsted acid sites), depending on the calcination temperature. Temperature-programmed desorption of ethanol, as well as steady state dehydration reactions of ethanol and methanol, indicate that the (100) facets are the primary active surfaces of γ-Al2O3. The active centers on both the hydroxylated and dehydroxylated (100) facets are related to the coordinatively unsaturated Al3+ ions

New Process for the Acid-Catalyzed Conversion of Cellulosic Biomass (AC3B) into Alkyl Levulinates and Other Esters Using a Unique One-Pot System of Reaction and Product Extraction

Abstract: A one-pot system used for the chemical/catalytic conversion of cellulosic biomass, and the product extraction was developed. The latter phase was carried out by a distillation technique that combines a temperature-programmed heating with a vacuum level-programmed evacuation (technique of mild vacuum-assisted distillation, MVAD). No environmentally harmful solvent was used: only a high boiling paraffin (n-dodecane) was used to help distil the heavy products. The obtained liquid fractions (light and heavy fractions) could be used, after drying and removal of unused alcohol, for blending into gasoline or diesel/biodiesel. Two different conversion procedures were used: ethanolysis (direct acid-catalyzed conversion in ethanol medium) and a sequential procedure, the latter consisting of the “acid hydrolysis followed by the esterification of resulting acids with ethanol”. By using wood residues as raw material, the yields in ethyl levulinate and other by-products—with the only exception of diethyl ether (DEE), were quite similar for both procedures. The incorporation of some H-USY zeolite could significantly decrease the yield of DEE in the ethanolysis procedure. Reported results obtained with some other biomass feedstocks (particularly, switch grass) showed a good relationship between the product levulinate yield and the cellulose content of the raw material.

Selective Aerobic Oxidation of 5-Hydroxymethylfurfural in Water Over Solid Ruthenium Hydroxide Catalysts with Magnesium-Based Supports

Abstract: Solid catalyst systems comprised of ruthenium hydroxide supported on magnesium-based carrier materials (spinel, magnesium oxide and hydrotalcite) were investigated for the selective, aqueous aerobic oxidation of the biomass-derived chemical 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid (FDA), a possible plastics precursor. The novel catalyst systems were characterized by nitrogen physisorption, XRPD, TEM and EDS analysis, and applied for the oxidation with no added base at moderate to high pressures of dioxygen and elevated temperatures. The effects of support, temperature and oxidant pressure were studied and optimized to allow a quantitative yield of FDA to be obtained.

Size and Shape Dependence on Pt Nanoparticles for the Methylcyclopentane/Hydrogen Ring Opening/Ring Enlargement Reaction

Abstract: Monodisperse Pt nanoparticles (NPs) with well-controlled sizes in the range between 15 and 108 nm, and shapes of octahedron, cube, truncated octahedron and spheres (~6 nm) were synthesized employing the polyol reduction strategy with polyvinylpyrrolidone (PVP) as the capping agent We characterized the as-synthesized Pt nanoparticles using transmission electron microscopy (TEM), high resolution TEM, sum frequency generation vibrational spectroscopy (SFGVS) using ethylene/H2 reaction as the surface probe, and the catalytic ethylene/H2 reaction by means of measuring surface concentration of Pt The nanoparticles were supported in mesoporous silica (SBA-15 or MCF-17), and their catalytic reactivity was evaluated for the methylcyclopentane (MCP)/H2 ring opening/ring enlargement reaction using 10 torr MCP and 50 torr H2 at temperatures between 160 and 300 °C We found a strong correlation between the particle shape and the catalytic activity and product distribution for the MCP/H2 reaction on Pt At temperatures below 240 °C, 63 nm Pt octahedra yielded hexane, 62 nm Pt truncated octahedra and 52 nm Pt spheres produced 2-methylpentane In contrast, 68 nm Pt cubes led to the formation of cracking products (ie C1–C5) under similar conditions We also detected a weak size dependence of the catalytic activity and selectivity for the MCP/H2 reaction on Pt 15 nm Pt particles produced 2-methylpentane for the whole temperature range studied and the larger Pt NPs produced mainly benzene at temperatures above 240 °C

Catalytic Conversion of Anisole: Evidence of Oxygen Removal in Reactions with Hydrogen

Abstract: The conversion of anisole, a prototypical bio-oil compound, was catalyzed by Pt/Al2O3 in the presence of H2 at 573 K, with the selectivity for C–O bond breaking approximately matching that for ring hydrogenation; these reactions were accompanied by methyl group transfers matching those in the conversion catalyzed by HY zeolite.

Selective Catalytic Oxidation (SCO) of Ammonia to Nitrogen over Hydrotalcite Originated Mg–Cu–Fe Mixed Metal Oxides

Abstract: Mg–Cu–Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia. Copper containing catalysts were active in low-temperature SCO processes; however, their selectivity to nitrogen significantly decreased at higher temperatures. The optimum composition of the catalyst to guarantee high activity and selectivity to N2 was proposed. Temperature-programmed experiments, SCO catalytic tests performed with various contact times and additional tests on the samples in the selective catalytic reduction of NO with ammonia showed that the SCO process over the studied calcined hydrotalcites proceeds according to the internal SCR mechanism and oxidation of ammonia to NO is a rate-determining step in the low-temperature range.

Novel SO3H-Functionalized Ionic Liquids Based on Benzimidazolium Cation: Efficient and Recyclable Catalysts for One-Pot Synthesis of Biscoumarin Derivatives

Abstract: In this article, a new group of SO3H-functionalized ionic liquids based on benzimidazolium cation was synthesized and used as environmentally benign catalysts for the one-pot synthesis of biscoumarin derivatives. The ionic liquids showed high catalytic activities and reusabilities with good to excellent yields of the desired products. H 0 (Hammett function) values and the minimum-energy geometries of SO3H-functionalized ionic liquids were determined and the results revealed that the acidities and catalytic activities of ionic liquids in the synthesis of biscoumarin derivatives were related to their structures. The simple, more efficient way for synthesis of biscoumarin derivatives has been developed. This new method abandon the traditional hazardous organic liquid and is carried out by using a one-pot reaction of 4-hydroxycoumarin with aromatic aldehydes in the presence of novel SO3H-functionalized ionic liquids based on benzimidazolium cation as catalysts. The ionic liquids showed high catalytic activities and reusabilities with good to excellent yields of the desired products. H 0 (Hammett function) values and the minimum-energy geometries of SO3H-functionalized ionic liquids were determined and the results revealed that the acidities and catalytic activities of ionic liquids in the synthesis of biscoumarin derivatives were influenced by their structures.

Single Stage Water-Gas Shift Reaction Over Supported Pt Catalysts

Abstract: Single stage water–gas shift reaction has been carried out at a gas hourly space velocity of 45,515 h−1 over supported Pt catalysts prepared by an incipient wetness impregnation method. CeO2, ZrO2, MgO, MgO–Al2O3 (MgO = 30 wt%) and Al2O3 were employed as supports for the target reaction in this study. 1 wt% Pt/CeO2 exhibited the highest CO conversion as well as very high CO2 selectivity due to high oxygen storage capacity of CeO2.

A One-Pot Two-Step Approach for the Catalytic Conversion of Glucose into 2,5-Diformylfuran

Abstract: One-pot two-step synthesis of DFF was achieved by catalytic conversion of glucose over CrCl3·6H2O/NaBr//NaVO3·2H2O catalysts, and a DFF yield of 55% based on glucose was obtained. This glucose conversion process is characterized by the abundance and low cost of starting material and no need for HMF separation or purification. An alternative one-pot one-step approach for the catalytic conversion of glucose into DFF with a yield of 18% in the CrCl3·6H2O/NaBr//NaVO3·2H2O system has been reported for the first time. Two-step process can give higher DFF yield than one-step, and the best DFF yield of 55% can be obtained under mild reaction conditions.

Promoting Effect of Ce in Ce/OMS-2 Catalyst for Catalytic Combustion of Dimethyl Ether

Abstract: A new route to synthesize efficient Ce-doped manganese oxide octahedral molecular sieves (OMS-2) catalysts using birnessite precursor was developed. Their catalytic activities in the combustion of dimethyl ether (DME) were evaluated. N2 adsorption, XRD, H2-TPR, O2-TPD and XPS techniques were employed in the catalyst characterization. A promoting effect of Ce in the Ce/OMS-2 catalysts on the catalytic activity was observed. For the most active sample with a Ce/Mn ratio of 0.07 (starting Ce/Mn molar ratio, Ce-7/OMS-2), the light-off temperature (the temperature acquired for 10% DME conversion, T 10) and full-conversion temperature (the temperature acquired for 90% DME conversion, T 90) were 149 and 159 °C, respectively. The catalytic activity of Ce-7/OMS-2 was stable up to 50 h. Ce-7/OMS-2 is a promising catalyst for DME catalytic combustion. The mobility of the active lattice oxygen, the larger amount and the more facile supply of the lattice oxygen species on the surface of Ce/OMS-2 are of crucial importance for the reaction. Ce-doped manganese oxide octahedral molecular sieves (OMS-2) catalysts were synthesized and the catalytic activities for the combustion of dimethyl ether (DME) are investigated. Introduction of Ce into OMS-2 greatly promoted the catalytic activity. For the most active sample with a Ce/Mn ratio of 0.07 (starting Ce/Mn molar ratio), the light-off temperature (temperature at 10% conversion, T 10) and full-conversion temperature (temperature at 90% conversion, T 90) were 149 and 159 °C, respectively.

Adsorption/Desorption Behavior of Ethanol Steam Reforming Reactants and Intermediates over Supported Cobalt Catalysts

Abstract: The interactions of reactants and intermediates with the surfaces in ethanol steam reforming over Co catalysts supported on ZrO2 and CeO2 were investigated using Temperature Programmed Desorption, Thermogravimetric Analysis-Differential Scanning Calorimetry (TGA-DSC), in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and isotopic labeling techniques. Possible mechanistic steps are proposed that lead to acetaldehyde and acetone formation, steam reforming and coking. The role of the support versus active metal (i.e., Co) and the involvement of water in the reaction network are discussed. The interactions of reactants and intermediates with the surfaces were investigated in ethanol steam reforming over Co catalysts supported on ZrO2 and CeO2 were investigated using Temperature Programmed Desorption, Thermogravimetric Analysis-Differential Scanning Calorimetry (TGA-DSC), in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and isotopic labeling techniques.

Practical One-Pot Synthesis of Secondary Amines by Zinc-Catalyzed Reductive Amination

Abstract: In the present study, the zinc-catalyzed reductive amination of various aldehydes has been examined in detail. Simple zinc(II) triflate was applied as hydrosilylation catalyst for the reduction of the in situ formed imine by condensation of an aldehyde with an amine. Using a practical Lewis acid catalyst and PMHS [poly(methylhydrosiloxane)] as cheap hydride source excellent yields and a broad functional group tolerance were achieved.

Surface Composition and Catalytic Evolution of AuxPd1―x (x = 0.25, 0.50 and 0.75) Nanoparticles Under CO/O2 Reaction in Torr Pressure Regime and at 200 °C

Abstract: Au x Pd1−x (x = 0, 0.25, 0.5, 0.75, 1) nanoparticle (NP) catalysts (8–11 nm) were synthesized by a one-pot reaction strategy using colloidal chemistry. XPS depth profiles with variable X-ray energies and scanning transmission electron microscopy (STEM) analyses show that the as-synthesized Au x Pd1−x (x = 0.25 and 0.5) bimetallic NPs have gradient alloy structures with Au-rich cores and Pd-rich shells. The evolution of composition and structure in the surface region corresponding to a mean free path of 0.6–0.8 nm (i.e., 2–3 layers to the bulk from the particle surface) was studied with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) under CO/O2 reaction in the Torr pressure regime. Under the reaction conditions of 80 mTorr CO and 200 mTorr O2 at 200 °C, the surface region of Au0.75Pd0.25 NP is Au-rich (~70% by Au). All Au x Pd1−x (x = 0.25, 0.5, 0.75) NP catalysts have higher turnover rates for the model CO/O2 reaction than pure Pd and pure Au NPs. The Pd-rich Au0.25Pd0.75 NPs show the highest turnover rates and the Pd-rich Au0.5Pd0.5 NPs the lowest turnover rates at 200 °C. Interestingly, the Au-rich Au0.75Pd0.25 NPs exhibit steady-state turnover rates which are intermediate to those of the Pd-rich bimetallic nanoparticles.

Effect of Sodium Addition to PtSn/AlSBA-15 on the Catalytic Properties in Propane Dehydrogenation

Abstract: The effect of Na addition to PtSn/AlSBA-15 on the catalytic properties in propane dehydrogenation was studied. The catalysts were characterized by XRF, BET, HR-TEM, NH3-TPD, TPO and TPR. Results showed that the presence of sodium could not only modify the acid function of the catalysts but also the structure of metallic phase, thus reduce the amount of coke deposition. Among the catalysts investigated, PtSnNa (1.0%)/AlSBA-15 had the best catalytic performance in terms of propane conversion and stability. The high catalytic performance may be owing to the strong interaction between metal and support. The effect of different amount of sodium added on the acid sites on the surface of the catalyst, pore structure and catalytic performance for PtSn/AlSBA-15 catalyst was studied in the paper. After the addition of Na, the propane conversion increased obviously and the stability of catalysts also improved. The optimum amount of Na was 1.0%.

Combined Steam and Carbon Dioxide Reforming of Methane on Ni/MgAl2O4: Effect of CeO2 Promoter to Catalytic Performance

Abstract: The catalytic performance during combined steam and carbon dioxide reforming of methane (SCR) was investigated on Ni/MgAl2O4 catalyst promoted with CeO2. The SCR catalyst was prepared by co-impregnation method using nickel and cerium metal precursors on hydrotalcite-like MgAl2O4 support. In terms of catalytic activity and stability, CeO2-promoted Ni/MgAl2O4 catalyst is superior to Ni–CeO2/Al2O3 or Ni/MgAl2O4 catalysts because of high resistance to coke formation and suppressed aggregation of nickel particles. The role of CeO2 on Ni/MgAl2O4 catalyst was elucidated by carrying out the various characterization methods in the viewpoint of the aggregation of nickel particles and metal-support interactions. The observed superior catalytic performance on CeO2-promoted Ni/MgAl2O4 catalyst at the weight ratio of MgO/Al2O3 of 3/7 seems to be closely related to high dispersion and low aggregation of active metals due to their strong interaction with the MgAl2O4 support and the adjacent contact of Ni and CeO2 species. The CeO2 promoter also plays an important role to suppress particle aggregation by forming an appropriate interaction of NiO–CeO2 as well as Ni–MgAl2O4 with the concomitant enhancement of mobile oxygen content. The catalytic performance during combined steam and carbon dioxide reforming of methane was investigated on Ni/MgAl2O4 catalyst promoted with CeO2. In terms of catalytic activity and stability, CeO2-promoted Ni/MgAl2O4 catalyst (b) is superior to Ni/MgAl2O4 catalyst (a) because of high resistance to coke formation and suppressed aggregation of nickel particles at the following reaction conditions; T = 850 °C, P = 1.0 MPa, CH4/CO2/H2O/N2 molar ratio of 3/1.2/3/3 and SV = 200,000 mL(CH4)/gcat/h.

Sulfated zirconia modified SBA-15 catalysts for cellobiose hydrolysis

Abstract: Zirconia modified SBA-15 becomes a very active catalyst for the selective hydrolysis of cellobiose to glucose after sulfation. Spectroscopic investigations indicate the presence of Bronsted acid sites with similar properties to those present in conventional sulfated zirconia. Indications are found that the sulfate groups attached to zirconia interact with silanol groups of SBA-15. The catalytic activity in cellobiose hydrolysis correlates well with results for temperature-programmed decomposition of i-propylamine for a range of sulfated ZrO2/SBA-15 catalysts. A glucose yield of 60% during cellobiose hydrolysis at a reaction time of 90 min at 160 °C is obtained.

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga2O3/Ce0.6Zr0.4O2 Catalysts: Effect of Acidity and Basicity of the Catalysts

Abstract: Ce X Zr1−X O2 catalysts with different cerium content (X) (X = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0) were prepared by a sol–gel method for use in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Among these catalysts, Ce0.6Zr0.4O2 was found to show the best catalytic performance. In order to enhance the acidity and basicity of Ce0.6Zr0.4O2 catalyst, Ga2O3 was supported on Ce0.6Zr0.4O2 (XGa2O3/Ce0.6Zr0.4O2 (X = 1, 5, 10, and 15)) by an incipient wetness impregnation method with a variation of Ga2O3 content (X, wt%). Effect of acidity and basicity of Ga2O3/Ce0.6Zr0.4O2 on the catalytic performance in the direct synthesis of dimethyl carbonate was investigated using NH3-TPD and CO2-TPD experiments. Experimental results revealed that both acidity and basicity of the catalysts played a key role in determining the catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Large acidity and basicity of the catalyst facilitated the formation of dimethyl carbonate. The amount of dimethyl carbonate produced over XGa2O3/Ce0.6Zr0.4O2 catalysts increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, 5Ga2O3/Ce0.6Zr0.4O2, which retained the largest acidity and basicity, showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. In the direct synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide over Ga2O3/Ce0.6Zr0.4O2 catalysts, the amount of DMC showed a volcano-shaped curve with respect to Ga2O3 content. The amount of DMC increased with increasing both acidity and basicity of the catalysts

Catalytic Methane Combustion over Co3O4/CeO2 Composite Oxides Prepared by Modified Citrate Sol–Gel Method

Abstract: Co–Ce–O composite oxides with high surface areas were firstly prepared by a modified citrate sol–gel method with N2 thermal treatment prior to calcination in air. The prepared Co–Ce–O catalysts have higher Brunauer–Emmett–Teller surface areas than those prepared by conventional calcination in air, and thus exhibit more effective catalytic activities. Adding CeO2 into Co3O4 can not only increase the activity of Co3O4 but also greatly enhance its thermal stability. When the bulk atomic ratio of Co/Ce is 3/1, Co–Ce–O composite oxide possesses the best activity and stability for the methane combustion.

Selective Oxidation of Glycerol Catalyzed by Rh/Activated Carbon: Importance of Support Surface Chemistry

Abstract: Noble metal catalysts (Pt, Ir, Pd, Rh, Au) supported on activated carbon were assessed for glycerol oxidation. Rhodium is a highly efficient catalyst when the support has neutral or basic properties. The surface chemistry of activated carbon plays a key role in the performance.

ZSM-5 Supported Cobalt Catalyst for the Direct Production of Gasoline Range Hydrocarbons by Fischer–Tropsch Synthesis

Abstract: Fischer–Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C5–C9) from syngas was investigated on cobalt-based FTS catalyst supported on the ZSM-5 possessing a four different Si/Al ratio. The FTS catalysts were prepared by impregnation method using cobalt nitrate precursor in a slurry of ZSM-5, and they were characterized by surface area, XRD, H2-TPR and NH3-TPD. Cobalt supported catalyst on ZSM-5 having a low Si/Al ratio of 15 was found to be superior to the other catalysts in terms of better C5–C9 selectivity due to the formation of small cobalt particle and the presence of larger number of weak acidic sites. It also exhibited the highest catalytic activity because of the higher reducibility and the small cobalt particle size. Figure shows the variation of hydrocarbon selectivity and olefin selectivity in C2–C4 with increasing density of weak acid sites. As can be seen from the figure, the increase of the weak acidic site density is responsible for increasing C5–C9 selectivity and olefin selectivity in C2–C4 range hydrocarbons. Consequently, it could be stated that the enhancement of C5–C9 selectivity is preferable on the Co/ZSM-5 catalyst possessing a higher density of weak acid sites.