A Comparative Study of Partial Oxidation of Methanol over Zinc Oxide Supported Metallic Catalysts

Au/ZnO, Pd/ZnO and Au–Pd/ZnO catalysts were prepared by PVP-stabilized reduction method by C₂H₅OH. The catalysts have been used successfully for hydrogen production by partial oxidation of methanol (POM). The influence of Au, Pd and Au–Pd on the performance of supported catalysts for POM has been investigated. The prepared samples were characterized by ICP, XRD, BET, TPR and TPD. The results show that the Au–Pd/ZnO catalyst are more active and exhibit higher hydrogen selectively compared to the Pd/ZnO and Au/ZnO catalyst, the methanol conversion of 99.5% and hydrogen selectivity of 65.6% were obtained at 573 K. The enhanced activity and stability of the bimetallic Au–Pd/ZnO catalyst has been explained in terms of the higher dispersion and basic density, smaller particles of gold and synergetic effect between gold and palladium.     

Gold-Based Nanoparticulate Catalysts for the Oxidative Esterification of 1,4-Butanediol to Dimethyl Succinate

The effect of the reaction conditions and catalyst composition on the oxidation of 1,4-butanediol has been investigated. We have shown that gold and gold–palladium nanoparticles supported on titania can be effective catalysts for this oxidation reaction. We have demonstrated that the formation of butyrolactone, methyl-4-hydroxybutyrate and dimethyl succinate follow a sequential reaction pathway. We have also investigated the role of acid/base on the reaction and have shown a beneficial synergistic effect of alloying gold with palladium on both the conversion and selectivity towards dimethyl succinate.     

Characterization by Mössbauer spectroscopy of trimetallic Pd–Sn–Au/Al2O3 and Pd–Sn–Au/SiO2 catalysts for denitration of drinking water

The reduction of nitrate using a catalytic process is one of the most interesting ways to solve the problem of drinking water pollution by this compound. The key parameter of this technique is the selectivity toward nitrogen formation. Palladium/tin-based bimetallic catalysts are well suited for this purpose, but the selectivity of these catalysts is not high enough for a direct application of this process. In the present study, alumina- and silica-supported catalysts were prepared by successive deposition of tin and gold onto palladium particles by using controlled surface reaction. The characterization of trimetallic Pd–Sn–Au catalyst evidenced that trimetallic catalysts supported on silica present a palladium/tin/gold phase. The catalytic test showed that this type of catalyst is very active and selective in nitrate and nitrite reduction. Moreover, the addition of gold improves the stability and the selectivity toward nitrogen formation of the catalyst compared to the parent Pd–Sn catalyst.     

Gold-Catalyzed Aerobic Oxidation of Benzyl Alcohol: Effect of Gold Particle Size on Activity and Selectivity in Different Solvents

The effect of the size of gold particles deposited on CeO₂ and TiO₂ supports on their catalytic behavior in the aerobic oxidation of benzyl alcohol in different solvents (mesitylene, toluene, and supercritical carbon dioxide) has been investigated. The size of supported gold particles deposited via a colloidal route was in the range 1.3–11.3 nm, as determined by means of EXAFS and HAADF-STEM measurements. The catalytic performance of the supported gold catalysts in the different solvents revealed a significant effect of the gold particle size. Optimal activity was observed for catalysts with medium particle size (ca. 6.9 nm) whereas smaller and bigger particles showed inferior activity. Identical trends for the activity–particle size relationship were found using Au/CeO₂ and Au/TiO₂ for the reaction at atmospheric pressure in conventional solvents (mesitylene, toluene) as well as under supercritical conditions (scCO₂). Selectivity to benzaldehyde was only weakly affected by the gold particle size and mainly depended on reaction conditions. In supercritical CO₂ (scCO₂) selectivity was higher than in the conventional solvents under atmospheric pressure. All catalysts tested with particle sizes ranging from 1.3 to 11.3 nm showed excellent selectivity of 99% or higher under supercritical conditions.     

Liquid Phase Oxidation of Glycerol Using a Single Phase (Au–Pd) Alloy Supported on Activated Carbon: Effect of Reaction Conditions

The liquid phase oxidation of glycerol has been studied over gold–palladium nanoparticles supported on activated carbon and synthesized by using a one-protocol synthesis. The effect of pressure, catalyst amount and base has been examined by using an autoclave reactor with molecular oxygen as oxidant at mild conditions. By choosing the appropriate reaction conditions control of selectivity could be possible, whereas activity is strongly dependent on catalyst amount and concentration of base.     

Oxidation of Cyclohexane with Molecular Oxygen Catalyzed by SiO2 Supported Palladium Catalysts

The di(ethylthio)ethane palladium (A) and di(ethylthio)propane palladium (B) complexes have been immobilized on the surface of silica gel and these catalyst systems are shown to serve as effective supported Pd catalysts for cyclohexane oxidation with O₂ under solvent free condition. The supported catalyst A provides best results (overall ca. 16.2% conversion, with a selectivity of 72 or 24% for cyclohexanol or cyclohexanone, respectively, which are further promoted in the presence of 2-pyrazinecarboxylic acid which acts as a co-catalyst (overall ca. 21.2% conversion).     

A Highly Effective Pt and H3PW12O40 Modified Zirconium Oxide Metal–Acid Bifunctional Catalyst for Skeletal Isomerization: Preparation, Characterization and Catalytic Behavior Study

A series of metal–acid bifunctional catalysts with varying quantities of platinum and tungstophosphoric acid (TPA) supported on zirconium oxide were prepared by co-impregnation method. In skeletal isomerization of n-pentane using catalyst with 1% Pt and 30% TPA loadings the conversion of the reactant which was close to the equilibrium conversion reached ca. 65% and the selectivity towards the product was as high as ca. 97% at atmospheric pressure and relatively low reaction temperature (200 °C). The phase structure, chemical structure, surface physicochemical properties, surface element oxidation states and hydrogen reduction behavior of the catalysts were well-characterized via XRD, FT-IR, N₂ adsorption–desorption determination (BET), XPS and TPR. The effects of Pt and TPA loadings, calcination temperature, reaction temperature and weight hourly space velocity (WHSV) on the catalytic performance were investigated. In addition, a long period catalytic stability test of the catalyst with optimal Pt and TPA loadings was carried out, which indicated that the bifunctional catalyst was in possession of good stability in skeletal isomerization along with high catalytic activity under the experimental conditions.     

Silica-Supported Gold Catalyst Modified by Doping with Titania for Cyclohexane Oxidation

Amorphous silica was modified by doping with titania through a surface sol–gel process and applied as the support for depositing gold. These doped silica-supported gold catalysts were tested in the selective cyclohexane oxidation to cyclohexanone and cyclohexanol using oxygen. Under the oxidation conditions of 150 °C, 1.5 MPa and 3 h, a selectivity of 91.7% for cyclohexanone and cyclohexanol could be reached over the gold catalyst, affording a cyclohexane conversion of 8.4% and a turnover frequency up to 40,133 per hour. Moreover, the catalytic activity and selectivity could be well retained in 4 recycling oxidation reactions, showing a high stability of the gold catalyst supported on titania-doped silica.     

Preparation and Study of Pd Catalysts Supported on Activated Carbon Cloth (ACC) for Direct Synthesis of H2O2 from H2 and O2

Activated carbon cloths (ACCs) were used as supports for Pd catalysts. The catalyst preparation was carried out by the impregnation method using acidic solution of palladium dichloride (PdCl₂) as metal precursor. The effects of the oxidation state of the loaded metal, heat treatment of the catalysts in different atmosphere (H₂, air) at different temperatures and surface chemistry of the support on the catalyst characterizations and the catalytic activities were investigated. Wet oxidation of ACC was done by nitric acid in order to induce oxygen-containing surface functional groups. Surface chemistry of the support and oxidation state of the metallic phase was investigated by means of XPS, TPD, SEM, DTA and TGA tests. Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed batch wise in a stainless steel autoclave. The reactions were conducted under high pressure (38 bar) at 0 °C and methanol was used as reaction medium. The direct synthesis results showed that the oxygen-containing surface functional groups increase the selectivity of the catalysts by reducing the rate of water production. Existence of the oxidized state of Pd (PdO) also makes the catalyst more selective than the corresponding zerovalent state (Pd0). PdO affected on selectivity by increasing the rate of H₂O₂ production and reducing the amount of production of water, simultaneously.     

Use of renewables for the production of chemicals: Glycerol oxidation over carbon supported gold catalysts

As a renewable feedstock and due to its high functionality glycerol is an attractive reactant for the production of a large number of valuable compounds. We report on an environmentally friendly alternative to produce chemicals from the glycerol oxidation, which are currently produced either by stoichiometric oxidation processes or by enzymatic routes. We investigate the heterogeneously catalyzed liquid-phase oxidation of glycerol with carbon supported gold catalysts. The prepared nanosized gold catalysts are highly active, so that the reaction could be performed under atmospheric pressure. The influence of the preparation method of the catalysts has been investigated. Moreover, the support effect on the catalytic process has been studied and discussed in terms of pore structure of the investigated carbon materials. The promotor effect of platinum on Au/C catalysts was examined and it could be shown that the presence of Pt increases not only the catalyst activity but also the selectivity. By promoting the gold catalysts with platinum the selectivity to dihydroxyacetone could be increased from 26% (Au/C) to 36% (Au–Pt/C).     

Adhesion optimization for catalyst coating on silicon-based reformer

CMZ (ca. 30.0 wt.% Cu, 20 wt.% Mn, and 50 wt.% Zn) catalyst was chosen for the partial oxidation of methanol (POM) reaction. To enhance adhesion between a silicon-based reactor and catalysts, boehmite and bentonite were used as binders. Changes in conditions such as pH value, ratio of bentonite/boehmite, amount of solid contents per area of substrate, and aging time have crucial effects on adhesion and result in variable performance of catalyst in POM reaction. Regarding optimized adhesion conditions, 13 wt.% weight loss was observed and methanol conversion could be kept at ca. 80–90% of original catalyst performance in a packed-bed reactor. However, poor performance was observed in the micro-channel reactor. The methanol conversion (C_MeOH), H₂ selectivity (S_H2), and H₂ yield (Y_H2) achieved 58%, 67%, 5.7 × 10^?6 mol/min in micro-channel reformer at 250 °C, respectively.     

Oxidation of benzyl alcohol using supported gold–palladium nanoparticles

A key discovery in the last two decades has been the realisation that gold, when prepared as supported nanoparticles, is exceptionally effective as an oxidation catalyst, particularly for the oxidation of alcohols. The catalytic efficacy is enhanced further by the alloying of gold with palladium. In this paper we study the effect of the method preparation of gold–palladium alloy nanoparticles supported on titania and investigate the activity of the materials for the selective oxidation of benzyl alcohol. We contrast impregnation and deposition–precipitation methods and demonstrate that the most active catalysts are prepared using the deposition–precipitation method.     

Palladium,Gold, and Gold–Palladium Nanoparticle-Supported Carbon Materials for Cyclohexane Oxidation

Transition metal supported porous carbon materials have become a promising aspirant in energy storage, solid catalysis, and material chemistry. Palladium, gold, and gold–palladium anchored carbon composites (CPC-25/170, CGC-25/170, and CGPC-25/170) with two different sized carbon cages (～25 and 170 nm) were constructed using nano-silica ball (NSB) as the template and a pyrolysis fuel oil (PFO) based pitch residue as the carbon source. The Pd, Au, and Au–Pd doped carbon nanoreactors were characterized by various physicochemical analysis methods. The developed materials were used as heterogeneous catalysts for the oxidation of cyclohexane to cyclohexanol and cyclohexanone using H₂O₂ at room temperature (25°C) and atmospheric pressure. The most active catalyst CGC-170 showed combined cyclohexanol and cyclohexanone yield of 7.7% after 4 h reaction time. The conversion of 2.4%, 0.05%, and 0.32% was achieved using CGC-25, CGPC-25, and CGPC-170 catalysts, respectively. Recyclability of the catalysts maintains no observable loss of performance during catalytic oxidation reaction.     

Characterization and oxidation states of Cu and Pd in Pd–CuO/ZnO/ZrO2 catalysts for hydrogen production by methanol partial oxidation

Copper and zinc oxide based catalysts prepared by coprecipitation were promoted with palladium and ZrO₂, and their activity and selectivity for methanol oxidative reforming was measured and characterized by N₂O decomposition, X-ray absorption spectroscopy, BET, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature programmed reduction. Addition of ZrO₂ increased copper dispersion and surface area, with little effect on activity, while palladium promotion significantly enhanced activity with little change of the catalytic structure. A catalyst promoted with both ZrO₂ and palladium yielded hydrogen below 150 °C. EXAFS results under reaction conditions showed that the oxidation state of copper was influenced by palladium in the catalyst bulk. A palladium promoted catalyst contained 90% Cu⁰, while the copper in an unpromoted catalyst was 100% Cu¹⁺ at the same temperature. Palladium preferentially forms an unstable alloy with copper instead of zinc during reduction, which persists during reaction regardless of copper oxidation state. A 100-h time on stream activity measurement showed growth in copper crystallites and change in copper oxidation state resulting in decreasing activity and selectivity. A kinetic model of the reaction pathway showed that palladium and ZrO₂ promoters lower the activation energy of methanol combustion and steam reforming reactions.     

An Attempt to Selectively Oxidize Methane over Supported Gold Catalysts

Abstract  

The potential of supported gold catalysts for the selective gas-phase oxidation of methane to methanol with molecular oxygen was investigated. A broad range of supported gold-based catalyst materials was synthesized using reducible and non-reducible support materials. Although the formation of small gold nanoparticles was established for all catalyst materials, only a very low activity for the total oxidation of methane was observed, at temperatures >250 °C. Since no traces of partial oxidation products, such as methanol, formaldehyde, formic acid, methyl formate, dimethyl ether and CO, were observed it was concluded that supported gold catalysts are not able to selectively oxidize methane to methanol under these experimental conditions.     

Promotional SMSI Effect on Supported Palladium Catalysts for Methanol Synthesis

High-temperature reduction (HTR) of palladium catalysts supported on some reducible oxides, such as Pd/CeO₂, and Pd/TiO₂ catalysts, led to a strong metal-support interaction (SMSI), which was found to be the main reason for their high and stable activity for methanol synthesis from hydrogenation of carbon dioxide. But low-temperature-reduced (LTR) catalysts exhibited high methane selectivity and were oxidized to PdO quickly in the same reaction. Besides palladium, platinum exhibited similar behavior for this reaction when supported on these reducible oxides. Mechanistic studies of the Pd/CeO₂ catalyst clarified the promotional role of the SMSI effect, and the spillover effect on the HTR Pd/CeO₂ catalyst. Carbon dioxide was decomposed on Ce₂O₃, which was attached to Pd, to form CO and surface oxygen species. The carbon monoxide formed was hydrogenated to methanol successively on the palladium surface while the surface oxygen species was hydrogenated to water by spillover hydrogen from the gas phase. A reaction model for the hydrogenation of carbon dioxide was suggested for both HTR and LTR Pd/CeO₂ catalysts. Methanol synthesis from syngas on the LTR or HTR Pd/CeO₂ catalysts was also conducted. Both alcohol and hydrocarbons were formed significantly on the HTR catalyst from syngas while methanol formed predominantly on the LTR catalyst. Characterization of these two catalysts elucidated the reaction performances.     

Oxidation of Glycerol Using Supported Gold Catalysts

A series of supported gold catalysts (0.25, 0.5, 1.0 wt% Au/graphite) have been investigated for the oxidation of glycerol and propan-1,2-diol. The 1 wt% Au/graphite catalyst is found to give 100% selectivity to the mono acid product, isolated as the sodium salt, as long as NaOH is present. The catalysts are characterized by TEM and cyclic voltammetry. By TEM, active catalysts all comprise fairly broad-size distributions (5–50 nm diameter) for the gold nanoparticles, although most are ca. 25 nm in diameter. An inactive 1 wt% Au/graphite is shown to have considerably larger particle sizes (>50 nm) and this indicates that there may be an optimum particle size for the desired catalysis. Characterization using cyclic voltammetry of active Au/graphite catalysts carried out in NaOH reveals the presence of an oxide species that may be responsible for the observed catalysis. In contrast, the inactive 1 wt% Au/graphite catalyst shows no oxidation in the cyclic voltammetry experiments.     

Pt/Ni wet impregnated over Al incorporated mesoporous silicates: a highly efficient catalyst for anisole hydrodeoxygenation

This work reports, formation of benzene from anisole via hydrodeoxygenation process using vapour phase fixed bed reactor. The surface properties of bimetallic catalysts such as textural properties, acidic, and Pt/Ni dispersion has established by various characterization techniques. The reaction was carried out at 370 and 420 °C with space velocity 3.3 & 6.6 h^??1, over acidic and non-acidic supported mono and bimetallic catalysts. The optimum conversion and selectivity was observed at 420 °C and WHSV?=?3.3 h^??1 for all mono and bimetallic catalysts. Pt/Ni/Al-SBA-15 acidic bimetallic catalyst shows maximum anisole conversion 59% with benzene selectivity 37% under atmospheric pressure, due to the more acidic centres and high dispersion of Pt/Ni species on the bimetallic catalyst, enhance the anisole conversion; this was proved by NH₃-TPD and HR-TEM analysis. The acidic Pt/Ni bimetallic catalyst shows higher anisole conversion as compared to the mono metallic Pt/Ni catalysts and it works predominantly through demethylation and hydrogenolysis reaction pathway.     

Selective conversion of cyclohexane to cyclohexanol and cyclohexanone using a gold catalyst under mild conditions

The oxidation of cyclohexane to cyclohexanol and cyclohexanone are investigated using supported gold catalysts using mild conditions of temperature and pressure. These catalysts are found to show some limited activity at 70 °C. However, the gold catalysts do not exhibit significantly different behaviour from supported Pt or Pd catalysts, and the selectivity observed is solely a function of conversion which in turn is a function of reaction time. It is clear that at very low conversions very high selectivities can be observed, but high selectivity under these mild reaction conditions cannot be maintained at higher conversions.     

Catalytic Deoxygenation of Tall Oil Fatty Acids Over a Palladium-Mesoporous Carbon Catalyst: A New Source of Biofuels

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.