Preparation of supported gold catalysts from gold complexes and their catalytic activities for CO oxidation

A phosphine-stabilized mononuclear gold complex Au(PPh₃)(NO₃) (1) and a phosphine-stabilized gold cluster [Aug(PPh₃)₈](NO₃)₃ (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as -Fe₂O₃, TiO₂, and SiO₂ were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h₂/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. -Fe₂O₃ and TiO₂ were much more efficient supports than SiO₂ for the gold particles which were characterized by XRD and EXAFS.     

Acetaldehyde Yield and Reaction Products in the Catalytic Destruction of Gaseous Ethanol

The catalytic destruction of ethanol (0.5% v/v) over a typical three-way catalyst (Pt/Rh/Ce) and two base catalysts (1% CuO and 10% CuO on -Al₂O₃) was studied in a continuous flow reactor, under atmospheric pressure. The effect of the temperature (100--500 °C) and of the oxygen concentration (0--10% v/v) on the operation of the tested catalysts and on the product profiles is presented. The formation of acetaldehyde during the catalytic destruction of ethanol, the main concern of ethanol addition to fuels, was extremely dependent on the oxygen concentration. It is noteworthy that more acetaldehyde was produced during the oxidation of ethanol in oxygen deficit conditions than during its decomposition in the absence of oxygen. Copper addition on -Al₂O₃ enhanced acetaldehyde formation, while less acetaldehyde amounts were produced over the noble metal catalyst.     

Reduction of NO by CO on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity for the reduction of NO by CO of five PdO-MoO₃/-Al₂O₃ catalysts is compared in the presence of varying amounts of oxygen at reaction temperatures from 25 to 550 °C. The samples were prepared by different methods and contain about 2% of Mo and 2% Pd. Results are compared with the activities and selectivities of PdO/ -A1₂O₃ and PdO-MoO₃/-Al₂O₃ containing 2% Pd and 2% Pd + 20% Mo, respectively. All catalysts showed appreciable activity at temperatures between 300 and 550 °C and at stoichiometric ratios,R, of the oxidizing to reducing gases of 0.1 <R < 1.1. The activity of three PdO-MoO₃/ -A1₂O₃ catalysts with low concentrations of Mo and Pd was found to be significantly higher than the activity of PdO/-Al₂O₃ at 1.1 <R < 1.3 and at temperatures between 300 and 500 °C. The improved activity is ascribed to the interaction of the active metals.     

Reduction of NO by H2 on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity and selectivity of three PdO-MoO₃/-Al₂O₃ catalysts containing about 2% Pd and 2% Mo were studied for the reduction of NO by h₂ in the presence of varying amounts of oxygen at temperatures from 50 to 550 °C. The results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. In the absence of oxygen, the conversion of NO to N₂ and N₂O is higher on the three catalysts than it is on PdO/-Al₂O₃ at 500 and 550 °C. In the presence of oxygen, the yields of N₂ and N₂O are generally lower on two of the PdO-MoO₃/-Al₂O₃ catalysts than on PdO/-Al₂O₃.     

Selective oxidation of methane to CO and H2 over unreduced NiO-rare earth oxide catalysts

NiO-LnO _x (Ln = lanthanide) catalysts (with NiLn=11) without prereduction show high activity/selectivity and very high productivity in the oxidative conversion of methane to CO and H₂. The catalysts are first activated in the initial reaction, which is started at 535–560°C, by the reduction of NiO and creation of active sites. The carbon deposition on the catalysts in the reaction, particularly for the NiO-Gd₂O₃, NiO-Tb₄O₇ and NiO-Dy₂O₃ catalysts, is quite fast but it has caused a little or no influence on the catalytic activity/selectivity. Pulse reaction of pure methane on NiO-Nd₂O₃ (at 600°C) shows involvement of lattice oxygen in the initial reaction and also reveals formation of carbon from CO on the catalyst reduced in the reaction.     

Copolymerization of ethene with norbornene using palladium(II) α-diimine catalysts: Influence of feed composition, polymerization temperature, and ligand structure on copolymer properties and microstructure

Four cationic palladium(II) α-diimine complexes, [{ArNC(R)-C(R)NAr}Pd(Me)(CH₃CN)] (1, R=H, Ar=2,6-Me₂C₆H₃, =B[3,5-C₆H₃(CF₃)₂]₄; 2, R=CH₃, Ar=2,6-iPr₂C₆H₃; 3, R=CH₃, Ar=2-tBuC₆H₄; 4, R,R=An, Ar=2,6-iPr₂C₆H₃) were used for the copolymerization of ethene with norbornene. The copolymerization behavior of the catalysts and the influence of the polymerization temperature were investigated. The copolymers were characterized using ¹³C NMR spectroscopy, differential scanning calorimetry, and gel permeation chromatography techniques. Sterically demanding ortho -N-aryl substituents and rigid bulky bridge units increase the copolymer molar masses, while the incorporation level of norbornene is decreased. Microstructures with isolated norbornene units and alternating sequences are predominant. Less bulky substituted catalysts yield copolymers with higher norbornene contents and lower molar masses. Norbornene diblock sequences are dominant which are exclusively racemic connected, indicating that the insertion proceeds under chain end control. Optimal polymerization results are achieved at temperatures between 10 and 30 °C, while temperatures below 0 °C result in lower polymerization rates and molar masses. Above 30 °C, activities, molar masses, and norbornene incorporation decreases due to catalyst decomposition.     

Propane oxidative dehydrogenation on silica based oxide catalysts

The oxidative dehydrogenation of propane to propylene with molecular O₂ (PPD) has been investigated on commercial bare SiO₂ and medium loaded V₂O₅ and MoO₃ catalysts at 450–525°C. The direct relationship between the density of reduced sites (, 10¹⁶ s_r g _cat– ¹ ), evaluated in steady-state conditions by O₂ chemisorption, and the POD reaction rate proves the occurrence of a concerted reaction mechanism involving the activation of gas-phase O₂ on the reduced sites of the catalyst surface. A straight-line correlation between the activity of such silica based catalysts in POD and methane partial oxidation to formaldehyde (MPO) at 525°C has been disclosed.     

Ni catalysts with Mo promoter for methane steam reforming

NiO/Al₂O₃ catalyst precursors were prepared by simultaneous precipitation, in a Ni:Al molar ratio of 3:1, promoted with Mo oxide (0.05, 0.5, 1.0 and 2.0 wt%). The solids were characterized by adsorption of N₂, XRD, TPR, Raman spectroscopy and XPS, then activated by H₂ reduction and tested for the catalytic activity in methane steam reforming.The characterization results showed the presence of NiO and Ni₂AlO₄ in the bulk and Ni₂AlO₄ and/or Ni₂O₃ and at the surface of the samples.In the catalytic tests, high stability was observed with a reaction feed of 4:1 steam/methane. However, at a steam/methane ratio of 2:1, only the catalyst with 0.05% Mo remained stable throughout the 500 min of the test.The addition of Mo to Ni catalysts may have a synergistic effect, probably as a result of electron transfer from the molybdenum to the nickel, increasing the electron density of the catalytic site and hence the catalytic activity.     

Selective Methanol Conversion to Methylal on Re-Sb-O Crystalline Catalysts: Catalytic Properties and Structural Behavior

Three crystalline compounds, SbOReO₄·2H₂O, Sb₄Re₂O₁₃ and SbRe₂O₆, and several supported Re catalysts were employed as catalysts for the selective oxidation of methanol to methylal (3CH₃OH+1/2O₂ CH₂(OCH₃)₂+2H₂O). A high selectivity of 92.5% to methylal at a conversion of 6.5% under conditions of GHSV = 10000 mL h^-1g^-1 _-cat and 573 K was obtained on the new SbRe₂O₆ catalyst, while no significant formation of methylal was observed with the other two catalysts. No structural change in the bulk and surface of SbRe₂O₆ and Sb₄Re₂O₁₃ occurred after methanol oxidation below 593 K, but SbOReO₄·2H₂O was transformed to Sb₄Re₂O₁₃, as characterized by XRD, Raman spectroscopy, XPS and SEM. The high performance of SbRe₂O₆ for the selective methylal synthesis was ascribed to Re oxide species stabilized by a specific connection with Sb oxides at the crystal surface.     

Highly selective supported Pd catalysts for steam reforming of methanol

Steam reforming of methanol, CH₃OH + H₂O 3H₂ + CO₂, was carried out over various Pd catalysts (Pd/SiO₂, Pd/Al₂O₃, Pd/La₂O₃, Pd/Nb₂O₅, Pd/Nd₂O₃, Pd/ZrO₂, Pd/ZnO and unsupported Pd). The reaction was greatly affected by the kind of support. The selectivity for the steam reforming was anomalously high over Pd/ZnO catalysts.     

Encapsulated Cobalt Oxide on Carbon Nanotube Support as Catalyst for Selective Continuous Hydrogenation of the Showcase Substrate 1‐Iodo‐4‐nitrobenzene

A carbon nanotube supported catalyst containing cobalt/cobalt oxide (Co/Co₃O₄) nanoparticles encapsulated within a shell of nitrogen‐doped graphene layers (Co₃O₄/NGr@CNT) was prepared. It shows excellent chemoselectivity in the hydrogenation of 1‐iodo‐4‐nitrobenzene, which contains an iodine substituent highly sensitive against hydrodehalogenation. In contrast to traditional activated charcoal‐supported catalysts such as Pt‐V/C or the closely related Vulcan carbon black supported Co₃O₄/NGr@C, the advantageous morphological properties of the CNT support allow for the application of the new Co₃O₄/NGr@CNT as a fixed bed catalyst in a continuous flow reactor. Under optimized conditions, no dehalogenation side products could be detected. This remarkable selectivity in combination with its mechanical stability under operation conditions render Co₃O₄/NGr@CNT a catalyst particularly relevant for application in continuous processes based on a packed bed reactor.

     

The importance of passivation in the study of iron Fischer-Tropsch catalysts

In the study of iron catalysts, careful passivation is necessary for study of microstructure by ex situ analytical techniques. The passivation procedure used in our study consists of heating the sample in He at the reaction temperature, cooling to room temperature and introducing small amounts of O₂ (<1%) in a flowing He stream. A properly passivated sample shows no more than a few nm of surface Fe₃O₄ on-Fe, when examined in a high resolution TEM. Proper passivation is also characterized by an exotherm of no more than 2–3 K. We show that a Fischer-Tropsch catalyst carbided in CO will show substantial amounts of magnetite, if exposed to air without proper passivation. Such surface oxidation may cause errors in determining the relative amounts of the magnetite and carbide phases in Fischer-Tropsch catalysts, which are important for proper identification of the catalytically active phase.     

Surface functionalization of vertically-aligned carbon nanotube forests by radio-frequency Ar/O2 plasma

Vertically-aligned carbon nanotube (CNT) forests were modified using radio-frequency Ar/O₂ plasma. The effect of plasma parameters on surface morphology, atomic composition and structure of CNT forests were studied. Functionalized CNT forests preserved vertical alignment and showed dramatic change in surface morphology, and bundle-like patterns were observed from scanning electron microscopy examination. X-ray photoelectron spectroscopy and Raman analyses reveal that the amount of sp²-hybridized graphite-like carbon bond in CNTs decreased significantly and oxygen-containing functionalities like C–O and O–CO groups were introduced after treatment. And the functionalization occurred exclusively on outer surface of CNT forests. Ar/O₂ plasma was found to be more efficient than pure Ar plasma for oxygen functionalization.     

Preparation and electrochemical studies of metal–carbon composite catalysts for small-scale electrosynthesis of H2O2

Numerous transition metal–carbon composite catalysts (M = V, Zn, Ni, Sn, Ce, Ba, Fe, Cu) have been synthesized and tested for electroreduction of O₂ to H₂O₂, The activity and selectivity of all synthesized catalysts for electrosynthesis of H₂O₂ were determined by the rotating ring-disk electrode method in acidic and neutral electrolytes. The Co-based catalysts in general showed the highest activity towards H₂O₂ formation. Experiments with different loading contents of Co showed that the activation overpotential losses of oxygen reduction to H₂O₂ reduces as loading increases to about 4 wt% Co. Addition of Co beyond this level did not seem to impact the overpotential losses. The cobalt-based catalysts, were spray-coated onto 120 μm thick Toray^® graphite substrates, and were studied in bulk electrolysis cells for up to 100 h at potentiostatic conditions (0.25 V vs. RHE) in pH 0, 3, and 7 electrolytes. At (25 °C and 1 bar) with a catalysts loading of about and using dissolved O₂ in 0.5 M H₂SO₄, typical H₂O₂ electrosynthesis rates of about were reached with current efficiencies of about 85 ± 5% at 0.25 V (vs. RHE).     

Study of elementary reactions of free radicals formed on oxide and platinum containing catalysts

The formation of alkylperoxy radicals on catalysts CuCr₂O₄/ -Al₂O₃, Pt /--Al₂O₃ and on alumina upon the interaction of amines and alcohols with oxygen has been observed applying the matrix isolation ESR technique. Surface-generated gas phase radicals are shown to initiate a radical chain reaction. The efficiency of the yield of radicals depends on the catalyst mass and its arrangement in a reactor: the desorption of radicals into the gas phase occurs primarily from the outer geometrical surface of catalyst granules.     

Solid oxide fuel cells with YSZ-BNO Bi-layer electrolyte film deposited by magnetron sputtering

Bi-layer electrolyte films of Zr_0.84Y_0.16O_1.92 (YSZ)- 0.79Bi₂O₃-0.21Nb₂O₅ (BNO) were deposited by RF magnetron sputtering on NiO-SDC anode substrates. The stoichiometry of the BNO electrolyte film was found strongly dependent on the ratio of Ar and O₂ during sputtering, and the BNO film deposited at a mixture of 31 sccm Ar and 7 sccm O₂ appeared to be the closest to the target composition. When deposited at 300 °C and subsequently annealed at 700 °C, the BNO electrolyte emerged to be crack free and dense with some scattering closed pores. The XRD patterns of the film are indexed to the cubic Fm m structure of Bi₃NbO₇. The as-deposited film was well-crystalline and consisted of fine grains and random orientation microstructures. For electrolyte thicknesses of approximately 4.0 μm YSZ and 1.5 μm BNO layers, the open circuit voltage (OCV) and the maximum power density of the single cell with Ag cathode read respectively 0.94 V and 10 mW/cm² at 600 °C. These OCV values are lower than the expected theoretical value due to the high partial electronic conductivity.     

Oxidative dimerisation of methane on supported palladium oxide catalysts

Supported palladium oxide catalysts are able to convert CH₄ to C₂H₆, CO, CO₂, H₂ and H₂O at temperatures 315 °C. Catalysts did not show any support effect when TiO₂, Al₂O₃, ZrO₂, La₂O₃ and MgO were used as supports. With sequential O₂ pulsing the catalyst showed long term activity when used at temperatures below 400 °C. Addition of Pt increased selectivity whereas with Ga it decreased. Results indicate participation of lattice O₂ from catalyst in the reaction pathway.     

On the kinetic mechanism of the reaction of NH2 with O2 in O-, H-, and N-containing flames. 1. Kinetic parameters of the NH2+O2=NHO+OH reaction

The reaction pathways for NH₂+O₂Products are considered on the basis of experimental data on the ignition of an NH₃/O₂/Ar mixture in reflected shock waves (p=1–10 atm, T=900–2160 K) and on the NH₃/O₂/Ar flame structure (p=35 torr, T=1050–2600 K) using a multistage kinetic mechanism. The rate constants of the NH₂+O₂=HNO+OH reaction, obtained from a comparison of experimental and calculated data, are reported (k=3·10¹¹ exp (–15,000/RT) cm³/(mole·s) at T1500–2160 L and k=3·10⁹ cm³/(mole·s) at T900–1400 K).Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 1, pp. 60–65, January–February, 1994.     

Palladium‐Catalyzed Carbonylative Synthesis of 2,3‐Disubstituted Chromones

An unexpected palladium‐catalyzed carbonylative synthesis of 2,3‐disubstituted chromones has been developed. Starting from 2‐bromofluorobenzenes and ketones, the corresponding chromones were produced in good yields. By control experiments, this transformation was found to proceed through a sequential carbonylation/Claisen–Hasse rearrangement/intramolecular nucleophilic aromatic substitution approach (S_NAr). More specifically, the reaction sequence started with a palladium‐catalyzed carbonylation of the ketone with o‐bromofluorobenzene to give the vinyl benzoates, which subsequently transformed into 1,3‐diketones via a Claisen–Hasse rearrangement. The final products were produced after an intramolecular S_NAr reaction of the in situ formed 1,3‐diketone.

     

Phosphorus promoted WS2/Al2O3 catalysts studied by transmission electron microscopy

A series of WS₂/Al₂O₃ catalysts containing a varied amount of phosphorus (0.0,2.5 and 6.0 wt% P₂O₅), sulfided at two different temperatures (873 and 1073 K), were studied by means of high-resolution transmission electron microscopy (HRTEM). The stacking of (002) layers in the WS₂-2H crystallites of the rag structure increases with the addition of phosphorus, whereas its length is kept almost constant. At high sulfidation temperatures phosphorus shows a stabilizing effect on the catalysts by retarding the stacking growth of WS₂ crystallites. Additionally, an aluminum phosphate crystalline phase is identified in the phosphorus promoted catalysts.