Kinetics and mechanism of catalytic acetylene hydrochlorination with gaseous HCl on the surface of mechanically activated K<Subscript>2</Subscript>PdCl<Subscript>4</Subscript>

The catalyst for acetylene hydrochlorination with gaseous HCl at room temperature is prepared by mechanical pretreatment of K₂PdCl₄ in an acetylene atmosphere. The rate-determining step of the reaction is the chloropalladation of π-coordinated acetylene involving an HCl molecule. As a consequence, the replacement of HCl with DCl brings about a kinetic isotope effect of 2.8 ± 0.4, which differs substantially from that observed in the protodemetalation of the intermediate palladium(II) chlorovinyl derivative yielding vinyl chloride (6.8 ± 0.6).     

Catalytic hydrochlorination of acetylene on mechanochemically-activated K<Subscript>2</Subscript>PdCl<Subscript>4</Subscript>

We report the catalysis of the hydrochlorination of acetylene on the surface of dry K₂PdCl₄ subjected to prior mechanical activation in an atmosphere of acetylene or propylene. The stereochemistry of the reaction corresponds to trans addition of the halogen and hydrogen atoms to the C-C triple bond. The hydrogen halide is the source of the halogen atom in the reaction product. The mechanical activation of K₂PdCl₄, in contrast to the case of K₂PtCl₄, is also capable of activating the C-C double bond: propylene is hydrochlorinated under similar conditions to isopropyl chloride. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 306–309, September–October, 2008.     

NH<Subscript>3</Subscript>(CH<Subscript>2</Subscript>)<Subscript>5</Subscript>NH<Subscript>3</Subscript>BiCl<Subscript>5</Subscript>: an efficient and recyclable catalyst for the synthesis of benzoxazole,benzimidazole and benzothiazole heterocycles

In this work, the condensation of aromatic aldehydes with different two-substituted aniline catalyzed by NH₃(CH₂)₅NH₃BiCl₅ as heterogeneous and recyclable catalyst was reported. It was demonstrated that NH₃(CH₂)₅NH₃BiCl₅ can act as an efficient and active catalyst and is reusable for six runs without a significant loss of their catalytic activity. Simple preparation of the catalyst, high catalytic activity and good reusability are noteworthy advantages of this catalytic system in the synthesis of benzoxazole, benzimidazole and benzothiazole heterocycles at room temperature under solvent-free conditions.     

Kinetics and mechanism of carbon monoxide oxidation on the supported metal complex catalyst PdCl<Subscript>2</Subscript>-CuCl<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The kinetics of carbon monoxide oxidation with atmospheric oxygen on a PdCl₂-CuCl₂/γ-Al₂O₃ catalyst was studied at T = 27°C and an N₂-O₂-CO mixture pressure of 1 atm. The catalyst was prepared by cold impregnation. Three groups of mechanistic hypotheses are considered, and two of them are demonstrated to be consistent with kinetic data, although they differ in the roles of water and oxygen in carbon monoxide oxidation.     

Changes in the course of reaction and regeneration of a Pd-Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the selective hydrogenation of acetylene

The samples of Pd-Ag/Al₂O₃ catalysts for the selective hydrogenation of acetylene impurities in an ethane-ethylene mixture were studied using the IR spectroscopy of adsorbed CO, X-ray diffraction analysis, and thermogravimetry. In the course of reaction and regeneration, the total concentration of the supported metals (Pd and Ag) changed only slightly. The degree of accessibility of silver atoms to CO adsorption and the amount of these atoms in the nearest environment of palladium atoms decreased to result in an increase in the selectivity of acetylene hydrogenation to ethane. The decrease in the accessibility of silver was due to a change in the phase composition of the alumina support as a result of its rehydration. It was hypothesized that the resulting aluminum hydroxide with the boehmite morphology is a source of the strongest Lewis acid sites, which catalyze oligomerization processes on the catalyst surface.     

Catalytic Iodination of Acetylene in the Iodopalladate(II)-I<Superscript>−</Superscript>-I<Subscript>2</Subscript>-MeOH System

We have studied the kinetics of catalytic iodination of acetylene to form trans-1,2-diiodoethylene in the system Pd^II-NaI-I₂-MeOH at 55 °C. The results obtained allow us to hypothesize that the reaction includes a step of iodopalladation of acetylene with intermediate formation of an σ-iodovinyl derivative of palladium, the decomposition of which by reductive elimination yields the end product and regenerates the catalyst. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 296–301, September–October, 2005.     

The activity and stability of PdCl<Subscript>2</Subscript>/C-N catalyst for acetylene hydrochlorination

Carbon supported PdCl₂ is highly active in catalyzing acetylene hydrochlorination reaction, but deactivates rather quickly. Upon nitrogen doping in the carbon structure, the stability of the PdCl₂ catalysts is significantly improved. Furthermore, the results show that 900 °C is a preferred doping temperature. The acetylene conversion keeps above 90% even after 1200 min time on stream whereas the one without nitrogen doping drops to below 10% after 450 min. The stabilizing mechanism of nitrogen doping on catalyst was studied.     

Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO₄/ZrO₂/Al₂O₃ catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al₂O₃ alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO₄/ZrO₂/Al₂O₃ superacid catalyst were used in this study. With the use of IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.     

Synthesis of cyclopropane-containing organoaluminum compounds by the reaction of acetylenes with CH<Subscript>2</Subscript>I<Subscript>2</Subscript> and Et<Subscript>3</Subscript>Al

Reactions of disubstituted and terminal acetylenes with CH₂I₂ and Et₃Al in the molar ratio 1: 4: 6 lead to the selective formation of organoaluminum compounds containing di-, tri-, or tetrasubstituted cyclopropane fragments depending on the nature of acetylene and reaction conditions.     

Reaction of Sulfur and Oxygen-Bridged 8-Quinolinolato Trinuclear Molybdenum Cluster [Mo<Subscript>3</Subscript>OS<Subscript>3</Subscript>(qn)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]<Superscript>+</Superscript> with Acetylene Carboxylic Acids

The reaction of a sulfur and oxygen-bridged 8-quinolinolato trinuclear molybdenum cluster [Mo₃OS₃(qn)₃(H₂O)₃]⁺ (3; Hqn = 8-quinolinol) with equimolar amounts of acetylene carboxylic acid, 4-pentynoic acid, 5-hexynoic acid, acetic acid, and pimelic acid gave clusters having μ-carboxylato groups, [Mo₃OS₃(qn)₃(H₂O)(μ-HC≡CCOO)] (6), [Mo₃OS₃(qn)₃(H₂O)(μ-HC≡C(CH₂)₂COO)] (7), [Mo₃OS₃(qn)₃(H₂O)(μ-HC≡C(CH₂)₃COO)] (8), [Mo₃OS₃(qn)₃(H₂O)(μ-CH₃COO)] (4), and [{Mo₃OS₃(qn)₃(C₂H₅OH)}₂(μ-C₇H₁₀O₄)] (5), respectively. X-ray structural analyses, ¹H NMR, and electronic spectra of these clusters made clear that each of the COO⁻ groups of the reagents bridges two Mo atoms in each cluster and that no adduct formation occurred at the sulfurs in the clusters. The reaction of 3 with a large excess-molar amount (50 times) of acetylene carboxylic acid gave [Mo₃OS(μ₃-SCH=C(COOH)S)(qn)₃(H₂O)(μ-HC≡CCOO)] (9) with two molecules of acetylene carboxylic acid, one acting as a carboxylato bridge and the other in adduct formation, as supported by the electronic and ¹H NMR spectra. The corresponding aqua cluster [Mo₃OS₃(H₂O)₉]⁴⁺ (1), on the contrary, reacts with acetylene carboxylic acid to give adduct [Mo₃OS(μ₃-SCH=C(COOH)S)(H₂O)₉]⁴⁺ (2). Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Study of the Influence Exerted by Zinc Additive on the Structure and Catalytic Properties of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Liquid-Phase Hydrogenation of Acetylene

Effect of the phase composition of aluminum oxide [γ- and (δ + θ) phase] and introduction of zinc additives on the catalytic properties of 0.5% Pd/Al₂O₃ systems in the reaction of liquid-phase hydrogenation of acetylene into ethylene under an elevated pressure in a flow-through mode was studied. An increase in the activity of the Pd catalyst upon modification with zinc is only observed in the case of a system supported by the mixed phase of (δ + θ) aluminum oxide. XAFS spectroscopy was used to find that the increase in the activity and selectivity with respect to ethylene (in the presence of carbon monoxide) on the (0.5% Pd–0.62% Zn)/(δ + θ)-Al2O3 catalyst is correlated with the formation of the PdZn intermetallic compound.     

Trimetallic NiMoW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalyst based on H<Subscript>4</Subscript>SiMo<Subscript>3</Subscript>W<Subscript>9</Subscript>O<Subscript>40</Subscript> mixed heteropoly acid

Trimetallic NiMoW/Al₂O₃ catalyst was prepared using mixed H₄SiMo₃W₉O₄₀ heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts based on H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀, respectively, were synthesized as reference samples. The use of mixed H₄SiMo₃W₉O₄₀ heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al₂O₃ catalyst. The synergistic enhancement of the activity of the NiMo₃W₉/Al₂O₃ catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.     

Hydrolysis of cellulose by the heteropoly acid H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The potential of heteropoly acid H₃PW₁₂O₄₀ to catalyze the hydrolysis of cellulose to glucose under hydrothermal conditions was explored. This technology could contribute to sustainable societies in the future by using cellulose biomass. A study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, and the amount of cellulose used, was performed. A remarkably high yield of glucose (50.5%) and selectivity higher than 90% at 453 K for 2 h with a mass ratio of cellulose to H₃PW₁₂O₄₀ of 0.42 were achieved. This was attributed to the high hydrothermal stability and the excellent catalytic properties, such as the strong Brønsted acid sites. This homogeneous catalyst can be recycled for reuse by extraction with diethyl ether. The results illustrate that H₃PW₁₂O₄₀ is an environmentally benign acid catalyst for the hydrolysis of cellulose.     

Effect of pretreatment conditions on the catalytic activity of coprecipitated Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> catalyst in soot oxidation

The temperature of soot oxidation and efficiency of Ce_0.5Zr_0.5O₂ catalyst depends on its morphology, which determines the area of intergranular contact between the solid substrate and the catalyst. The temperature-programmed reduction in hydrogen to 1000°C and oxidation at 500°C (redox cycles) cause the mobility of oxygen in oxide to be enhanced and decrease the temperature of soot combustion. Oxidation of soot in the air flow on the Ce_0.5Zr_0.5O₂ catalyst result in its activation. Reuse of the catalyst decreases the temperature of soot oxidation.     

Oxidative dehydrogenation of propane on the VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CeZrO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> supported catalyst

The oxidative dehydrogenation of propane on a supported vanadium catalyst was studied (the support was a complex oxide system consisting of a ceria–zirconia solid solution deposited on γ-Al₂O₃ (CeZrO/γ-Al₂O₃)). A comparative analysis of the properties of the support and the catalyst prepared on its basis was performed. The support and catalyst were characterized by the BET method, scanning electron microscopy, X-ray diffraction analysis, and Raman spectroscopy. The catalytic properties of the catalyst and support were studied in propane oxidation at 450 and 500°C with pulse feeding of the reagent. The effect of propane on the support was found to improve the oxidative properties of the latter. This behavior of the support is related to the preparation procedure, which leads to the formation on its surface of the crystalline phase of the ceria–zirconia solid solution and amorphous ZrO₂ and Al₂O₃ phases and/or their solid solution. Similar processes occur with the catalyst support during the oxidative dehydrogenation, giving rise to additional active centers (CeVO₄).     

X-ray photoelectron study of the interaction of H<Subscript>2</Subscript> and H<Subscript>2</Subscript>+O<Subscript>2</Subscript> mixtures on the Pt/MoO<Subscript>3</Subscript> model catalyst

The effects of H₂ and H₂ + O₂ gas mixtures of varying composition on the state of the surface of the Pt/MoO₃ model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H₂O₂ is discussed.     

Selective Catalytic Reduction of NO by NH<Subscript>3</Subscript> over MoO<Subscript>3</Subscript> Promoted Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst

A series of MoO₃ doped Fe₂O₃ catalysts prepared by the co-precipitation method were investigated in the selective catalytic reduction of NO by NH₃ (NH₃-SCR). The catalysts displayed excellent catalytic activity from 225 to 400°C and high tolerance to SO₂/H₂O poisoning at 300°C. To characterize the catalysts the N₂-BET, XRD, Raman, NO-TPD, NH₃-TPD and in situ DRIFTS were carried out. It was found that the main reason explaining a high NH₃-SCR performance might be the synergistic effect between Fe and Mo species in the catalyst that could enhance the dispersion of Fe₂O₃ and increase NH₃ adsorption on the catalyst surface.     

Facile synthesis of Fe@Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> core-shell nanowires as O<Subscript>2</Subscript> electrode for high-energy Li-O<Subscript>2</Subscript> batteries

Fe@Fe₂O₃ core-shell nanowires were synthesized via the reduction of Fe³⁺ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe₂O₃ shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O₂ batteries with the charge voltage plateau reduced to ～3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g^?1. The excellent electrochemical properties of Fe@Fe₂O₃ as an O₂ electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O₂ batteries.     

Adsorption of NO,NH<Subscript>3</Subscript> and H<Subscript>2</Subscript>O on V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalysts

The adsorption of small molecules NO, NH₃ and H₂O on V₂O₅/TiO₂ catalysts is studied with the semiempirical SCF MO method MSINDO as pre-stage for the selective catalytic reduction of NO. The mixed catalyst is represented by hydrogen-terminated cluster models. The local arrangement of the cluster atoms is in accordance with available experimental information. Partial relaxation of cluster atoms near the adsorption sites is taken into account. Calculated adsorption energies are compared with experimental literature data. Rapid convergence of computed properties with cluster size is observed. A possible reaction mechanism for the catalytic reduction of NO with NH₃ and O₂ is outlined.     

Development of RuO<Subscript>2</Subscript>/Rutile-TiO<Subscript>2</Subscript> Catalyst for Industrial HCl Oxidation Process

Sumitomo Chemical has developed a low energy consuming and green process for the catalytic oxidation of HCl to Cl₂, especially when compared with the electrolysis process. The RuO₂/rutile-TiO₂ catalyst has high catalytic activity and thermal stability due to ultra-fine RuO₂ crystallites that cover the surface of the TiO₂ primary particles with strong interaction. In addition, the silica modified RuO₂/rutile-TiO₂ catalyst shows higher thermal stability by preventing the RuO₂ sintering due to using dispersed SiO₂ particles. With these catalysts, high reaction rates required for industrial applications are achieved, even at low temperatures.