Separation performance of foils from Pd—In(6%)—Ru(0.5%), Pd—Ru(6%), and Pd—Ru(10%) alloys and influence of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, and water vapor on the H<Subscript>2</Subscript> flow rate through the test membranes

The H₂ flow rate through the 30-μm thick foil from Pd—Ru(6%) and Pd—Ru(10%) alloys at 673 and 773 K was found to be controlled by the diffusion of H atoms in the foil bulk. The interrelation between hydrogen permeability through the Pd—In(6%)—Ru(0.5%), Pd—Ru(10%), Pd—Ru(6%), and Pd—Ag(23%) membranes and the permeability pre-exponential factors in the Sieverts equation in the 573—773 K temperature interval indicated that the hydrogen permeability depended on the structural characteristics of palladium alloys. The influence of the CO₂, CH₄, and water vapor impurities on the H₂ flow rate through the studied membranes depended on the driving force nature (the sweep gas or transmembrane pressure) used for the development of the partial hydrogen pressure difference across the membrane. The negative influence of CH₄ and CO₂ was observed only when using a transmembrane pressure and at the impurity content of 20% or more. This effect increased with increasing temperature in the 573—773 K range, with the influence of CO₂ being more pronounced due to its reaction with hydrogen leading to the formation of CO. The influence of water vapor was studied at its 11—23% content in hydrogen and at 573 and 773 K of temperature. The negative influence of water vapor was found to subside as its content in the hydrogen mixture decreased and the temperature increased. It was shown that water vapor can be used as a sweep gas and at T = 773 K its influence on the H₂ flow rate through the membrane was almost the same as that of N₂.     

Bis(triphenylphosphan)Palladium-Komplexe mit Schwefeloxid-Liganden

Bis(triphenylphosphine)Palladium Complexes with Sulfur Oxide Ligands New examples in the series of sulfur oxide complexes of the type (PPh₃)₂Pd(S_nO_m) (n = 1,2; m 1–4) were found by the synthesis of (PPh₃)₂Pd(SO) and (PPh₃)₂Pd(S₂O₃. The SO complex is obtained by the reaction of Pd(PPh₃)₄ or (PPh₃)₂Pd(RCCR) (R=COOMe) and thiirane-S-oxide. The thiosulfato complex (PPh₃)₂Pd(S₂O₃) is formed from (PPh₃)₂Pd(SO) and SO₂ or, alternatively, from (PPh₃)₃Pd(SO₂) and C₂H₄SO. Both SO und SO₂ complexes can be oxidized to the corresponding sulfato compound (PPh₃)₂)Pd(SO₄). The SO complex is used as a SO-source for the formation of 3,4-dimethyldihydrothiophene-S-oxide from 2,3-dimethyl-1,3-butadiene.     

Continuous and selective determination of water vapor evolved during thermal decomposition reactions

A method suitable for the continuous and selective determination of water vapor evolved during thermal decomposition processes is described. The water detector can be connected to thermoanalytical equipment of controlled gas atmosphere without any difficulty. Water vapor, together with other gaseous decomposition products, is collected by the carrier gas and transported through a glass reaction vessel containing the measuring and reference cells. The change in cell temperature is sensed by a resistance thermometer coil connected to a bridge circuit. The relationship between the area under the recorded curve and the amount of water released is linear. Hydrocarbons, organic crack products, CO, CO₂, SO₂, SO₃ and NH₃ do not interfere. The detection limit is about 0.1 mg water, the reproducibility of the recorded curves is better than 10 per cent. In addition to the semi-quantitative determination of water, the detector trace can be recorded simultaneously along with the TG, DTG and DTA curves and used to identify the decomposition step(s) in which water was formed.     

The kinetics of silica reduction in hydrogen

The kinetics of the reduction of SiO₂ in hydrogen have been examined using a thermalgravimetric method. The mechanism of the reaction SiO₂ + H₂ = SiO + H₂O can be described on the basis of a reaction interface moving at a constant velocity toward the center of the reacting sample. The velocity of the moving interface depends on the reaction temperature and water vapor content of the ambient gas. The reaction was studied in the temperature range 1115–1630°C and was found to be isokinetic in this range. The activation energy for the reaction is 85 kcal/mole in pure, dry hydrogen and 135 kcal/mole in hydrogen with a dew point of 24°C.     

Confined Ultrathin Pd‐Ce Nanowires with Outstanding Moisture and SO2 Tolerance in Methane Combustion

An efficient strategy (enhanced metal oxide interaction and core–shell confinement to inhibit the sintering of noble metal) is presented confined ultrathin Pd‐CeO_x nanowire (2.4 nm) catalysts for methane combustion, which enable CH₄ total oxidation at a low temperature of 350 °C, much lower than that of a commercial Pd/Al₂O₃ catalyst (425 °C). Importantly, unexpected stability was observed even under harsh conditions (800 °C, water vapor, and SO₂), owing to the confinement and shielding effect of the porous silica shell together with the promotion of CeO₂. Pd‐CeO_x solid solution nanowires (Pd‐Ce NW) as cores and porous silica as shells (Pd‐CeNW@SiO₂) were rationally prepared by a facile and direct self‐assembly strategy for the first time. This strategy is expected to inspire more active and stable catalysts for use under severe conditions (vehicle emissions control, reforming, and water–gas shift reaction).     

Mechanistic study on the atmospheric formation of acid rain base on the sulfur dioxide

The reaction pathways of acid rain formation from reaction of sulfur dioxide vapor and water vapor on the singlet potential energy surface have been investigated theoretically. The calculated results show that the reactants are initially associated with the adduct SO₂–H₂O through a barrier less process. Subsequently, via a variety of transformations of isomer SO₂–H₂O, three kinds of products H₂SO₃, SO₃ + H₂, and H₂O₂ + ³SO are obtained. The cleavage and formation of the chemical bonds in the reaction pathways have been discussed using the structural parameters. Also, by means of the transition states and their connected intermediates or products at the CCSD(T)//B3LYP level, mechanism of H₂O + SO₂ reaction on the singlet potential energy surface are plotted. The calculation results show that the most suitable reaction pathways are the formation of H₂SO₃. Finally, the rate constants have been calculated only for these suitable pathways by the RRKM and TST theories at temperature range of 250–2500 K.     

Quantum chemical calculations of the structure of hydrogen-bonded sulfuric acid-dimethylformamide complexes

The most characteristic structures of hydrogen-bonded (H₂SO₄)₂, H₂SO₄-dimethylformamide (DMF) and (H₂SO₄)₂-DMF complexes are obtained by means of B3LYP/cc-pVQZ. The changes in the geometric parameters of the complexes are analyzed and the energy values of the intermolecular interaction are estimated. The electronic mechanism for the formation of hydrogen bonds between molecules is considered. It is shown that complexes of (H₂SO₄)₂-DMF composition are more energy-stable than complex with one H₂SO₄ molecule. It is established that molecular complexes with very strong hydrogen bonds and complexes with proton transfer can be formed between an acid dimer and N,N-dimethylformamide. It is concluded that protons can be transferred in the gas phase in (H₂SO)₂-DMF, where the molecules in (H₂SO₄)₂ are bound by three hydrogen bonds.     

Enhanced catalytic performance of Pd‐Ga bimetallic catalysts for 2‐ethylanthraquinone hydrogenation

A series of Pd and Pd‐Ga bimetallic catalysts were prepared by a co‐impregnation method for 2‐ethylanthraquinone (EAQ) hydrogenation to produce hydrogen peroxide. Compared with 0.6Pd catalyst, the hydrogenation efficiency of 0.6Pd1.2Ga catalyst (11.9 g L^?1) increases by 32.2%, and the stability of 0.6Pd1.2Ga catalyst is also higher than that of 0.6Pd catalyst. The structures of the samples were determined by N₂ adsorption–desorption, ICP, XRD, CO chemisorption, TEM, H₂‐TPR, in situ CO‐DRIFTS and XPS. The results suggest that incorporation of Ga species improves Pd dispersion and generates a strong interaction between Ga₂O₃ and Pd interface or between Pd and support. DFT calculation results indicate that the strong adsorption of carbonyl group on Ga₂O₃/Pd interface facilitates the activation of EAQ and promotes the hydrogenation efficiency.     

Effect of metals on the catalytic activity of sulfated zirconia for light naphtha isomerization

We studied on the function of the metal in the sulfated zirconia(SO₄^2–/ZrO₂) catalyst for the isomerization reaction of light paraffins. The addition of Pt to the SO₄^2–/ZrO₂ carrier could keep the high catalytic activity. The improvement in this isomerization activity is because Pt promotes removal of the coke precursor deposited on the catalyst surface. Though this catalytic function was observed in other transition metals, such as Pd, Ru, Ni, Rh and W, Pt exhibited the highest effect among them. It was further found that the Pd/SO₄^2–/ZrO₂–Al₂O₃ catalyst possessed a catalytic function for desulfurization of sulfur-containing light naphtha in addition to the skeletal isomerization. The sulfur tolerance of catalyst depended on the method of adding Pd, and the catalyst prepared by impregnation of the SO₄^2–/ZrO₂–Al₂O₃ with an aqueous solution of Pd exhibited the highest sulfur tolerance.Further, we investigated the improvement in sulfur tolerance of the Pt/SO₄^2–/ZrO₂–Al₂O₃ catalyst by impregnation of Pd. The results of EPMA analysis indicated that this catalyst was a hybrid-type one (Pt/SO₄^2–/ZrO₂–Pd/Al₂O₃) in which Pt/SO₄^2–/ZrO₂ particles and Pd/Al₂O₃ particles adjoined closely. This hybrid catalyst possessed a very high sulfur tolerance to the raw light naphtha that was obtained from the atmospheric distillation apparatus, although this light naphtha contained much sulfur. We assume that such a high sulfur tolerance in the hybrid catalyst is brought about by the isomerization function of Pt/SO₄^2–/ZrO₂ particles and the hydrodesulfurization function of Pd/Al₂O₃ particles. Besides, since the hybrid catalyst also provides high catalytic activity in the isomerization of HDS light naphtha, we suggest that the Pd/Al₂O₃ particles supply atomic hydrogen to the Pt/SO₄^2–/ZrO₂ particles by homolytic dissociation of gaseous hydrogen and also enhance the sulfur tolerance of Pt/SO₄^2–/ZrO₂ particles. Finally, we also propose the most suitable location of Pd and Pt in the metal-supported SO₄^2–/ZrO₂–Al₂O₃ catalyst.     

Correlations between hydrogen electrosorption properties and composition of Pd-noble metal alloys

Hydrogen adsorption on and absorption into Pd alloys with other noble metals was studied in acidic solutions (0.5 M H₂SO₄) using cyclic voltammetry. Correlations were found between the potentials of adsorbed/absorbed hydrogen oxidation peaks and surface/bulk compositions of Pd–Rh alloys. The potential of the α–β-phase transition depends linearly on Pd bulk content in Pd–Au, Pd–Rh, Pd–Pt and Pd–Pt–Rh alloys. The obtained relationships can be utilized for the determination of the composition of homogeneous Pd-noble alloys from hydrogen electrosorption experiments.     

Water as a Hydride Source in Palladium‐Catalyzed Enantioselective Reductive Heck Reactions

Pd‐catalyzed intramolecular asymmetric carbopalladation of N ‐aryl acrylamides followed by reduction of C(sp³)‐Pd intermediate using diboron–water as a hydride source afforded enantioenriched 3,3‐disubstituted oxindoles in high yields and enantioselectivities. When heavy water was used as a deuterium donor in combination with bis(catecholato)diboron (Cat₂B₂), deuterium was incorporated into the products with high synthetic efficiency. The ligand determined both the enantioselectivity of the reaction and the reaction pathways, thereby affording either hydroarylation (reductive Heck) or carboborylation products.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMSI effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO?H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMST effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO-H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

A study of Pt–Pd/γ-Al2O3 catalysts for methane oxidation resistant to deactivation by sulfur poisoning

The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al₂O₃ catalysts, in the presence and the absence of SO₂ in the CH₄–O₂ reaction feed. The effect of sulfation (SO₂ + O₂ for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al₂O₃ catalysts resulted in a strong deactivation for the CH₄–O₂ reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al₂O₃ catalyst for CH₄–O₂ reaction remained rather unaffected in the presence and in the absence of SO₂ in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al₂O₃ catalysts, the presence of Pt(0) metallic surface species on which SO₂ interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO₂ and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al₂O₃ catalysts for CH₄–O₂ reactions remained rather unaffected despite the presence of SO₂ in the reaction feed.     

Mechanistic Insight into the Reaction of Organic Acids with SO3 at the Air–Water Interface

The gas‐phase reaction of organic acids with SO₃ has been recognized as essential in promoting aerosol‐particle formation. However, at the air–water interface, this reaction is much less understood. We performed systematic Born–Oppenheimer molecular dynamics (BOMD) simulations to study the reaction of various organic acids with SO₃ on a water droplet. The results show that with the involvement of interfacial water molecules, organic acids can react with SO₃ and form the ion pair of sulfuric‐carboxylic anhydride and hydronium. This mechanism is in contrast to the gas‐phase reaction mechanisms in which the organic acid either serves as a catalyst for the reaction between SO₃ and H₂O or reacts with SO₃ directly. The distinct reaction at the water surface has important atmospheric implications, for example, promoting water condensation, uptaking atmospheric condesation species, and incorporating “SO₄^2?” into organic species in aerosol particles. Therefore, this reaction, typically occurring within a few picoseconds, provides another pathway towards aerosol formation.     

Pd(111), Pd(100)及Pd(110)表面H2和O2直接合成H2O2的密度泛函理论研究

采用周期性密度泛函理论研究了H₂和O₂在Pd(111),Pd(100)及Pd(110)表面上直接合成H₂O₂的反应机理,对反应的主要基元步骤进行了计算和分析.结果表明,Pd(111)表面对H₂O₂直接合成的催化选择性最好,表面原子密度较低的Pd(100)表面和Pd(110)表面上含有O-O键的表面物种解离严重,不利于H₂O₂的生成.H₂O₂的选择性与含有O-O键表面物种的O-O键能和表面物种的结合能有关.含有O-O键的表面物种在表面的结合能越大,越容易发生解离,不利于形成H₂O₂.     

Correction to: The effect of small silver inclusions on the palladium activity in formicacid oxidation reaction and corrosion stability

A PdAg deposit containing ~ 25 at.% Ag is obtained by the electrochemical codeposition from an aqueous solution of Pd and Ag sulfates (Au support, 0.5 M H₂SO₄). The deposit is characterized by means of various physical, physicochemical, and electrochemical methods. The PdAg deposit demonstrates the ~ 2 times higher specific activity (per the electrochemically active surface area (EASA) of Pd) in the formic acid oxidation reaction (FAOR) as compared with the individual Pd deposit prepared under the same conditions. The effect of silver additions on the palladium activity depends on many factors. The corrosion stability of PdAg is studied in 0.5 M H₂SO₄ solution based on the overall cyclic voltammograms (CVAs) and also on anodic and cathodic half-cycles in the region E = 0.3 − 1.25 V (vs. reversible hydrogen electrode (RHE)). The electrochemical estimates are compared with the results of direct analytical determination of dissolution products in solution after anodic polarization of deposits. The total amounts of Pd dissolved substantially increase with incorporation of Ag, which is associated, first of all, with the considerable increase in the EASA; at the same time, the specific dissolution of Pd also substantially increases. The possible factors determining the active dissolution of PdAg deposits are discussed; in particular, the specific mechanism of their dissolution via silver adatoms is proposed.

     

Hydroesterification of styrene using an in situ formed Pd(OTs)2(PPh3)2 complex catalyst

Hydroesterification of styrene to 3-phenyl propionate 1, and 2-phenyl propionate 2, has been studied using a Pd(OTs)₂(PPh₃)₂ catalyst formed in situ from Pd(OAc)₂, PPh₃ and p-toluenesulfonic acid (p-tsa). Because of the weakly coordinating properties of the TsO⁻ ligand, the catalyst has vacant coordination sites capable of easy activation of reactants. The presence of water is found to be necessary for the reaction and hydrogen enhances the catalytic activity under certain conditions (with Pd:p-tsa=1). The beneficial effect of hydrogen, p-tsa and water is discussed in terms of favoring the formation of a Pd–H species, which initiates the catalytic cycle through the insertion of styrene into this bond with formation of a Pd-alkyl intermediate, which inserts CO to give a Pd-acyl intermediate, which, upon nucleophilic attack of the alkanol on the carbon atom of the acyl ligand, yields the final product and the starting hydride back to the catalytic cycle. p-tsa would favor the formation of a Pd–H species by reactivating any Pd(0) species that may form during the course of catalysis. Water would favor the formation of a Pd–H species through a reaction closely related to the water–gas shift reaction. The effect of various ligands, promoters, solvents and alcohols on catalytic activity as well as selectivity pattern has been studied. Regioselectivity to the branched product, 2, increases with decrease in basicity of the phosphorous ligands as well as steric bulk around the palladium center and polarity of the medium.     

Thermisches Verhalten und Thermochromie von Übergangsmetallkomplexen pyridylsubstituierter Sulfonamide

Thermal Behavior and Thermochromism of Transition Metal Complexes of Pyridyl Substituted Sulfonamides The thermal behavior of 1,2-complexes of nickel(II), copper(II) and cobalt(II) with pyridyl substituted sulfonamides (N1NHSO₂PhH, N2NHSO₂PhH, N3NHSO₂PhH and N1SO₂NHPhH) is studied between 20° and 600°C by TG, DTG, and DTA and more precisely characterized by identification of volatile decomposition products. In general the thermal decomposition starts by the reaction of one of the ligands with coordinated water or with the water vapor of air. Undecomposed N1NHSO₂PhH and N3NHSO₂PhH pass over to the vapor-phase, in the other cases the elimination is connected with a hydrolytic cleavage of the ligand. The thermal decomposition of Ni(N1NSO₂PhH)₂(NH₃)₂ is initiated by a transamidation. A study of Ni(N1NSO₂PhH)₂ demonstrates the influence of reaction conditions on the course of thermal decomposition. As far as milligram amounts are used, hydrolysis by the water vapor of air is dominating; but sulfur dioxide is eliminated when working in a preperative scale. The thermochromism of Ni(N2NSO₂PhMe)₂(H₂O)₂ goes back to the reversible transition of coordination water to lattice water. This is the first example of isomerism of the Lifschitz-type in the field of neutral chelates.     

The role of doped Fe on the activity of alumina-supported Pt and Pd diesel exhaust catalysts

Supported Pt and Pd are most commonly used for oxidation catalysts. They have similar and different characteristics for deactivation factors. The catalytic activity of Pt and Pd catalysts supported on ??-Al₂O₃ was studied in the presence and absence of H₂O and SO₂ during CO oxidation under simulated conditions of diesel exhaust gas. Without the addition of H₂O and SO₂ to the feed gas, Pd/Al₂O₃ had a superior catalytic activity compared to Pt/Al₂O₃. The addition of H₂O to the feed gas strongly and negligibly affected the activity of Pd and Pt, respectively, while the addition of SO₂ to the feed gas had a strong poisoning effect on the catalytic activity of both Pt and Pd catalysts. Although being the most active, Pd catalysts exhibited a strong sensitivity to water and sulfur-containing compounds. Fe was added to the Pt and Pd catalysts to introduce sulfur resistance. The addition of Fe enhanced the activity of the catalysts by suppressing the phase transition of Al₂O₃ to Al₂(SO₄)₃ and by hindering metal sintering.