One-step synthesis of carbon-supported Pd–Pt alloy electrocatalysts for methanol tolerant oxygen reduction

A facile, one-step reduction route was developed to synthesize Pd-rich carbon-supported Pd–Pt alloy electrocatalysts of different Pd/Pt atomic ratios. As-prepared Pd–Pt/C catalysts exhibit a single phase fcc structure and an expansion lattice parameter. Comparison of the oxygen reduction reaction (ORR) on the Pd–Pt/C alloy catalysts indicates that the Pd₃Pt₁/C bimetallic catalyst exhibits the highest ORR activity among all the Pd–Pt alloy catalysts and shows a comparative ORR activity with the commercial Pt/C catalyst. Moreover, all the Pd–Pt alloy catalysts exhibited much higher methanol tolerance during the ORR than the commercial Pt/C catalyst. High methanol tolerance of the Pd–Pt alloy catalysts could be attributed to the weak adsorption of methanol induced by the composition effect, to the presence of Pd atoms and to the formation of Pd-based alloys.     

High catalytic activity of ultrafine nanoporous palladium for electro-oxidation of methanol, ethanol, and formic acid

Nanoporous palladium (NPPd) with ultrafine ligament size of 3–6 nm was fabricated by dealloying of an Al–Pd alloy in an alkaline solution. Electrochemical measurements indicate that NPPd exhibits significantly high electrochemical active specific surface area (23 m² g⁻¹), and high catalytic activity for electro-oxidation of methanol, ethanol, and formic acid. Mass activities can reach 149, 148, 262 mA mg⁻¹ for the oxidation of methanol, ethanol and formic acid, respectively. Moreover, superior steady-state activities can be observed for all the electro-oxidation processes. NPPd will be a promising candidate for the anode catalyst for direct alcohol or formic acid fuel cells.     

Electrooxidation of Methanol on Platinum–Ruthenium Catalysts Applied to a Cation-Exchange Membrane

Possibilities for production of active Pt–Ru electrodes for the direct methanol fuel cell with a decreased content of platinum-group metals in them are studied. Platinum and ruthenium are electrodeposited on a thin layer of carbon black applied to a Nafion 117 membrane. The deposition potential effect on the specific surface area of the catalyst and its electrochemical activity in the methanol oxidation is studied. The oxidation currents are related to unit true surface area or unit catalyst mass. The dependence of activity on the Pt : Ru ratio in the plating solution and in the deposit is studied. The effect of the catalyst amount deposited and the particle size on the activity is studied. It is shown that the catalytic activity decreases at the average diameter of Pt–Ru particles less than 4 nm. The results are compared with the size effects observed earlier.     

Reaction of 1-bromo-2-acylacetylenes with thiobenzhydrazide

Conclusions The reactions of 1-bromo-2-acylacetylenes with thiobenzhydrazide at from –10 to –30°C in ether, acetonitrile, methanol without catalyst, or methanol in the presence of triethylamine gave 2-acylmethyl-5-phenyl-1,3,4-thiadiazoles and their hydrobromide salts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2637–2638, November, 1988.     

Interactions of water and methanol with a mixture of copper and zinc metals: a theoretical <Emphasis Type="Italic">ab initio</Emphasis> study

Ab initio cluster quantum chemical calculations at the Hartree–Fock and second-order Møller–Plesset perturbation theory levels were carried out to mimic the interactions of water and methanol with a mixture of Cu and Zn metals. It was shown that both molecular and dissociative adsorption of methanol on a mixture of Cu and Zn metal catalyst are preferred over the corresponding adsorptions of water. Estimated transition-state structures for dissociation of methanol into CH·₃ and OH· lie about 9.0 and 22.0 kcal/mol higher compared to the dissociated (forward reaction) and molecular adsorption (reverse reaction) complexes, respectively. Based on distinct radicals' bond energies with the active sites of the catalyst considered, it is suggested that hydrogen molecules could be formed through a chain of homogeneous reactions of methyl radicals released into the gas phase with the water and/or methanol molecules.     

Study of Methanol Conversion over Fe-Zn-Zr Catalyst

The methanol conversion over Fe-Zn-Zr catalyst was studied at 0.1 MPa and 280-360℃. The experimental results indicate that the main products of methanol conversion are methane and butane, and that other hydrocarbons are scarcely produced.All results show that propylene is most probably the olefin formed first in methanol conversion rather than ethene over Fe-Zn-Zr catalyst.Methane is formed from methoxy group,and C_4 is possibly yielded on the surface from propylene through binding with a methoxy group.     

Methanol Decomposition in a Water–Methanol Equimolar Mixture on a Nickel-Promoted Copper–Zinc–Cement Catalyst

Methanol decomposition in a water–methanol equimolar mixture is studied in the presence of a nickel-promoted copper–zinc–cement catalyst. Methanol decomposition at 200–300°C on the oxide and reduced forms of the catalyst yields a gas with an H₂/CO ratio close to two. The use of an equimolar CH₃OH–H₂O mixture under analogous conditions enables obtaining gaseous products with a hydrogen concentration up to 75 vol %.     

Oxidation of Methanol on Pt,Pt–Ru,and Pt–Ru–Mo Electrocatalysts Dispersed in Polyaniline: An in situ Infrared Reflectance Spectroscopy Study

The electrochemical oxidation of methanol was investigated on a Pt–Ru–Mo catalyst with an in situ infrared reflectance spectroscopy. The electrocatalysts were prepared by an electrochemical deposition and dispersed in a conducting three-dimensional matrix of polyaniline (PAni). We observed that CO₂ is produced from methanol oxidation at 350 mV vs. RHE on PAni/Pt–Ru–Mo, which is 100 mV less negative than on PAni/Pt–Ru and 200 mV less than on PAni/Pt. The results suggest that Pt–Ru–Mo is less sensitive to CO_ADS poisoning than Pt–Ru and much more sensitive than Pt. Large differences are observed concerning the average wavenumber of _ADS between Pt–Ru–Mo, Pt–Ru, and Pt.     

Methanol synthesis from CO2-H2 and from CO-H2 under atmospheric pressure over Pd and Cu catalysts

Under atmospheric pressure, methanol was produced from CO₂–H₂ over Pd/ZnO and from CO–H₂ over Pd/MgO catalyst. Similar support effects were observed over Cu catalysts.     

Highly efficient Pt/TiO2 photocatalyst prepared by plasma-enhanced impregnation method

Highly efficient Pt/TiO₂ photocatalyst has been prepared using plasma-enhanced impregnation method. Impregnated 0.5 wt%Pt/TiO₂ was treated by plasma followed with thermal calcinations and hydrogen reduction. The catalyst characterizations show that Pt is highly dispersed with a size of 3–5 nm. UV–Vis reflection spectrum suggests it a high photosensitivity in near UV region. Such plasma prepared catalyst exhibits a much higher activity and better metal stability for hydrogen generation from methanol/water mixture, compared to the catalyst prepared conventionally. This highly efficient photocatalyst should have extensive applications in photocatalytic processes.     

IR-spectroscopic investigation of the nature of surface centers and of the adsorption of methanol on an iron-molybdenum oxide catalyst

Molecular-probe IR spectroscopy was used to investigate the nature of surface centers on an iron-molybdenum oxide catalyst. The acid properties of Fe/Mo catalysts with stoichiometric composition and with an excess of molybdenum have been studied; the presence of Lewis (LAS) as well as Brönsted acid sites (BAS) on their surface has been detected. The concentration of BAS increases significantly in the presence of an excess of molybdenum; the amount of coordination-unsaturated cations on the surface of the samples decreases at the same time. The interaction of methanol and isopropanol with the surface of the investigated catalysts has been studied and the determining role of BAS in complex formation and the conversion of alcohols on the Fe/Mo-oxide catalyst established. A mechanism has been proposed for the conversion of methanol on the Fe/Mo-oxide catalyst.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 474–480, July–August, 1990.     

Vapor Pressures, Osmotic and Activity Coefficients of Electrolytes in Protic Solvents at Different Temperatures. 1. Lithium Bromide in Methanol

Precise vapor pressure data for LiBr solutions in methanol are given for temperatures ranging from 298.15 to 333.15 K. The molality range is from 0.0411 to 6.8675 mol-kg^–1. Osmotic coefficients were calculated by taking into account the second virial coefficient of methanol. The parameters of the Pitzer–Mayorga model, the Archer extension of the Pitzer–Mayorga model, the mole-fraction-based thermodynamic model of Clegg–Pitzer, and the recently developed MSA–NRTL model are evaluated, along with the corresponding standard deviation. These equations were used to calculate activity coefficients of LiBr in methanol solutions.     

Cyclization of diols with ammonia over CuO-ZnO-Al2O3 catalyst in the presence of H2

Cyclization of diols with ammonia in an H₂ atmosphere over an industrial CuO-ZnO-Al₂O₃ catalyst for the synthesis of methanol (SNM-1) gives nitrogen-containing five-, six-, or seven-membered heterocyclic compounds. The yields of cyclic amines in the 180–230 °C temperature range are 46 to 97 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2046–2048, October, 1995.     

Catalytic Activity of a Mordenite Catalyst in Alkylation of Xylenols with Methanol

The catalytic activity of a palladium-containing mordenite catalyst in alkylation of 2,6-, 2,4-, 2,5-, 2,3-, 3,4-, and 3,5-xylenols with methanol was studied. The main and by-products of catalysis and the activity of the catalyst in synthesis of individual trimethylphenols were determined.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005, pp. 690–691.Original Russian Text Copyright © 2005 by Agaev, Madatzade.     

Oxidation of cyclohexane with molecular oxygen using a Schiff base cobalt complex bonded to carbamate-modified silica gel

The Schiff base [1,2-bis(salicylidene amino)phenylene]cobalt(II) complex, chemically bonded to a carbamate-modified silica gel catalyst, has been prepared by a four step procedure. The oxidation of cyclohexane was studied in the presence of this catalyst under relatively mild conditions (150–200 °C, 15–20 atm) using molecular oxygen. The catalyst was found to be very selective for the production of cyclohexanol, with cyclohexanone formed in only a small amount (45:1). This is in contrast to the commercially available processes in which cyclohexanol and cyclohexanone are both formed in appreciable amounts. The t.g.a. analysis shows the catalyst to be stable up to 211 °C and atomic absorption spectroscopy indicated negligible metal loss during 50 h use of the catalyst up to 180 °C.     

Reaction Mechanism of Methanol to Formaldehyde over Fe‐ and FeO‐Modified Graphene

We employed periodic DFT calculations (PBE‐D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O?H cleavage. As a result, a methoxo‐containing intermediate is formed. Subsequently, H‐transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H₂O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol^?1.     

Nonstationary Phenomena in the Low-Temperature Gas-Phase Catalytic Oxidation of H2S with Oxygen

The conditions of the existence were determined and reasons were revealed for the appearance of periodic oscillations of the SO₂concentration in the reaction products and warming temperature in the catalyst bed in the oxidation of H₂S with oxygen at temperatures below the dew point of sulfur on the V–Al–Ti oxide catalyst. The formation of polysulfides during the reaction was experimentally found. It was proposed that the adsorption of sulfur and polysulfides on the catalyst surface is responsible for the observed oscillatory processes.     

Methanol oxidation to formaldehyde on bismuth phosphate-based catalysts

A bismuth (III) phosphate catalyst has been prepared by precipitation and characterized by X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron and infrared spectroscopy. Its activity and selectivity toward selective methanol oxidation to formaldehyde has been studied by a flow method. A high selectivity has been found, similar to that reported for typical catalysts used for this reaction. The possible importance of the strength and covalency of the P–O bonds is discussed.     

Photocatalytic liberation of hydrogen from C1-C4 alcohols with the participation of titanium complexes

It was established that in UV irradiation of solutions of TiCl₄ in methanol, ethanol, isopropanol, and butanol, alcohol-chloride complexes of titanium(III) are formed. The quantum yields of the formation of coordination compounds of titanium(III) depend on the nature of the alcohol: 0.08 (methanol); 0.13 (ethanol); 0.20 (butanol); 0.22 (isopropanol). As complexes of titanium(III) accumulate in solution, there is a liberation of molecular hydrogen. The quantum yields of the formation of hydrogen, determined in a steady-state process, are correlated with the values of the C-H bond energy at the -carbon atom of the alcohol and are equal to 2·10^–3, 3.4·10^–3, 4.3·10^–3 and 1·10^–2 for solutions in methanol, butanol, ethanol, and isopropanol, respectively. A substantial increase in the quantum yield of the formation of molecular hydrogen was detected when a heterogeneous catalyst (palladium on silica gel) was used, and the possible mechanism of the process of photocatalytic liberation of hydrogen from alcohols with the participation of titanium complexes is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 3, No. 2, pp. 181–186, March–April, 1987.The authors would like to thank V. M. Granchak for his participation in the discussion of the results.     

Formation of Ethers from Alcohols with Chloride Complexes of Platinum(II) as Catalysts

A new catalytic reaction of the etherification of alcohols in the system ROH-PtCl ₄ ²⁻ has been observed. At 70 °C in the presence of catalytic amounts of chloride complexes of platinum(II) methanol gave dimethyl ether. Methyl tert-butyl ether and di-tert-butyl ether were formed analogously from a mixture of methanol and tert-butanol. In the reaction with ethanol the products were diethyl ether and a π-ethylene complex of platinum(II). It is suggested that the step-wise mechanism includes the oxidative addition of the alcohol with the intermediate formation of an alkyl complex of platinum(IV), the decomposition of which by reductive elimination under the influence of a second molecule of alcohol or an alkoxide anion gives an ether and regenerates the catalyst, a chloride complex of platinum(II).__________Translated from Teoreticheskaya i Eksperimental’naya Khimiya, Vol. 41, No. 3, pp. 190–193, May–June, 2005.