Cu2O Catalyst Research Articles

Enhanced photoelectrochemical CO2-reduction system based on mixed Cu2O – nonstoichiometric TiO2 photocathode

Photoelectrochemical reduction of CO2 is explored here with respect to the possible production of simple organic fuels. While the photoelectrochemical system is based on p-type Cu2O semiconductor, special attention has been paid to its stabilization, intentional modification and fabrication, as well as to optimization of experimental conditions permitting control and diversification of the CO2 reduction products. Utilization of the mixed oxides photoelectrochemical system consisting of the electrodeposited, onto transparent conductive oxide (TCO) coated glass support, Cu2O catalyst and next coupled to non-stoichiometric TiO2, acting as a charge transfer enhancing layer. Such a heterojunction allows, from one side, increase density of charge carries in the conduction band of the photocathode and, on the other side, improve conductivity of the whole system. Moreover, the outer-most over-layer of Nafion is expected to facilitate attraction of CO2 (dissolved in the sodium sulfate electrolyte) at the photoelectrochemically active mixed-metal-oxides interface. Consequently, the overall photoelectrochemical efficiency is improved, and the cathodic photocurrent (related to the CO2-reduction) of ca. 1.2mA cm−2 (at 0.1V vs. RHE). The reported hierarchical (layered mixed-oxide) system consisting of copper(I) oxide and titania over-layer (covered with the Nafion outer-most film) exhibits remarkable stability with time.

Mechanistic analysis of ultrasound-assisted biodiesel synthesis with Cu2O catalyst and mixed oil feedstock using continuous (packed bed) and batch (slurry) reactors

This paper has investigated the mechanistic issues of ultrasound-assisted transesterification process using solid Cu2O catalyst and mixed feedstock of non-edible oils. The optimum conditions for transesterification have been determined using statistical experimental design in packed bed catalytic reactor. The kinetic constants of different steps of transesterification process have been determined using kinetic model based on Eley-Rideal mechanism coupled to time profiles of reactants and products of transesterification in batch slurry reactors. The batch experiments have been performed at optimum conditions predicted by statistical experimental design: alcohol/oil molar ratio=10.6, temperature=62.5°C, catalyst concentration=7.25wt% oil. It is revealed that adsorption of methanol is the slowest and rate determining step of transesterification process. Sonication enhanced the kinetics of reaction steps of transesterification process, but its effect on methanol adsorption on Cu2O catalyst was adverse. The activation energy of overall transesterification process was 90.14kJ/mol; while, the sum total of activation energies of the three reaction steps of triglyceride conversion was 40.98kJ/mol. These results essentially point to strong mass transfer influence on Cu2O-catalyzed transesterification process, even in presence of sonication. The adsorptive mass transfer of methanol to catalyst sites is not enhanced by microturbulence generated by sonication. Two probable causes leading to this effect are: discrete and intermittent nature of acoustic (or shock) waves generated by the transient cavitation, and secondly, the high temperature of reaction that offsets the methanol adsorption on catalyst websites.

Cu2O-promoted degradation of sulfamethoxazole by α-Fe2O3-catalyzed peroxymonosulfate under circumneutral conditions: synergistic effect, Cu/Fe ratios, and mechanisms

ABSTRACTTo promote the application of iron oxides in sulfate radical-based advanced oxidation processes, a convenient approach using Cu2O as a catalyst additive was proposed. Composite catalysts based on α-Fe2O3 (CTX%Cu2O, X = 1, 2.5, 5, and 10) were prepared for peroxymonosulfate (PMS) activation, and sulfamethoxazole was used as a model pollutant to probe the catalytic reactivity. The results show that a synergistic catalytic effect exists between Cu2O and α-Fe2O3, which was explained by the promoted reduction of Fe(III) by Cu(I). Iron K-edge X-ray absorption spectroscopy investigations indicated that the promoted reduction probably occurred with PMS acting as a ligand that bridges the redox centers of Cu(I) and Fe(III). The weight ratio between Cu2O and α-Fe2O3 influenced the degradation of sulfamethoxazole, and the optimal ratio depended on the dosage of PMS and catalysts. With 40 mg L–1 PMS and 0.6 g L–1 catalyst, a pseudo-first-order constant of ∼0.019 min–1 was achieved for CT2.5%Cu2O, whereas only 0.004 min–1 was realized for α-Fe2O3. Nearly complete degradation of the sulfamethoxazole was achieved within 180 min under the conditions of 40 mg L–1 PMS, 0.4 g L–1 CT2.5%Cu2O, and pH 6.8. In contrast, less than 20% degradation was realized with α-Fe2O3 under similar conditions. The CT2.5%Cu2O catalyst had the best stoichiometric efficiency of PMS (0.317), which was 4.5 and 5.8 times higher than those of Cu2O (0.070) and α-Fe2O3 (0.054), respectively. On the basis of the products identified, the cleavage of the S–N bond was proposed as a major pathway for the degradation of sulfamethoxazole.

High efficiency graphene/Cu2O electrode for the electrochemical reduction of carbon dioxide to ethanol

Fabrication of an efficient catalyst for the electrochemical reduction of CO2 to valuable products at low overpotential remains a severe challenge. Herein, graphene (GN)/Cu2O catalyst, with an average particle size of 20–50nm has been synthesized and coated on copper foil. The linear seep voltammetry studies showed that the 0.1mg of GN/Cu2O loaded catalyst exhibited the highest current density in CO2 saturated 0.5M NaHCO3 electrolyte. The GN/Cu2O electrode was significantly more active towards CO2 reduction showing a current density of approximately 12.2mA/cm2 at −1.7V versus Ag/AgCl, which is higher than Cu2O electrode (8.4mA/cm2). Gas chromatography-mass spectrometry analysis of the liquid products revealed that ethanol (~0.34ppm) was found to be the predominant product at −0.9V with high reasonably Faradaic efficiency up to 9.93%. These results suggest that graphene may be used as a promising non-metallic support for the electrochemical reduction of CO2.

Diversification of Indoles via Microwave‐assisted Ligand‐free Copper‐catalyzed N‐Arylation

A simple, efficient Cu2O catalyst system under microwave irradiation was developed for N‐arylation of various indoles without ligands and additives. Diverse N‐heteroarylated indoles were prepared by coupling indoles with various heteroaryl halides within 1 h. The selective reactivity of bromoindole with aryl iodide provided N‐aryl bromoindoles, which could be useful intermediates for palladium‐catalyzed Heck and Suzuki coupling reactions.

A novel process for the production of aromatic hydrocarbons from brown coal in water medium by hydrothermal oxidation and catalytic hydrothermal decarboxylation

With no use of hydrogen or a hydrogen donor, a novel process is proposed for the production of aromatic hydrocarbons from brown coal in water medium, which consists of hydrothermal oxidation at 240°C and Cu2O-catalysed hydrothermal decarboxylation at 350°C. Using this hydrothermal oxidation and catalytic hydrothermal decarboxylation method, aromatic carboxylic acids were formed from brown coal by an oxidation process, and then decarboxylated to the corresponding aromatic hydrocarbons. The validity of the decarboxylation method was examined using several aromatic carboxylic acids as model compounds for the acid products after hydrothermal oxidation of brown coal, including o-phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, 1-naphthoic acid, 2-naphthoic acid, and 2,6-naphthalic acid. Use of Cu2O catalyst increased the decarboxylation yields of all the aromatic carboxylic acids. Especially for benzene carboxylic acids, all decarboxylation yields were above 90% with 100% selectivity. The Cu2O-catalysed hydrothermal method was proven to be effective, not only for the decarboxylation reactions from monocarboxylic acids to hydrocarbons, but also for the decarboxylation reactions from tricarboxylic acids to dicarboxylic acids and from dicarboxylic acids to monocarboxylic acids. In the presence of alkali and oxygen during the oxidation process, various valuable aromatic hydrocarbons and heterocyclic compounds, especially benzene, were obtained from Loy Yang coal using the hydrothermal oxidation and catalytic decarboxylation process. Based on analyses of aromatic carboxylic acids or ions before and after the decarboxylation process, it was found that decarboxylation reactions were the major reactions and the use of Cu2O was effective not only for the decarboxylation from monocarboxylic acids but also from polycarboxylic acids to monocarboxylic acids, consistent with the results for the model aromatic carboxylic acids. Additionally, it was found that a Cu2O catalyst was also effective for the conversion of ‘heavy’ compounds in oxidised coal to ‘light’ compounds.

The accelerating effect of silver ion on the degradation of methyl orange in Cu2O system

In this paper we reported an interesting phenomenon that additive Ag+ ion can rapidly and continuously capture the activated electrons which accumulated on the surface of as-prepared Cu2O catalyst, resulting in residual holes directly and rapidly reacting with methyl orange (MO) to be degraded. When 10−2M Ag+ was added rapidly into the suspension containing 800mg/L MO, the decolorizing rate immediately reached 38%, and rapidly increased to 88% in 30min. This accelerating effect of Ag+ ion on MO degradation was first observed in Cu2O system. Although the as-prepared Cu2O shows a very large particle size (∼2.2μm), it possesses loose crystal structure with rough multiple surfaces and various defect levels in the interior and on the surface to promote the massive accumulation and fast migration of electron and hole. As a result, when Ag+ ion was added into the suspension, it immediately reacted with the accumulated electron to turn into metallic Ag and deposited on the surface of Cu2O to form a core-shell structured catalyst Cu2O@Ag, resulting in fast degradation of MO via directly reacting with residual hole. The Schottky barriers which generate at the junctions of Cu2O and metallic Ag crystals can speed up the directional migration of electron and hole, resulting in effective separation of electron–hole pair. In addition, Cu2O@Ag catalyst shows strong light absorption in UV, vis and NIR region. These results indicate that the as-prepared Cu2O catalyst exhibits a very high photocatalytic activity in the case of adding high concentration Ag+ ion.

ChemInform Abstract: A Highly Efficient, Ligand‐Free and Recyclable SBA‐15 Supported Cu2O Catalyzed Cyanation of Aryl Iodides with Potassium Hexacyanoferrate(II).

AbstractThe highly selective supported Cu2O catalyst exhibits wide functional group tolerance.

酸化銅触媒を用いた水熱酸化法による有機塩素系汚染水の高度処理

Catalytic hydrothermal oxidation of 4-chlorophenol (CP) has been examined using the slurry flow reactor system. The mixed suspension containing CP, hydrogen peroxide and Cu2O catalyst was reacted with pressure, temperature and flow rate controlled at 10 MPa, 100-200°C and 1.0-16.0 cm3/min, respectively. The remarkable enhancement of CP decomposition by Cu2O catalyst was observed at 133-166°C. The semi-quantitative analysis of hydroxyl radicals generated by catalytic hydrothermal oxidation using salicylic acid as a molecular probe revealed that the production of hydroxyl radical was substantially enhanced by Cu2O catalyst at the same temperature as the decomposition of CP was enhanced. It was thus indicated that hydroxyl radicals were formed by Fenton-like reaction with Cu+ ions. It was also found that the degradation of CP was complete in less than 10 sec and that oxalic acid was produced as an intermediate.

Cu-Based Catalysts Show Low Temperature Activity for Glycerol Conversion to Lactic Acid

Cu based catalysts with a base promoter are reported for the first time for the synthesis of lactic acid from glycerol without using either a reductant or an oxidant. The catalytic route presented here gives high yields at lower temperatures (473 K) and lower molar NaOH/glycerol ratios (1.5) compared to the known hydrothermal (553−573 K) route. Further, the Cu2O catalyst shows excellent recyclability.

Preparation of MgO-Supported Cu2O Catalyst and Its Catalytic Properties for Cyclohexanol Dehydrogenation

Abstract To obtain a more effective catalyst for the dehydrogenation of cyclohexanol to cyclohexanone, the MgO-supported Cu 2 O catalyst was prepared by chemical reduction combined with impregnation using MgO as the support and hydrazine hydrate as the reducing agent. The effects of the preparation conditions on the catalytic properties of the catalyst were studied, and the catalyst was characterized by N 2 adsorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and temperature-programmed reduction. Cu 2 O is reduced to Cu 0 when the amount of N 2 H 4 ·H 2 O used is high. With increasing amount of NaOH used, catalyst particles congregate and the specific surface area of catalyst decreases. The catalyst activity for dehydrogenation of cyclohexanol reaches the maximum at a molar ratio Cu 2+ :N 2 H 4 ·H 2 O:NaOH of 1:1:2. The catalyst reduced by N 2 H 4 ·H 2 O is composed of only Cu + , whereas the traditional Cu/MgO catalyst contains Cu 0 and a little Cu + . Because Cu + is more active than Cu 0 , the activity of the Cu 2 O/MgO catalyst is much higher than that of the traditional Cu/MgO catalyst.

A study of copper oxide catalysts used in the methylchorosilane reaction and determination of the fate of oxygen

The relative effectiveness of CuO and Cu2O were compared as catalysts for the methylchlorosilane (MCS) reaction. MCS reactions catalyzed by CuO had higher rates (0.15 g/g Si-h) than MCS reactions catalyzed by Cu2O (0.08) AND higher selectivities (4–5 points in % Di higherfor CuO). A synthetic method was found for making 17O-labeledCu2O based on reaction of CuCl with excess NaCl and >2equivalents of Na17OH. The Na17OH was made from17O-enriched water and Na. The % enrichment of theCu2O was determined by reduction of the Cu2O with H2 to form Cu and water and then subsequent reaction of the water product with Me2SiCl2 to make cyclo-octamethyltetrasiloxane (D4). The 17O enrichment of the D4 wasthen determined by mass spectroscopy. Thus Cu2O was made with27% 17O ±5%. The labeled Cu2Owas used as the catalyst in the MCS lab reactor. A 14% enrichmentin 17O in D4 and dichlorotetramethyldisiloxane(MClMCl) was found vs. the controlexperiment with natural abundance oxygen Cu2O. Thus all of the oxygen from the copper oxide catalyst ends up as siloxane; 50% of the oxygen in the product siloxane comes from other sources. Copper oxide catalyst was used in the presence of the phosphorus promoters Cu3P and PEt3. In both phosphorus promoter experiments, the resultant MCS lab beds were subjected toacetonitrile extraction and then NMR analysis of the extracts. Theseextracts showed that phosphorus-containing species were present and thatwhen Cu3P was the promoter, phosphorus products containing17O were present. Thus for Cu3P, some of thephosphorus reacts with the 17O from the Cu2O catalyst.

Reactions of o-tolyl isocyanide with isocyanate and isothiocyanate syntheses of n-substituted indole-3-carboxamides and indole-3-thiocarboxamides

o-Lithomethylphenyl isocyanide is reacted at −78° with isocyanates and isothiocyanates to produce o-isocyanophenyl-acetamides (2a) and -acetothioamides (2b) . Isocyanides (2a) and (2b) are cyclized to indole-3-carboxamides (3a) and -3-thiocarboxamides (3b) via lithiathion, respectively. Isocyanides 2a are also cyclized by Cu 2O catalyst to produce 4,5-dihydro-1,3-benzodiazepin-4-ones (4a) with (3a) .

Synthesis of Indole Derivatives by Cu2O-Catalyzed Cyclization of o-(α-Cyanoalkyl)phenyl Isocyanides and o-[α-(Methoxy-carbonyl)alkyl]phenyl Isocyanides

Abstract o-(Cyanomethyl)phenyl isocyanide and o-(methoxycarbonylmethyl)phenyl isocyanide were heated with a catalytic amount of Cu2O in benzene to give 3-cyanoindole and 3-(methoxycarbonyl)indole in 86 and 92% yields, respectively. Lithiations of o-(cyanomethyl)phenyl isocyanide and o-(methoxycarbonylmethyl)phenyl isocyanide with butyllithium at −78 °C followed by the reaction with alkyl halides such as methyl iodide, allyl bromide, butyl bromide, benzyl bromide and methyl α-bromoacetate afforded the corresponding o-(α-cyanoalkyl)phenyl isocyanides and o-[α-(methoxycarbonyl)alkyl]phenyl isocyanides. o-(α-Cyanoalkyl)phenyl isocyanides and o-[α-(methoxycarbonyl)alkyl]phenyl isocyanides thus obtained were also cyclized by Cu2O catalyst producing 3-alkyl-3-cyano-3H-indoles and 3-alkyl-3-(methoxycarbonyl)-3H-indoles, respectively, in moderate yields.

Synthetic Reactions by Complex Catalysts. XXV. The Copper-catalyzed Reaction of Allyl Isocyanide with Carbonyl Compounds and Olefins. Syntheses of 4-Vinyl-2-oxazoline and 5-Vinyl-1-pyrroline Derivatives

Abstract This paper describes two reactions of allyl isocyanide (AIC) by means of the Cu2O catalyst; these reactions produce heterocyclic compounds with vinyl substituents. First, the reactions of AIC with such carbonyl compounds as ketones and aldehydes produce 4-vinyl-2-oxazoline derivatives (1) in good yields. Second, AIC also reacts with the C=C double bond of α,β-unsaturated nitriles and esters to produce 5-vinyl-1-pyrroline derivatives (4,5, and 6). A mechanistic scheme involving an isocyanoallylcopper complex (11) has been assumed.