Supported Copper Catalysts Research Articles

Mesoporous silica–supported copper catalysts for dehydrogenation of biomass-derived 1,4-butanediol to gamma butyrolactone in a continuous process at atmospheric pressure

A series of Cu/SBA-15 catalysts were prepared by wet impregnation method and tested for dehydrogenation of 1,4-butanediol (1,4-BDO) to γ-butyrolactone (GBL). As-synthesized catalysts were characterized by different techniques such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), N2 physisorption, N2O pulse chemisorption, and transmission electron microscopy (TEM) analysis. Among the series of Cu/SBA-15 catalysts, 10 wt% Cu/SBA-15 catalyst exhibited a complete conversion of 1,4-BDO with 98% selectivity to GBL. The superior catalytic performance of the 10 wt% Cu/SBA-15 catalyst was attributed to the well dispersion of Cu particles with much number of active metallic Cu sites over high surface area, SBA-15 support, and surface acidity.

Selective Dehydrogenative Mono- or Diborylation of Styrenes by Supported Copper Catalysts

The selective dehydrogenative borylation of alkenes is an attractive method for synthesizing useful borylalkenes. However, very few catalytic systems have been reported that fulfill this objective. All the reported examples are homogeneous catalysts with special ligands requiring the usage of bases. This study describes the heterogeneously catalyzed dehydrogenative borylation by supported copper hydroxide catalysts (Cu(OH)x/support). In the presence of Cu(OH)x/support and suitable ketones, the dehydrogenative borylation of styrenes with bis(pinacolato)diboron efficiently proceeded to selectively afford the corresponding β-monoboryl- or β,β-diborylstyrenes. The observed catalysis was truly heterogeneous, and the catalysts could be reused several times, though their catalytic performance gradually declined.

Stability of mesocellular foam supported copper catalysts for methanol synthesis

Mesocellular foam is a well-defined mesoporous silica comprising large cages (˜20 nm), connected by small windows (2–10 nm). Here, we used mesocellular foam as a support material in the preparation of Cu based model catalyst for methanol synthesis at high temperature and pressure. To this end, we synthesized two types of mesocellular foam, with the same cage size, but a different window size of 8 and 2.3 nm, and compared them to the use of a silica gel support. Cu particles were deposited by impregnation with a copper nitrate precursor solution and decomposition in either N2 or H2-containing gas stream. We followed the phase evolution in situ, and identified a method using direct reduction in H2 to deposit 3 nm Cu particles on all different supports. The catalysts prepared on the mesocellular foam displayed a much higher stability than the silica gel supported catalysts. The impact of the window size of the MCF was small, but significant: the catalysts supported on the small window mesocellular foam were more stable on the long term. However, they also had a lower activity due to embedment of the Cu particles in the windows, as revealed with electron tomography. A higher metal loading on the small window mesocellular foam resulted in enhanced coalescence of the Cu particles, which was attributed to smaller interparticle distances. Increasing the loading on this support even further increased the size and polydispersity of the Cu nanoparticles, leading to a higher deactivation rate due to Ostwald ripening. Hence, the loading and size polydispersity are important parameters in determining the catalyst stability. We also found that the nature of the SiO2 support has more impact on the catalyst stability than the restricting pore sizes, probably due to the fact that Ostwald ripening dominates particle growth on the longer time scales.

Magnesium Aluminate Supported Cu Catalyst for Selective Transfer Hydrogenation of Biomass Derived Furfural to Furfuryl Alcohol with Formic Acid as Hydrogen Donor

AbstractCatalytic transfer hydrogenation (CTH) was concerned great attention because it does not need the use of high pressure H2. A series of Cu catalysts has been prepared for transfer hydrogenation of biomass derived furfural to furfuryl alcohol with formic acid. The prepared Cu based catalysts are thoroughly characterized by various technique such as XRD, TPR, TPD (NH3, CO2), TEM, FT‐IR, UV‐Vis, N2O pulse chemisorption and N2‐physorption method. For a comparison point of view, the activity tests of various copper based catalysts have also been carried out. Among all these, MgAl2O4 (MA) supported copper catalyst was found to be the best to give 90% selectivity of furfuryl alcohol from transfer hydrogenation of furfural. The excellent yield of furfuryl alcohol could be attributed to high density of surface active Cu species, proper surface acidic‐basic properties and metal support interaction. Moreover, Cu/MA catalyst was simply recovered and reused, which retained its original activity even after reaction without significant loss of original activity. Supporting its reusability and stability.

The transient reduction of NO with CO and naphthalene in the presence of oxygen using a core–shell SmCeO2@TiO2-supported copper catalyst

This work studied the reaction of common pollutants on a catalytic surface under oxidizing conditions.

Highly efficient and practical aerobic oxidation of alcohols by inorganic-ligand supported copper catalysis

An inorganic-ligand supported copper catalyst which can effectively catalyze the aerobic oxidation of alcohols to afford aldehydes or ketones with excellent selectivity and yields.

Activated carbon aerogel supported copper catalysts for the hydrogenation of methyl acetate to ethanol: effect of KOH activation

Methyl acetate (MA) hydrogenation is crucial for indirect ethanol synthesis through syngas (CO + H2).

Heterogeneous copper-catalyzed decarboxylative cyclization of 2-benzoylpyridines with α-amino acids leading to imidazo[1,5-a]pyridines

The heterogeneous decarboxylative cyclization reaction between 2-benzoylpyridines and α-amino acids was achieved in toluene at 120 °C in the presence of 15 mol% of l-proline-functionalized MCM-41-supported copper(II) complex [l-Proline-MCM-41-Cu(OTf)2] and iodine with di-tert-butyl peroxide (DTBP) as oxidant, yielding a variety of 1,3-disubstituted imidazo[1,5-a]pyridines in good to excellent yields. The new supported copper catalyst can be prepared from commercially available and inexpensive reagents, and recovered from the reaction mixture by a simple filtration and recycled up to eight times with almost consistent activity.

Alcohol Amination Catalyzed by Copper Powder as a Self-Supported Catalyst.

Catalytic alcohol amination is a sustainable reaction for N-alkyl amine synthesis. Homogeneous and supported copper catalysts have long been studied for this reaction and have given some impressive results. In this study, copper powder is found to behave as an active catalyst for alcohol amination, giving better catalytic performance than metal-oxide-supported nanocopper catalysts. Catalyst characterization suggests that the copper powder can be considered as a self-supported nanocopper catalyst (i.e., nanocopper supported on copper particles). These results might promote the study of unsupported transition metal powders in sustainable catalytic reactions.

Conversion of methyl ethyl ketone to butenes over bifunctional catalysts

The direct conversion of methyl ethyl ketone (MEK) to butene over supported copper catalysts was investigated in a fixed bed reactor over Cu-Al2O3, Cu-zeolite Y sodium (Cu-ZYNa) and Cu-zeolite Y hydrogen (Cu-ZYH). In this reaction, MEK is hydrogenated to 2-butanol over metal sites which is further dehydrated on acid sites to produce butene. Experimental results showed that the selectivity of butene was the highest over Cu-ZYNa, and it was improved by finding the optimum reaction temperature, hydrogen pressure and the percentage of copper loaded on ZYNa. The highest selectivity of butene (97.9%) was obtained at 270 °C and 20 wt% Cu-ZYNa. Over Cu-Al2O3, the selectivity of butenes was less than Cu-ZYNa since subsequent hydrogenation of butene occurred to produce butane. It was also observed that with increasing H2/MEK molar ratio, butane selectivity increased. However, when this ratio was decreased, hydrogenation of butene was reduced, but dimerization to C8 alkenes and alkane began to be favored. The main products over 20% Cu-Al2O3 were butene and butane, and a maximum selectivity of butene (87%) was achieved at an H2/MEK molar ratio of five. The lowest selectivity of butene was obtained using Cu-ZYH, reaching ∼40%. All catalysts were characterized by (NH3-TPD), (CO2-TPD), XPS and TPR to probe catalyst acidity, basicity and the reducibility of Cu loaded on the supports. It was found that the amount of acidity in Cu-ZYH is much higher than in Cu-ZYNa. This could have caused the selectivity of butene to decrease as a result of dimerization, oligomerization and cracking reactions.

Novel Rh(Pd)-Cu(Ni) supported catalysts for oxy-steam reforming of methanol

Monometallic copper, nickel and bimetallic Pd(Rh)-Cu(Ni) catalysts supported on a binary oxide containing various content of ZrO2 and Al2O3 were prepared by impregnation method. Their physicochemical and catalytic properties in oxy-steam reforming of methanol reaction (OSRM) were extensively investigated. Selecting an optimal composition of the catalyst for the OSRM process was the main goal of this work. The influence of zirconia content on the reactivity and physicochemical properties of supported copper catalysts in OSRM was also studied. The reactivity measurements showed that the supported copper catalyst was more active than the nickel catalyst. The catalytic measurements showed that the catalyst properties depend on their surface composition, acidity and adsorption properties. High selectivity of supported copper catalyst with composition 20%Cu/ZrO2·Al2O3 (Zr:Al = 1:2) towards carbon dioxide and hydrogen was confirmed. In addition, the promotion effect of palladium and rhodium on the activity of monometallic supported copper and nickel catalysts in OSRM was confirmed. The most active system in the OSRM process was 0.5%Rh-20%Cu/ZrO2·Al2O3.

One-Pot Synthesis of Secondary Amines from Nitroarenes and Aldehydes on Supported Copper Catalysts in a Flow Reactor: The Effect of the Support

The effect of the support on the properties of copper catalysts supported on γ-Al2O3, SiO2, and TiO2–SiO2 with a ~5 wt % Cu content was studied in the one-pot synthesis of N-heptyl-p-toluidine from p-nitrotoluene and n-heptanal. The catalysts were characterized by elemental analysis, X-ray diffraction analysis, transmission electron microscopy, temperature-programmed reduction, and low-temperature nitrogen adsorption. The reaction was carried out in a flow reactor with the use of molecular hydrogen as a reducing agent. It was established that the nature of the support exerts a profound effect on the yield of the target secondary amine; in this case, 5%Cu/Al2O3 was found the most active catalyst. A combination of high catalyst activity in the hydrogenation of a nitro group to an amino group with the presence of acid sites, which facilitate imine formation as a result of the interaction of n-heptanal with p-toluidine, on the catalyst surface is necessary for reaching the greatest yield of N-heptyl-p-toluidine. The study of reaction mechanism on the 5%Cu/Al2O3 catalyst showed that p-nitrotoluene inhibits the hydrogenation of n-heptanal, and aldehyde hydrogenation into alcohol begins only after the conversion of the major portion of p-nitrotoluene as a result of the selective adsorption of the nitroarene under the conditions of the simultaneous presence of p-nitrotoluene and n-heptanal in the reaction mixture.

KA2‐Coupling Reaction Catalyzed by Semi‐Heterogeneous Magnetically Graphene Oxide Supported Copper Catalyst under Microwave Condition

AbstractFunctional Schiff base chelating groups (PCA) were covalently grafted onto the surface of magnetic graphene oxide (GO‐Fe3O4) via a facile silanization reaction under mild condition. The obtained GO‐Fe3O4‐PCA was further chelated with CuCl2 as an efficient, robust, and recyclable semi‐heterogeneous catalyst (GO‐Fe3O4‐CuCl2) for one‐pot three‐component KA2 coupling of ketones, amines, and alkynes. It exhibited environmentally benign, excellent magnetic separation performance, and higher catalytic activity than other commercially available copper sources. A series of propargylamines are prepared from cycloketones, cycloamines, and phenylacetylene in moderate to excellent yields under microwave (MW) irradiation (70–93%). Interestingly, the catalyst can be separated conveniently by a simple magnetic separation and reused at least four consecutive runs with a slight drop in the product yields. The semi‐heterogeneous property and excellent accessibility of GO‐Fe3O4‐CuCl2 might cause high catalytic activity.

Conversion of levulinic acid to N-substituted pyrrolidinones over a nonnoble bimetallic catalyst Cu15Pr3/Al2O3

A nonnoble bimetallic metal catalyst Cu15Pr3/Al2O3 readily prepared through incipient-wetness impregnation method was developed for the reductive amination of levulinic acid (LA) with amines to N-substituted-5-methyl-2-pyrrolidinones. A wide variety of N-substituted-5-methyl-2-pyrrolidinones were obtained in high yield over this catalyst. The characterization results from XRD, H2-TPR, XPS, TEM, NH3-TPD and N2 adsorption-desorption revealed that Cu0 species are the active species for the hydrogenation in the reductive amination reaction. Besides, the doping of praseodymium into γ-Al2O3 supported copper catalyst greatly enhanced the catalytic performance of Cu/γ-Al2O3 due to better dispersion of Cu0.

Textural, structural and catalytic behavior of low specific area silica-supported copper catalysts: effect of preparation method

Supported copper catalysts on low surface area silica were prepared by several methods and characterized by AAS, XRD, N2 adsorption, SEM, H2-TPR, N2O titration, TGA-DTA, UV–Vis techniques. Their hydrogenating properties were examined in the gas-phase hydrogenation of benzaldehyde. The analysis of characterization results revealed that the choice of preparation method affected the texture, composition, and structure of the calcined and reduced Cu/SiO2 catalysts. The dispersion and size distribution of copper species was present in different forms in the catalysts that exhibited low specific surface areas. In gas-phase hydrogenation of benzaldehyde to benzyl alcohol, the catalysts tested at the reaction temperatures of 160 and 200 °C were stable and conducted to a good catalytic activity and benzyl alcohol selectivity ranging between 5 and 39 µmol min−1 g−1 and 0–95%, respectively. The activity of the catalysts in gas-phase hydrogenation also depended on the particle size and the nature of copper species formed on low surface area silica.

Transfer-hydrogenation of furfural and levulinic acid over supported copper catalyst

Transfer-hydrogenation (TH) has attracted great attention because it does not require the use of high pressure H2. In this work, we report a facile ultrasound-assisted impregnation method with the aid of carbothermal reduction property of activated carbon (AC) to synthesize AC supported copper catalyst (Cu/AC) for efficient TH of bio-derived unsaturated oxygenated compounds such as furfural (FAL) and levulinic acid (LA). In the presence of 2-propanol as the hydrogen donor, within 5 h under 200 °C, the resultant Cu/AC catalyst can convert FAL into 2-methylfuran (2-MF, a high-value fuel additive) with a superior selectivity of 91.6%. The Cu/AC catalyst can also covert LA into γ-valerolactone (GVL) with a high selectivity of 89.9% under 220 °C for 5 h. The superior TH catalytic performance of the Cu/AC catalyst could be attributed to the uniform size and well dispersed Cu nanoparticles supported on the high surface area AC with the suitable proportion of Cu2+, Cu0 and Cu+. Cycling test results confirm the reusability of the Cu/AC catalyst. Additionally, the reported Cu/AC catalyst is cheap and massive producible, advantageous for large-scale conversion of bio-derived platforms to value-added chemicals and bio-fuels.

The effect of ionic liquid on alumina supported copper catalysts for the competitive hydrogenation of octanal in the presence of octene

The influence of 1-butyl-3-methylimidazolium bis(trifluromethanesulfonyl)imide ([BMIM][NTf2]) on Cu/γ-Al2O3 was investigated for the competitive hydrogenation of octanal in the presence of octene in a continuous flow reactor. The role of the solid catalyst was investigated by comparing the activities of one-step (N15Cu) vs two step (2N15Cu) wet impregnated catalyst. Characterization techniques included nitrogen physisorption, temperature programmed studies, electron microscopy and X-Ray Photoelectron Spectroscopy which were used to determine the catalyst properties and metal-ionic liquid interaction of the uncoated and IL coated catalysts. The Cu SCILL catalyst (solid catalyst with an ionic liquid layer) showed enhanced catalytic performance as compared to the uncoated catalyst. Under optimized conditions, the 2N15Cu SCILL catalyst favoured the desired hydrogenation of the octanal, whilst minimizing the undesired octene hydrogenation. The octene conversion decreased from 26% to 6% over the SCILL catalyst. The presence of the ionic liquid also increased the selectivity towards the desired product, 1-octanol, from 93.5% over the uncoated catalyst to 99.8% over the SCILL catalyst. Investigation into the interaction between the copper and the ionic liquid revealed that the ionic liquid is physically adsorbed onto the catalyst’s surface, and induced changes in the SCILL catalysts surface acidity, BET surface area and hydrogen-metal interaction. It seems likely that the thermal and chemical properties of the ionic liquid also contributed to the SCILL catalyst behaviour, for example, the polar nature of the ionic liquid favours the diffusion of octanal as opposed to octene within the ionic liquid layer. This results in a greater selectivity towards CO hydrogenation which is desired.

Efficient conversion of furfural into cyclopentanone over high performing and stable Cu/ZrO2 catalysts

Currently, biomass transformation to produce high value-added chemicals and liquid biofuels is attracting more and more interest by the virtue of its importance in the sustainable development of human society. Herein, we reported the conversion of furfural (FFA) into cyclopentanone (CPO) in water over high performing and stable Cu/ZrO2 catalysts prepared by our developed one-pot reduction-oxidation method. It was demonstrated that surface structures and catalytic performances of catalysts could be delicately adjusted by varying the calcination temperatures for catalyst precursors. Especially, an appropriate calcination temperature of 500 °C could significantly enhance the interactions between surface Cu species and the ZrO2 support, thus greatly facilitating the formation of Cu+-O-Zr-like structure at the metal-support interface, and the resulting Cu/ZrO2 catalyst showed a superior catalytic performance with a high CPO yield of 91.3% under mild reaction conditions (i.e. a low hydrogen pressure of 1.5 MPa and 150 °C) to other metal oxides supported copper catalysts prepared by the conventional impregnation. It was revealed that in addition to surface acidic sites, surface Cu+/(Cu°+Cu+) ratio also played a key role in promoting the formation of CPO in the present Cu/ZrO2 catalytic system.

Study the Thermal Stability of Nitrogen Doped Reduced Graphite Oxide Supported Copper Catalyst

The thermal stability of the as-synthesized Nitrogen-doped reduced graphite oxide supported copper catalyst was investigated by a thermogravimetric analyzer (TGA) at a temperature range 273–1173 K under purified N2 atmosphere using three different heating rates (15, 20 and 25 K min−1). Firstly, to obtained nitrogen-doped reduced graphite oxide (N-rGO), the functionalized graphite oxide was synthesized using Staudenmaier’s method reduced by continuously stirring in an ammonia solution subsequently. The rGO was doped with nitrogen and impregnated with Cu-precursor to obtain Cu/N-rGO. The as-synthesized GO; N-rGO and Cu/N-rGO were characterized by FESEM, EDX, TEM, XRD and XPS. All these analyses were resulted in successfully samples synthesized. The TGA kinetic data were fitted into Kissinger and Flynn–Wall–Ozawa model free expressions to obtain apparent activation energies of 83.34 and 102.59 J mol−1 and pre-exponential factors of 2.40 × 107 and 5.01 × 1011 s−1. The high R2 values of 0.9999 and 0.9666 obtained from fitting TGA kinetic data using the Kissinger and Flynn–Wall–Ozawa model free expressions show that the data were well fitted to the expressions. This implies that the thermal behavior of nitrogen doped reduced graphite oxide supported Cu catalyst can be investigated using Kissinger and Flynn–Wall–Ozawa model free expressions.

Ozonation of Reactive Orange 4 dye aqueous solution using mesoporous Cu/SBA-15 catalytic material

The catalytic ozonation using mesoporous SBA-15 supported copper catalyst (Cu/SBA-15) was employed for the degradation of reactive orange 4 (RO4) azo dye in aqueous solution. The catalyst was synthesized and characterized using BET, SEM, TEM and EDX techniques. The characteristic results revealed highly ordered mesoporous structure, uniform pore sizes, parallel arranged channels and large surface area for the catalyst. The effects of copper loading on SBA-15, initial solution pH and ozone dose on the degradation of RO4 dye were studied. The complete colour removal from RO4 azo dye aqueous solution was obtained after 21 min of ozonation. The maximum TOC removal efficiency of 86% was obtained at optimum operational conditions of 2% copper loadings, initial solution pH 9 and ozone dose of 5 g/m3 after 60 min reaction time. The degradation pathway of catalytic ozonation reaction was studied by adding t-butanol as radical scavenger and it was found that the presence of radical scavenger had no effect on colour removal efficiency suggesting direct ozone molecular type mechanism. However, TOC removal efficiency was significantly reduced with the addition of t-butanol, thereby, indicating a hydroxyl radical based mechanism. The catalytic ozonation reaction followed pseudo-first order kinetics with respect to RO4 dye concentration. The reusability study for the catalyst suggested a negligible loss in the degradation efficiency after five runs of experiments. The stability of the catalyst was studied by performing leaching experiments which suggested that the catalyst has the potential to be utilized for the degradation of aqueous dye solution.