CuO Al2O3 Catalyst Research Articles

Synthesis of Novel CuO–Al2O3 Catalyst for Biodiesel Production

Synthesis of Novel CuO–Al₂O₃ Catalyst for Biodiesel Production

Preparation and characterization of CuO[sbnd]Al2O3 catalyst for dimethyl ether production via methanol dehydration

In the present study, a CuOAl2O3 catalyst with CuAl2O4 spinel structure was prepared by a co-precipitation method and used for dimethyl ether (DME) production via methanol dehydration at 50 bar and different reaction temperatures (150, 250, and 350 °C). Upon XPS analysis of the copper and aluminum species in the fresh and used CuOAl2O3 catalyst, CuAl2O4 was found to be the dominant species with more than 50% of total composition. Three reductive reactions and temperatures for the formation of CuH (102.3 °C), the interaction between Cu2+ and Al atoms (356.6 °C), and the reduction of CuO (520.1 °C) were analyzed by H2-TPR. Furthermore, the copper oxidation state in the fresh and used catalyst was Cu(II), as determined by the XANES spectra. The fine structural parameters revealed that the coordination number of Cu changed from 2.75 to 2.44 during the catalytic reaction, and that the CuO bond distance increased from 1.94 to 1.98 Å due to strengthened Cu2+Al interactions. On-line FTIR spectra revealed that the optimum temperature for the formations of HCOOH (by-product) and DME (product) were 150 and 250 °C, respectively. The catalytic reactions in the duration of DME synthesis were found that included methanol decomposition, methanol/formic acid formations, and methanol dehydration occurring at CuO, Cu, and Al2O3/CuAl2O4 active sites, respectively. The highest methanol conversion (67.3%) and DME yield (40.6%) were obtained at 250 °C and 50 bar, as demonstrated by the catalyst performance. In addition, optimum DME formation (equilibrium constant 1.76 × 10−2 L mol−1 h−1 and activation energy 5.14 kJ mol−1) occurred at 250 °C, as determined from the linear regression of the second order model with a high R2 value (0.98). The exothermal and non-spontaneous nature of DME formation at high temperature was evaluated through thermodynamic calculations of the reaction enthalpy, entropy, and Gibbs energy.

Support-dependent active species formation for CuO catalysts: Leading to efficient pollutant degradation in alkaline conditions

Redox metal ions play the crucial role in versatile advanced oxidation technologies, in which controlling the active species formation through catalyst design is one of the key challenges in oxidant utilization. This work describes an example of different active species formations in CuO-mediated degradation just because of supporting material differences. Although three CuO catalysts were prepared by similar procedures, it was found that CuO-MgO catalyst demonstrated high efficiency in phenol degradation with bicarbonate activated H2O2, in which the superoxide radical is crucial, while hydroxyl radical and singlet oxygen are ignorable. For the CuO-MgO-Al2O3 and CuO-Al2O3 catalysts, the degradation proceeds by popular hydroxyl radical based process, however, the efficiency was poor. The EPR experiments also confirmed the absence of hydroxyl radical in CuO-MgO system but its presence in CuO-MgO-Al2O3 and CuO-Al2O3 system. The high catalytic efficiency with ignorable hydroxyl radical in the CuO-MgO system leads us to propose that an alternative Cu(III) species dominates the degradation. The basic MgO support may facilitate the formation of the Cu(III) species, whereas the neutral MgO-Al2O3 and acidic Al2O3 supports are unable to stabilize the high valent Cu(III) species, leading to the common hydroxyl radical mechanism with low efficiency of H2O2 in alkaline conditions.

Activities for phenol formation using Cu catalysts supported on Al2O3 in the liquid-phase oxidation of benzene in aqueous solvent with high acetic acid concentration

Abstract The liquid-phase oxidation of benzene to phenol using a Cu catalyst supported on Al2O3 was studied at 303 K in an aqueous solvent with a variety of concentrations of acetic acid. Gaseous O2 and ascorbic acid were utilized as an oxidant and a reducing reagent, respectively. An aqueous solvent with more than around 70–80 vol.% acetic acid concentration was confirmed to cause a sharp apparent decrease in the Cu leaching from a Cu catalyst (Cu/Al2O3) impregnated on Al2O3, as well as a CuO-Al2O3 catalyst prepared by a co-precipitation method reported previously, during the benzene oxidation, keeping the yield of phenol comparatively high. The apparent Cu leaching was largely inhibited in an aqueous solvent with high acetic acid concentration in comparison with a solvent of low acetic acid concentration, irrespective of the presence of benzene and/or ascorbic acid. The influences of both the Cu amount supported on the Cu/Al2O3 catalyst and the amount of ascorbic acid on the yield of phenol were investigated in the aqueous solvents with acetic acid concentrations of both 5.7 and 80 vol.%. The Cu/Al2O3 catalyst in the aqueous acetic acid solvent was deactivated in the comparatively initial stage of the oxidation of benzene. The catalytic activity of the used Cu supported catalyst for phenol formation was almost completely recovered by calcining the catalyst at 773 K. The amount of the deactivated Cu species based on a XRD peak at 2θ=23° in the used Cu/Al2O3 catalyst was found to have a correlation with the yield of phenol.

Ozonation of Substituted Phenols in Aqueous Solutions over CuO-Al2O3 Catalyst

The oxidation of aqueous solutions of substituted phenols, chlorophenols (CPs) and nitrophenols (NPs), at 21±0.5°C and atmospheric pressure, by ozone over a copper–alumina catalyst system was studied. The total disappearance of phenol compounds for 15 to 30 minute reaction times was observed. The presence of the catalyst increased the reaction rate, diminished the ozone consumption and caused an advanced degradation of phenols. A number of six by-products was identified by gas chromatography/mass spectrometry technique (GC/MS), with or without silylation. Based on the experimental data several mechanistic suggestions for the catalytic ozonation are made.

Local Structure Stability of Cu-Al2O3 NOx Removal Catalyst

The crystal phases, microstructural features, and local atomic coordination of CuO-Al2O3 catalyst for NOx removal were studied by some experimental techniques. A spinel-like phase, which exhibits short-range structure, appears at around 900°C. Catalytic activity can be maintained at 1100°C. The activity of catalyst is controlled by the Cu-containing crystal phase of surface spinel. At low heating temperatures, the diffusion of copper into alumina will be important to surface modification to create active sites. The ESR and XANES results suggest that atomic structures in the interfacial area appear to play an important role in the lean-NOx removal activity.

Surface and catalytic properties of Co3O4-doped CuO–Al2O3 catalysts

Abstract The effect of Co3O4-doping on surface and catalytic properties of CuO–Al2O3 solids was investigated by using nitrogen adsorption at −196 °C and catalytic oxidation of CO by O2 at 125–225 °C. Pure and doped solids were subjected to thermal treatment at 600 and 800 °C prior to surface and catalytic measurements. The results showed that Co3O4-doping of CuO–Al2O3 solids at 600 °C caused a measurable increase in their specific surface area and the activity of CO oxidation. However, this treatment of solids calcined at 800 °C brought about a marked decrease in their catalytic activity and specific surface area. This discrepancy is discussed in terms of the effect of Co3O4-doping in increasing the dispersity of CuO crystallites for solids calcined at 600 °C and the role of Co3O4 in enhancing CuAl2O4 and CoAl2O4 formation upon heating at 800 °C. The activity of pure CuO–Al2O3 catalyst samples decreased progressively by regeneration while that of Co3O4 containing catalysts increased monotonically by regeneration to attain a high constant value after the fourth regeneration. Co3O4-treatment did not modify the mechanism of catalytic oxidation of CO with O2 but changed the concentration of catalytically-active constituents.

Liquid-phase oxidation of benzene to phenol by CuO–Al2O3 catalysts prepared by co-precipitation method

The liquid-phase catalytic oxidation of benzene to directly produce phenol was attempted under mild reaction conditions using supported Cu catalysts in aqueous acetic acid solvent. Gaseous oxygen and ascorbic acid were used as an oxidant and a reductant, respectively. Among the supported Cu catalysts studied, the Cu catalysts prepared by the impregnation method, irrespective of the oxide supports, the Cu species were considerably leached during the benzene oxidation. A supported Cu catalyst (CuO–Al2O3) prepared by co-precipitation of Cu(NO3)2·3H2O and Al(NO3)3·9H2O inhibited the leaching of Cu species in comparison with the Cu catalysts supported by the impregnation method on Al2O3, SiO2, MCM-41, etc. The influences of the amount of supported Cu, the partial pressure of O2, the amount of ascorbic acid, the concentration of acetic acid in the solvent, and the reaction temperature on the phenol yield were investigated using the CuO–Al2O3 catalyst. The aqueous solvent including high concentration of acetic acid (around 80vol.%) dramatically inhibited the leaching of Cu species in the CuO–Al2O3 catalyst. H2O2, which is considered to play an important role in phenol formation, was detected during the benzene oxidation catalyzed by CuO–Al2O3.

A Novel Application of Trapping Catalysts for the Selective Low-Temperature Oxidation of NH3 to N2 in Simulated Biogas

The low-temperature selective oxidation of NH3 to N2 in simulated biogas containing a large excess of CO and H2 has been examined using a novel NH3 and a standard NOx trapping catalyst. The N2 selectivity during NH3 oxidation at 200°C for a 1%Pt–20%BaO–Al2O3 NOx trapping material, with typical lean/rich switches, was initially good (>90%) but decreased markedly over a small number of cycles. In contrast, the N2 yield obtained using a novel NH3 trapping material (1%Pt–20%CuO–Al2O3) with rich/lean fuel switching exceeded 95% and was stable over many switching cycles, while an unmodified 1%Pt–Al2O3 catalyst displayed poor N2 selectivity under all conditions. The data obtained from probe reactions between the various potential adsorbates and gaseous species of the reaction indicate that the N2 yields obtained from the 1% Pt–20% CuO–Al2O3 catalyst are formed via an Internal Selective Catalytic Reduction (iSCR) between NHx species adsorbed on the trapping component and NO formed from NH3 total oxidation on the Pt during the lean cycle of operation. For the 1%Pt–20%BaO–Al2O3 catalyst, NOx, formed during lean operation, is reduced to N2 in the rich cycle by a combination of reactions with NH3, CO, and H2. The use of a hybrid catalyst, based upon a combination of iSCR and NOx trapping processes, gave a peak N2 yield of >95% and an integrated N2 production over the entire rich/lean cycle of 75%. These results reflect the potentially dramatic improvements possible by rational design of catalyst systems based upon a fundamental knowledge of the processes involved.

Structural and surface aspects of thermally treated copper aluminium mixed hydroxides

CuO–Al2O3 catalysts containing various amounts of copper oxide have been prepared by precipitation. The phase changes were studied by X-ray diffraction. The results obtained revealed that the thermal treatment of solid CuO–Al2O3 at 700 °C produced only crystalline CuO. Heating to 900 °C led to the formation of copper alumina spinel together with unreacted CuO and γ-Al2O3. The spinel content was found to increase with increasing copper content. Nitrogen adsorption–desorption isotherms on the calcined samples have been measured. Surface areas have been calculated and the pore structure analysed. The textural properties of the system were found to depend on both the copper content and the calcination temperature. Key words: CuO, Al2O3 catalysts, structure, surface area, pore structure.

HIGHLY ACTIVE AND LESS AMMONIA FORMING Fe2O3–CuO–Al2O3 CATALYST FOR NO–H2–CO REACTION

Abstract Fe2O3–CuO–Al2O3 catalyst of a CuO/Fe2O3 molar ratio near 0.5 showed a high activity for NO–H2–CO reaction, with a simultaneous formation of NH3 being very limited. The catalyst also exhibited a high activity for decomposition of NH3 when the reaction temperature was higher than 500°C.