Alumina-supported Copper Oxides Research Articles

Kinetic and thermodynamic analysis of ammonia electro-oxidation over alumina supported copper oxide (CuO/Al2O3) catalysts for direct ammonia fuel cells

In this work, ammonia electrooxidation (AEO) is studied to probe the electrochemical behavior of aqueous NH3 as direct fuel by implication of gamma alumina supported copper oxide catalysts (CuO/Al2O3). Precipitation and impregnation techniques are adapted to synthesize the substrate Al2O3, and loading of different ratios (1%, 2%, 3%, 4%) of active precursor i.e., CuO, respectively. Small average crystallite sizes (DAvg) in range of 1.46–6.76 nm and smaller particle sizes from micrographs proposed a superb activity of the catalysts. Modified GCE exhibited the excellent conductive properties towards standard redox probe K4[Fe(CN)6] and KCl, displaying a high active electrochemical surface area of up to 0.0021 cm2. Current profiles in response to increase in scan rates, concentrations of ammonia and temperature have been observed in 0.1 M KOH, thereby estimating the thermodynamic and kinetic constraints of the AEO process. Attributed to the electroactive properties towards AEO, CuO/Al2O3 is found to exhibit the desirable physiochemical properties owing to large oxidation current, large diffusion coefficient “D°” (3.6 × 10-9 cm2 s-1), large rate constant “ko” (1.2 × 10-5 cm s-1), large system entropy “ΔS” (-108 J K-1 mol-1), high change in enthalpy “ΔH” (72.3 J mol-1) and low activation energy “ΔG” (32.8 kJ mol-1). Resultingly, the oxidation of ammonia is found to be facile and robust by incorporation of CuO/Al2O3 catalysts owing to large ko, ΔH and ΔH. This study opened a gateway towards eco-benign and economical efficient energy generation and viable market entry of direct ammonia fuel cells.

Alumina supported copper oxide nanoparticles (CuO/Al2O3) as high-performance electrocatalysts for hydrazine oxidation reaction

Direct hydrazine liquid fuel cell (DHFC) is perceived as effectual energy generating mean owing to high conversion efficiency and energy density. However, the development of well-designed, cost effective and high performance electrocatalysts is the paramount to establish DHFCs as efficient energy generating technology. Herein, gamma alumina supported copper oxide nanocatalysts (CuO/Al2O3) are synthesized via impregnation method and investigated for their electrocatalytic potential towards hydrazine oxidation reaction. CuO with different weight percentages i.e., 4%, 8%, 12%, 16% and 20% are impregnated on gamma alumina support. X-ray diffraction analysis revealed the cubic crystal structure and nanosized particles of the prepared metal oxides. Transmission electron microscopy also referred to the cubic morphology and nanoparticle formation. Electrochemical oxidation potential of the CuO/Al2O3 nanoparticles is explored via cyclic voltammetry as the analytical tool. Optimization of conditions and electrocatalytic studies shown that 16% CuO/Al2O3 presented the best electronic properties towards N2H2 oxidation reaction. BET analysis ascertained the high surface area (131.2546 m2 g1) and large pore diameter (0.279605 cm³ g−1) for 16% CuO/Al2O3. Nanoparticle formation, high porosity and enlarged surface area of the proposed catalysts resulted in significant oxidation current output (600 μA), high current density (8.2 mA cm−2) and low charge transfer resistance (3.7 kΩ). Electrooxidation of hydrazine on such an affordable and novel electrocatalyst opens a gateway to further explore the metal oxide impregnated alumina materials for different electrochemical applications.

Alumina-Supported Copper Oxide Hydrogenation Catalyst

Alumina-Supported Copper Oxide Hydrogenation Catalyst

Sulfur dioxide removal by sol-gel sorbent derived CuO/Alumina sorbents in fixed bed adsorber

Nanostructured alumina supported copper oxide granular sorbents were prepared by the sol-gel method. The properties of the sol-gel derived sorbents were compared with a similar commercial sorbent which has been used in the pilot scale moving-bed copper oxide process for flue gas treatment. The crushing strength of the sol-gel derived sorbents is about 6–7 times that of the commercial samples, while the attrition rate of the former is at least 3 times smaller. At temperatures below 400 °C, SO2 sorption capacity of the sol-gel derived sorbent is about 3 times that of the commercial sorbent with a similar amount of CuO loading (7–9 wt%). The better mechanical properties and higher sulfation capacity of the sol-gel derived alumina supported copper oxide sorbents are due to their unique microstructure and the coating method for CuO.

Effect of copper loadings on product selectivities in microwave-enhanced degradation of phenol on alumina-supported copper oxides

Alumina-supported copper oxides catalysts were prepared using impregnation method and characterized using XRD, SEM and BET. Catalytic activities in phenol removal from its aqueous solution (200ppm) were studied using hydrogen peroxide as an oxidant under microwave irradiation. Effects of copper loadings, reaction temperatures (50 and 70°C) and pH (5 and 9) were studied. The high loading samples (9–14wt%) exhibited 97% phenol removal efficiency corresponding to 90% total organic carbon (TOC) value. Lower loading samples (1wt%) showed significantly lower phenol removals and inferior catalyst stability. At similar levels of phenol degradations, there was higher proportion of high molecular weight products or intermediates on 14 than on 1wt% copper/Al2O3.

Microwave-enhanced catalytic degradation of 2-nitrophenol on alumina-supported copper oxides

Abstract Copper oxides/alumina catalyst was prepared using impregnation method. It was characterized by XRD, SEM and FTIR. The crystallography of the catalyst indicated presence of bulk copper oxide in the catalyst matrix. SEM showed different sizes of ensembles of the active component on the support. The catalyst was tested in degradation of 2-nitrophenol from its aqueous solution (200 mg/l) using hydrogen peroxide as an oxidant under microwave irradiation obtained at 2450 MHz and 300 W. The effects of catalyst dosage (0–30 g/l), hydrogen peroxide (0–30 mM), pH (4 or 10) and temperature (40–60 °C) on the degradation were studied. Catalyst dosage of 5 g/l was observed to be the optimum required in generation of hydroxyl radicals for the degradation at 60 °C. The degradation was higher in acidic than in basic medium. This was associated with radical scavenging effect of bicarbonate in the basic media. About 97% 2-nitrophenol removal corresponding to 79% TOC removal rate was achieved at 60 °C. The apparent activation energy of 2-nitrophenol degradation was estimated to be 73.1 kJ/mol. The catalyst was subjected to several experimental runs and found to have limited stability. The nitrophenol degradation declined from 97 to 93% after four consecutive experimental runs.

A Study of NO+CO Reaction over Various Supported Catalysts in the Presence of O2and H2O

NO and CO are the main gases emitted into the atmosphere from both stationary and mobile combustion systems. These toxic gases represent major form of pollutants and contribute mainly to the formation of smog, acid rain and ozone depletion in the stratosphere. The simultaneous elimination of these two toxic gases leading to non-toxic compounds such as N2 and CO2 is considered an efficient process. Although the studied reaction is spontaneous, it is well known that the presence of a catalyst is necessary. For the catalytic reduction of NOx, reducing agents such as carbon monoxide (CO), hydrogen (H2), ammonia (NH3), urea ((NH2)2CO) and different hydrocarbons are usually being employed. Many supports such as alumina, titania, zirconia, ceria were usually used for dispersing the active phase for the elimination of nitrogen oxide. It is well known that supports play an important role in determining the nature and number of active sites, and consequently in the activity of the catalysts. The metal oxides are advantageous for the stability of the catalyst support and/or for enhancement of the catalyst activity under dynamic operations. Among the transition metals studied, copper show a potential activity in the NO+CO reaction and have been extensively studied. Sakurai et al. tested catalytic activities of cupric oxide and alumina-supported copper oxides in NO reduction by CO. Metal oxides such as Ce and Ni are commonly employed O2 storage component, which are frequently added to the catalyst to enhance the catalytic active sites. These oxides improve the performance of the catalyst, further making it less sensitive to temporary variations in the air-fuel ratio by getting reversibly oxidized or reduced at typical operating temperatures. Loof et al. stated that at higher temperatures, the O2 storage capacity in catalysts containing Pt, Rh, Ni and Ce supported on Al2O3, Ni is found to be the dominant storage metal and Ce predominates over Pt and Rh. The reduced surface of Ce in contact with reduced noble metals is the most effective state of the catalyst and greater activity is detected with decreasing CeO2 crystallite size. Addition of cerium oxide play an important role in providing oxygen storage by transforming between Ce2O3 under reducing conditions and CeO2 under oxidizing conditions. It is further believed that doped ceria inhibits the deactivation of active components in the reaction due to the sintering of the metals and surface deterioration of the support. Garcia et al. pointed out that the Cu-Ce interaction affected the reactivity of the catalysts towards NO thereby increasing the amount of adsorbed species which in turn lead to high NO adsorption at low temperature. The NO dissociation peaks were shifted towards low temperature upon addition of ZrO2 onto CuO/TiO2, indicating NO decomposition activity was higher in CuO-ZrO2/ TiO2 than by CuO/TiO2. Hernandez et al. suggested that the presence of acid-base sites on Pt/ZrO2-CeO2 seemed to be important for the NO+CO reaction. The Cu-Ce synergism for NO reduction with CO in the presence of O2, H2O and SO2 has been investigated by Wen and He. The results suggested that the synergistic effect between Cu and Ce ions could enhance the performance of catalyst both in activity and resistance to H2O and SO2. Redox Mechanism involving lattice oxygen/oxygen vacancy participation was proposed for CO oxidation on CeO2. Sayle et al. conducted atomic simulation of a CO oxidation mechanism on CeO2 and suggested that the surface oxygen of CeO2 is more active than the bulk oxygen. In the present study the importance of (i) method involved in preparation of catalyst, (ii) metal support interaction of catalyst and (iii) Cu-Ce synergistic effect in the NO reduction by CO are discussed.

One-electron reducibility of isolated copper oxide on alumina for selective NO–CO reaction

The H2-TPR (temperature-programmed reduction) study was performed for supported copper oxide catalysts with low loading (0.5wt% as copper). Among the various kinds of support materials (γ-Al2O3, TiO2, ZrO2, SiO2, ZSM-5), alumina-supported copper oxide indicated a one-electron reduction behavior of Cu2+ into Cu+ ions in the presence of H2. The reduction of the isolated Cu2+ species in a tetragonally distorted octahedral symmetry into the low coordinated Cu+ ions was identified by means of X-ray absorption spectroscopy (XANES and EXAFS). The isolated Cu+ ions hosted by γ-Al2O3 surface were prevented from further reduction into metallic Cu0 state under reducing condition with H2 at 773K. Less dispersed supported copper oxide species were easily reduced to Cu0 metal particles with H2 at 573K regardless of the kinds of support materials. It is suggested that the one-electron redox behavior of the isolated copper oxide species over γ-Al2O3 promotes the catalytic reduction of NO with CO in the presence of oxygen on the basis of redox-type mechanism between Cu2+ and Cu+ in atomically dispersed state.

Characteristics and desulfurization-regeneration properties of sol–gel-derived copper oxide on alumina sorbents

Mesoporous alumina supported copper oxide granular sorbents were synthesized by the sol–gel method using different raw materials. The copper loading in the sorbents was varied from 5 to 20-wt.% CuO. The effect of the copper content on the surface area of the sorbents and dispersion of the active species was studied. Samples with <14 wt.% CuO did not show any crystalline copper containing phase. For CuO/γ-Al 2O 3 with 8 wt.% CuO, most of the copper species consisted of Cu 2+ ions and no sulfide species were found. The optimum temperature for operation of the sol–gel derived sorbents was 400 °C at which more than 85% of the initial sulfation capacity is maintained up to three sulfation-regeneration cycles. The pore structure, crush strength, sulfation capacity and regeneration properties of the sol–gel derived sorbents were studied and compared with those of the similar commercial sorbents used in pilot scale fluidized-bed copper oxide process for flue gas treatment. The sol–gel-derived mesoporous copper oxide coated alumina granules, with a surface area of 220–248 m 2/g, pore volume of 0.46–0.48 cm 3/g, and pore diameter of 6.7–8.8 nm, offer higher surface area, more uniform pore size distribution, and higher crush strength than the commercially available sorbents for the copper oxide process. For similar copper oxide content the sol–gel derived sorbents showed superior sulfation and regeneration properties than the commercial sorbents, in terms of sulfation capacity, regenerability, and SO 2 concentration in the regenerated effluent.

Copper oxide supported on carbon modified alumina as catalyst for reduction of NO with CO

Carbon-modified alumina-supported copper oxide catalysts have been investigated. The samples have been prepared by modified incipient techniques. The γ-Al 2O 3-supported carbon phase permits sufficient modification of the chemical nature of the support surface in the region of low carbon contents without changing the specific surface area and the mesoporous character of the samples as compared to those of initial γ-Al 2O 3. In addition, the surface oxygen groups of the carbon phase, similar to the hydroxyl groups of the alumina surface, affect the formation and type of copper oxide phase. It has been established that the catalysts investigated have high activity in the reduction of NO with CO, the highest activity belonging to the Cu17AC/AL catalyst, which contains the largest amount of carbon. This sample is also active with respect to the direct decomposition of NO.

Promoting Effect of Chloride on the SO2 Adsorption Capacity and Adsorption Rate of Alumina-Supported Copper Oxide Adsorbents: Thermogravimetric and Infrared Studies

Alumina-supported copper oxide materials were examined for their capacity to adsorb SO2 from a SO2/O2/He gas stream at relatively low temperature (150 °C). The adsorbent (8 wt % copper oxide) was t...

Catalytic purification of flue gas from civil-used stove

Effects of the method of burning and addition of catalysts in the chimney of civil-used stove on emission of air pollutants were studied. Alumina-supported copper and manganese oxides and palladium catalysts were used to purify the flue gas emitted from the civil-used stoves. The results show that, in upper burning case, both Cu–Mn–O/Al 2O 3 and Pd/CuO/Al 2O 3 catalysts can decrease the ratio of CO/CO 2 to <0.01, and remove SO 2 and volatile organic chemicals (VOC) from the flue gas to some extent. Deactivation of the catalyst results from the accumulation of sulfate groups on catalyst support. The life of the catalyst can be extended by adding a honeycomb of lime before the catalyst.

Sol−Gel-Derived Alumina-Supported Copper Oxide Sorbent for Flue Gas Desulfurization

Nanostructed mesoporous CuO/γ-Al2O3 granular sorbents were prepared by the sol−gel method. Performance of the sol−gel-derived CuO/γ-Al2O3 sorbents for SO2 removal was studied in a fixed-bed adsorption system. SO2 breakthrough curves with a feed stream of air containing 2000 ppm SO2 were measured at different temperatures (300−500 °C) and flow rates (interstitial velocity of 0.25−6.96 cm/s). The optimum sulfation and regeneration temperature on the sol−gel-derived sorbent was found to be 400 °C. The properties of the sol−gel-derived sorbents are compared with a similar sorbent from a commercial source used in the pilot-scale copper oxide flue gas desulfurization process. At high temperatures (>400 °C) the sol−gel-derived CuO sorbents exhibit catalytic properties for converting SO2 to SO3. The crush strength of the sol−gel-derived sorbents is about 5 times that of the commercial sample, while the attrition rate of the former is about 4−10 times smaller than the latter. The SO2 sorption capacity of the sol−g...

Effect of γ-irradiation on the sorptive properties of alumina-supported copper oxide catalysts

CuO–Al 2O 3 samples containing different amounts of copper oxide were prepared by the mechanical mixing of individual oven-dried hydroxides of copper and aluminium and calcination at 823 K. The calcined samples were γ-irradiated with 10, 25, 50 or 90 Mrad. The textural properties of unirradiated and γ-irradiated CuO–Al 2O 3 catalysts were determined from N 2-adsorption at 77 K. The surface acidities of these unreduced catalysts were determined from the adsorption of pyridine at 423 K. Chemisorption of hydrogen and benzene on the reduced samples was performed at 400 K. The surface area S BET decreases and the mean pore radius r ̄ increases upon increasing CuO content of the unirradiated and γ-irradiated samples. The same situation was also observed with increasing irradiation dose. The adsorption of benzene and hydrogen increases with increasing copper content and irradiation dose, whereas the chemisorption of pyridine depicts an opposite trend. Moreover, the catalytic parameters of the samples investigated are influenced strongly by the metal loading and γ-irradiation dose.

The influence of surface structure on the catalytic activity of alumina supported copper oxide catalysts. Oxidation of carbon monoxide and methane

X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron spin resonance (ESR) have been used to characterize a series of Cu/Al 2O 3 catalysts. The information obtained from surface and bulk characterization has been correlated with CO and CH 4 oxidation activity of the catalysts. For catalysts with Cu/Al atomic ratios ⩽0.051, XPS data indicated that most of the Cu was present as a dispersed surface phase. ESR results showed that the ratio of isolated/interacting copper surface phase decreased with increasing Cu content. For catalysts with Cu/Al atomic ratio ⩾0.077, large CuO crystallites were detected by XRD. XPS results indicated that Cu dispersion decreased with increasing Cu content. The turn over frequency (TOF) for CO oxidation increased with increasing Cu content. This has been attributed to an increase in the amount of crystalline CuO present in the catalysts. The TOF for CH 4 oxidation decreased with increasing Cu content up to Cu/Al = 0.051. This was paralleled by a significant decrease in the relative Cu ESR signal measured for the catalysts. We propose that the isolated Cu surface phase is more active for CH 4 oxidation than the interacting copper surface phase or crystalline CuO. CH 4 oxidation activities were similar for the catalysts with Cu/Al atomic ratio ⩾0.077.

Surface Models of Alumina Supported Copper Oxide Prepared by Laser Ablation: Dispersion and Electron Structure Changes Following Reduction and Oxidation Cycles

ABSTRACTWe have explored and developed laser ablation as a tool to synthesize realistic planar models of high surface area catalysts as well as novel materials, not accessible with wet chemical methods. The process is illustrated by data for dispersion and electron structure modifications following thermal treatments of alumina supported copper oxide. Planar models of different wet and dry carrier/overlayer combinations were prepared and exposed to oxidizing and reducing atmosphere at 500°C. Characterization was made by XPS/ESCA. The data reveal the importance of surface hydroxyl groups in the two initial components to control coalescence and interdiffusion. The ablation route is part of our ongoing DENOX project and comparisons are made with other materials, tested for their materials properties and catalytic behavior in HC/NO reactions.

Use of catalytic detector in temperature-programmed reduction

Results for the reduction of unsupported CuO and NiO and alumina-supported copper oxides and chlorides, obtained by temperature-programmed reduction in flowing 6% H 2/N 2 using both thermal conductivity and catalytic detectors, are comparable, but wider applicability of the latter may make it more attractive for temperature-programmed studies.

Electron spin resonance studies of adsorption of alkynes and allene over alumina supported copper oxide

The formation of an interesting new type of paramagnetic species ( g = 2.00, width 3.5 G) is observed over alumina supported copper oxide catalyst by alkynes and allene at 360 °C. Alkenes and alkanes do not give paramagnetic species (PMS) under experimental conditions. Alumina supported copper oxide contains at least two types of active sites. While one has electron acceptor property (thiodiphenylamine cation radical formation) the other, Cu 2+, has the property to give PMS with alkynes and allene. The affinity of the studied hydrocarbons for the formation of PMS were in the following sequence: acetylene > methylacetylene > allene > ethylacetylene > dimethylacetylene. The intensity of ESR signals dropped drastically as soon as PMS came into contact with air or oxygen. However, on removing the oxygen from O 2 adsorbed PMS either by evacuating or passing CO, CO 2, H 2, D 2, N 2 or acetylene over Cu-alumina at room temperature, the ESR signal reappeared to almost original shape and intensity. A possible mechanism for the formation of these radicals and the effect of oxygen on these is discussed on the basis of charge transfer and an equilibrium shift between PMS and oxygen.