Cu-Al Catalysts Research Articles

Why do CuAl catalysts outperform in CO2 electro-reduction to C2H4?

Why do CuAl catalysts outperform in CO2 electro-reduction to C2H4?

Construction of a dual catalytic mechanism controlled by multiple active sites in Cu-Al catalysts to facilitate gas-phase hydrogenation of diethyl oxalate to ethyl ethoxyacetate

The hydrogenation of diethyl oxalate (DEO) to synthesize ethanol, ethylene glycol (EG), and ethyl glycolate (Egly) is always a hot topic in the field of carbon catalytic conversion, but its catalytic hydrogenation to synthesize ethyl ethoxyacetate (EEA) has received significantly insufficient attention. Here, a series of bifunctional Cu-Al catalysts with different Lewis acid distributions were synthesized using a self-assembly method and employed to interpret the effect of the dependence of Cu-Al multisite on the hydrogenation of DEO to EEA. A trend of volcano shape is observed between the reactivity of the catalyst and the increasing amount of Cu loading, indicating that the active Cu site determines the hydrogenation of DEO. The highest conversion of about 40% is obtained for the Cu10Al100 catalyst over a reaction time of 56 h. Meanwhile, the specific relationship between the selectivity of EEA and the content of the medium-strong Lewis acid site (LAS) on the catalyst surface is indicative of the decisive role of the amount of the medium-strong acid on the production of EEA. The highest EEA selectivity of ∼55% is achieved over the Cu1Al100 catalyst. The results show (e.g·NH3-TPD, 27Al MAS-NMR, H2-TPR) that EEA is the product of synergistic catalysis between the Cu site and the medium-strength LAS in the CuxAl100 catalyst. It is demonstrated that EEA synthesis involves two reaction pathways: dehydration of ethyl 2-hydroxy-2-ethoxyacetate intermediate at LAS and etherification of Egly and ethanol at LAS. The multi-reactivity pathway driven by this Cu-Al double site can be extended to the gas-phase hydrogenation of dialkyl oxalate for the synthesis of a variety of Alcohol-Ethers-Esters (AEE) compounds.

Ga doping disrupts C-C coupling and promotes methane electroproduction on CuAl catalysts

The electrochemical CO 2 reduction reaction (CO 2 RR) provides a route to store intermittent electricity in the form of fuels like methane. We reasoned that disrupting C-C coupling while maintaining high ∗CO coverage could enhance methane selectivity and suppress the hydrogen evolution reaction (HER). We studied the effect of doping CuAl, a material at the top of the CO 2 RR activity and selectivity volcano plot, with elements having low ∗CO binding energies: Au, Zn, and Ga. Encouraged by initial improvements in selectivity to methane, we optimized the Ga content and showed that the presence of uniformly dispersed Ga is crucial in CO 2 RR-to-methane performance enhancement. We rule out porosity and roughness and conclude that the presence of Ga in the doped catalysts enables high methane selectivity. The Ga-doped CuAl catalysts achieve a methane Faradaic efficiency (FE) of 53% by suppressing HER to 23% in neutral electrolyte at −1.4 V versus reversible hydrogen electrode. • Tuning the CO 2 reduction reaction product distribution by disrupting C-C coupling • Porous Ga-doped CuAl catalysts were synthesized • Methane current density of 234 mA/cm 2 and faradaic efficiency of 53% were achieved • Stable operation over 10 h The energy grid needs to shift from fossil fuels to renewable energies, such as wind, solar, nuclear, and hydroelectric energy, in order for society to keep below the 1.5°C global warming threshold. One challenge in achieving this goal is the intermittency of wind and solar electricity. An approach is the electrically powered production of methane, a commodity for which the infrastructure for storage, transportation, and use is well developed. CO 2 RR-to-methane catalysts are in need of improved selectivity, productivity, and stability. Herein, we show how the CO 2 RR product distribution can be redirected from C 2+ products to methane by disrupting carbon-carbon coupling. The material design principles herein contribute to the roadmap for CO 2 RR electrocatalyst design. We shift the CO 2 reduction reaction (CO 2 RR) product distribution from C 2+ products toward methane. Ga doping in CuAl catalysts disrupts carbon-carbon coupling and results in a selectivity shift from ethylene to methane while maintaining low hydrogen evolution activity.

Mesoporous Cu Catalysts for Dimethyl Oxalate Selective Hydrogenation: Impact of the Cu/Al interface on the Textural Properties and Catalytic Behavior

AbstractIn this paper, mesoporous monometallic Cu catalysts reinforced by the Al3+ dopants with different chemical features were successfully synthesized by controlling the preparation process. The N2‐Adsorption/Desorption, XRD, H2‐TPR, SEM, TEM, H2‐TPD and XPS were conducted to explore the structure evolution of the as‐synthesized samples focusing on the interface effect between Cu nano‐particles (NPs) and Al3+ dopants. It is found that the precipitants used for preparing precursors show drastically effect on the Al3+ chemical form and Cu/Al bonding manners of the as‐synthesized CuAl catalysts, further determining the resultant physicochemical properties and catalytic behavior in dimethyl oxalate (DMO) hydrogenation. In gas‐phase DMO hydrogenation, 98.0 % ethylene glycol (EG) and 90.0 % ethanol (EtOH) yield from DMO selective hydrogenation can be achieved over the CuAl catalyst by regulating the reaction temperature. The correlation between the catalytic behavior and physicochemical features shows that the surface Cu+ sites generated in the Cu/(hydr)oxide interface should be essential for DMO selective hydrogenation in presence of the adequate Cu0 sites. Additionally, the Cu−O−Al patterns in the Cu/Al interface intend to promote more electron transferred from the Al3+ dopants to Cu species through the O bridging, facilitating the CuAl(O) stronger Cu/Al interaction than that of the CuAl(C) catalyst in form of Cu−Al−OH mode. Thus, the Cu NPs growth of the CuAl(O) catalyst was effectively retarded, favoring enhanced catalytic stability.

Effect of Calcination Temperature on the Textural Properties and Catalytic Behavior of the Al2O3 Doped Mesoporous Monometallic Cu Catalysts in Dimethyl Oxalate Hydrogenation

Al2O3 doped mesoporous monometallic Cu catalysts were successfully synthesized though the self-assembly Cu species derived from the oxalate precursor undergoing thermal decomposing. The evolutions of microstructures, physicochemical and surface properties of the CuAl catalysts have been systematically characterized focusing on the effect of the calcination temperature during catalyst preparation. It is found that the textural and surface properties of the CuAl catalysts were profoundly affected by the calcination temperature, further determining the resultant catalytic behavior in dimethyl oxalate (DMO) hydrogenation. Particularly, the CuAl-500 possessing the maximum surface Cu+ sites and proper surface acid features exhibits 100.0% DMO conversion and 98.0% ethylene glycol (EG) selectivity in presence of the adequate active Cu0 sites, which is superior to that of the other catalysts under the identical reaction conditions. And no activity loss occurred for more than 200 h demonstrated of the outstanding stability of the CuAl-500 catalyst. Moreover, the synergistic effect between surface Cu+ and Cu0 sites should be responsible for DMO selective hydrogenation. Additionally, the strengthened chemical interaction between Cu and Al species endows the catalysts outstanding stability by suppressing the dispersive Cu NPs agglomeration during DMO hydrogenation.

Highly active and efficient Cu-based hydrotalcite-like structured materials as reusable heterogeneous catalysts used for transcarbonation reaction

A series of robust and efficient Cu-Al hydrotalcite-like compounds (HTLc) as catalysts were prepared by the simple precipitation method with different Cu/Al molar ratios and investigated for the transcarbonation of glycerol with dimethyl carbonate (DMC) for glycerol carbonate (GC) synthesis in a batch reactor. The structural and textural properties of the Cu-Al (HTLc) catalysts were analyzed by several methods like N2-sorption, SEM-EDX/TEM, XRD, FTIR, CO2-TPD, TGA/DTA and ICP-OES. It was found that the transcarbonation of glycerol is directly dependent on the strong basic sites of the catalysts. The Cu/Al molar ratio has easily tuned the glycerol conversion and the GC yield. Among all synthesized catalysts, the Copper-Aluminum (3Cu-Al@500) catalyst showed excellent catalytic activity for a glycerol conversion (96%) and a GC yield (86%) with reaction rate (irrespective to glycerol) of approximately 0.106 mol L−1 h−1. Furthermore, the optimization of the reaction conditions (i.e. molar ratio of the reactants, catalyst mass, reaction time and temperature) and the reusability of the 3Cu-Al@500 catalyst for glycerol conversion and GC yield with TOF value were studied. In addition, the effect of stirring speed and particle size on the minimization of external and internal mass transfer resistance, respectively, was investigated.

Preparation and Activity of Copper–Gallium Nanocomposite Catalysts for Carbon Dioxide Hydrogenation to Methanol

Copper (Cu) nanocomposite catalysts with gallium (Ga) and aluminum (Al) were prepared using the simultaneous co-precipitation digestion method. The catalysts were characterized by N2 adsorption, N2O titration, XRD (X-ray diffraction), H2-TPR (H2 temperature-programmed reduction), XPS (X-ray photoelectron spectroscopy), and CO2-TPD (CO2 temperature-programmed desorption) techniques, and CO2 hydrogenation to methanol synthesis was performed. The use of Ga in Cu catalysts enhanced the weak basic sites more than the Cu catalysts with Al. With the CuGa nanocomposite formation, the catalyst showed a sequential reduction of CuO, for example, Cu+2 to Cu+ to Cu0, and the Cu surface area was also high in comparison with CuAl. These findings confirmed that both the Cu surface area and CuO reducibility in the catalyst helped to boost the conversion of CO2, whereas selectivity to methanol was associated with the basicity of the catalyst. CuAl catalysts showed very poor selectivity to methanol despite CO formation, which could be due to the weak interaction of the CuAl nanocomposite catalysts compared to the CuGa nanocomposite catalysts.

Effect of Pt on Zn-Free Cu-Al Catalysts for Methanol Steam Reforming to Produce Hydrogen

Steam reforming of methanol can be considered as an attractive reaction aiming at hydrogen production for PEM fuel cells. Although Cu/Al-contained catalysts are considerably evaluated in this reaction, further evaluation is essential to evaluate the impact of some promoters like Pt in order to find a comprehensively optimized catalyst. Pt promoter is employed with different methods in this study. Firstly, the amount of Cu loading in Cu/Al ratio is optimized via coprecipitation method. The sample containing 30% wt. of Cu exhibits better performance with methanol conversion of 70% and CO selectivity of 0.44%. Besides, impregnating a different amount of Pt onto Al2O3 reveals an inadequate potential for this reaction. In contrary, doping Pt into Cu/Al catalyst increases the methanol conversion as high as 81% and CO selectivity reaches to approximately zero at 270 °C. In addition, using a dual-bed reactor including Cu/Al and Pt/Al2O3 catalyst displays a relatively satisfactory performance by which the conversion and selectivity are found 83.7% and 1.5%, respectively. In this study, analyses of X-Ray Diffraction, Scanning Electron Microscopy, and BET surface area are used to characterize the synthesized catalysts.

Synthesis of quinoxaline derivatives from terminal alkynes and o-phenylenediamines by using copper alumina catalyst

An efficient method for the synthesis of quinoxaline derivatives through oxidative coupling of o-phenylenediamines (OPD) with terminal alkynes by using copper-alumina (Cu-Al) catalyst was described. A series of Cu-Al catalysts with different mole ratios of $$\hbox {Cu}^{2+}/\hbox {Al}^{3+}$$ , 2:1 (Cu-Al-1), 2.5:1 (Cu-Al-2) and 3:1 (Cu-Al-3) were prepared by co-precipitation method followed by calcination and their activity was checked for the synthesis of quinoxaline derivatives. Cu-Al-2 showed excellent activity at $$60\,^{\circ }\hbox {C}$$ in presence of $$\hbox {K}_{2}\hbox {CO}_{3}$$ . The catalyst is inexpensive, recyclable and environmentally benign. The fresh and recycled catalysts were characterized by different analytical techniques. Different reaction parameters were optimized; catalyst screening, solvent, base and temperature. The protocol was extended towards different substrates. Synopsis. An efficient, robust and recyclable catalyst (Cu-Al catalyst) was developed for the synthesis of quinoxaline. A series of Cu-Al with different molar ratios of $$\hbox {Cu}^{2+}/\hbox {Al}^{3+}$$ , 2:1 (Cu-Al-1), 2.5:1 (Cu-Al-2) and 3:1 (Cu-Al-3) were prepared by co-precipitation method, followed by calcination and the activity of these catalysts was checked for the quinoxaline synthesis. Cu-Al-2 (2.5:1) was found to be the best catalyst with 95% yield of the desired product.

Gas-Phase Conversion of Glycerol to Acetol: Influence of Support Acidity on the Catalytic Stability and Copper Surface Properties on the Activity

Mesoporous mixed copper-aluminum oxides and copper-silicon oxides were synthesized with polymeric precursors route in order to evaluate the effect of the support acidity on the catalytic stability due to the carbon deposit and the copper surface characteristics on the catalytic activity for the gas-phase conversion of glycerol to acetol. The samples were characterized by different techniques such as inductively coupled plasma (ICP), thermogravimetry and differential thermal analyses (TGA-DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption isotherms, temperature-programmed reduction with H2 (H2-TPR) and microcalorimetry of NH3 adsorption. The metallic copper surface was shown by XPS, which was observed an increase with the copper loading without marked changes between Si or Al support using the same copper content. The Cu-Al catalysts present acidic properties close to that of the pure alumina support while the Cu-Si solid is not acid, as expected. Reduced catalysts were evaluated in the reaction of glycerol conversion. The catalytic results showed a clear dependence of the glycerol conversion to acetol with the Cu metal surface and the initial catalytic properties did not depend on the support acidity, since the copper is the major active site. It was observed 95% of acetol selectivity and 80% of glycerol conversion for the best catalyst. However, the support acidity influenced the catalyst stability, since Cu-Al solid deactivated continuously by contrast to Cu-Si sample, which reached stability after 2 h of reaction. The higher acidity for the Al support leads to a greater carbon deposit compared to Si support, blocking the active sites and providing a rapid catalytic deactivation.

Catalytic Hydrolysis of Hydrogen Cyanide on Cu-Al Catalyst

Cu-Al catalysts were synthesized by the co-precipitation method to study hydrolysis of hydrogen cyanide. During the synthesis, the impact of Cu/Al molar ratio, pH value and calcination temperature was investigated and the best synthesis condition was found. The results indicate that the remove of hydrogen cyanide first increases and then decreases with increasing Cu/Al molar ratio, pH value and calcination temperature, which reaches the maxima and remains above 95% at 360 min when Cu/Al molar ratio is 2:1, pH value is approximately 8.0 and calcination temperature is 400°C around. The analysis of X-ray diffraction (XRD) shows that Cu content is the main influence factor at Cu/Al molar ratio below 2:1 whereas crystallinity of catalysts is the key factor at Cu/Al molar ratio above 2:1.

INFLUENCE OF Pt ON THE PROPERTIES AND ACTIVITY OF CuO-BASED CATALYSTS FOR LOW TEMPERATURE OXIDATION OF CARBON MONOXIDE

A series of mono-oxide and multi-oxide catalysts: 10 wt.%CuO/γ-Al2O3; 10 wt.%CuO +10 wt.%Cr2O3/γ-Al2O3; 10 wt.%CuO + 20 wt.%CeO2/γ-Al2O3, and 10 wt.%CuO + 10 wt.%Cr2O3 +20 wt.%CeO2/γ-Al2O3 have been prepared and modified by Pt with contents from 0.05 up to 0.3 wt.%. Physico-chemical properties of the catalysts were determined by the methods of BET N2- Adsorption, Hydrogen Pulse Chemisorption (HPC), XRD, TPR, EDS and IR-CO adsorption. The oxidative activity of the catalysts was studied at the temperature range 75 - 300 oC and CO concentration of 0.5 mol.%. Addition of Pt led to weakening of the interaction between CuO and Al2O3, CuO and Cr2O3 that enhanced the reducibility of CuO, resulting in increase of activity of CuAl, CuCeAl and CuCrCeAl catalysts. Meanwhile, due to the reduction of CuCr2O4 formation, the activity of catalysts CuCrAl decreased. The catalyst sample CuCeAl, containing 0.1 wt.% Pt, has been shown to be the best one for the complete oxidation of CO. At the given conditions on this catalyst the complete oxidation of CO to CO2 occurred at 125 oC and space velocity 75,000 h-1 .

Kinetic Modeling of the Liquid-Phase Hydrogenation of Cinnamaldehyde on Copper-Based Catalysts

Fil: Marchi, Alberto Julio. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Investigaciones en Catalisis y Petroquimica Ing. Jose Miguel Parera. Universidad Nacional del Litoral. Instituto de Investigaciones en Catalisis y Petroquimica Ing. Jose Miguel Parera; Argentina

XRD and TPR studies of Cu-Al hydrotalcite derived highly dispersed mixed metal oxides

A series of Cu/Al catalysts, containing different proportions of copper and aluminium, have been prepared by coprecipitation using metal nitrate precursors and Na2CO3. The dried precipitate catalyst precursors were characterized by X-ray diffraction (XRD) to show the presence of Cu-Al binary hydrotalcite-like phase. The dried precipitates were calcined at 873 K for 3 h. The calcined catalysts were characterized by XRD and temperature-programmed reduction (TPR) methods to show the presence of unidentified mixed oxides. The results showed that the extent of metal-support interaction increased with copper loading due to the mixed oxides formed from the hydrotalcite-type phase during calcination. High dispersion of the mixed metal oxides was indicated by comparison with similar studies on Cu-Al catalysts, prepared by similar methods, whose precursors showed no hydrotalcite formation.

Production of Hydrogen from Methanol over Promoted Coprecipitated Cu-Al Catalysts: The Effects of Various Promoters and Catalyst Activation Methods

The influence of various promoters and activation methods on the low-temperature methanol-steam reforming performance of promoted Cu-Al catalysts was studied at atmospheric pressure in a microreactor over a reaction temperature range of 170-250 o C at a methanol space velocity (WHSV) of 16.7 h -1 . Minimum methanol conversions of 93 and 99 mol % and H 2 selectivities of 99 and 93 mol % were obtained from the Mn-promoted and vaporized feed-activated catalyst at 200 and 250 o C, respectively. The overall results showed that favorable catalyst characteristics were such that the promoter and the activation process not only conditioned the catalyst to produce optimum amounts of active Cu 0 , Cu 2 O, Cu I , and Bronsted ZnO base sites but also ensured that these catalyst sites were maintained during the reaction

The catalytic conversion of amines of the furan series into homologues of pyrrole

1. A comparative study of the hydrogenation of 1-furyl-2-methyl-aminopropane in the vapor phase at 300° on Os-C, Rh-C, and skeletal Pd-Al and Cu-Al catalysts is reported. 2. On all these catalysts the initial reaction was hydrogenolysis of the furan ring at the C-O bond not adjacent to the substituent. This led to the formation of 2-n-propyl-4-methylpyrrole (50–85%). The best catalyst for this conversion was skeletal Cu-Al (85%).