Surface Area Of Metallic Copper Research Articles

Impact of Cu complex anions on CuZnAl intercalated hydrotalcite-like catalysts for low-carbon alcohols synthesis from syngas

Elucidating the structure-performance relationship of catalysts for low-carbon alcohols synthesis from syngas is crucial for designing efficient catalysts. In this study, CuO particle size, reducibility, and the number of oxygen vacancies could be adjusted by changing intercalated Cu complex anions, thereby affecting the catalyst's performance. The characterization results indicated that the insertion of [Cu(C2O4)2]2- between ZnAl layered double hydroxide resulted in the largest CuO particles (26.5 nm), leading to an increase in the metallic copper surface area. Consequently, the highest CO conversion (13.0 %) was achieved without altering alcohol distribution. On the other hand, when [Cu(EDTA)]2- was inserted, the catalyst possessed the smallest CuO particle size (8.9 nm), more abundant oxygen vacancies, and enhanced interaction between Cu species and ZnO, which promoted carbon chain growth and resulted in a high C2+OH proportion of 75.8 %. Our study thus provides a new perspective on catalyst structures for the syngas production of low-carbon alcohols.

Influence of Al, Cr, Ga, or Zr as promoters on the performance of Cu/ZnO catalyst for CO2 hydrogenation to methanol

Different promoters can be applied to increase the activity, selectivity, and stability of the Cu/ZnO for the CO2 hydrogenation to methanol. Herein, we investigated the effect of the promoters' addition on the physicochemical properties of the Cu/ZnO-based catalysts and their performance in the CO2 hydrogenation to methanol. A series of Cu/ZnO catalysts, Cu/ZnO/X (X = Al2O3, Cr2O3, Ga2O3, ZrO2), were prepared by a co-precipitation method and characterized by XRF, XRD, SEM, TEM, TEM-EDS, H2-TPR, N2O passivation, and CO2-TPD. Under the explored conditions, the promoters enhanced the catalyst activity and selectivity to methanol in the CO2 hydrogenation reaction. The superior performance of the promoted materials was associated with the increase of specific surface area, metallic copper surface area, basicity, and the decrease of the size of copper oxide crystallites and particles. Among the investigated materials, Cu/ZnO/Ga2O3 (CZG) catalyst showed the best performance in terms of activity (XCO2, 200°C = 5.2%) and methanol selectivity (SMeOH, 200°C = 50%).

Influence of the Zn/Zr ratio in the support of a copper-based catalyst for the synthesis of methanol from CO2

CuO-ZnO-ZrO2 catalysts were synthetized by co-precipitation synthesis. Copper content in catalysts was kept constant (30 wt% of Cu °) and ZnO was gradually substituted by ZrO2 in the support to have a greater understanding of the support’s effect and to find the optimal ZnO/ZrO2 ratio. These catalysts were fully characterized and then tested in the methanol synthesis via CO2 hydrogenation. The effects of reaction temperature and GHSV on the catalytic behavior were investigated. The mix of the characterization results predicted the optimum support that is composed of 50 wt% of ZnO and 50 wt% of ZrO2 with higher metallic copper surface area and higher copper dispersion. Surprisingly the optimum catalytic results were obtained for the 30Cu-ZZ66/34 catalyst, whose support was composed of 66 wt% of ZnO and 34 wt% of ZrO2. This catalyst presented good CO2 conversion (19.6%) and methanol selectivity (50%), leading to a methanol productivity of 725 gMeOH kgCata−1 h−1 at 280 °C, 50 bar and a GHSV of 25,000 h−1 (STP). Finally, the determining factor for the best catalytic activity is not the Zn/Zr ratio. To have the optimal catalytic activity in CO2 hydrogenation to methanol other parameters should be considered as well. They are: the nature and the state of copper species over the composite support; the homogeneity of the final composite sample, the ZnO particles size, and the number of ZnO-ZrO2 interactions. The perfect combination of them all plays an important role in the determination of the best copper-based catalyst for the synthesis of methanol from CO2.

Enhanced Stability of Spatially Confined Copper Nanoparticles in an Ordered Mesoporous Alumina for Dimethyl Ether Synthesis from Syngas

A spatial confinement effect of copper nanoparticles in an ordered mesoporous γ-Al2O3, which is synthesized by an evaporation induced self-assembly (EISA) method, was investigated to verify the enhanced catalytic activity and stability with less aggregation of copper crystallites during direct synthesis of dimethyl ether (DME) from syngas. The surface acidity of the mesoporous Al2O3 and the metallic copper surface area significantly altered catalytic activity and stability. The ordered mesopore structures of Al2O3 were effective to suppress the aggregation of copper nanoparticles even under reductive CO hydrogenation conditions through the spatial confinement effect of the ordered mesopores of Al2O3 as well as the formation of strongly interacted copper nanoparticles with the mesoporous Al2O3 surfaces by partial formation of the interfacial CuAl2O4 species. The aggregation of copper nanoparticles on the bifunctional Cu/meso-Al2O3 having an ordered mesoporous structure was effectively suppressed due to the...

Facile preparation of highly efficient CuO-ZnO-ZrO2/HZSM-5 bifunctional catalyst for one-step CO2 hydrogenation to dimethyl ether: Influence of calcination temperature

CuO-ZnO-ZrO2/HZSM-5 bifunctional catalysts were prepared by a facile route of solid-state reaction and tested for one-step synthesis of dimethyl ether (DME) from CO2 hydrogenation. The effects of calcination temperature (300–600°C) on the physicochemical and catalytic properties of the bifunctional catalysts were investigated by XRD, N2 adsorption, XPS, N2O chemisorption, SEM, H2-TPR, NH3-TPD, and CO2-TPD techniques. The results show that both the CO2 conversion and DME selectivity of the bifunctional catalysts decrease with the increase in calcination temperature, which can mainly be attributed to the decrease of metallic copper surface area (SCu), adsorption capacity of CO2, specific surface area, and reducibility of CuO.

Hydrogenolysis of Glycerol over Cu/ZnO-Based Catalysts: Influence of Transport Phenomena Using the Madon–Boudart Criterion

Batch hydrogenolysis of concentrated glycerol has been conducted over different Cu/ZnO-based catalysts prepared by the coprecipitation method. The catalysts were characterized by X-ray diffraction, H2 temperature-programmed reduction, and the N2O titration technique of measurement of the metallic Cu surface area. Results show that the reaction system is affected by hydrogen pressure, temperature, glycerol concentration, and the surface area of metallic copper. Our results tend to show that the reaction scheme is more complicated than the commonly accepted dehydration–hydrogenation mechanism. Tests conducted with varying hydrogen pressure indicate that the mechanism may begin with the dehydrogenation of glycerol to glyceraldehyde. Tests conducted with varying water content tend to show that high water content favors ethylene glycol (EG) formation. The selectivity to 1,2-propanediol (12PG) versus ethylene glycol is a function of the relative reaction rates where the glyceraldehyde can react to either yield ...

CO2 hydrogenation to methanol over Cu/ZnO nanocatalysts prepared via a chitosan-assisted co-precipitation method

In this study, CuO–ZnO nanocomposites were prepared by chitosan-assisted co-precipitation method and performed as catalyst for CO2 hydrogenation to methanol. Effects of chitosan concentration on the physicochemical properties of the nanocomposites as well as the catalytic activity have been investigated. The obtained catalysts were characterized by means of scanning electron microscopy, X-ray diffraction, N2 adsorption–desorption, N2O chemisorption and temperature-programmed reduction. Chitosan was found to act not only as a coordination compound to produce a homogeneous combination of CuO–ZnO nanocomposite, but also as a soft template for the formation of hollow nanospheres. The CuO and ZnO crystallite sizes of the hollow nanospheres were found to be 11.5 and 18.8nm, respectively, which were smaller than those of other catalysts. The increase of chitosan concentration caused a change in catalyst morphology and a reduction in BET surface area as well as metallic copper surface area, but still higher than those of the unmodified catalyst. The catalysts prepared by using chitosan as precipitating agent exhibited a higher space time yield of methanol than the unmodified catalyst, which was attributed to a synergetic effect of the CuO nanoparticle incorporated in the CuO–ZnO nanocatalyst. However, when the reaction temperature was increased up to 533K, a decline in the space time yield of methanol was observed for the catalysts prepared at high chitosan concentration.

Methanol synthesis from CO2 hydrogenation over copper based catalysts

A series of Cu–ZnO/Al2O3 catalysts prepared by coprecipitation were used for methanol synthesis by CO2 hydrogenation in a fixed bed reactor system. The effect of the catalysts composition and the reaction temperature on the catalytic activity was investigated. The main results show that the highest CO2 conversion and the best yield of methanol are obtained with the catalyst containing 51 wt% Cu and 22 wt% Zn. This result is assigned to the highest metallic copper surface area and to the interaction between copper and zinc oxide. However, the reaction temperature increase is disadvantageous for the methanol synthesis reaction.

The relationship between the structure and catalytic performance Cu/ZnO/ZrO2 catalysts for hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate

The gas-phase hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate to 1,4-cyclohexane dimethanol (CHDM) was conducted on well-dispersed supported Cu/ZnO/ZrO2 catalysts. The results indicated that the structure and catalytic performance of resulting copper-based catalysts were profoundly affected by the addition of zirconium. Moreover, the as-synthesized catalyst with 35.0 wt.% ZrO2 component was found to exhibit superior catalytic performance with a high CHDM yield of 96.8% to other catalysts, which should be mainly attributed to the significant dispersion effect of ZrO2 on the copper-containing species resulting in a higher metallic copper surface area as well as a larger number of Cu+ species.

Effects of Cu–ZnO Content on Reaction Rate for Direct Synthesis of DME from Syngas with Bifunctional Cu–ZnO/γ-Al2O3 Catalyst

The effects of Cu–ZnO content on the performance of bifunctional Cu–ZnO/γ-Al2O3 catalysts for dimethyl ether (DME) synthesis from syngas were investigated by varying the weight ratios of Cu–ZnO/γ-Al2O3 prepared by the coprecipitation of Cu–ZnO in a slurry of γ-Al2O3. A higher rate of DME production with CO conversion of 47.6 % and DME selectivity of 61.1 % was observed with the bifunctional catalyst at an optimal weight ratio of CuO/γ-Al2O3 of two, providing a higher surface area of metallic copper and an abundance of weak acid sites. The number of acidic sites on solid-acid γ-Al2O3 is a more crucial factor to enhance DME yield, due to the faster dehydration rate of methanol to DME than that of CO hydrogenation to methanol. Although the first step of methanol synthesis on active copper sites is a rate-limiting step with a low equilibrium value, the second step of the dehydration of methanol to DME on acid sites adjusts the overall rate by enhancing the forward reaction rate of CO hydrogenation to methanol with a simultaneous formation of surplus hydrogen by a water–gas shift reaction. Therefore, the proper design of a high surface area of metallic copper with larger acid sites on the bifunctional CuO–ZnO/γ-Al2O3 catalysts at an optimal ratio, produced by adjusting the weight ratio of CuO/γ-Al2O3, is an important factor for improved catalytic performance.

Effect of copper surface area and acidic sites to intrinsic catalytic activity for dimethyl ether synthesis from biomass-derived syngas

The crucial effects of copper surface area and acidic sites to intrinsic catalytic activity on the bifunctional catalysts such as Cu-ZnO/Al2O3 and Cu-ZnO-Al2O3/Zr-modified ferrierite catalysts have been investigated to find out the correlation between these two characteristics for the direct synthesis of dimethyl ether (DME) from biomass-derived syngas. The well-dispersed copper particles with a high reducibility as well as a large amount of weak acidic sites on bifunctional catalysts are responsible for their high catalytic performance. The high activity for methanol synthesis could be obtained by designing a high surface area of metallic copper with a low aggregation character, however, the quantity of the acidic sites on solid-acid components is also crucial factor for a high DME yield than the surface area of copper, which could be obtained by preparing proper bifunctional catalysts. It is mainly due to the fast reaction rate of methanol dehydration to DME compared to CO hydrogenation to methanol. The two important characteristics of the metallic surface area of copper and the amount of acidic sites are well correlated with the intrinsic catalytic activity on this consecutive reaction. The intrinsic activity for the direct DME synthesis from syngas on bifunctional catalysts initially decreases and maintains at constant value with the increase of the values of the copper surface area multiplied by the amount of acidic site.

Study on factors controlling catalytic activity for low-temperature water–gas-shift reaction on Cu-based catalysts

Influence of metal oxide added to Cu catalysts on the catalytic activity of the low-temperature water-gas-shift (LT-WGS) reaction was investigated. Catalytic activity was linearly correlated with both surface area of metallic copper (Cu0) and surface Cu content in the identical copper-metal oxide system. However, activity per Cu0 surface area changed depending on the metal oxide added. CO2-TPD profile demonstrated that the amount of strong basic sites on Cu–ZnOx and Cu–AlOx catalysts with high activity LT-WGS reactions was much less than those on Cu–FeOx and Cu–CeOx catalysts with low activity. Activity per Cu0 surface area increased with increasing amount of weak basic sites on Cu–AlOx and Cu–ZnOx catalysts. From these results, it is suggested that in addition to Cu0 surface area, basicity of a catalyst is one of the factors controlling the catalytic activity of Cu-based catalysts for LT-WGS reaction.

Preparation of Cu/ZnO/Al2O3 catalysts in a solvent-free routine for CO hydrogenation

The synthesis of methanol and dimethyl ether (DME) from CO hydrogenation has been investigated on Cu-based catalysts. A series of Cu/ZnO/Al2O3 catalysts were prepared using a solvent-free routine which involved a direct blend of copper/zinc/aluminum salts and citric acid, followed by calcination at 450 °C. The calcination processes were monitored using thermogravimetry differential scanning calorimetry (TG-DSC). Catalysts were further characterized using N2 adsorption, scanning electronic microscopy (SEM), X-ray diffraction (XRD), N2O oxidation followed by H2 titration, and temperature-programmed reduction with H2 (H2-TPR). The reduction processes were also monitored with in-situ XRD. The physicochemical properties of catalysts depended strongly on the types of precursor salts, and catalysts prepared using Al acetate and Cu nitrate as starting materials had a larger surface area, larger exposed metallic copper surface area, and lower reduction temperature. The CO hydrogenation performances of these catalysts were compared and discussed in terms of their structures. Catalysts prepared with copper nitrate, zinc and aluminum acetates exhibited the highest catalytic activity.

Catalytic performance on CuO–Cr2O3–Ga2O3 mixed oxides for water gas shift reaction: Effects of Ga/Cr molar ratio

Water gas shift (WGS) reaction was carried out on the coprecipitated CuO–Cr2O3–Ga2O3 mixed oxides to elucidate the effects of Ga2O3 species to catalytic performances. WGS catalysts are prepared at a fixed molar ratio of Cu/(Cr + Ga) at 1.0/0.1 by varying Ga/Cr molar ratio from 0 to 4. The catalytic activities on CuO–Cr2O3–Ga2O3 are found to be in the shape of volcano curve in terms of Ga/Cr molar ratio and the highest activity was observed on the catalyst having equimolar ratio of Ga/Cr in all tested temperature ranges of 160–280 °C. The observed activities are strongly related with the metallic surface area of copper crystallites, and the high surface area of metallic copper could be obtained by controlling the formation rate of copper–chromium nuclei at an optimum Ga/Cr molar ratio on CuO–Cr2O3–Ga2O3 mixed oxides.

Effect of Copper Precursors to the Activity for Dimethyl Ether Synthesis from Syngas over Cu–ZnO/γ-Al2O3 Bifunctional Catalysts

The effect of precursors, such as copper nitrate, acetate, and chloride, on the bifunctional Cu–ZnO/γ-Al2O3 catalysts was investigated for the direct dimethyl ether (DME) synthesis from syngas. The catalysts were characterized by measuring the reducibility and the surface area of metallic copper, together with their acidity. The well-dispersed copper particles with a high reducibility as well as a large amount of weak acidic sites on the bifunctional Cu–ZnO/γ-Al2O3 catalysts, prepared from a copper acetate precursor, are responsible for its high catalytic activity. The quantity of the acidic sites is a more crucial factor for obtaining a high DME yield than the surface area of metallic copper on the bifunctional catalyst.

The influence of B-doping on the catalytic performance of Cu/HMS catalyst for the hydrogenation of dimethyloxalate

The influence of boron introduction on the performance of 20 wt.% Cu/HMS catalysts for the catalytic hydrogenation of dimethyloxalate was systematically investigated. It is shown that the boron loading, boron source and the preparation method all have great effect on the catalytic behaviors of the catalyst. Characterization methods including N 2-physisorption, X-ray diffraction, H 2-temperature-programmed reduction, N 2O titration, NH 3 temperature-programmed desorption, and X-ray photoelectron spectroscopy were carried out to elucidate the structure evolution of the catalyst with the introduction of boron. Experimental results showed that the B 2O 3 modified catalyst prepared via the ammonia-evaporation-induced synthesis method exhibited the highest conversion and ethylene glycol selectivity because of the higher metallic copper surface area and copper dispersion. The optimum Cu/B mole ratio, which strongly affects the surface composition of the catalyst, was found to be 2/1. 100% DMO conversion and 98% EG selectivity could be obtained over the CuB/HMS(2/1) catalyst under 2.5 h −1 liquid hour space velocity, which is almost four times higher than that of the one without boron introduction.

Glycine–nitrate combustion synthesis of CuO–ZnO–ZrO 2 catalysts for methanol synthesis from CO 2 hydrogenation

A series of CuO–ZnO–ZrO 2 (CZZ) catalysts were synthesized by a glycine–nitrate combustion method and characterized by XRD, BET, N 2O chemisorption, SEM and TPR techniques. The results show that the physicochemical properties of the catalysts are strongly influenced by the fuel content used in the combustion process. The dispersion of CuO exhibits an inverse-volcano variation trend with an increase in the glycine amount from 50% to 150% of the stoichiometry. The relationship between physiochemical properties and the fuel content is discussed in detail in terms of combustion temperature. The catalytic performance for the synthesis of methanol from CO 2 hydrogenation was examined. The CZZ catalyst exhibits an optimum catalytic activity when 50% of stoichiometric amount of glycine was used. The turnover frequency has been calculated for various CZZ catalysts, and it reveals that the catalytic activities depend not only on the surface area of metallic copper but also on the phase state of ZrO 2.

Ion‐Exchange Temperature Effect on Cu/HMS Catalysts for the Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

AbstractA series of Cu/HMS (HMS=hexagonal mesoporous silica) catalysts, synthesized by ion exchange at temperatures from 303 to 363 K, are extensively investigated as catalysts for the hydrogenation of dimethyl oxalate to ethylene glycol. The physicochemical properties and catalytic activity are compared with those of a catalyst prepared by the conventional impregnation method. Characterization of the Cu/HMS catalysts shows that the surface and textural structure of the HMS support as well as the dispersion and nature of copper species depend strongly on the ion‐exchange temperature. Temperature‐programmed reduction patterns reveal the presence of three types of copper species. N2O titration experiments show that the catalyst prepared by ion‐exchange treatment at 333 K has the highest metallic copper surface area. A 98 % ethylene glycol yield is attained over the catalyst ion‐exchanged at 333 K, illustrating that an optimum ion‐exchange temperature is beneficial for the generation of copper catalysts with enhanced activity.

Influence of the preparation methods and redox properties of Cu/ZnO/Al 2O 3 catalysts for the water gas shift reaction

Different coprecipitation sequences were used to prepare Cu/ZnO/Al 2O 3 catalysts for the water gas shift reaction. The interdispersion of the components of the obtained mixture of hydroxycarbonates seemed to be influenced by the coprecipitation sequence, at constant pH and temperature. High metallic copper surface area was observed when Cu 2+ and Zn 2+ ions were simultaneously coprecipitated. A remarkable activity was found to be related to the catalyst ability to restore the copper surface dispersion after reduction or oxidation pre-treatment. These last findings were evidenced by temperature-programmed reduction and X-ray photoelectron spectroscopy experiments.

Synthesis of DME from syngas on the bifunctional Cu–ZnO–Al2O3/Zr-modified ferrierite: Effect of Zr content

The catalytic activity on the coprecipitated Cu–ZnO–Al2O3/Zr-ferrierite (CZA–ZrFER) with different Zr content from 0 to 5wt.% was investigated for the direct synthesis of dimethylether (DME) from H2-deficient and biomass-derived model syngas (H2/CO molar ratio=0.93). The catalytic functionalities, such as CO conversion and DME selectivity, showed their maxima on the bifunctional catalyst with 3wt.% Zr-modified ferrierite. Detailed characterization studies were conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH3-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), copper surface area measurements by N2O titration method, electronic states of copper by IR analysis and particle size measurement by XRD and TEM analysis. The number of acid sites measured by NH3-TPD on the bifunctional catalysts decreased monotonously with the increase of Zr content, meanwhile, the acidic strength is found to be minimal on the catalyst showing best performance. The reducibility of copper oxide and the surface area of metallic copper also exhibited their maximum values at the same Zr composition indicating that these are responsible for the optimum functionality of the bifunctional CZA–ZrFER catalyst. The role of easily reducible copper species with small particle size and the suppressed strong acidic sites is also emphasized in the consecutive reaction from syngas to DME on the bifunctional catalyst. The different behavior of intrinsic rate of the bifunctional catalysts is also well correlated with the metallic surface area of copper and the amount of acidic sites with their acidic strength.