CuO-ZnO Catalysts Research Articles

Rich oxygen vacancies in core–shell structured Co3O4-CuO-ZnO@ZIF-8 for boosting CO2 hydrogenation to methanol

Converting carbon dioxide (CO2) into high-quality methanol to alleviate the energy crisis is a promising strategy. However, as a traditional catalyst for CO2 hydrogenation to methanol, Cu/ZnO exhibits low CO2 conversion and low methanol selectivity at low temperature. In order to improve the catalytic performance of CO2 hydrogenation to methanol, Co3O4 was introduced to form Co3O4-CuO-ZnO with flower-like structure, and then diamond-shaped ZIF-8 particles with large specific surface area and rich oxygen vacancies were synthesized on the surface of Co3O4-CuO-ZnO by hydrothermal method. A series of characterizations showed that the synthesis of ZIF-8 greatly increased the specific surface area of the catalyst. The oxygen vacancy is the site of CO2 adsorption and activation, and stabilizes the reaction intermediate, which promotes the conversion of CO2 and the formation of methanol. The introduction of Co promotes the formation of the alloy phase, enhances the interaction between the metals, makes the active center more dispersed, reduces the sintering of the catalyst, and thus exhibits better catalytic performance. Among co-precipitated CuO-ZnO, hydrothermal CuO-ZnO, CuO-ZnO@ZIF-8, Co3O4-CuO-ZnO and Co3O4-CuO-ZnO@ZIF-8 catalysts, Co3O4-CuO-ZnO@ZIF-8 exhibits the best catalytic performance (CO2 conversion 16.06% and CH3OH selectivity 94.58%). Based on the above design, ZIF-8 and Co3O4 synergistic CuO-ZnO catalyst effectively improved CO2 conversion and CH3OH selectivity.

Effect of CuO–ZnO catalyst layer on proton-conducting electrochemical cell reactor for CO2 reduction reaction

A catalyst layer is coated on the fuel electrode in a proton-conducting solid oxide electrolysis cell reactor, which can optimize electrochemical performance and expand the application range of the reactor. In this work, CuO–ZnO catalyst is prepared by oxalate co-precipitation method and combined with a single cell to obtain a reactor with the structure of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) ǀ BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) ǀ NiO-BZCYYb (active layer) ǀ NiO-BZCYYb (support layer) | CuO–ZnO (catalyst layer). The electrolysis current density of this reactor with humid air as oxidant and 20%CO2–80%H2 as fuel is 2751 mA cm−2 under 1.3 V at 750 °C. It operates steadily for 138 h under 1.3 V electrolysis at 650 °C, which is better than the reactor without a catalyst layer under this condition. Additionally, CO and CH4 are detected in the exhaust gas on the fuel electrode side, and the CO selectivity reaches over 90% at 750-550 °C.

CuO–ZnO catalyst decorated on porous CeO2-based nanosheets in-situ grown on cordierite for methanol steam reforming

Development of efficient and durable structured catalysts for hydrogen production by methanol steam reforming (MSR) is becoming extremely appealing owing to their low pressure drop and large open area. In this work, porous CeO2-based nanosheet array is in-situ grown on the surface of cordierite honeycomb ceramic by a simple hydrothermal approach. The generated porous nanosheet structure not only surpasses the obstacle of low specific surface area of cordierite (increasing from 4.4 to 252.6 m2 g-1), but also the peak area ratio of oxygen vacancies on the support surface rises from 19.7% to 29.7%, which are favorable to promote the catalytic activity and reduce by-product CO selectivity of structured catalysts in MSRreaction. Importantly, the structured catalysts formed by decorating CuO–ZnO catalysts on CeO2-based nanosheets via sol-gel combustion method remain porous structure, offering an ideal space for reactant entry and mass transfer diffusion, which facilitates reaction triggering and product discharge. The optimal structured catalyst achieves 100% methanol conversion at 260 °C without CO and the methanol conversion remains at 94.7% after 100 h of the reaction, exhibiting the excellent catalytic activity and durability. Thus, the structured catalyst has potential for industrial-scale preparation and application, especially for on-site hydrogen production in vehicles.

Molecular-level understanding of interfacial carbonates in stabilizing CuO-ZnO(Al2O3) catalysts

A descriptor of active CuO-ZnO(Al2O3) methanol-synthesis and water–gas-shift catalysts is the presence of high-temperature carbonates (HT-CO3) in the oxidic catalyst precursor. Previous reports have shown that such HT-CO3 lead to an appropriate interaction between the oxides; as a result, a high Cu surface area (or Cu-Zn or Cu/ZnO interphase areas) can be achieved. Yet, their nature is not well understood. In this study, the nature of these carbonates was investigated by experimental and theoretical methods in the oxidic precatalyst. A calcined Cu-Zn-Al hydrotalcite model compound revealed to have well-dispersed ZnO and CuO phases, together with highly stable HT-CO3. It was hypothesized that these HT-CO3 groups may be placed at critical locations at nano-scale as a glue, thus avoiding the growth of the oxide crystallites during calcination. This is an excellent pre-condition to achieve a high Cu surface area (or Cu-Zn or Cu/ZnO interphase areas) upon reduction, and therefore a high activity. To prove that, first-principles calculations were carried out based on the density functional theory (DFT); alumina was not considered in the model as the experimental data showed it to be amorphous but it may still have an effect. Comprehensive calculations provided evidence that such carbonate groups favourably bind the CuO and ZnO together at the interface, rather than being isolated on the individual oxide surfaces. The results strongly suggest that the HT-CO3 groups are part of the structure, in the calcined precatalyst, where they would prevent thermal sintering through a bonding mechanism between CuO and ZnO particles, which is a novel interpretation of this important catalyst descriptor.

Fe–Ni–Ce–Zr-modified CuO–ZnO catalyst for methanol steam reforming

Four copper-based catalysts were prepared by co-precipitation method. The catalysts were characterized by scanning electron microscopy, N2 adsorption-desorption, temperature programmed reduction process (H2-TPR), X-ray diffraction (XRD) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) to explore the effects of different components on catalyst activity. The performance of different catalysts for hydrogen production via methanol steam reforming was evaluated on a fixed-bed reactor. The effects of different components, reaction temperature and gas hourly space velocity (GHSV) on the catalytic performance were investigated. The results exhibited that among the investigated catalysts, 1# and 2# catalysts had the higher catalytic activity and stability. Under the conditions of 280 °C, a molar ratio of methanol to water of 1:1.3, and a GHSV of 13.3 L/(g·h), the methanol conversion rate reached 99.9%, the CO concentration was as low as 0.29%, and the selectivity was only 1.16%. The H2 production flow rate per unit mass of catalyst was 270 mL/(min·g). After 60 h of start-stop experiments, the methanol conversion rate remained above 98.4%, the CO concentration was always lower than 0.5%, and the start-up speed was significantly faster than that of the commercial catalyst M650. This study provided an effective method for the preparation of catalysts for methanol steam reforming.

Surface conversion of CuO–ZnO to ZIF-8 to enhance CO2adsorption for CO2hydrogenation to methanol

A novel CuO–ZnO@ZIF-8 catalyst with abundant oxygen vacancies and high CO2adsorption capacity is synthesized for converting CO2into CH3OH. Compared to the traditional CuO–ZnO catalyst, the catalyst in this work significantly improves the conversion and selectivity.

Hydrogen production by supercritical water gasification of lignin over CuO–ZnO catalyst synthesized with different methods

In this study, lignin was gasified in supercritical water with catalysis of CuO–ZnO synthesized by deposition precipitation, co-precipitation and sol-gel methods. Sol-gel synthesized CuO–ZnO showed the highest catalytic performance, and the gasification efficiency was increased by 37.92% with it. The XRD, SEM-EDS and N2 adsorption/desorption analysis showed that the priority of the sol-gel catalyst was the smallest crystallite size, largest specific surface area and high dispersion. For sol-gel synthesized CuO–ZnO, the increase of CuO/ZnO ratio improved the gasification efficiency but reduced H2 selectivity. And the catalytic activity was reduced with the calcination temperature above 600 °C due to enlarged crystallites and reduced pores. During sol-gel preparation, both the addition of ethanol and PEG in the solvent reduced the agglomeration and improved the catalytic activity. With CuO–ZnO prepared with 1 g PEG + water as the solvent, the highest H2 yield of 6.86 mol/kg was obtained, which was over 1.5 times of that without catalyst.

Role of preparation parameters of Cu–Zn mixed oxide catalyst in solvent free glycerol carbonylation with urea

Solvent-free carbonylation of glycerol with urea to glycerol carbonate (GC) was achieved over heterogeneous Cu–Zn mixed oxide catalyst. Cu–Zn catalysts with different ratios of Cu:Zn were prepared using co-precipitation (CP) and oxalate gel (OG) methods. As compared to CuO–ZnO(2:1) catalyst prepared by oxalate gel (OG) method, much higher conversion of glycerol and highest selectivity towards glycerol carbonate (GC) was achieved with CuO–ZnO_CP(2:1) catalyst. Physicochemical properties of prepared catalysts were investigated by using XRD, FT-IR, BET, TPD of CO2 and NH3 and TEM techniques. The effect of stoichiometric ratio of Cu/Zn, calcination temperature of CuO–ZnO catalysts and effect of reaction parameters such as molar ratio of substrates, time and temperature on glycerol conversion to GC were critically studied. Cu/Zn of 2:1 ratio, glycerol–urea 1:1 molar ratio, 145 ​°C reaction temperatures were found to be optimized reaction conditions to achieve highest glycerol conversion of 86% and complete selectivity towards GC. The continuous expel of NH3 from reaction the mixture avoided formation of ammonia complex with CuO–ZnO catalyst. As a result of this, CuO–ZnO catalyst could be recycled up to three times without losing its initial activity.

Effect of Precipitated Precursor on the Catalytic Performance of Mesoporous Carbon Supported CuO-ZnO Catalysts

As part of concepts for chemical energy storage of excess chemical energy produced from renewable sources, we investigated the performance of CuO/ZnO catalysts supported on mesoporous carbon to convert CO2 hydrogenation to methanol. In this work, mesoporous carbon was used as the catalyst support for CuO-ZnO catalysts. Four catalysts with different precipitated precursors were synthesized and analyzed by N2-physisorption, X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that catalyst CZ-in situ had the highest turnover frequency (TOF) (2.8 × 10−3 s−1) and methanol production rate (0.8 mmol g−1·h−1). The catalysts for co-precipitation of copper and zinc on carbon precursors are more active. Cu/ZnO domains that are accessible to the reactant gas are another reason for the catalysts being active. The Cu-ZnO interface is crucial to methanol catalyst activity.

Impact of oxygen vacancy in CuO-ZnO catalysts on the selectivity of dimethyldichlorosilane monomer in the Rochow reaction

Abstract In metal oxides, oxygen vacancies (OV) are ubiquitous and intrinsic defects that can pronouncedly impact the physicochemical properties of the catalysts. In this work, we investigated the effect of the OV concentration in CuO-based catalysts on the performance of the Rochow reaction. A series of foamed CuO-ZnO composite catalysts with a highly porous structure were synthesized by a facile co-precipitation method, followed by hydrogen reduction at different times. When used in the Rochow reaction to synthesize dimethyldichlorosilane (M2), the CuO-ZnO-20 catalyst with an appropriate OV concentration exhibited the highest M2 selectivity at a similar Si conversion level of the other CuO-ZnO catalysts with different OV concentrations. By correlating the structure and performance of the catalysts, we found that the OV at an appropriate concentration in CuO-ZnO-20 acted as the adsorption sites for the reactant CH3Cl molecules, and generated an optimized electronic structure for surface CuO as confirmed by the X-ray photoelectron spectroscopy analysis (XPS), thereby optimizing the adsorption strength of CH3Cl and ultimately promoting the formation of alloyed CuxSi active phase. This work provides an effective strategy for designing heterogeneous catalysts with high selectivity by controlling the OV concentration in the catalysts.

CO2 Hydrogenation to Methanol and Methane over Carbon-Supported Catalysts

Methanol and methane are among the important products obtained during the hydrogenation (HYD) of CO2. The distribution of products and their yields can be influenced by operating conditions. In this case, the type of catalyst has a dominant effect. Gradual transformation of CO2 involves several surface intermediates. Special geometry of active site is required for maximizing the yield of methanol and for minimizing the reaction run-away to methane. Such a state can be attained over catalysts that contain CuO-ZnO components. Catalysts containing other transition metals and noble metals are less suitable, while the same catalysts exhibit good performance during the HYD of CO2 to methane. In industrial applications, catalysts supported on oxidic supports, i.e., Al2O3, SiO2, TiO2, etc., have been used. During HYD of CO2, 1 and 2 mol of water are generated for every mole of methanol and methane, respectively. The stability of catalysts used for HYD of CO2 can be enhanced by replacing oxidic supports with carbon supports. Amorphous carbons, such as activated carbon, and carbon nanomaterials, such as carbon nanotubes, carbon nanofibers, and graphene-derived solids, have been tested both as catalysts and supports. For methanol synthesis, CuO-ZnO catalysts supported on these carbons have been evaluated. Similar carbon supports have been used for the preparation and testing of methanation catalysts consisting of a wide range of transition and noble metals as active metals. Both monometallic and bimetallic catalysts were evaluated.

Synthesis of light olefins from CO2 hydrogenation over (CuO-ZnO)-kaolin/SAPO-34 molecular sieves

Abstract Cu Zn oxide/SAPO-34 molecular sieves was used as bifunctional catalyst for the direct synthesis of light olefins from CO2 and H2, but the production of SAPO-34 molecular sieves required high cost and the Cu Zn oxide (CuO-ZnO) particles were prone to sintering, which severely restricted its industrial application. Herein, kaolin was used as raw material to prepare SAPO-34 molecular sieves and as supports to prepare kaolin-supported CuO-ZnO catalysts. The samples were characterized by X-ray diffraction, Scanning Electron Microscope, Energy Dispersive Spectroscopy, N2 sorption, H2 temperature programmed reduction, NH3 temperature programmed desorption and Fourier Transforms Infrared spectra techniques. The results showed that the SAPO-34 molecular sieves presented lamellar structure and the CuO-ZnO particles were well dispersed on the surface of kaolin. The results of catalytic reaction for the direct synthesis of light olefins from CO2 and H2 indicated that the (CuO-ZnO)-kaolin/SAPO-34 molecular sieves could enhance not only the yield of light olefins, but also the lifetime.

Enhanced activity of CuO/ZnO catalyst on the decomposition of dimethylhexane-1,6-dicarbamate into dimethylhexane-1,6-diisocyanate

To decompose dimethylhexane-1,6-dicarbamate (HDC) to hexamethylene diisocyanate (HDI), mixed CuO and ZnO catalysts with Cu/(Cu + Zn) ratio of 4 and 8% were prepared by coprecipitation (CP), sequential precipitation (SP) and incipient wetness impregnation (IW). The SP-derived CuO/ZnO catalysts showed higher HDC yields than those derived by CP and IW. The IW method produced CuO/ZnO catalysts consisting of larger CuO and ZnO particles compared to the two precipitation methods. The CP method led to substitution of Zn2+ by Cu2+ in the hydrozincite precursor phase, resulting in higher BET and Cu surface areas of CuO–ZnO catalysts due to intimate intergrowth of nano-sized particles. However, the inherent character of ZnO in the CP-derived catalysts was modified by interfacial contact between CuO and ZnO identified by UV–visible and Raman spectra. In contrast, the properties of CuO and ZnO, as well as the relatively large surface areas, were kept in the SP-derived catalysts owing to deposition of Cu precipitates to fully aged Zn precipitates. This is believed to be a benefit of the SP method for the reaction. Therefore, our preparation approach has great potential to be extended to various mixed oxide catalysts.

Optimization of the Zr Content in the CuO-ZnO-ZrO2/SAPO-11 Catalyst for the Selective Hydrogenation of CO+CO2 Mixtures in the Direct Synthesis of Dimethyl Ether

Zr incorporation in the CuO-ZnO catalyst for methanol synthesis from CO+CO2 mixtures, for its later use in the bifunctional catalyst conformation for dimethyl ether (DME) direct synthesis, has been studied. Different Cu/Zn/Zr ratio catalysts were prepared, via coprecipitation method, and characterized regarding to physical, chemical, structural, and metallic properties. Specific Cu surface area and dispersion are responsible for boosting the activity of CuO-ZnO based catalysts, which increases when incorporating ZrO2. Based on the kinetic behavior (COx conversion and methanol yield and selectivity) and stability in the methanol synthesis, CZZr1 (Cu:Zn:Zr = 2:1:1) was selected as the most suitable metallic function, with 8.14% of COx conversion and methanol selectivity over 98%. A bifunctional catalyst was prepared by physical mixture of CZZr1 with SAPO-11. The bifunctional catalyst activity was tested on the DME direct synthesis, showing a good performance providing a high DME yield and selectivity, with ...

Effect of Gallium Loading on Reducibility and Dispersion of Copper-Based Catalyst

The effect of gallium-promoted copper-based catalysts has been investigated in connection with the characteristic of the active copper phase. CuO-ZnO-Ga2O3catalysts with different gallium loadings were prepared using oxalate co-precipitation method. The effects of gallium loading on the properties of catalysts were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature-programmed reduction (TPR). The dispersion and metal area of copper were also determined by dissociative nitrous (N2O) adsorption technique conducted on a metal dispersion analyzer (BELCAT). The TPR profiles showed that the presence of two different reduction regions in the CuO-ZnO catalysts can be attributed to the reduction of highly dispersed copper oxide species (reduced at 246 °C) and bulk-like CuO (reduced at above 390 °C). By contrast, the only low-temperature reduction peak was presented in the TPR profiles after the Ga2O3loading was higher than 4 wt%. With the same molar ratio (Cu/Zn = 2:1), the reducibility of CuO-ZnO-Ga2O3was found to be more facile than CuO-ZnO due to the lower copper oxide crystallite sizes of gallium-promoted catalysts. Higher Ga2O3loadings resulted in an increase in both copper dispersion and metal surface area of all the catalysts studied in good agreement with the reduction behaviors in the TPR profiles, although all the gallium-promoted catalysts were slightly different for the reducibility.

Effect of TiO2, ZrO2, and TiO2–ZrO2 on the performance of CuO–ZnO catalyst for CO2 hydrogenation to methanol

The influence of TiO2, ZrO2, and TiO2–ZrO2 mixed oxide on the catalytic performance of CuO–ZnO catalyst in the methanol synthesis from CO2 hydrogenation was studied. The catalysts were prepared by oxalate co-precipitation method and characterized by TGA, N2 adsorption, XRD, reactive N2O adsorption, XPS, H2-TPR, H2-TPD, and CO2-TPD techniques. Characterization results reveal that all the additives improve the CuO dispersion in the catalyst body and increase the Cu surface area and adsorption capacities of CO2 and H2. The results of catalytic test reveal that the additives increase both the CO2 conversion and methanol selectivity, and TiO2–ZrO2 mixed oxide is more effective than single components of TiO2 or ZrO2. Moreover, the activity of methanol synthesis is correlated directly with CO2 adsorption capacity over the catalysts.

Nanosized CuO and ZnO Catalyst Supported on Honeycomb-Typed Monolith for Hydrogenation of Carbon Dioxide to Methyl Alcohol

The greenhouse effect of carbon dioxide (CO2) has been recognized as one of the most serious problems in the world. Conversion of CO2 to methyl alcohol (CH3OH) was studied using catalytic chemical methods. Honeycomb-typed monolith used as catalyst support was 400 cell/inch2. Pretreatment of the monolith surface was carried out by thermal treatment and acid treatment. Monolith-supported nanosized CuO-ZnO catalysts were prepared by wash-coat method. The prepared catalysts were characterized by using SEM, TEM, and XRD. The catalytic activity for CO2 hydrogenation to CH3OH was investigated using a flow-type reactor with varying reaction temperature, reaction pressure and contact time. Conversion of CO2 was increased with increasing reaction temperature, but selectivity to CH3OH was decreased. Optimum reaction temperature was about 250 degrees C under 20 atm. Because of the reverse water gas shift reaction.

Methanol Synthesis from CO2 Hydrogenation over CuO–ZnO–TiO2 Catalysts: The Influence of TiO2 Content

AbstractA series of CuO–ZnO–TiO2 catalysts with various TiO2 loadings were prepared by using a co‐precipitation method. The prepared catalysts were characterized by using X‐ray diffraction (XRD), N2 adsorption, reactive N2O adsorption, X‐ray photoelectron spectroscopy (XPS), temperature‐programmed reduction (TPR), hydrogen temperature programmed desorption (H2‐TPD), and CO2‐TPD techniques, and tested the extent of methanol synthesis from carbon dioxide (CO2) hydrogenation. The results indicate that the addition of TiO2 to the CuO–ZnO catalyst makes the copper species exist in an amorphous‐like structure or in much smaller crystallites, which promotes the reduction of CuO. Upon increasing the TiO2 loading, the metallic Cu surface area (SCu) of the catalyst rises first and then decreases, exhibiting a maximum at a TiO2 loading of 10 %. The results of the catalytic experiments reveal that the addition of TiO2 favors the production of methanol, and an optimum catalytic activity is obtained at a TiO2 loading of 10 %. Moreover, the methanol yield increases linearly with the SCu of the catalysts, thereby indicating that the addition of TiO2 enhances the SCu but not the intrinsic activity.

Synthesis of dimethyl ether from syngas over core–shell structure catalyst CuO–ZnO–Al2O3@SiO2–Al2O3

A core–shell structure catalyst, CuO–ZnO–Al2O3@SiO2–Al2O3, with commercial methanol synthesis catalyst CuO–ZnO–Al2O3 as the core and amorphous SiO2–Al2O3 as the shell, was prepared by facile hydrothermal treatment. In the synthesis procedure, the core–shell catalyst was synthesized using tetraethylorthosilicate, silica sol, or water glass as the silica source, aluminum nitrate as the aluminum source, and without using any aid, alkali or amine template to avoid etching of core material, CuO–ZnO–Al2O3. The core–shell structure and acidic property of the catalyst materials were characterized by XRD, SEM and NH3-TPD. The results indicated that an amorphous SiO2–Al2O3 shell coated the surface of the core materials. The thickness of shell and acidity of the catalysts could be altered by adjusting the quantity of silicon source added. The core–shell structure catalysts were utilized as bifunctional catalysts in the syngas to dimethyl ether reaction (STD). The acidity and the thickness of the shell affect the catalytic performance in the STD reaction. The conversion of CO and the selectivity of dimethyl ether on the core–shell catalyst, with moderate acidity and suitable shell thickness, are 71.1% and 61.9%, respectively.

C2–C4 hydrocarbons synthesis from syngas over CuO–ZnO–Al2O3/SAPO‐34 bifunctional catalyst

AbstractBACKGROUNDThe synthesis of C2–C4 hydrocarbons from coal or biomass‐derived syngas has received increasing attention because of the resource constraints of petroleum. The present study explores direct production of hydrocarbons from syngas over bifunctional catalyst containing methanol synthesis catalyst CuO–ZnO–Al2O3 (CZA) and SAPO‐34 zeolite.RESULTSThe synthesis of C2–C4 hydrocarbons from syngas was investigated over CZA/SAPO‐34 bifunctional catalyst at temperatures ranging from 240 to 440°C. The results indicate that higher temperatures aggregate Cu metal and lead to the deactivation of CZA. The predominant products are dimethyl ether (DME) and methanol at temperatures from 280 to 360°C and a small amount of hydrocarbons are found due to the deactivation of SAPO‐34 caused by a type of coke named ‘inert coke’. While 96.5% selectivity of C2–C4 hydrocarbons in products of all hydrocarbons can be obtained at 400°C with less coke named ‘active coke’.CONCLUSIONReaction temperatures have significant effect on the selectivity of C2–C4 hydrocarbons and coke species of SAPO‐34. The ‘active coke’ of poly methyl‐substituted benzene/naphthalene (MB/MN) acts both as an intermediate and as coke deposition. The ‘inert coke’ of poly methyl‐substituted adamantine (MA) and other groups‐substituted benzene/naphthalene acts only as coke depositions. Comprehensive consideration of the characteristics of this bifunctional catalyst, shows that a moderate temperature for C2–C4 hydrocarbons synthesis from syngas might be approximately 400°C. © 2014 Society of Chemical Industry