CuO ZnO Al2O3 Catalysts Research Articles

Microrod networks CuO–ZnO–Al2O3 catalyst for methanol synthesis from CO2: Synthesis, characterization, and performance demonstration

Microrod-shaped CuO–ZnO–Al2O3 (CZA) catalysts are synthesized in a single-step hydrothermal method. Several characterization techniques, such as XRD, SEM, BET, XPS, H2-TPR, HR-TEM, and CO2-TPD, are used to investigate the physico-chemical properties of the prepared catalysts. A bench-scale high-pressure fixed-bed flow reactor is used to evaluate the performance of the synthesized catalysts. XRD analysis confirmed the presence of monoclinic CuO and hexagonal ZnO phases in the CZA catalysts. A uniform distribution of interconnected microrod-like morphology is observed in the CZA-4 catalyst. The metal dispersion, metal-support interactions, and surface basicity of CZA-4 are significantly improved during the hydrothermal synthesis under the continuous stirring and addition of CTAB, which positively impacts the CO2 conversion (14%) and methanol yield (7%). The CO2 conversion and methanol yield increases in the following order CZA-3 < CZA-1 < CZA-2 < CZA-4. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis confirmed the formate-methoxy pathway for methanol formation.

Pd-modified CuO-ZnO-Al2O3 catalysts via mixed-phases-containing precursor for methanol synthesis from CO2 hydrogenation under mild conditions

A series of palladium-modified (Pd-modified) CuO-ZnO-Al2O3 (CZA) catalysts with various Pd loadings (0.3 wt% to 2.4 wt%) were prepared using the wetness impregnation method, on two CZA supports with different structures that are CZA-aged precursor composed of a mixture of zincian-malachite and hydrotalcite-like phases (CZA-zH), and CuO-ZnO-Al2O3 metal oxide nanoparticles (CZA-MO). Enhancement on catalytic activity can be observed on both Pd-modified CZA catalysts in a temperature range of 180–240 °C for methanol synthesis via CO2 hydrogenation. Pd/CZA-zH catalysts exhibited a more efficient and stable production of methanol at a relatively low reaction temperature of 180 °C for 100 hrs of reaction. The improvement of activity is mainly ascribed to a higher surface area and abundant oxygen-containing functional groups (e.g., –OH) of CZA-zH support, which is beneficial for better adsorption and distribution of Pd promoter. Hydrogen temperature programmed reduction and X-ray photoelectron spectroscopy results demonstrated a better interaction between Pd and Cu on Pd/CZA-zH catalysts via enhanced reducibility of CuO, and peak shift of Cu to a lower binding energy. The difference in the efficient utilization of hydrogen spillover effect of Pd promoter over two CZA supports resulted in the different performances for methanol synthesis under mild reaction conditions.

Ultra-thin ZrO2 overcoating on CuO-ZnO-Al2O3 catalyst by atomic layer deposition for improved catalytic performance of CO2 hydrogenation to dimethyl ether

An ultra-thin overcoating of zirconium oxide (ZrO2) film on CuO-ZnO-Al2O3 (CZA) catalysts by atomic layer deposition (ALD) was proved to enhance the catalytic performance of CZA/HZSM-5 (H form of Zeolite Socony Mobil-5) bifunctional catalysts for hydrogenation of CO2 to dimethyl ether (DME). Under optimal reaction conditions (i.e. 240 °C and 2.8 MPa), the yield of product DME increased from 17.22% for the bare CZA/HZSM-5 catalysts, to 18.40% for the CZA catalyst after 5 cycles of ZrO2 ALD with HZSM-5 catalyst. All the catalysts modified by ZrO2 ALD displayed significantly improved catalytic stability of hydrogenation of CO2 to DME reaction, compared to that of CZA/HZSM-5 bifunctional catalysts. The loss of DME yield in 100 h of reaction was greatly mitigated from 6.20% (loss of absolute value) to 3.01% for the CZA catalyst with 20 cycles of ZrO2 ALD overcoating. Characterizations including hydrogen temperature programmed reduction, x-ray powder diffraction, and x-ray photoelectron spectroscopy revealed that there was strong interaction between Cu active centers and ZrO2.

Thermocatalytic Hydrogenation of CO2 to Methanol Using Cu-ZnO Bimetallic Catalysts Supported on Metal–Organic Frameworks

The thermocatalytic hydrogenation of carbon dioxide (CO2) to methanol is considered as a potential route for green hydrogen storage as well as a mean for utilizing captured CO2, owing to the many established applications of methanol. Copper–zinc bimetallic catalysts supported on a zirconium-based UiO-66 metal–organic framework (MOF) were prepared via slurry phase impregnation and benchmarked against the promoted, co-precipitated, conventional ternary CuO/ZnO/Al2O3 (CZA) catalyst for the thermocatalytic hydrogenation of CO2 to methanol. A decrease in crystallinity and specific surface area of the UiO-66 support was observed using X-ray diffraction and N2-sorption isotherms, whereas hydrogen-temperature-programmed reduction and X-ray photoelectron spectroscopy revealed the presence of copper active sites after impregnation and thermal activation. Other characterisation techniques such as scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis were employed to assess the physicochemical properties of the resulting catalysts. The UiO-66 (Zr) MOF-supported catalyst exhibited a good CO2 conversion of 27 and 16% selectivity towards methanol, whereas the magnesium-promoted CZA catalyst had a CO2 conversion of 31% and methanol selectivity of 24%. The prepared catalysts performed similarly to a CZA commercial catalyst which exhibited a CO2 conversion and methanol selectivity of 30 and 15%. The study demonstrates the prospective use of Cu-Zn bimetallic catalysts supported on MOFs for direct CO2 hydrogenation to produce green methanol.

Enhanced catalytic performance of Zr modified CuO/ZnO/Al2O3 catalyst for methanol and DME synthesis via CO2 hydrogenation

Zirconium (Zr) modified CuO/ZnO/Al2O3 (CZA) catalysts with different aluminum (Al) and Zr contents were synthesized by the co-precipitation method. The synthesized CuO/ZnO/ZrO2/Al2O3 (CZZA) catalysts were comprehensively characterized and studied for methanol synthesis via CO2 hydrogenation. The CZZA catalyst showed the highest methanol yield of 12.4 % at 220 °C and 2.76 MPa with an optimized catalyst composition of Cu/Zn/Zr/Al (atomic ratio) at 4:2:1:0.5. The CZZA catalyst showed better activity than that of the CZA catalyst and a superior stability for methanol synthesis. There was no decrease in the BET surface area and very little coke formation for the spent CZZA catalyst, after 300 h of methanol synthesis. Bifunctional catalysts, composed of CZZA and HZSM-5, were investigated for dimethyl ether (DME) synthesis directly from CO2 hydrogenation, and a maximum DME yield of 18.3 % was obtained at a reaction temperature of 240 °C and a pressure of 2.76 MPa. The stability of the bifunctional CZZA and HZSM-5 catalyst during the DME synthesis also significantly improved, as compared to that of the CZA and HZSM-5. A significant decrease in the BET surface area and an increase in coking on the spent CZZA catalyst were observed after 100 h of DME synthesis, indicating a detrimental effect on CZZA stability when a HZSM-5 catalyst was present. The changes in structural properties (e.g., BET surface area and crystallinity) and coking for HZSM-5 could be responsible for the deactivation of the bifunctional catalyst.

Preparation of mesoporous nanocrystalline CuO–ZnO–Al2O3 catalysts for the H2 purification using catalytic preferential oxidation of CO (CO-PROX)

In this article, CuO–ZnO–Al2O3 catalysts with various copper contents were synthesized by a co-precipitation method and employed for the elimination of carbon monoxide from a mixture of 97% H2, 1% CO and 2% O2 at atmospheric pressure via carbon monoxide preferential oxidation (CO-PROX). The influence of the copper and zinc contents on the physicochemical characteristics and catalytic performance was investigated. The prepared samples were characterized using the N2 adsorption-desorption (BET), X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM) and temperature programmed reduction (TPR) techniques. The increment in CuO loading improved the activity of CuO–ZnO–Al2O3 catalysts for CO oxidation reaction. Among the prepared catalysts, the 50%CuO-3% ZnO-47% Al2O3 catalyst calcined at 400 °C with a BET area of 82.3 m2/g exhibited the best activity with a CO conversion of 88.9% at 125 °C. The effects of the presence of CO2 and H2O in the reaction feed stream and gas hourly space velocity (GHSV) were also studied.

BASF, Lutianhua sign MoU for eco-friendly production process for DME

The effects of three different mixing methods of CuO/ZnO/Al2O3 (CZA) and HZSM-5 bifunctional catalyst on the stability for dimethyl ether (DME) synthesis from carbon dioxide (CO2) hydrogenation were investigated. When the bifunctional catalyst was prepared by method A (mixing powder without pelletization), there was no significant change in DME production and catalyst stability when the HZSM-5 loading was varied between 0.1 g and 0.5 g with a fixed CZA loading of 0.5 g,. When the bifunctional catalysts were prepared by method B (pressed into pellets of CZA and pellets of HZSM-5 and then mixed) and method C (mixed CZA and HZSM-5 powders, then pressed into pellets), the mixing methods did not initially impact CO2 conversion and had a minor effect on DME yield. However, long-term tests (100 h) indicated that the mixing method had a significant influence on the catalyst stability. Method B showed the best stability and the extent of catalyst deactivation followed the sequence of method B < method A < method C. Characterizations of spent catalysts indicated that method B could reduce the extent of copper (Cu) oxidation, which due to the relatively low surface contact between Cu active sites and HZSM-5. Large amounts of water generated in CO2 hydrogenation to synthesize DME and intimate contact between CZA and HZSM-5 catalyst could induce severe oxidation of Cu and metal ions migration from hydrogenation catalyst to HZSM-5, which can result in the number reduction of acidic sites.

Influence of Tandem Catalysis and Optimised Parameters on Syngas-Dimethyl Ether Co-fed Process for Ethanol Direct Synthesis in a Dual Bed Reactor

Ethanol use mainly as an alternative green fuel has attracted global attention, hence need for the development of more improved synthesis pathways. In this work, we proposed an in situ direct ethanol synthesis pathway, where dimethyl ether (DME) was co-fed with syngas (CO + H2) over a combination of metal impregnated zeolite (Cu-MOR) and ternary oxide CuO/ZnO/Al2O3 (CZA) catalysts, disjointly packed in a dual bed reactor. The route first transformed DME into an intermediate ester (methyl acetate) by carbonylation reaction on the upper modified zeolite catalyst, followed by hydrogenation of the intermediate ester into ethanol on the lower CZA catalyst. Dimethyl ether conversion reached 75.72% with an ethanol selectivity of 48.05% under Cu loading amount of 13 wt% of zeolite support.

Effects of mixing methods of bifunctional catalysts on catalyst stability of DME synthesis via CO2 hydrogenation

The effects of three different mixing methods of CuO/ZnO/Al2O3 (CZA) and HZSM-5 bifunctional catalyst on the stability for dimethyl ether (DME) synthesis from carbon dioxide (CO2) hydrogenation were investigated. When the bifunctional catalyst was prepared by method A (mixing powder without pelletization), there was no significant change in DME production and catalyst stability when the HZSM-5 loading was varied between 0.1 g and 0.5 g with a fixed CZA loading of 0.5 g,. When the bifunctional catalysts were prepared by method B (pressed into pellets of CZA and pellets of HZSM-5 and then mixed) and method C (mixed CZA and HZSM-5 powders, then pressed into pellets), the mixing methods did not initially impact CO2 conversion and had a minor effect on DME yield. However, long-term tests (100 h) indicated that the mixing method had a significant influence on the catalyst stability. Method B showed the best stability and the extent of catalyst deactivation followed the sequence of method B < method A < method C. Characterizations of spent catalysts indicated that method B could reduce the extent of copper (Cu) oxidation, which due to the relatively low surface contact between Cu active sites and HZSM-5. Large amounts of water generated in CO2 hydrogenation to synthesize DME and intimate contact between CZA and HZSM-5 catalyst could induce severe oxidation of Cu and metal ions migration from hydrogenation catalyst to HZSM-5, which can result in the number reduction of acidic sites.

Improved Cu- and Zn-based catalysts for CO2 hydrogenation to methanol

Abstract In this study the influence of metal dispersion, spinel formation, and surface properties of binary and ternary catalysts (CuO CeO2, ZnO CeO2, CuO ZnO CeO2, and CuO ZnO Al2O3) was evaluated. The catalysts prepared by polyol method using polyethylene glycol as a solvent have been tested in the CO2 hydrogenation to methanol performed at atmospheric pressure. The catalysts prepared by polyol method presented improved properties in terms of metal oxide dispersion, morphology (i.e. sponge-like shape for the CeO2-containing catalysts), and a large variety of metal and metal oxide species on the surface. Moreover, the CuO ZnO CeO2 and CuO ZnO Al2O3 catalysts exhibited a higher activity and selectivity in the methanol synthesis by CO2 hydrogenation than those displayed by catalysts prepared by more conventional methods.

Correlation between the porosity of γ-Al2O3 and the performance of CuO–ZnO–Al2O3 catalysts for CO2 hydrogenation into methanol

The influence of the porosity of γ-Al2O3 on the performance of CuO–ZnO–Al2O3 catalysts for methanol synthesis from H2 + CO2 mixture was studied. Various types of γ-Al2O3 with different surface areas (from 130 to 280 m2/g) and pore sizes (from 3 to 11 nm) were investigated. N2 adsorption, XRD, TPR studies and grand canonical Monte Carlo simulation were utilized to determine the correlation between their physico-chemical properties and catalytic performance. It was shown that the crystallite size of CuO (determined by XRD) and BET surface area of supports are not the key factors for methanol productivity. The TPR profiles of catalysts demonstrated a direct relationship between CuO–ZnO interaction with their catalytic performance. Interestingly, samples with the uniform pore size of 5 nm exhibit a higher CuO–ZnO interaction and the highest methanol yield. In addition, at this pore size, simulation results showed that the ratio of H2 and CO2 inside the γ-Al2O3 pore was 1.5, which could be an appropriate feed ratio for high methanol productivity.

Synthesis of CuO–ZnO–Al2O3 @ SAPO-34 core@shell structured catalyst by intermediate layer method

AbstractThe present study focuses on synthesis of SAPO-34 zeolite membrane on the surface of CuO–ZnO–Al2O3 (CZA) catalyst particles to form CZA@SAPO-34 core@shell structured catalyst. In contrast to the traditional support of porous alumina, CZA catalyst particles have a relatively brittle surface, which leads to a big challenge to coat SAPO-34 zeolite membrane on their surface. Moreover, the hydrothermal synthesis of SAPO-34 zeolite membrane is carried out under weakly alkaline condition at 200 °C for hours, which causes part of the surface of CZA to be fragmented. To overcome these shortcomings, the intermediate layer of alumina is introduced to the surface of the CZA particles and acts as a barrier to the high-temperature hydrothermal and alkaline condition. It also takes as a transition to enhance SAPO-34 zeolite seeds adherence to the surface of CZA particles. With the help of an alumina layer, a continuous and dense zeolite membrane has been obtained on the surface of CZA particles. The prepared core@shell structured catalyst has better selectivity in CO hydrogenation for producing light hydrocarbons because of the synergetic effects between the membrane and core catalyst.

The beneficial use of ultrasound irradiation and nitrate/acetate metal precursors in the co-precipitation synthesis and characterization of nanostructured CuO–ZnO–Al2O3 catalyst for methanol synthesis

A CuO–ZnO–Al2O3 catalyst was synthesized by an ultrasound assisted co-precipitation method and compared with the one synthesized by a conventional co-precipitation method. The characterization results of XRD, BET, FESEM and FTIR indicated that the physicochemical properties of the catalysts are strongly influenced by the formulated precursor and the synthesis method. The morphology of the catalyst precipitated under ultrasound irradiation was well-defined and agglomoration-free with average size particle of 32.3 nm. The dispersion of CuO and the surface area of the catalyst exhibited an improvement in acetate based catalyst. The high degree of synergism effect between CuO and other components in CuO–ZnO–Al2O3 catalyst was expected in the acetate-based catalyst synthesized with ultrasound assisted co-precipitation method due to low crystallinity and small size of copper species. The catalytic performance for the synthesis of methanol was examined at 200–300 °C and 10–40 bar in a stainless steel reactor. The CuO–ZnO–Al2O3 catalyst synthesized from acetate precursor precipitated under ultrasound irradiation exhibited a supreme catalytic activity at 275 °C, 40 bar, 18,000 cm3/g h and H2/CO = 2 in terms of CO conversion and methanol yield.

The effect of CuO–ZnO–Al2O3 catalyst structure on the ethanol synthesis from syngas

CuO–ZnO–Al2O3 catalysts were prepared by complete liquid phase technology with different addition sequences. The results indicated that the catalyst prepared by the addition of (C3H7O)3Al to Cu(NO3)2 and Zn(NO3)2 solutions shows excellent ethanol selectivity at the initial stages of reaction, reaching approximately 40%. X-ray photoelectron spectroscopy results showed that ethanol synthesis requires a higher Cu+ content and higher Cu/Zn ratio on the catalyst surface. The temperature-programmed reduction test revealed strong interactions between Cu species and zinc or aluminum oxide. The increase in the difficulty of catalyst reduction indicated higher ethanol selectivity.

A single-step synthesis of isobutyraldehyde from methanol and ethanol over CuO–ZnO–Al2O3catalyst

Selective synthesis of isobutyraldehyde from methanol and ethanol in a single step over CuO–ZnO–Al2O3 catalyst is reported.