Supported ZnO Catalysts Research Articles

Titanosilicate-1 Supported ZnO Catalysts for Steady Propane Dehydrogenation Performance

Titanosilicate-1 Supported ZnO Catalysts for Steady Propane Dehydrogenation Performance

Front Cover: Nickel‐Tin Nanoalloy Supported ZnO Catalysts from Mixed‐Metal Zeolitic Imidazolate Frameworks for Selective Conversion of Glycerol to 1,2‐Propanediol (ChemSusChem 3/2024)

Front Cover: Nickel‐Tin Nanoalloy Supported ZnO Catalysts from Mixed‐Metal Zeolitic Imidazolate Frameworks for Selective Conversion of Glycerol to 1,2‐Propanediol (ChemSusChem 3/2024)

Nickel-Tin Nanoalloy Supported ZnO Catalysts from Mixed-Metal Zeolitic Imidazolate Frameworks for Selective Conversion of Glycerol to 1,2-Propanediol.

The successful synthesis of finely tuned Ni1.5 Sn nanoalloy phases containing ZnO catalyst with a small particle size (6.7 nm) from a mixed-metal zeolitic imidazolate framework (MM-ZIF) is investigated. The catalyst was evaluated for the efficient production of 1,2-propanediol (1,2-PDO) from crude glycerol and comprehensively characterized using several analytical techniques. Among the catalysts, 3Ni1Sn/ZnO (Ni/Sn=3/1) showed the best catalytic performance and produced the highest yield (94.2 %) of 1,2-PDO at ~100 % conversion of glycerol; it also showed low apparent activation energy (15.4 kJ/mol) and excellent stability. The results demonstrated that the synergy between Ni-Sn alloy, finely dispersed Ni metallic sites, and the Lewis acidity of SnOx species-loaded ZnO played a pivotal role in the high activity and selectivity of the catalyst. The confirmation of acetol intermediate and theoretical calculations verify the Ni1.5 Sn phases provide the least energetic pathway for the formation of 1,2-PDO selectively. The reusability of solvent for successive ZIF synthesis, along with the excellent recyclability of the ZIF-derived catalyst, enables an overall sustainable process. We believe that the present synthetic protocol that uses MM-ZIF for the conversion of various biomass-derived platform chemicals into valuable products can be applied to various nanoalloy preparations.

Particle size effect of SiO2-supported ZnO catalysts in propane dehydrogenation

The mass specific rates and propylene selectivity of ZnO catalysts exhibit a volcano relation with the size of ZnO in the propane dehydrogenation (PDH) reaction.

Enhanced catalytic performance of ZnO/carbon materials in the green synthesis of poly-substituted quinolines

A highly efficient methodology for the selective synthesis of nitrogen heterocycles via Friedländer reaction using carbon materials supported ZnO catalysts under the green chemistry domain is presented. The influence of the physicochemical properties of different carbon supports, in particular an activated carbon (AC), multi-walled carbon nanotubes (MWCNT) and a carbon aerogel (CA), on the catalytic performance is discussed. The developed catalysts are easily prepared by simple incipient wetness impregnation and a subsequent thermal treatment. These ZnO/carbon catalysts showed a great performance in the Friedländer condensation of 2-amino-5-chlorobenzaldehyde and carbonylic compounds with enolizable hydrogens, under solvent-free and mild conditions, affording in all cases selectively a total conversion to the corresponding quinoline. Both the Zn loading in combination with the developed microporosity of the selected carbon supports seem to be the key factors determining the catalytic performance. Yields obtained with ZnO/carbon composites catalysts are superior to those obtained by others widely used in fine chemistry such as, Zn-catalysts supported on mesoporous silica (SBA-15) and Zn-metal-organic-frameworks (MOF).

Silicalite‐1 Supported ZnO as an Efficient Catalyst for Direct Propane Dehydrogenation

AbstractDirect propane dehydrogenation (PDH) is an attractive on‐purpose strategy for propylene production. Compared with high‐priced Platinum and toxic Chromium oxide, ZnO based catalysts attract wide attention due to its low‐cost and environment‐friendly character. Herein we report silicalite‐1 supported ZnO catalysts for PDH reaction. They exhibited an excellent catalytic performance. The catalyst with 5 wt% Zn exhibited the best propane yield with propane conversion reaching 49 % and propylene selectivity around 90 % at a space velocity of 5000 ml ⋅ g−1 ⋅ h−1. Characterization with N2 adsorption, XRD, SEM, TEM, EDS, NH3‐TPD, UV–vis, XPS, 29Si MAS NMR, FT‐IR, Py‐IR and TGA reveal that the high activity and stability can be attributed to the dispersed ZnO species due to the interaction between silanol nests of silicalite‐1 support and ZnO species. This study may open a promising way for development of highly efficient PDH catalysts.

Nitrogen-doped carbon supported ZnO as highly stable heterogeneous catalysts for transesterification synthesis of ethyl methyl carbonate

Nitrogen-doped carbon material (NCM) supported ZnO catalysts were prepared by wet impregnation method, following a high-temperature thermal treatment process. The resultant ZnO/NCM catalysts calcined at different temperatures were characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption–desorption, elemental analysis, X-ray photoelectron spectroscopy (XPS) to investigate their physicochemical properties and the interaction between ZnO and NCM support. Their catalytic properties were studied by liquid phase transesterification of dimethyl carbonate (DMC) with diethyl carbonate (DEC). Of these the catalyst calcined at 800 °C, named ZnO/NCM-800 exhibits the highest catalytic activity, as well as excellent stability and recyclability for the synthesis of ethyl methyl carbonate (EMC). The NCM support possesses abundant mesopores, rich surface oxygen-containing and nitrogen-containing functional groups, which are beneficial to build relatively strong interaction between ZnO nanoparticles and the NCM support, resulting in the generation of a highly active and stable acidic-basic bifunctional catalyst for the transesterification of DMC with DEC.

Electrochemical syngas production from CO2 and water with CNT supported ZnO catalysts

Electrochemical reduction of CO2 and H2O can provide a promising pathway to synthesis gas generation for renewable electric energy storage and fuel production with the closed anthropogenic carbon cycle. However, the lack of affordable highly active catalysts to activate the stable CO2 and H2O molecules presents a substantial challenge. Here we report ZnO supported on nanocarbon as a cost-effective and active catalyst for selective conversion of CO2 and H2O to predominately synthesis gas, with higher selectivity and activity compared to polycrystalline metal catalysts such as Ag and Cu. The H2/CO ratio can be tailored for different industrial processes by tuning the applied potential and the particle size of ZnO. Density functional theory calculations showed that the higher activity of ZnO is related to more significantly stabilized intermediates, CO2*, COOH, and CO* compared to Cu and Ag. Our results highlight a promising class of low-cost, abundant oxide as active electrocatalysts for synthetic fuel production from CO2.

Degradation of Acid Orange 7 by an ultrasound/ZnO-GAC/persulfate process

Abstract Granular activated carbon (GAC) supported ZnO catalyst (ZnO-GAC) was prepared to activate persulfate (PS) for the decolorization of Acid Orange 7 (AO7) in the presence of ultrasonic irradiation (US). The effects of initial pH, PS concentration, catalyst dosage, initial dye concentration, and reaction temperature were investigated. The results showed that the decolorization efficiency increased with the increase of catalyst dosage and temperature, but decreased with the increase of initial dye concentration and initial pH, and the optimal PS concentration for color removal was 0.5 g L−1. Radical quenching tests were performed by using ethanol, tert-butanol and phenol to verify the formation of sulfate radicals and hydroxyl radicals in the US/ZnO-GAC/PS process. Under the optimal conditions, 91.2% of decolorization was achieved and 83.1% of TOC was removed after 60 min treatment. Activated sludge inhibition tests were carried out to monitor the change of toxicity during the treatment of AO7 solution.

Promoting Effect of CeO2and MgO for CO2Reforming of Methane over Ni-ZnO Catalyst

The purpose of this study was to find out the effect of CeO2 and MgO (as a promoter) on CO2 reforming of methane or dry reforming of methane (DRM) for the production of synthesis gas. In this aspect, CeO2 and MgO promoted Ni-nanoparticles supported ZnO catalyst was prepared by surfactant induced hydrothermal method, using cetyltrimethylammonium bromide (CTAB) as surfactant, morphology controlling agent and polyvinylpyrrolidone (PVP) as size controlling agent. The prepared catalysts were characterized by BET-Surface area, X-ray diffraction study (XRD), Scanning Electron Microscropy (SEM), Transmission Electron Microscopy (SEM), Inductively coupled plasma atomic emission spectroscopy (ICPAES), Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS) and Thermogravimetric Analysis (TGA) techniques. Highly basic nature of MgO and excellent redox properties of CeO2 increased nickel dispersion and created strong metal-support interaction, which effectively reduced the coke deposition on the catalyst surface. MgO promoted Ni-ZnO catalyst showed better low temperature activity compared to CeO2 promoted Ni-ZnO catalyst for DRM and Ni-MgO/ZnO catalyst also exhibited better coke resistivity, because of comparatively smaller nickel nanoparticles. Both the promoted catalysts showed more than 24 h of time on stream (TOS) stability at 800 °C without any significant deactivation of the catalysts. The catalysts produced H2/CO ratio 0.99 at 800 °C during the TOS.

Nano sized ZnO composites: Preparation, characterization and application as photocatalysts for degradation of AB92 azo dye

ZnO and Mordenite zeolite (MOR) nanoparticles were prepared by precipitation process using ultrasonic irradiation and hydrothermal method, respectively. Supported ZnO catalysts were prepared and the effect of different supports on the photocatalytic activity of ZnO nanoparticles was investigated. All prepared samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform-Infra Red Spectroscopy (FTIR), UV–vis spectroscopy (UV–vis) and BET surface area technique. The photocatalytic activity of the synthesized catalysts was elucidated using the photo-oxidation of Acid Blue 92 (AB92) as a hazardous pollutant under UV light. The effect of different parameters such as catalyst concentration, initial dye concentration, pH, UV irradiation and amount of ZnO loaded on the nanocomposites have been examined on the yield and the rate of photocatalytic degradation process. The photodegradation results of AB92 in aqueous medium under UV irradiation revealed that nanocomposite of ZnO and mordenite zeolite exhibit much higher photocatalytic activity than the other nanocomposites and pure ZnO. It was found that the type of support plays an important role in photocatalytic oxidation of AB92 and significantly improved the photocatalytic activity of ZnO. Chemical Oxygen Demand (COD) for dye solutions were examined at regular intervals and gave a good idea about mineralization of the dye.

Solar Photodegradation of Methyl Orange and Phenol Using Silica Supported ZnO Catalyst

Solar Photodegradation of Methyl Orange and Phenol Using Silica Supported ZnO Catalyst

Supported ZnO catalysts for the conversion of alkanes: About the metamorphosis of a heterogeneous catalyst

ZnO could be a suitable catalyst for the oxidative conversion of CH4, C2H6 and C3H8. However, the main drawback is its thermal instability. Therefore, ZnO supported on ZrO2, TiO2, γ-Al2O3 and SiO2 was investigated for the oxidative dehydrogenation of propane and ethane, and the oxidative coupling of methane. The stability of the supported ZnO is partially improved, but ZnO reacts with the support material, forming new compounds (Zn-zirconates, -titanates, -aluminates and -silicates), which already occurs below reaction temperature. This might also be the case for many other heterogeneous catalysts.

Combination of adsorption, photochemical and photocatalytic degradation of phenol solution over supported zinc oxide: Effects of support and sulphate oxidant

SiO 2, ZSM-5 and MCM-22 supported ZnO catalysts were prepared. Elemental analysis and Zn element mapping were conducted to evaluate the dispersion of ZnO on the supports. The prepared materials were tested in adsorption, photochemical oxidation, and photocatalytic degradation of phenol in aqueous solution. Peroxydisulphate (PDS) and peroxymonosulphate (PMS) were used as oxidants to provide sulphate radicals for chemical oxidation. It was found that adsorptive property of the supports played an important role in photochemical and photocatalytic oxidation. MCM-22 was found to exhibit stronger adsorption, giving 68% of phenol removal in 25 ppm solution, compared to 0%, 3%, and 4% removal on ZnO, SiO 2, and ZSM-5, respectively. The PDS and PMS oxidants could be activated by low intensity UV at wavelength greater than 380 nm. However, under low UV intensity, SiO 2 and ZSM-5 supported ZnO did not exhibit synergistic effect for phenol degradation. The phenol removal efficiencies in PDS/UV, ZnO/PDS, ZnO/UV, ZnO(10%)/MCM-22/UV/PDS, and ZnO(10%)/MCM-22/UV/PMS at 90 min and 60 μW/cm 2 were 34.2, 13.8, 14.2, 79.0, and 72.1%, respectively. The apparent reaction rate constants of PDS/UV, ZnO/PDS, ZnO/UV, ZnO(10%)/MCM-22/UV/PDS, and ZnO(10%)/MCM-22/UV/PMS were 0.00473, 0.00154, 0.00262, 0.00831, and 0.00365 min −1, respectively.

ZnO supported on high silica HZSM-5 as new catalysts for dehydrogenation of propane to propene in the presence of CO 2

Dehydrogenation of propane to propene in the presence of CO 2 was investigated over zinc oxide supported on HZSM-5 with high Si/Al ratios. The stability of supported ZnO catalysts for the reaction improves with increasing the Si/Al ratio of the HZSM-5 support, while the catalytic activity shows a contrary trend. A highly active and stable catalyst, ZnO supported on HZSM-5 with a Si/Al ratio of 160, was obtained, with a propane conversion of 41.5% and a propene yield of 25.8% at steady state. The results of NH 3-TPD and FT-IR spectra of pyridine adsorption reveal that the enhancement of the catalytic stability stems from the decrease in acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking, oligomerization and aromatization. This can be verified by the fact that the amount of coke deposited on the catalyst diminishes with raising the Si/Al ratio of the HZSM-5 support. The promoting effect of CO 2 on the dehydrogenation reaction is observed, which can be attributed to the reverse water-gas shift reaction. The catalytic stability is also enhanced by the introduction of CO 2 to the feed gas.

The catalytic reforming of bio-ethanol over SiO 2 supported ZnO catalysts: The role of ZnO loading and the steam reforming of acetaldehyde

In this study, the activity and the product distributions of sol–gel made SiO 2 supported ZnO catalysts in the steam reforming of ethanol and acetaldehyde is presented as a function of ZnO loading and temperature. We show that although highly dispersed ZnO in SiO 2 (upto 50% ZnO loading) can be prepared using a single step sol–gel method, a precise control of crystallite size could not be achieved. From CO 2 TPD measurements, we found that the basic site densities of ZnO/SiO 2 catalysts stays < 0.05 μ mol / m 2 and do not increase linearly with ZnO loading. The highest basic site density among the catalysts occurs on pure ZnO. All ZnO/SiO 2 catalysts are active at 350 °C whereas pure ZnO catalyst is active at 450 °C. Iso-conversion activity tests show that ethanol steam reforming activities of the catalysts seem to be dependent on the ZnO crystallite size rather than the basic site density of the catalysts when the surface coverage of the basic site density is < 0.32 % but acetone is not formed only on catalysts with ZnO crystallite size < 5 nm regardless of their basic site densities. Interestingly, we found that ethanol was mostly dehydrogenated to acetaldehyde and hydrogen although H 2O/C 2H 5OH molar ratio in the feed was 12. CO was not also produced in the steam reforming of ethanol over all the catalysts. Acetone and propene are produced from acetaldehyde as observed in the steam reforming of acetaldehyde. The steam reforming of acetaldehyde as compared to its decomposition was found to be more favorable over the catalysts with small ZnO crystals, such as 30% and 50% ZnO catalysts.

Effects of support and modifiers on catalytic performance of zinc oxide for hydrogenation of methyl benzoate to benzaldehyde

The ZnO supported on γ-Al2O3, SiO2, MCM-41, and β-zeolite were prepared and examined in the hydrogenation of methyl benzoate (MB). ZnO supported on γ-Al2O3 had a higher activity than ZnO. ZnO/γ-Al2O3 modified with 23ppm lithium had a high catalytic activity (97%) and high selectivity to benzaldehyde (BD, 87%) in a fixed-bed reactor at atmospheric pressure and 400°C. Chromium oxide modified ZnO/γ-Al2O3 also had a high selectivity to BD. Hydrogenolysis of MB occurred over copper modified catalysts. X-ray powder diffraction (XRD) revealed that in the ZnO/γ-Al2O3 catalysts, the ZnO, ZnAl2O4 and γ-Al2O3 phases exited mainly, the border of ZnO and ZnAl2O4 might be important for the hydrogenation of MB to BD. XPS and FT-IR revealed that the chemical environment of ZnO on the ZnO/γ-Al2O3 catalyst is different to ZnO and other supported ZnO catalysts, which gives the ZnO/γ-Al2O3 catalyst having a higher activity than ZnO or ZnO on SiO2, MCM-41 or β-zeolite. The presence of third metal (Li, Cr or Cu) oxide in ZnO/γ-Al2O3 could change the electronic structure of Zn and the chemical phenomena of Zn–Al in catalyst and lead to change of the catalytic performance.

A novel preparation method of ZnO/MCM-41 for hydrogenation of methyl benzoate

A series of supported ZnO catalysts were prepared by a novel method, hydrothermal-impregnation–precipitation (HIP). The activities of catalysts were tested for hydrogenation of methyl benzoate (MB). ZnO supported on MCM-41 behaves much higher activity than that on γ-Al 2O 3, β-zeolite and SiO 2. Changing the loading of ZnO on MCM-41 can adjust the depth of hydrogenation of MB, and high loading of ZnO is available for the hydrogenolysis of MB to benzene. XRD, FT-IR and N 2 absorption were used to reveal that zinc oxide incorporated into the pore channels of MCM-41 in single or double molecular ZnO layer. After supporting 10%ZnO on MCM-41 by HIP, the structure of MCM-41 is unchanged, its pore diameter decreases from 3.14 to 2.62 nm.