Composite Oxide Catalysts Research Articles

Enhancement effect of Mn doping on Co3O4 derived from Co-MOF for toluene catalytic oxidation

The design of Co-Mn composite oxides catalysts derived from MOF is significant for catalytic combustion of toluene. Here, a series of M-CoaMnbOx, with enhanced catalytic properties compared with that of M-Co3O4, were successfully prepared through pyrolysis of Mn-doped Co-MOF. The as-synthesized M-Co1Mn1Ox (Co:Mn = 1:1) exhibits an optimal catalytic activity with 90% toluene conversion reached at 227 °C, which benefits from the increase of Co3+, Oads and the synergistic effect between Mn and Co. According to the analysis of the in situ diffuse reflectance infrared Fourier transform spectroscopy, toluene could be degraded easier on M-Co1Mn1Ox with lower activation energy than M-Co3O4. The main intermediate products are benzaldehyde, benzoic acid, anhydride, and maleate species. Those findings reveal the value of Mn doping for improved activity of toluene oxidation on MOF derived Co3O4, which provide a feasible method for the construction of toluene-oxidation catalysts.

Influence of Ba on Co-Al-Ba composite oxide catalysts in auto-thermal reforming of acetic acid for hydrogen production

Influence of Ba on Co-Al-Ba composite oxide catalysts in auto-thermal reforming of acetic acid for hydrogen production

Au@Cu2O core@shell nanocrystals as sustainable catalysts for efficient hydrogen production from ammonia borane

The use of Au@Cu2O core@shell nanocrystals as sustainable catalysts for efficient hydrogen (H2) production from ammonia borane (AB) is demonstrated. By combining the attributes associated with core@shell structural features and electronic interactions, Au@Cu2O exhibited remarkable performance toward AB hydrolysis. The effect of shell thickness on H2 production performance was systematically investigated. Results showed that H2 production rate increased monotonically with shell thickness, while degree of dehydrogenation of AB was subject to optimization by shell thickness. A maximal 3.0 equivalents of H2 production can be achieved by Au@Cu2O with an optimal Cu2O shell thickness. The H2 produced from AB hydrolysis on Au@Cu2O was introduced to power a fuel cell for lightening light emitting diodes. The findings from the work not only enrich the family of metal/metal oxide composite catalysts for AB hydrolysis, but also deepen the fundamental understanding of implications of core@shell structural features and electronic interactions in dehydrogenation of AB.

Interfacial oxygen vacancies at Co3O4-CeO2 heterointerfaces boost the catalytic reduction of NO by CO in the presence of O2

Simultaneously improving both NOx conversion and N2 selectivity in the selective catalytic reduction of NO by CO (CO-SCR) under O2-containing conditions is highly challenging because of the competitive reactions of NOx and CO with O2. Here, we demonstrate that the interfacial oxygen vacancies (IOVs) generated at the Co3O4-CeO2 heterointerfaces by ball-milling-induced strain can remarkably boost both NOx conversion and N2 selectivity in the temperature range of 100–400 °C. The Co3O4-CeO2-IOV catalyst achieved approximately 100% NOx conversion and 100% N2 selectivity (200–350 °C, 1–5 vol% O2, and 20,000 h−1); even under 10 vol% O2, it still showed good catalytic performance. The spectroscopy analysis and theoretical calculations reveal that compared with O2 activation, IOVs are more favorable for the rate-limiting step of NO adsorption and dissociation. This work provides an effective strategy to create IOVs within metal oxide composite catalysts using ball-milling-induced interfacial strain for improving CO-SCR performance.

One-step electrodeposition of ZnO/graphene composites with enhanced capability for photocatalytic degradation of organic dyes.

Zinc oxide is a popular semiconductor used in catalysts due to its wide bandgap and high exciton binding energy. However, the photocatalytic performance of ZnO was compromised by its insufficient electron-hole separation efficiency and electron transfer rate. Herein, ZnO-reduced graphene oxide (rGO) composite solid catalyst was synthesized by one-step electrodeposition method on FTO substrate using lithium perchlorate (LiClO4) as the supporting electrolyte. Scanning electron microscopy, Raman, Fourier Transform Infrared, and XRD characterizations confirmed the deposition of ZnO and the reduction of graphene oxide Owing to the cooperative effect between rGO and ZnO, the as-prepared ZnO-rGO composites show much enhanced photocatalytic degradation ability compared with pure ZnO nanorods. By optimizing the conditions of electrodeposition of ZnO-rGO composites, the degradation rate of methylene blue can reach 99.1% within 120min. Thus, the simple preparation and the excellent performance could endow the ZnO-rGO composites with promising application in practical dye-polluted water treatment.

CeO2-doped WO3 composite catalyst based on acid site enhancement for diesel exhaust gas denitration

Based on the complicated preparation of current diesel vehicle exhaust gas denitration catalysts, an in-situ deposited composite oxide catalyst, CeO2-WO3 mixed oxide catalyst, was prepared by electrodeposition and hydrothermal methods, which was loaded on the titanium mesh and applied to the selective catalytic reduction denitration of diesel vehicle exhaust. Denitration performance of the catalysts was tested by a fixed bed reactor, and the influence of different electrodeposition time of CeO2 was investigated. The results demonstrate that 20 min is the best electrodeposition time of CeO2 (100% NOx conversion at 250–350 °C). The high dispersion of active CeO2 on WO3 promotes the synergistic effects among different components. The as-prepared catalysts were characterized by SEM, XRD, XPS, H2-TPR, NH3-TPD and in-situ DRIFTS. It is evident that Ce3+ is successfully introduced by loading CeO2, which enhances the chemisorption of oxygen. Meanwhile, the increased acidity including both weak acid and medium-strong acid sites of CeO2-WO3 composite catalyst is observed, which improves the co-adsorption of NH3 on Lewis acid and Brønsted acid simultaneously and facilitates the denitration process. Through the characterization by in-situ DRIFTS, it is elucidated that the NH3-SCR reactions are mainly carried out following the Eley-Rideal (E-R) pathway in a medium-temperature range (250–350 °C).

Resource utilization of high-concentration SO2 for sulfur production over La-Ce-Ox composite oxide catalyst.

Sulfur dioxide is one of the main causes of air pollution such as acid rain and photochemical smog, and its pollution control and resource utilization have become important research directions. La2O3 was incorporated into CeO2 to enhance the surface basicity of La-Ce-Ox catalyst and increase the concentration of chemisorbed oxygen, thereby promoting the improvement of catalytic performance of SO2 reduction by CO. Results have showed that the incorporation of La2O3 would not only increase the concentration of chemisorbed oxygen and hydroxyl on the catalyst surface, but also increase the basicity of the catalyst, thereby facilitating the adsorption of SO2 on the catalyst surface. The 12%La-Ce-Ox was the optimal catalyst, and its SO2 conversion at 350-400 ℃ reached close to 100%, and the sulfur yield at this temperature range was higher than 93%. Finally, according to the in situ infrared diffuse reflectance spectrum, it was found that the main reaction intermediates of 12%La-Ce-Ox in the catalytic reduction of SO2 were weakly adsorbed sulfate, SO32-, non-coordinating CO32-, monodentate carbonate, and CO, so the catalytic reaction followed the L-H and E-R mechanisms simultaneously.

Synthesis of clay-reduced graphene oxide composite catalysts for the electrochemical detection of flubendiamide: application in food samples

This paper presents a simple and low-cost approach to synthesizing reduced graphene oxide/clay modified pencil electrode (rGO/Clay/PGE) through thermal reduction of GO/Clay for ultrasensitive detection of Flubendiamide (FBD). The graphene oxide (GO) was prepared by exfoliation of graphite with an eco-friendly procedure. The as-produced rGO/Clay was characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), and Scanning electron microscopy (SEM). The electrochemical behavior of the synthesized electrode was studied by cyclic voltammetry (CV). Under optimized conditions, rGO/Clay/PGE exhibited excellent analytical properties toward FBD determination. A calibration curve was well-established from 0.1 to 100 μmol/L for FBD with a detection limit of 0.006 μmol/L. The method was successfully adopted for the detection of FBD in white rice samples.

Fe‐Ce Composite Oxide Catalysts Supported on 3D Nickel Foam for Catalytic Oxidation of Soot

AbstractTo reduce the combustion temperature of diesel soot, the Fe−Ce composite oxide catalysts with varying composition supported by three‐dimensional nickel foams were prepared by hydrothermal reaction and impregnation method. The internal structure and performance of the monolithic catalysts were characterized by X‐ray diffraction, Raman, scanning electron microscope, X‐ray photoelectron spectroscopy and catalyst activity evaluation techniques. The results revealed that when the molar ratio of Ce and Fe was 0.5, the CeO2/Fe2O3@NF catalyst showed the best catalytic activity of soot oxidation, good stability and water resistance. Besides, the addition of NO and H2O was helpful to improve the catalytic performance for soot oxidation, when 10 % H2O and 800 ppm NO were mixed into 20 %O2/N2 atmosphere, the T10, T50 and T90 values could decrease to 299 °C, 344 °C and 389 °C, respectively.

Evaluation of an ε-manganese (IV) oxide/manganese vanadium oxide composite catalyst enriched with oxygen vacancies for enhanced formaldehyde removal

Formaldehyde removal is vital to health, but the construction of high-performance non-precious metal catalysts still faces great challenges, in which increasing oxygen vacancies by dopant modification is an advanced strategy to enhance catalytic activity. In this work, a novel ε-MnO2/Mn2V2O7 composite catalyst with a synergistic effect was synthesized on the basis of a thermal decomposition strategy. Meanwhile, the precursor for the catalyst was synthesized from the reaction among CO2-storage material, Mn2+, and vanadate without additional template agents and surfactants. Aided by the catalyst, the degradation rate of a 20 mg/L 10 mL formaldehyde (HCHO) solution can reach 72.0% and maintain above 67% after 5 cycles at 30 °C for 1 h. Subsequently, the as-obtained synergistic catalytic mechanism showed that the high-valent V5+ may partially replace Mn4+ in the MnO2 framework, promoting the formation of enriched oxygen vacancies (V4+-□-Mn3+) on the surface of the composite catalyst via the redox coupling of Mn4+/Mn3+ and V5+/V4+. This leads to an increase in adsorbed oxygen, significantly improving the degradation performance of HCHO. This work provides a novel and advanced strategy for dopant modification to develop superior non-precious metal catalysts.

Resource utilization of high concentration SO2 for sulfur production over La–Ce-Ox@ZrO2 composite oxide catalyst

Sulfur dioxide is one of the main causes of air pollution such as acid rain and photochemical smog, and its pollution control and resource utilization become an important research direction of air pollution control. The active component La–Ce-Ox is loaded on SiO2, γ-Al2O3, TiO2 and ZrO2, and the La–Ce-Ox@ZrO2 exhibits the best catalytic activity. By adjusting the loading amount of La–Ce-Ox, La–Ce-Ox@ZrO2 with different mass fractions was prepared. The results show that the activity of 15%La–Ce-Ox@ZrO2 catalyst is the best. The SO2 conversion is 100%, and the S yield and S selectivity are more than 96% at 350 °C. According to the analysis results of H2-TPR, CO2-TPD and NH3-TPD, ZrO2 as a support not only reduces the acidity of the catalyst, but also improves the weak alkaline sites of the catalyst, which is conducive to the adsorption and activation of SO2 molecules at low temperature. The incorporation of La and Ce increases the oxygen concentration adsorbed on the catalyst. The strong interaction between the support ZrO2 and the active component La–Ce-Ox is conducive to the electron transfer between the active component and the support, and improves the activity of the catalyst. For the 15%La–Ce-Ox@ZrO2, the main reaction intermediates are weakly adsorbed SO2 (SO32−), bicoordinated CO32−, monodentate carbonate and CO in the gas phase. Therefore, the catalytic reaction follows both L-H and E-R mechanisms.

Mechanistic insights into methanol steam reforming over a ZnZr oxide catalyst with improved activity

Methanol steam reforming (MSR) holds great potential for mobile hydrogen production, but it still requires an active and stable catalyst. In this work, we report a high-performance ZnZr-0.5 composite oxide catalyst for this reaction, with a hydrogen production rate of 2.80 mol·gcat−1·h−1 and CO2 selectivity of 99.6% at a methanol space velocity of 22,762 mL·gcat−1·h−1. It also exhibits superior long-term durability in the TOS test for more than 100 h. Such good activity results from a synergistic effect of ZnO–ZrO2 dual sites. ZrO2 is capable of stabilizing and storing more CH3O∗ and HCOO∗ intermediates while ZnO is in charge of the dehydrogenation of these key intermediates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption results reveal that the MSR reaction experiences successively the hydrolysis of methyl formate and dehydrogenation of formate. More importantly, it is found that H2O significantly promotes the dehydrogenation of HCOO∗ intermediate by directly participating in this reaction from pulse chemisorption experiments.

Preparation of a Novel NiAlO Composite Oxide Catalyst for the Dehydrogenation of Methylcyclohexane

A series of NiAlO composite oxide catalysts with high surface areas and high Ni dispersion were prepared through an improved co-precipitation method. The new preparation method effectively improved the specific surface area and pore volume of the catalyst, promoted the dispersion of nickel species, alleviated the agglomeration of the catalyst, and improved the stability of the catalyst by strengthening the interaction between Ni and Al. The typical catalyst Ni20Al had a specific surface area of 359 m2/g and a NiAl2O4 phase. In the dehydrogenation of methylcyclohexane over the Ni20Al catalyst, the conversion of methylcyclohexane could reach 77.4%, with toluene selectivity of 85.6%, and a hydrogen release rate of 63.94 mmol g−1 h−1, and did not show any significant inactivation during the stability test over 29 h under the reaction conditions of reaction temperature 450 °C and LHSV = 4 mL g−1 h−1. However, the conversion of methylcyclohexane with the IM-NiAl catalyst prepared through the traditional impregnation method was only 50.75%, with toluene selectivity of 70.5%, and with a hydrogen release rate of 35.84 mmol g−1 h−1, and the lifetime of the catalyst was only 15 h.

High-performance Fe-Cu composite oxide for selective catalytic reduction of NOx with NH3: Driving of Cu on α-Fe2O3

One kind of driving of Cu on α-Fe2O3 was successfully created for removing NOx. It brought excellent low-temperature performance, high N2 selectivity and strong water and sulfur resistance. The concrete process was that Cu2+ ions entered into the crystal lattice of Fe2O3, forming solid solution with Cu-O-Fe structure and further changed the property of Fe2O3. On the one hand, Cu2+ ions adjusted the electrophilicity of Fe3+ species, thereby facilitating the generation and adsorption of NO2, nitrate and nitrite species and increasing Lewis acid sites. The increase of NH3 and NOx adsorbed species on the catalyst surface conduced to excellent low-temperature NH3-SCR activity. On the other hand, the regulation of Cu brought abundant lattice defects to Fe2O3 which strengthened the redox ability and generated oxygen vacancy. It led to the growth of surface adsorbed oxygen, which was crucial for the “fast SCR” reaction. In-situ DRIFTS results revealed that the NH3 on Lewis acid sites preferred to react with weakly adsorbed NO2 through Langmuir-Hinshelwood (L-H) mechanism over the Fe-Cu composite oxide catalyst. Meanwhile, the NH3 on Lewis acid sites was also able to react with monodentate nitrates, bidentate nitrates and nitrites through L-H reaction mechanism. This work provided a new inspiration for the construction of green and efficient catalysts to remove NOx in the practical industrial applications.

Investigation on aquathermolysis desulfurization by cutting off C-S bond in thiophene over Fe-Zr-Al catalyst facilitated by surfactants

ABSTRACT This study aimed to apply aquathermolysis technology to remove thiophene sulfur in vacuum residue to obtain qualified petroleum coke products based on a well-designed Fe-Zr-Al catalyst. A coprecipitation method was first developed to synthesize Fe-Zr-Al composite metal oxide catalyst. The thiophene model oil was selected as the reaction system to investigate the process conditions. By adding surfactants into the reaction system to strengthen the mass transfer process of oil–water two-phase, the desulfurization rate of aquathermolysis was improved. It was shown in this study that under the conditions of oil–water ratio of 3:7, temperature of 280°C, pressure of 4 MPa and reaction duration of 60 h, the desulfurization rate could reach 44.39%. The further introduction of 2.4% Sorbitan oleate into the above reaction system could significantly enhance the desulfurization rate to 60.20%. Under the action of Fe2O3 lattice oxygen, thiophene was oxidized and C-S bond was broken, so as to achieve the purpose of desulfurization. The decomposition of water generated active oxygen to continuously replenish lattice oxygen of Fe2O3. The current founding can provide a new way for the effective desulfurization of vacuum residue to produce qualified petroleum coke products.

Green Synthesis of 3-Hydroxybutyraldehyde from Acetaldehyde Catalyzed by La-Ca-Modified MgO/Al2O3

3-hydroxybutyraldehyde (3-HBA) is mainly employed to synthesize 1,3-BDO (1,3-butanediol), which is one of the most important components in cosmetics moisturizers. In this study, a series of composite oxide catalysts were prepared by bringing alkaline earth metal Ca and rare earth metal La to the composite oxide MgO/Al2O3, which were made through the co-precipitation method. These catalysts were applied in the synthesis of 3-HBA through acetaldehyde (AcH) condensation. The structure, texture, and acidic properties of these catalysts were characterized using various characterization methods, and the effects of catalyst composition, reaction temperature, reaction pressure, and residence time on the conversion of AcH were investigated as well. The results showed that the introduction of Ca and La weakened the acidic property and enhanced the basic property, which favored the AcH condensation to synthesize 3-HBA. At a temperature of 20 °C, pressure of 200 kPa, and residence time of 70 min, 0.5%La-2.3%Ca-2MgO/Al2O3 exhibited a better catalytic activity, and the conversion of AcH reached 95.89%. The selectivity and yield of 3-HBA were 92.08% and 88.30%, respectively. The stability test indicated that the high AcH conversion could be maintained for 5 h.

1,4-Butanediol Selective Dehydration to 3-Butene-1-ol over Ca–Zr–Sn Composite Oxide Catalysts

Ca–Zr–Sn composite oxides catalysts for 1,4-butanediol (BDO) selective dehydration to 3-butene-1-ol (BTO) are synthesized by impregnation and co-precipitation in the present work. The results show that Ca–Zr–Sn catalysts prepared from co-precipitation by using NaOH-Na2CO3 mixing alkali solution as precipitant exhibit an excellent catalytic property for BDO dehydration to BTO. For instance, Ca–Zr–Sn oxide with Ca/Zr and Sn/Zr molar ratio of 0.68 and 0.28 calcined at 650 °C gives a BDO conversion and BTO selectivity of about 97% and 82%, respectively, and exhibits no deactivation during 1000 h scale-up experimental testing. X-ray diffraction results indicate that catalytic active centers for BDO dehydration to BTO are from Ca0.15Zr0.85O crystal phase. NH3- and CO2-temperature programmed desorption prove that the surface of obtained catalysts can provide a large amount of acid and base sites simultaneously. FT-IR spectra of pyridine-adsorbed samples show that acid sites on the surface of Ca–Zr–Sn oxide catalyst mainly exist in a state of Lewis acid, which activates terminal -OH groups of BDO molecule through complexing. The activated -OH interacts with β-H activated on base sites O2− anions relative to Ca species, thereby the CH2=CH- bonds are produced through dehydration to form BTO.

Transesterification of Glycerol to Glycerol Carbonate over Mg-Zr Composite Oxide Prepared by Hydrothermal Process.

A series of Mg-Zr composite oxide catalysts prepared by the hydrothermal process were used for the transesterification of glycerol (GL) with dimethyl carbonate (DMC) to produce glycerol carbonate (GC). The effects of the preparation method (co-precipitation, hydrothermal process) and Mg/Zr ratio on the catalytic performance were systematically investigated, and the deactivation of the catalyst was also explored. The Mg-Zr composite oxide catalysts were characterized by XRD, TEM, TPD, N2 adsorption-desorption, and XPS. The characterization results showed that compared with the co-precipitation process, the catalyst prepared by the hydrothermal process has a larger specific surface area, smaller grain size, and higher dispersion. Mg1Zr2-HT catalyst calcined at 600 °C in a nitrogen atmosphere exhibited the best catalytic performance. Under the conditions of reaction time of 90 min, reaction temperature of 90 °C, catalyst dosage of 3 wt% of GL, and GL/DMC molar ratio of 1/5, the GL conversion was 99% with 96.1% GC selectivity, and the yield of GC was 74.5% when it was reused for the fourth time.

Recent Advances of Chlorinated Volatile Organic Compounds' Oxidation Catalyzed by Multiple Catalysts: Reasonable Adjustment of Acidity and Redox Properties.

The severe hazard of chlorinated volatile organic compounds (CVOCs) to human health and the natural environment makes their abatement technology a key topic of global environmental research. Due to the existence of Cl, the byproducts of CVOCs in the catalytic combustion process are complex and toxic, and the possible generation of dioxin becomes a potential risk to the environment. Well-qualified CVOC catalysts should process favorable low-temperature catalytic oxidation ability, excellent selectivity, and good resistance to poisoning, which are governed by the reasonable adjustment of acidity and redox properties. This review overviews the application of different types of multicomponent catalysts, that is, supported noble metal catalysts, transition metal oxide/zeolite catalysts, composite transition metal oxide catalysts, and acid-modified catalysts, for CVOC degradation from the perspective of balance between acidity and redox properties. This review also highlights the synergistic degradation of CVOCs and NOx from the perspective of acidity and redox properties. We expect this work to inspire and guide researchers from both the academic and industrial communities and help pave the way for breakthroughs in fundamental research and industrial applications in this field.

Research Progress of a Composite Metal Oxide Catalyst for VOC Degradation

Volatile organic compounds (VOCs) are atmospheric pollutants that have been of concern for researchers in recent years because they are toxic, difficult to remove, and widely sourced and easily cause damage to the environment and human body. Most scholars use low-temperature plasma biological treatment, catalytic oxidation, adsorption, condensation, and recovery techniques to treat then effectively. Among them, catalytic oxidation technology has the advantages of a high catalytic efficiency, low energy consumption, high safety factor, high treatment efficiency, and less secondary pollution; it is currently widely used for VOC degradation technology. In this paper, the catalytic oxidation technology for the degradation of multiple types of VOCs as well as the development of a single metal oxide catalyst have been briefly introduced. We also focus on the research progress of composite metal oxide catalysts for the removal of VOCs by comparing and analyzing the metal component ratio, preparation method, and types of precursors and the catalysts' influence on the catalytic performance. In addition, the reason for catalyst deactivation and a correlation between the chemical state of the catalyst and the electron distribution are discussed. Development of a composite metal oxide catalyst for the catalytic oxidation of VOCs has been proposed.