Mixed Metal Oxide Catalysts Research Articles

Forced Dynamic Operation of Propylene Selective Oxidation to Acrolein on Bismuth-Molybdate Structured Catalysts

Forced dynamic operation (FDO) of selective oxidation of propylene to acrolein is evaluated on a structured alumina foam coated with a mixed metal oxide catalyst (bismuth molybdate-based). Reactor experiments examine feed composition modulation as a strategy to increase the yield of acrolein. At lower temperatures, separating the oxidant (O2) and reductant (C3H6) enhances propylene conversion and acrolein selectivity. Variation in the reaction-regeneration switching amplitude and frequency gives a 40% higher cycle-averaged acrolein yield compared to steady-state operation (SSO) for the same overall feed composition. The results suggest that FDO maintains a higher concentration of selective oxygen species during the propylene feed, while pre-oxidation of the catalyst maximizes the amount of selective oxygen species, leading to increased acrolein yield at the beginning of the reaction cycle. Experiments at lower temperature for both commercial promoted and in-house, unpromoted catalysts reveal both catalysts are most active and selective at their highest oxidation states.

Mo–V–Al–K–O catalyst for low-temperature oxidative dehydrogenation of propane

Compared with propane dehydrogenation (PDH) technology, oxidative dehydrogenation (ODH) of propane is an effective way to break through the thermodynamic constraints, which has changed the endothermic reaction into exothermic. Meanwhile, coking in PDH was significantly reduced by the presence of an oxidant in ODH of propane. Therefore, ODH of propane has attracted wide interest and has been studied in recent years. However, the contradiction between the conversion of propane and the selectivity of propene was the intrinsic problem of ODH of propane that required further study. In this work, a novel aluminum/potassium-doped mixed metal oxide catalyst Mo1V0.5Al0.02K0.03Ox was synthesized using a simple co-impregnation method, whose selectivity for propene (83.2 %) and conversion of propane (12.7 %) at 300 °C were the best among all other alkali metal/alkaline-earth metal-doped catalysts. The further discussion illustrated that doping potassium and alumina could synergistically adjust the density of acid sites on the catalyst, establishing an equilibrium between high propane conversion and the ideal propene selectivity. After modification, the density of Brønsted acid decreased, leading to an enhancement in the selectivity of propene. Simultaneously, the addition of steam in the feed gas promotes propene to oxygenates and improves the conversion of propane under the condition of constant contact time.

Effect of sodium zeolite mixed metal oxide catalysts on catalytic conversion of mixed-density plastic into carbon nanotubes and hydrogen fuel

A combination of experimental and statistical analysis presents a comprehensive understanding of the microwave pyrolysis technique for catalytic deconstruction of mixed-density plastics. By optimizing the process parameters and catalyst selection, it is possible to maximize the production of valuable solid and energy products, contributing to sustainable waste management. In this work, different mixed-density plastics were pyrolyzed with different catalysts and residence times to yield liquid fuel, syngas, and structured carbon residue. The effect of inputs on the product type, yield and composition was statistically evaluated using ANOVA, which showed an F value of 4.108 and a p-value of 0.098 (>1.00). FTIR and GC-MS revealed that the oil product consisted of C13+ fractions in the form of alkanes, alkenes, and aromatics. The microscopic analysis of the residue confirmed the formation of carbon nanotubes along with other amorphous products. The presence of impurities in the solid product was further analyzed through XRD analysis. The pyrolytic liquid fuel revealed the presence of conjugated aromatic structure and carbonyl group in their concentration. This research demonstrated that converting mixed-density plastics using sodium zeolite, aluminum oxide, and nickel oxide catalysts yields 84% valuable products, confirming wasted plastics as a lucrative energy feedstock for producing hydrogen and high-value carbon compounds.

NiMo-MMO catalyst derived from LDHs precursors toward the deep hydrogenation of pyrene

A series of Ni-based catalysts were prepared via structural topological transformation from the Ni@Al2O3 layered double hydroxides (LDHs) precursors, and applied for the deep catalytic hydrogenation saturation of pyrene in a high-pressure reactor. The pore structures, active species dispersion, surface morphology, amount and type of acid of the prepared catalysts were characterized by BET, XRD, SEM, TEM, XPS, SEM, NH3-TPD and Py-IR. We studied the influence of physicochemical properties of Ni-based catalysts on the regularity and mechanism of deep hydrogenation of pyrene. Meanwhile, the synergy between Ni and Mo, and the interaction between active metals and support were discussed to further reveal the constitutive relationship during the hydrogenation reaction of pyrene. The results of the evaluation of the catalytic hydrogenation of pyrene show that the as-prepared NiMo mixed metal oxide (MMO) catalyst showed excellent catalytic activity: ∼95% pyrene conversion, 90.12% for the selectivity of deep hydrogenation products (hexahydropyrene, decahydropyrene and hexadecahydropyrene). It was expected that the successfully preparation and utilization of NiMo-MMO catalyst could provide a theoretical basis for the design of this kind of catalysts for deep catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs).

Heteropolyacid and Lithium Infused Calcium Oxide Catalyst for Biodiesel Production from Food Waste

The advancement of mixed metal oxide catalysts has attracted considerable attention among various workers. Supported MoOx catalyst materials possess more Lewis and Brønsted acid functionalities which assist in the efficient biodiesel production. In this study, ammonium molybdate and Li+ were loaded over eggshells-derived calcium oxide to transesterify the frying oil/waste cooking oil (WCO) to produce biodiesel/fatty acid methyl ester (FAME). Characterization techniques i.e., X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis were employed to confirm the material. The surface modelling predicted the transesterification reaction parameters. The optimal condition to transesterify WCO with synthesized Mo/Li/CaO catalyst was 6 wt.% catalyst dose, 13.70:1 ratio of methanol:oil (m/o), time of 1 h and 60 ºC temperature. The optimum FAME yield of 97% was observed. The gas chromatography-mass spectroscopy (GC-MS) and other spectroscopic techniques were used to analyze produced FAME. The reusability of catalyst was good and the catalyst can be reutilized effectively up to a limit of 5 runs. By leveraging this innovative catalyst derived from eggshells, this study contribute to a more sustainable and cost-effective biodiesel production process.

Zn0.5Ni0.5MnxFe2-xO4 magnetically separable nano ferrite: A highly efficient photocatalyst for environmental remediation

The escalating pollution from industries poses a severe threat to water resources, necessitating efficient photocatalysts for environmental remediation. In this study, we introduce a novel Zn0.5Ni0.5MnxFe2-xO4 nano ferrite, synthesized via sol–gel auto-combustion method. The phase purity of Zn0.5Ni0.5MnxFe2-xO4 nano ferrites was confirmed from X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. The microstructural investigation of nano ferrites was investigated using Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The catalyst’s magnetic properties allow easy separation, addressing the challenge of catalyst retrieval in photocatalysis. Incorporating Zn, Ni, and Mn at tetrahedral and octahedral sites enhances crystallinity, crucial for catalytic efficiency. This mixed metal oxide catalyst demonstrates superior photocatalytic activity, with Zn0.5Ni0.5MnFeO4 exhibiting a remarkable 97% degradation of Reactive Orange (RO) dye under sunlight. Notably, the photocatalyst displays stability and reusability over multiple cycles. The study provides valuable insights into the potential of Zn0.5Ni0.5MnxFe2-xO4 ferrite as a magnetically separable, efficient photocatalyst for environmental remediation.

Manipulation of Mn/Ce ratio for deep chlorobenzene oxidation: Catalytic mechanisms and byproducts analysis

In this research, a sequence of spatial porous MnCeOx catalysts with varying Mn/Ce from 3:1 to 1:7 were synthesized using the sol–gel method for chlorobenzene (CB) oxidation. Mn1Ce1 exhibited the best performance due to its high lattice oxygen content and the strong interaction between Ce and Mn. The increase in Mn content in CeO2 catalysts resulted in enhanced redox properties and acidity, which was beneficial for the adsorption and activation of CB, thus enhancing the selectivity and the desorption of HCl on the catalyst surface. Carbon deposition and the formation of metal chloride were the main reasons for catalyst deactivation. At low temperature regions (150 ∼ 300 °C), insufficient oxidation capability and the chlorine deposition on the catalyst surface resulted in the formation of various chlorinated compounds. As the temperature increases (300 ∼ 450 °C), the release of HCl and more reactive oxygen species is available on the catalytic interface, generating various oxygen-containing degradation intermediates. This work proposed a fine-designed, low-cost mixed metal oxide catalysts for low temperature CB oxidation, and provided novel in-depth understandings of degradation intermediate formation thermodynamics. Our findings would be helpful for deep purification of chlorinated VOCs polluted industrial tail gas.

Effect of mixed metal oxide‐based catalysts for the removal of hydrophobic phthalates from water

AbstractContaminants of emerging concern (CECs) such as phthalic acid esters (PAEs) are ubiquitous, toxic and persistent in aquatic environments. Current study explored mixed metal oxide catalysts derived from magnesium aluminium (MAH), magnesium aluminium ruthenium (MAR‐H), magnesium aluminium nickel (MANH) hydroxides and copper aluminium hydroxides of ammonium (CAM‐Am) and sodium molybdate (CAM‐Na) to remove dibutyl phthalate (DBP) and di‐2‐ethyl hexyl phthalate (DEHP) from water. Powder X‐ray diffraction (XRD) studies of the catalysts before and after the treatment showed that their structures were stable and robust. During Fourier Transform Infrared (FTIR) studies, vibrational bands or peaks of ester and alkane functional groups of DBP and DEHP were observed at all the catalysts after treatment. Thermogravimetric analysis (TGA) confirmed phthalate adsorption at the five catalysts. Hydrolysis of DBP and DEHP was observed during treatment using CAM‐Am and CAM‐Na that was analysed and quantified using total organic carbon (TOC), high performance liquid chromatography (HPLC) and high‐resolution mass spectrometry (HRMS). From TOC analyses, optimal conditions of 500 mg L−1 catalyst dosage and 30 h treatment time were deduced for catalytic hydrolysis of DBP and DEHP. Present study illustrated that the catalysts MAH and MANH can adsorb PAEs while CAM‐Na can adsorb and hydrolyse them.

Strong water-resistant Co-Mn solid solution derived from bimetallic metal–organic frameworks for catalytic destruction of toluene

The construction of Co-Mn mixed metal oxides catalysts derived from bimetallic MOFs has great significance for catalytic destruction of toluene. Hence, a series of CoaMnbOx-MOFs with different physicochemical properties were successfully synthesized via pyrolysis of Co-Mn bimetallic MOFs. Attributing to the higher specific surface area, more active sites (Co3+ and Mn3+), stronger reducibility and abundant defect sites, the as-prepared Co1Mn1Ox-MOFs dispalyed an optimal catalytic performance, especially the excellent water vapor resistance. The result of the In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy demonstrated that toluene can be degraded at relatively low temperatures (＜100 °C). Benzyl alcohol, benzaldehyde, benzoic acid and maleic anhydride were the main intermediate products in toluene degradation process. This work reveals the value of bimetallic MOFs derived Co-Mn oxides for toluene oxidation and presents a novel avenue for designing mixed metal oxide catalysts with potential applications in VOCs catalytic oxidation.

Quantum Chemical Modeling of the Full Catalytic Cycle for Selective Oxidation of Propane to Propene on the M1 Phase of Mo–Te–Nb–O Mixed-Metal Oxide Catalysts

Quantum Chemical Modeling of the Full Catalytic Cycle for Selective Oxidation of Propane to Propene on the M1 Phase of Mo–Te–Nb–O Mixed-Metal Oxide Catalysts

Designing Heterogeneous Catalysts for Microwave Assisted Selective Oxygenation

AbstractMicrowave dielectric heating is an emerging technology in heterogeneous catalysis. However, catalyst design in this field is not as well developed as when conventional heating is used. In this study the selective oxidation of propene to acrolein has been used as a model reaction to understand the how the properties of bismuth mixed metal oxide catalysts can be tuned for use in microwave assisted catalysis. The role of the dielectric properties, that are crucial to enable the catalyst to be heated in the microwave electric field, were determined using cavity perturbation methods. Catalysts with a very high loss tangent reached high temperatures leading to combustion products, whereas materials with a low loss tangent could not be heated and were inactive. Bi2MoO6 and BiVO4 both showed promising performance during an initial screening and were investigated further. For Bi2MoO6, a partial substitution of molybdenum with vanadium resulted in the formation of Bi1−X/3V1−xMoxO4, with a decrease in particle size and dielectric loss tangent, and the highest rate of acrolein production was found when x=0.6 at 15 W microwave power. Higher microwave power resulted in thermal runaway which decreased the activity of the catalyst.

Highly efficient aerobic epoxidation of styrene using mesoporous Co-Ni catalysts

This work reports the synthesis and characterization of mesoporous cobalt-nickel mixed metal oxide catalysts with varying Co:Ni ratios using an inverse micelle template self-assembly method. Their structural and morphological properties and catalytic performance in styrene epoxidation were evaluated. Among them, the 73CoNi-250 catalyst (Co: Ni70:30 mol/mol%, calcined 250°C) exhibited a unique flower-like morphology and the highest surface area, which XPS analysis linked to a higher concentration of oxygen vacancies. Notably,73CoNi-250 demonstrated exceptional catalytic activity for styrene epoxidation, achieving near-complete styrene conversion (>99 %) and high selectivity (94 %) for styrene epoxide under mild reaction conditions without the need for oxidants such as peroxides. Furthermore, the catalyst exhibited excellent reusability (≥ 4 cycles) without significant activity loss or changes in mesoporosity. Kinetic studies revealed a first-order reaction profile and a significantly enhanced rate constant compared to the best-reported values (fivefold) in the literature, further underlining the catalyst's efficiency, and emphasizing the environmentally friendly approaches in chemical synthesis.

Acid-base synergistic effect towards catalytic transfer hydrogenation reactions

Catalytic transfer hydrogenation (CTH) of aldehydes/ketones by using alcohols as hydrogen donors is an attractive and environmentally friendly hydrogenation technology, which has evoked widespread attention in synthesis of fine chemicals from biomass resources. In this work, a Co-Al mixed metal oxide catalyst (Co1Al2-MMO-200) was obtained through structural topological transformation process of layered double hydroxides, which was used in the CTH reaction of furfural with isopropanol. Notably, the reaction rate achieves 0.023 mol g−1 h−1, which is preponderate to acid-base catalysts earlier reported. The joint research based on CO2-TPD, NH3-TPD and poisoning experiment substantiates that the synergy effect of acid-base sites plays an essential role in this catalytic system. Isotopic labelling MS, in-situ FT-IR and DFT studies further verify that the CTH reaction of furfural occurs via the Meerwein-Ponndorf-Verley (MPV) route, in which the basic site promotes the deprotonation of isopropanol whilst the acid site facilitates the formation of a six-membered ring transition state. This work demonstrates an acid-base synergetic catalysis for the CTH reaction by revealing the structure-property correlation and exploring reaction route, which is instructive for designing high-performance heterogenous catalysts.

Synthesis of Mo–Cr Mixed Metal Oxide Catalyst Based on Pentagonal Unit Assembly and Selective Oxidation of Ethanol

Synthesis of Mo–Cr Mixed Metal Oxide Catalyst Based on Pentagonal Unit Assembly and Selective Oxidation of Ethanol

Structural study of mixed metal oxide catalysts comprising Mg, Ca, and Al used for upgrading biodiesel byproduct glycerol to glycerol carbonate

Glycerol is a by-product in biodiesel production. It is possible to convert glycerol to glycerol carbonate by carbonylation with CO2. In this work, novel mixed metal oxides of Mg-Ca, Mg-Al, and Ca-Al were prepared by co-precipitation method, and used as catalysts for this reaction for the first time. Catalysts were characterized through XRD, BET surface area analyzer, XPS, ICP-OES, SEM, and CO2-TPD analyses. Mg0.75Ca0.25O catalyst showed the highest glycerol conversion of 18.2±0.7%, and glycerol carbonate yield of 12% at initial conditions. Reaction parameters including pressure, temperature, and catalyst loading were optimized, when Mg0.75Ca0.25O catalyst was used, to achieve the highest glycerol carbonate yield. The optimal reaction parameters were pressure of 7 MPa, temperature of 180 ⁰C, and catalyst loading of 8.5%. Glycerol conversion was 25.7% and the glycerol carbonate yield was 16% at optimized condition. Morphology and chemical structure of Mg-Ca catalyst were also investigated.

A biobased mixed metal oxide catalyst for biodiesel production from waste cooking oil: reaction conditions modeling, optimization and sensitivity analysis study

This study assessed the utilization of a heterogeneous catalyst derived from waste marble tiles and cow horn for waste cooking oil-derived biodiesel synthesis. The synthesized composite catalyst was prepared from waste marble tiles and cow horn through sequential calcination and wet impregnation. The catalyst and its precursors were characterized to analyze their composition, structural, and surface properties. The biodiesel production process was modeled and optimized via the response surface methodology (RSM) and artificial neural networks (ANN). Characterization of waste cooking oil revealed its suitability in biodiesel production. The catalyst had a surface area of 301.510 m2/g, while the pore volume and pore diameter were 0.165 cm3/g and 2.110 nm respectively, which contributed to the optimum biodiesel yield of 98% at a reaction time of 119.92 min, a catalyst concentration of 5.12 wt%, a reaction temperature of 74.86 °C, and methanol-to-oil ratio of 11.43:1. The catalyst was reusable for up to seven cycles while retaining significant activity. The optimized biodiesel sample had properties that met standards. RSM and ANN demonstrated adequate representation of the biodiesel yield as shown by their high R2 values although ANN was superior since it had higher R2 (0.9993) and adjusted R2 (0.9977) values. Global sensitivity analysis results showed reaction temperature as the most important input variable. This work has provided insights into the valorization of waste cooking oil for sustainable biodiesel production through heterogeneous catalysis.

Catalytic Transfer Hydrogenolysis of Switchgrass Lignin with Ethanol Using Spinel-Type Mixed-Metal Oxide Catalysts Affords Control of the Oxidation State of Isolated Aromatic Products

Catalytic Transfer Hydrogenolysis of Switchgrass Lignin with Ethanol Using Spinel-Type Mixed-Metal Oxide Catalysts Affords Control of the Oxidation State of Isolated Aromatic Products

A switchable hydrogenation chemoselectivity of biomass platform compounds based on solvent regulation

Selective catalytic conversion of biomass-derived compounds to fuels and fine chemicals serves as a renewable energy pathway for the partial substitution of fossil resources, in which reaction pathway and selectivity control are key issues. Herein, we report a fully exposed Pt clusters immobilized on CoAl mixed metal oxides catalyst (denoted as Ptn/CoAl-MMOs), which exhibits prominent catalytic performance towards liquid phase hydrogenation reaction of furfural (FAL). Noteworthily, the hydrogenation chemoselectivity can be switched among four products via using four different solvents: tetrahydrofurfuryl alcohol (THFA; yield: 91.4%), furfuryl alcohol (FA; yield: 97.7%), 2-methylfuran (2-MF; yield: 92.1%) and furan (FU; yield: 90.8%) are obtained in ethanol, dioxane, isopropanol and n-hexane solvent, respectively. Experimental studies (in situ FT-IR and TPSR-Mass) combined with theoretical calculations (DFT) reveal that solvent molecules exert an essential influence on the adsorption configuration of FAL via changing the solvent-catalyst and/or substrate-catalyst interaction, which ultimately determines the hydrogenation pathway, key intermediate and final product. This work demonstrates a facile solvent-dependent product-switching strategy within one catalytic system, which opens up potential opportunities for tailoring hydrogenation selectivity in liquid-solid catalytic reactions towards biomass upgrading.

Hydrogenolysis of furfuryl alcohol over CuCeMgAl mixed metal oxide catalysts derived from layered double hydroxides

LDH-derived CuCeMgAl mixed metal oxide catalysts were synthesized. Ce addition promoted Cu dispersion and improved catalyst basicity, resulting in high activity in furfuryl alcohol hydrogenolysis and high selectivity toward 1,2-pentanediol.

Intelligent Chemometric Modelling of Al2O3 Supported Mixed Metal Oxide Catalysts for Oxidative Dehydrogenation of n-Butane Using Simple Features

The development of efficient and selective catalysts for the oxidative dehydrogenation (ODH) of n-butane to produce butenes and butadiene with high performance has been subject of intense research in recent...