Catalytic oxidation performances of typical oxygenated volatile organic compounds (acetone and acetaldehyde) over MAlO (M = Mn, Co, Ni, Fe) hydrotalcite-derived oxides

Insight into modified CeMn based catalysts for efficient degradation of toluene by in situ infrared

Trace activated carbon (AC) and diatomaceous earth (DE) were used as structural promoters to be incorporated into Ce-Mn-based solid-solution catalysts by the redox precipitation method. The modified catalysts exhibit superior reducibility, with abundant Ce3+, Mn3+and reactive oxygen species, which are facilitated to the migration of oxygen and the generation of oxygen vacancies. In particular, the catalytic combustion temperatures of 90 % toluene (3000 ppm) on Ce1Mn3Ox-AC/DE were 84 °C (dry) and 123 °C (10 vol% H2O), respectively. The role of lattice oxygen and adsorbed oxygen was revealed by in situ DRIFTS. Additionally, in situ DRIFTS was employed to verify that the degradation of toluene by Ce1Mn3Ox-AC/DE satisfied the Langmuir-Hinshelwood (L-H) mechanism and the Mars-Van Krevelen (MvK) mechanism. The possible reaction pathway was elucidated (toluene → benzyl alcohol → benzoic acid → maleic anhydride → CO2 + H2O). Furthermore, final products attributed to toluene oxidation were detected by in situ DRIFTS at 50 °C in the absence of oxygen, confirming that the catalyst possessed outstanding performance at low temperatures beyond mere adsorption.

Revealing the mechanism of high water resistant and excellent active of CuMn oxide catalyst derived from Bimetal-Organic framework for acetone catalytic oxidation

Environmental H₂O is an influential factor in the low-temperature catalytic oxidation of volatile organic compounds (VOCs), and it significantly impacts the reaction process and mechanism. Here, a series of rod-like Cu-Mn oxides were synthesised by pyrolysing Cu/Mn-BTC for acetone oxidation. The results confirm that the formation of multiphase interfaces have more excellent catalytic performance compared to single-phase catalysis. This phenomenon can be attributed to the formation of multiphase interfaces, which resulted in the synthesized catalysts with more active oxygen species and defective sites. The CuMn₂O_x catalyst exhibited superior catalytic performance (T₉₀ = 150 °C), high water resistance and long-term stability. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy and thermal desorption-gas chromatography-mass spectrometry results indicated that the degradation pathway of acetone was as follows: acetone ((CH₃)₂CO*) → enolate complexes ((CH₂) = C(CH₃) O*) → acetaldehyde ((CH₃CHO*) → acetate (CH₃COO*) → formate (HCOO*) → CO₂ and H₂O. At a low-temperature, water vapour dissociated a large number of activated hydroxyl groups on the multiphase interface, which promoted the dissociation of enolate complexes and acetaldehyde species. This composite oxide is a promising catalyst for removing oxygenated VOCs at high humidity.

Accelerating the Low-Temperature Catalytic Oxidation of Acetone over Al-Substituted Mn-Al Oxides by Rate-Limiting Step Modulation

In order to enhance the catalytic activity and improve the stability of Mn-Al oxides in acetone oxidation, it is interesting to have found that modulating and accelerating the rate-limiting step by Al substitution rather than just mixing of Mn and Al is crucial for hydrocarbon efficient catalytic destruction. Here, a series of Mn-Al oxides with different Al substitution ratios were prepared by a scalable and facile hydrothermal-redox strategy. The reaction rate, selectivity, and stability of the representative α-MnO₂ catalyst in acetone oxidation can be remarkably promoted by simple replacing of the partial framework Mn with Al, which changes the rate-limiting step from acetic acid dissociation to ethanol decomposition accelerated by H₂O molecules. Among them, MnAl_0.5 displays the best catalytic performance with 90% of acetone converted at just 165 °C and a remarkable CO₂ yield. DFT results suggest that the p_y and p_x orbitals of the O element take part in the formation of the carbonyl group when the intermediate of removing H* from ethanol reacts with the hydroxyl group of H₂O. The d_xz orbital of Mn with p-electron of Al plays a vital role in the rate-limiting step. The work provides new insights into engineering catalysts for industrial VOC efficient and economical mineralization.

Promotional effects of calcination temperature and H2O on the catalytic activity of Al-substituted MnAlO catalysts for low-temperature acetone oxidation

In order to enhance the role of Al in the materials, Al-substituted MnAlO catalysts were synthesized via the hydrothermal-redox method at different calcination temperatures for acetone oxidation. There were Al-substituted α-MnO₂ and amorphous aluminum oxide existed with homogeneous dispersion of elements in the catalysts. The surface property, reaction rate, CO₂ yield and water resistance of MnAlO catalysts were greatly affected by calcination temperatures. MnAlO-450 catalyst exhibited the best catalytic performance (acetone conversion of 90% at 165 °C) with CO₂ yield higher than 99.7%, which was mainly related to the weaker Mn-O bond strength, lower temperature reducibility and abundant Lewis acid sites. The acetone conversion of MnAlO-450 increased by as much as 16% in the presence of 1 vol% H₂O compared to that in the absence of H₂O at T₅₀ (the temperature for 50% conversion of acetone). The acceleration consumption of ethanol as the main by-product by H₂O improved the catalytic performance. This work would shed light on the Al substitution based catalysts for OVOC oxidation with highly efficient and water resistance.

A critical review on plasma-catalytic removal of VOCs: Catalyst development, process parameters and synergetic reaction mechanism

It is urgent to control the emission of volatile organic compounds (VOCs) due to their harmful effects on the environment and human health. A hybrid system integrating non-thermal-plasma and catalysis is regarded as one of the most promising technologies for VOCs removal due to their high VOCs removal efficiency, product selectivity and energy efficiency. This review systematically documents the main findings and improvements of VOCs removal using plasma-catalysis technology in recent 10 years. To better understand the fundamental relation between different aspects of this research field, this review mainly addresses the catalyst development, key influential factors, generation of by-products and reaction mechanism of VOCs decomposition in the plasma-catalysis process. Also, a comparison of the performance in various VOCs removal processes is provided. Particular emphasis is given to the importance of the selected catalyst and the synergy of plasma and catalyst in the VOCs removal in the hybrid system, which can be used as a reference point for future studies in this field.

Interface-Enhanced Oxygen Vacancies of CoCuOx Catalysts In Situ Grown on Monolithic Cu Foam for VOC Catalytic Oxidation

The development of highly efficient and stable monolithic catalysts is essential for the removal of volatile organic compounds (VOCs). Copper foam (CF) is a potential ideal carrier for monolithic catalysts, but its low surface area is not conducive to dispersion of active species, thus reducing the interface interaction with active species. Herein, a vertically oriented Cu(OH)₂ nanorod was in situ grown on the CF, which acted as the template and precursor to synthesize CoCu-MOF. The optimized catalyst (12CoCu-R) delivers excellent performance for acetone oxidation with a T₉₀ of 195 °C. Impressively, the catalyst demonstrated satisfactory stability in long-term, cycle, water resistance, and high airspeed tests. Therefore, the present study provides a novel strategy for rationally designing efficient monolithic catalysts for VOC oxidation and other environmental applications.

MgO modified zeolite facilitated low temperature chemisorptive removal of gaseous acetaldehyde into value added intermediate as desorption product

The adsorptive removal of acetaldehyde is more compatible for real-world applications. However, it must be upgraded from simple adsorption to a high efficiency process with value added products. This study develops a modified zeolite with Mg²⁺ ions that possesses acid-base sites for the removal of acetaldehyde at room temperature. Through a modified procedure, MgO is coated on commercial zeolite (13x), achieving a porosity of 501 m² g^-1 with MgO particles of 100 nm and pore diameter of 2.6 nm, and high breakthrough capacity of 50.00 mg/g. The initial pH and concentration of Mg²⁺ ion 12.5 and 0.2 M, respectively, with a maximum breakthrough capacity of 12.72 mg/g at 10% humidity. Significant variations in breakthrough capacity with respect to humidity in the presence of H₂S and NH₃ demonstrate the effects of water and gases on adsorption efficiency. Desorptive oxidation of adsorbed acetaldehyde at 250 °C yielded a high molecular weight intermediate ethylene oxide formation. The oxidation is followed by aldol condensation and hydrogenation. The higher breakthrough capacity and the intermediate product yielded using the developed MgO-zeolite proves the acid-base reaction sites involved in acetaldehyde removal follows chemisorption and possible process scale-up.

Synthesis of MnO2 derived from spent lithium-ion batteries via advanced oxidation and its application in VOCs oxidation

In this work, manganese is selectively and efficiently recovered from spent lithium-ion batteries via advanced oxidation by using potassium permanganate and ozone, and the transition metal-doped α-MnO₂ and β-MnO₂ are one-step prepared for catalytic oxidation of VOCs. The recovery rate of manganese can be approximately 100% while the recovery efficiency of cobalt, nickel, and lithium is less than 15%, 2%, and 1%, respectively. Compared with pure α-MnO₂ and β-MnO₂, transition metal-doped α-MnO₂ and β-MnO₂ exhibit better catalytic performance in toluene and formaldehyde removal attributed to their lower crystallinity, more defects, larger specific surface area, more oxygen vacancies, and better low-temperature redox ability. Besides, the introduction of the appropriate proportion of cobalt or nickel into MnO₂ can significantly improve its catalytic activity. Furthermore, the TD/GC-MS result indicates that toluene may be oxidized in the sequence of toluene - benzyl alcohol - benzaldehyde-benzoic acid - acetic acid, 2-cyclohexen-1-one, 4-hydroxy-, cyclopent-4-ene-1,3-dione - carbon dioxide. This method provides a route for the resource utilization of spent LIBs and the synthesis of MnO₂.

Synergistic Effects of Ternary PdO-CeO2-OMS-2 Catalyst Afford High Catalytic Performance and Stability in the Reduction of NO with CO

We developed a robust ternary PdO-CeO₂-OMS-2 catalyst with excellent catalytic performance in the selective reduction of NO with CO using a strategy based on combining components that synergistically interact leading to an effective abatement of these toxic gases. The catalyst affords 100% selectivity to N₂ at the nearly full conversion of NO and CO at 250 °C, high stability in the presence of H₂O, and a remarkable SO₂ tolerance. To unravel the origin of the excellent catalytic performance, the structural and chemical properties of the PdO-CeO₂-OMS-2 nanocomposite were analyzed in the as-prepared and used state of the catalyst, employing a series of pertinent characterization methods and specific catalytic tests. The experimental as well as theoretical results, based on density-functional theory calculations suggest that CO and NO follow different reaction pathways, CO is preferentially adsorbed and oxidized at Pd sites (Pd^II and Pd⁰), while NO decomposes on the ceria surface. Lattice oxygen vacancies at the interfacial perimeter of PdO-CeO₂ and PdO-OMS-2, and the diffusion of oxygen and oxygen vacancies are proposed to play a critical role in this multicenter reaction system.

SnNb2O6/NiCo-LDH Z-scheme heterojunction with regulated oxygen vacancies obtained by engineering the crystallinity for efficient and renewable photocatalytic H2 evolution

SnNb2O6/NiCo-LDH Z-scheme heterojunction with abundant oxygen vacancies exhibited highly activity and stability toward photocatalytic H2 evolution, ascribed to the regeneration of oxygen vacancy by engineering the crystallinity.

Enhanced Acetone Oxidation over the CeO2/Co3O4 Catalyst Derived from Metal-Organic Frameworks

A novel CeO₂/Co₃O₄ catalyst with a high catalytic activity has been designed and prepared by pyrolysis of metal-organic frameworks, and its catalytic performance was evaluated by the acetone catalytic oxidation reaction. The Co₃O₄-M catalyst with T₉₀ at 194 °C was prepared by pyrolysis of the MOF-71 precursor, which was 56 °C lower than that of commercial Co₃O₄ (250 °C). By the addition of cerium to the MOF-71 precursor, an enhanced CeO₂/Co₃O₄ catalyst with T₉₀ at 180 °C was prepared. Importantly, the CeO₂/Co₃O₄ catalyst exhibited superior stability for acetone oxidation. After 10 cycle tests, the conversion could also be maintained at 97% for at least 100 h with slight activity loss. Characterization studies were used to investigate the influence of cerium doping on the property of the catalyst. The results showed that addition of cerium could facilitate the expansion of the surface area and enhance the porous structure and reducibility at low temperature. Furthermore, the surface ratio of Co³⁺/Co²⁺ and mobile oxygen obviously improved with the addition of cerium. Therefore, the metal oxides prepared by this method have potential for the elimination of acetone.

Enhanced catalytic performance for volatile organic compound oxidation over in-situ growth of MnOx on Co3O4 nanowire

Hierarchical Co₃O₄@MnOx material has been synthesized by in-suit growth of MnOx on the Co₃O₄ and applied in catalytic oxidation of volatile organic compounds (VOCs). Results revealed that T₉₀ of acetone on the Co₃O₄@MnOx was 195 °C, which was 36 °C and 32 °C lower than that on the Co₃O₄ and MnOx/Co₃O₄, respectively. The universality experiments demonstrated that T₉₀ of ethyl acetate and toluene on the Co₃O₄@MnOx were 200 °C and 222 °C, respectively. The above results indicated that Co₃O₄@MnOx catalyst presented a robust catalytic performance. Characterization results showed that high catalytic activity of the Co₃O₄@MnOx catalyst could be attributed to the improvement of low temperature reducibility, the enhancement of Co³⁺ and adsorbed oxygen species resulted from the sufficient reaction between MnO₄^- and Co²⁺ during secondary hydrothermal process. Furthermore, stability and water-resistance experiments showed the Co₃O₄@MnOx catalyst with high cycle and long-term stability, satisfied endurability to 5.5-10 vol. % water vapor at 210 °C.

A facile chemical synthesis of CuxNi(1-x)Fe2O4 nanoparticles as a nonprecious ferrite material for electrocatalytic oxidation of acetaldehyde

In the present work, Cu-doped nickel ferrite (CuxNi(1-x)Fe2O4) nanoparticles (CuNFNPs) were chemically fabricated by adding citric acid as a capping agent followed by combustion and calcination for acetaldehyde oxidation reaction (AOR) in KOH electrolytes. The as-prepared CuNFNPs were studied in terms of Fourier-transform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM), Field emission scanning electron microscope (FE-SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) specific surface area analyses. The morphology of CuNFNPs has sponges-structure containing irregular pores. Additionally, XRD analysis indicated that the prepared CuNFNPs have a cubic-crystals ferrite without the existence of impurities and the crystal size around 20.2 nm. The electrooxidation of acetaldehyde by the presented CuNFNPs was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) in -OH media. Furthermore, the effects of -OH and acetaldehyde on the electrocatalytic performance were studied with and without Cu-doping in addition to EIS and CA studies which confirm the high-performance of CuNFNPs as an electrocatalyst for AOR.