Catalytic combustion of volatile organic compounds over group IB metal catalysts on Fe2O3

Boosted Light Alkane Deep Oxidation via Metal Bond Length Modulation-Induced C-C Bond Preferential Activation

Light alkanes (LAs), typical VOCs existing in both stationary and mobile sources, pose significant environmental concerns. Although noble metal catalysts demonstrate strong C-H bond activation, their effectiveness in degrading LAs is hindered by inherent challenges, including poor chemical stability and water resistance. Here, from a new perspective, we propose a feasible strategy that adjusting the metal bond lengths within Pd clusters through partial substitution of smaller radius 3d transition metals (3dTMs) to prioritize the activation of low-energy C-C bonds within LAs. Benefiting from this, PdCo/CeO2 exhibits exceptional catalytic performance in propane degradation due to their high capacity for C-C cleavage stemming from the shorter Pd-Co length (2.51 Å) and lower coordination number (1.73), boosting the activation of α-H and β-H of propane simultaneously and accelerating the mobility of postactivated oxygen species to prevent Pd center deep oxidation. The presence of 3dTMs on Pd clusters improves the redox and charge transfer ability of catalysts, resulting in an amplified generation of oxygen vacancies and facilitating the adsorption and activation of reactants. Mechanistic studies and DFT calculations suggest that the substitution of 3dTMs significantly accelerate C-C bond cleavage within C3 intermediates to generate the subsequent C2 and C1 intermediates, suppressing the generation of harmful byproducts.

OH-initiated degradation of 1,2,3-trimethylbenzene in the atmosphere and wastewater: Mechanisms, kinetics, and ecotoxicity

1,2,3-Trimethylbenzene (1,2,3-TMB) is an important volatile organic compound (VOC) present in petroleum wastewater and the atmosphere. This compound can be degraded by OH radicals via abstraction, addition and substitution mechanisms. Results show that the addition mechanism is dominant and H-abstraction is subdominant, while methyl abstraction and substitution mechanisms are negligible in the gas and aqueous phases. Moreover, H-abstraction products undergo further reactions with O₂, NO, NO₂, H₂O, and OH radicals in the atmosphere. Time-dependent density functional theory (TDDFT) calculations show that the degraded products, including 2,3,4-trimethylphenyl-nitroperoxoite, 1,2,3-trimethyl-4-nitrobenzene, 1,2,3-trimethyl-5-nitrobenzene, 2,6-dimethylbenzyl nitroperoxoite, 2,3-dimethylphenyl nitroperoxoite, 2,6-dimethylbenzaldehyde, and 2,3-dimethylbenzaldehyde, can photolyze under the sunlight. Kinetically, the calculated total rate constant is 5.57 × 10^-11 cm³ molecule^-1·s^-1 at 1 atm and 298 K, which is consistent with available experimental values measured in the atmosphere. In addition, the calculated total reaction rate constant in water is close to that in the gas phase. In terms of ecotoxicity, all degradation products are less toxic than the initial reactant to fish, green algae and daphnia. For mammals represented by rats, 1,2,3-TMB and its products are moderately toxic, except for 2,3-dimethylphenol and 2,6-dimethylphenol, which are slightly toxic.

Harnessing Waste Heat from Indoor lamps for Sustainable Thermocatalytic Mineralization of Acetaldehyde using Platinized TiO2

This study demonstrates the first reported thermocatalytic oxidation of an indoor volatile organic compound (VOC), acetaldehyde, by harnessing the waste-heat energy from indoor light sources (e.g., halogen lamps) without additional energy inputs. With an optimal Pt-TiO₂ catalyst, the designed catalyst-coated lampshade was successfully activated under waste-heat energy (∼120 °C) and achieved the complete mineralization of CH₃CHO into CO₂ (k = 0.02 min^-1). The catalytic activity of Pt-TiO₂ was extremely dependent on its preparation method which greatly influenced the characteristics (e.g., oxidation state and size) of Pt. The thermocatalytic oxidation mechanism of CH₃CHO over Pt-TiO₂ was investigated, which revealed that O₂ and H₂O sources play vital roles. Although Pt is an expensive noble metal, the thermocatalytic process on the Pt-TiO₂-coated lampshade without additional energy, along with its outstanding activity, can offset the high material cost. The proposed strategy offers a sustainable and feasible method for the degradation of indoor VOCs.

Effect of palladium on the black mass-based catalyst prepared from spent Zn/Mn alkaline batteries for catalytic combustion of volatile organic compounds

A large amount of spent batteries is produced annually. When spente batteries are buried, their harmful components may contaminate soil and water. Therefore, recycling of spent batteries is essential for environmental reasons. We evaluated the BM (black mass) of spent Zn/Mn alkaline batteries as a catalyst substance for the catalytic combustion of volatile organic compounds (VOCs: benzene, toluene, and o-xylene). The SBM catalyst (black mass-based catalyst) was prepared by treating BM with 0.1 N of sulfuric acid solution. Major elements of the SBM catalyst were manganese, zinc, iron, aluminum, potassium, and sodium except for carbon. In addition, to find out the additive effect of palladium on the SBM catalyst, we prepared the Pd/SBM catalysts using a conventional impregnation method. We investigated the physicochemical properties of the SBM and Pd/SBM catalysts by instrumental analysis. Benzene, toluene, and o-xylene (BTX) were oxidized completely over the SBM catalyst at reaction temperatures less than 410, 340, and 410 °C, respectively (gas hourly space velocity: 40,000 h^-1). As expected, for the Pd/SBM catalysts, increasing the palladium loading on the SBM from 0.1 wt% to 1.0 wt% increased the conversions of BTX. In the 1.0 wt% Pd/SBM catalyst, the reaction temperatures for catalytic combustion of BTX were greatly reduced to 310, 260, and 250 °C, respectively (gas hourly space velocity: 40,000 h^-1). Instrumental analysis indicated that the increase in activity by adding palladium resulted from the active ingredient (palladium oxide: PdO) and better redox properties.

Performance of platinum doping on spent alkaline battery-based catalyst for complete oxidation of o-xylene

Oxidation of o-xylene was performed using alkaline battery-based catalyst doped with platinum to investigate the properties and activities. O-xylene was selected as the model of volatile organic compound (VOC) in this work. Physicochemical properties of the selected catalysts were characterized by FE/TEM (field emission transmission electron microscopy), BET (Brunauer-Emmett-Teller) analysis, XRD (X-ray powder diffraction), SEM/EDX (scanning electron microscopy/energy dispersive X-ray spectroscopy), and H₂-TPR (hydrogen temperature programmed reduction). Major elements of the spent alkaline battery-based catalyst treated with sulfuric acid solution [SAB (400) catalyst] were manganese, zinc, iron, oxygen, carbon, chlorine, aluminum, sodium, silicon, and potassium. Increasing the doping amount of platinum on SAB (400) catalyst from 0.1 to 1 wt% increased particle size of platinum and lowered the temperature of TPR (TTP) for SAB (400) catalyst. Better redox properties were achieved with an increase in the o-xylene conversion according to the doping amount of platinum. When GHSV (gas hourly space velocity) was 40,000 h^-1, o-xylene was oxidized completely over SAB (400) catalyst and 1.0 wt% Pt/SAB(400) catalyst at temperatures of 400 °C and 280 °C, respectively.

Recycling of a spent alkaline battery as a catalyst for the total oxidation of hydrocarbons

A spent alkaline battery-based (SB) catalyst was prepared from the black mass of a spent alkaline battery to determine the potential of recycling spent alkaline batteries as catalysts for the total oxidation of hydrocarbons. Five different acids (H₂SO₄, HNO₃, C₂H₂O₄, HCl, and H₃PO₄) were used to examine the effect of acid treatment on catalytic activity during catalyst preparation. Hexane, benzene, toluene, and o-xylene (HBTX) were adopted as the VOCs for experiments. The properties of the prepared catalysts were studied using ICP/OES, BET, XRD, ATR/FTIR, TGA, SEM, and H₂-TPR analyses. The results showed that acid treatment significantly influenced the activity of the SB (400) catalyst, with the type of acid also found to greatly influence the activity of the catalyst. The order of activity according to the type of acid was H₂SO₄ > HNO₃ > C₂H₂O₄ > HCl > H₃PO₄ > none. Good performance of an acid-treated SB catalyst was associated with high concentrations of manganese and iron and a large BET surface area. In addition, the sequence in which the TPR peaks appeared at low temperatures according to each acid treatment was consistent with that of catalyst activity.

Enhanced removal of toluene by pulse discharge plasma coupled with MgO cathode and graphene Mn-Ce bimetallic oxide

Herein, MgO cathode and graphene Mn-Ce bimetallic oxide were utilized to jointly enhance the removal of toluene in pulsed discharge plasma (PDP). Compared to the common cathode, the MgO cathode enhanced the density of high energy electrons, and then induced to higher removal of toluene. However, the removal of toluene by PDP/MgO system was still insufficient, and there was a large amount of underutilized O₃ in the products. Based on this, Mn-Ce/graphene catalysts were introduced into PDP/MgO system. The Mn-Ce (8:1)/graphene catalyst had the highest catalytic activity. Under the discharge power of 2.1 W, toluene degradation rate and CO₂ selectivity increased by 27.5% and 22.0%, respectively. This was ascribed to the synergistic effect of the solid solution formed between MnO_x and CeO_x, increasing the proportion of O_ads on the surface of the catalyst. The higher O_ads/O_latt ratio lead to the better catalytic activity, which was conducive to the complete transformation of the intermediate products to CO₂ and H₂O. According to the detected products, the degradation pathway and the mechanism of toluene degradation were proposed finally. The PDP itself, field emission effect of MgO cathode and catalytic effect of Mn-Ce/graphene for jointly improve the toluene removal and CO₂ selectivity.

On the Activity and Selectivity of CoAl and CoAlCe Mixed Oxides in Formaldehyde Production from Pulp Mill Emissions

Contaminated methanol has very good potential for being utilized in formaldehyde production instead of its destructive abatement. The activities, selectivities and stabilities of cobalt–alumina and cobalt–alumina–ceria catalysts prepared by the hydrotalcite-method were investigated in formaldehyde production from emissions of methanol and methanethiol. Catalysts were thoroughly characterized and the relationships between the characterization results and the catalytic performances were drawn. The preparation method used led to the formation of spinel-type structures in the form of Co2AlO4 based on x-ray diffraction (XRD) and Raman spectroscopy. Ceria seems to be present as CeO2, even though interaction with alumina is possible in the fresh catalyst. The same structure is maintained after pelletizing the cobalt–alumina–ceria catalyst. The cobalt–alumina–ceria catalyst was slightly better in formaldehyde production, probably due to lower redox temperatures and higher amounts of acidity and basicity. Methanol conversion is negatively affected by the presence of methanethiol; however, formaldehyde yields are improved. The stability of the pelletized catalyst was promising based on a 16 h experiment. During the experiment, cobalt was oxidized (Co2+ → Co3+), cerium was reduced (Ce4+ → Ce3+) and sulfates were formed, especially on the outer surface of the pellet. These changes affected the low temperature performance of the catalyst; however, the formaldehyde yield was unchanged.

Recent Development of Catalysts for Removal of Volatile Organic Compounds in Flue Gas by Combustion: A Review

Volatile organic compounds (VOCs) emitted from anthropogenic sources pose direct and indirect hazards to both atmospheric environment and human health due to their contribution to the formation of photochemical smog and potential toxicity including carcinogenicity. Therefore, to abate VOCs emission, the catalytic oxidation process has been extensively studied in laboratories and widely applied in various industries. This report is mainly focused on the benzene, toluene, ethylbenzene, and xylene (BTEX) with additional discussion about chlorinated VOCs. This review covers the recent developments in catalytic combustion of VOCs over noble metal catalysts, nonnoble metal catalysts, perovskite catalysts, spinel catalysts, and dual functional adsorbent-catalysts. In addition, the effects of supports, coke formation, and water effects have also been discussed. To develop efficient and cost-effective catalysts for VOCs removal, further research in catalytic oxidation might need to be carried out to strengthen the understanding of catalytic mechanisms involved.

Property and performance of red mud-based catalysts for the complete oxidation of volatile organic compounds

Red mud (RM) was assessed as a catalyst for the complete oxidation of volatile organic compounds (VOCs). The catalytic activity of RM was influenced by an acid treatment and the calcination temperature. Acid-treated RM (HRM) catalysts with a platinum loading (Pt/HRM) were prepared using a conventional impregnation method. Platinum catalysts supported on γ-Al2O3 (Pt/Al) were prepared for comparison. The physicochemical properties of the RM, HRM and Pt/HRM catalysts were characterized by BET analysis, ICP-AES, H2-TPD, XRD, FTIR, SEM, and FE-TEM. The acid treatment increased the BET surface area of the RM significantly, resulting in an increase in catalytic activity. Increasing the calcination temperature from 400°C to 600°C caused a decrease in its catalytic activity. Increasing the platinum loading on HRM(400) from 0.1 wt.% to 1 wt.% led to an increase in the toluene conversion, which was attributed to the better redox properties. The catalytic activities of the Pt/HRM(400) catalysts were superior to those of the Pt/Al catalysts. Benzene, toluene, o-xylene, and hexane were oxidized completely over the 1 wt.% Pt/HRM(400) catalyst at reaction temperatures less than 280°C. The presence of water vapor in the feed had a negative effect on the activity of the 1 wt.% Pt/HRM(400) catalyst.

Low temperature catalytic oxidation of volatile organic compounds: a review

Volatile organic compounds (VOCs) are toxic and recognized as one of the major contributors to air pollution.

Effect of Temperature and Catalyst Type on the Catalytic Combustion of Formaldehyde

In this study, the catalytic combustion of a volatile organic compound (VOC) namely formaldehyde on manganese oxide catalysts supported on silica or alumina, and on an industrial catalyst, i.e. a mixture of copper oxide and zinc oxide, was studied in the temperature range 125 – 225 °C. Formaldehyde was used as the aqueous solution. It was found that as the temperature was increased, the combustion of the produced and feed formaldehyde was enhanced whereas methanol combustion decreased. Also, the degree of conversion increased with the percentage of MnO in the catalysts.

TAP study of toluene total oxidation over a Co3O4/La-CeO2 catalyst with an application as a washcoat of cordierite honeycomb monoliths

The total oxidation of toluene was studied over a Co₃O₄/La-CeO₂ catalyst in a Temporal Analysis of Products (TAP) set-up in the temperature range 713 K to 873 K in the presence and absence of dioxygen.

Kinetic Study of Combustion of Isopropanol and Ethyl Acetate on Monolith-Supported CeO2 Catalyst

The complete catalytic combustion kinetics of isopropanol and ethyl acetate were investigated using a CeO2 catalyst coated on a monolith support. The combustions were carried out at low temperatures and atmospheric pressure, on a fixed-bed monolithic reactor. The Mars and van Krevelen model, power rate law model and Langmuir – Hinshelwood model were used to analyse the experimental results. The differential reactor assumption was used to fit the kinetic models. Due to the low activation energies of the reactions, both the Mars – Van Krevelen and power rate law models showed good agreement between the measured and calculated reaction rates, with the Mars – Van Krevelen model being slightly better.