Utilization of Volatile Organic Compounds as an Alternative for Destructive Abatement

A comprehensive review and perspective research in technology integration for the treatment of gaseous volatile organic compounds

Volatile organic compounds (VOCs) are harmful pollutants emitted from industrial processes. They pose a risk to human health and ecosystems, even at low concentrations. Controlling VOCs is crucial for good air quality. This review aims to provide a comprehensive understanding of the various methods used for controlling VOC abatement. The advancement of mono-functional treatment techniques, including recovery such as absorption, adsorption, condensation, and membrane separation, and destruction-based methods such as natural degradation methods, advanced oxidation processes, and reduction methods were discussed. Among these methods, advanced oxidation processes are considered the most effective for removing toxic VOCs, despite some drawbacks such as costly chemicals, rigorous reaction conditions, and the formation of secondary chemicals. Standalone technologies are generally not sufficient and do not perform satisfactorily for the removal of hazardous air pollutants due to the generation of innocuous end products. However, every integration technique complements superiority and overcomes the challenges of standalone technologies. For instance, by using catalytic oxidation, catalytic ozonation, non-thermal plasma, and photocatalysis pretreatments, the amount of bioaerosols released from the bioreactor can be significantly reduced, leading to effective conversion rates for non-polar compounds, and opening new perspectives towards promising techniques with countless benefits. Interestingly, the three-stage processes have shown efficient decomposition performance for polar VOCs, excellent recoverability for nonpolar VOCs, and promising potential applications in atmospheric purification. Furthermore, the review also reports on the evolution of mathematical and artificial neural network modeling for VOC removal performance. The article critically analyzes the synergistic effects and advantages of integration. The authors hope that this article will be helpful in deciding on the appropriate strategy for controlling interested VOCs.

Investigation on removal of multi-component volatile organic compounds in a two-stage plasma catalytic oxidation system - Comparison of X (X=Cu, Fe, Ce and La) doped Mn2O3 catalysts

Mn₂O₃-X catalysts (X = Cu, Fe, Ce and La) were prepared based on γ-Al₂O₃ for the mixture degradation of muti-component volatile organic compounds (VOCs) composed of toluene, acetone, and ethyl acetate. The catalysts were characterized, and the density functional theory (DFT) simulation of ozone adsorption on Mn₂O₃-X were carried out to investigate the influence of adsorption energy on catalytic performance. The results showed that the removal efficiency (RE) of each VOC component was similarly improved by Mn₂O₃-X catalysts, and the greatest increase in VOCs' removal efficiency was obtained (7.8% for toluene, 86.2% for acetone, and 82.5% for ethyl acetate) at a special input energy (SIE) of 700 J L^-1 with Mn₂O₃-La catalyst. Characterization results demonstrated that Mn₂O₃-La catalyst had the highest content of low valence Mn elements and the greatest O_ads/O_latt ratio, as well as the lowest reduction temperature. Mn₂O₃-La catalyst also presented superior catalytic effect in improving carbon balance (CB) and CO₂ selectivity ( [Formula: see text] ). The CB and [Formula: see text] were increased by 47.7% and 12.61% respectively with Mn₂O₃-La at a SIE of 400 J L^-1 compared with that when only γ-Al₂O₃ was applied. The DFT simulation results of ozone adsorption on Mn₂O₃-X catalysts indicated that the adsorption energy of catalyst crystal was related to the catalytic performance of the catalyst. The Mn₂O₃-La/γ-Al₂O₃ catalyst, which had the highest absolute value of adsorption energy, presented the best performance in improving VOCs' RE.

New iron(iii) complex of bis-bidentate-anchored diacyl resorcinol on a Fe3O4 nanomagnet: C-H bond oxygenation, oxidative cleavage of alkenes and benzoxazole synthesis

We have synthesized a novel, bis-bidentate, covalently anchored, 4,6-diacetyl resorcinol (DAR) ligand on silica-coated magnetic Fe₃O₄ nanoparticles and the corresponding bi-metallic iron(iii) complex (Fe₃O₄@SiO₂-APTESFe₂L^DAR). Both the chemical nature and the structure of the homogeneously heterogenized catalyst were investigated using physico-chemical techniques. The results obtained by XPS, XRD, FT-IR, TGA, VSM, SEM, TEM, EDX, ICP and AAS revealed a magnetic core, a silica layer and the grafting of a binuclear iron complex on the Fe₃O₄@SiO₂-APTES, as well as its thermodynamic stability. Despite many reports of metal complexes on different supports, there are no reports of anchored, bi-metallic complexes. To the best of our knowledge, this is the first report of a bi-active site catalyst covalently attached to a support. This study focuses on the catalytic activity of an as-synthesized, bi-active site catalyst for C-H bond oxygenation, the oxidative cleavage of alkenes, and the multicomponent, one-pot synthesis of benzoxazole derivatives with excellent yields from readily available starting materials. Our results indicated high conversion rates and selectivity under mild reaction conditions and simple separation using a magnetic field. The leaching and recyclability tests of the catalyst were investigated for the above processes, which indicated that all the reactions proceed via a heterogeneous pathway and that the catalyst is recyclable without any tangible loss in catalytic activity for at least 8, 5 and 5 cycles for C-H bond oxygenation, C[double bond, length as m-dash]C bond cleavage and benzoxazole synthesis, respectively.

Influence of the Thermal Processing and Doping on LaMnO3 and La0.8A0.2MnO3 (A = Ca, Sr, Ba) Perovskites Prepared by Auto-Combustion for Removal of VOCs

Single-phase oxygen stoichiometric LaMnO3 and doped La0.8A0.2MnO3 (A = Ca, Sr, Ba) perovskites have been prepared by a simple one-step auto-combustion method. Cation-deficient LaMnO3+δ and La0.8A0.2MnO3+δ were obtained by calcination of the former samples in air at 750 °C. The samples were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxygen desorption, and N2 physisorption in order to apply them as catalysts in the complete catalytic oxidation of acetone as a model volatile organic compound. The studied phases show the expected orthorhombic and rhombohedral perovskite crystal structures. Catalytic experiments performed with all the samples show measurable activity already at 100 °C. At 200 °C, doped La0.8A0.2MnO3 samples show higher activity than undoped LaMnO3, with increasing conversion with larger A-cation size. Calcined samples also show higher activity than as-prepared ones making La0.8Ba0.2MnO3+δ the best catalyst at this temperature. All doped samples show >95% acetone conversion at T ≥ 250 °C with a weak dependence on the sample processing or A cation doping. The collected evidence confirms that the most important factors for the catalytic activity of these oxides are the Mn4+/Mn3+ molar ratio on the surface of the samples and the cation-deficiency of the bulk perovskite structure. In addition, increasing the symmetry of the bulk crystal structure appears to have an additional favourable effect. Despite the observation of the presence of surface carbonates, we show that it is possible to use the as-prepared samples without further thermal treatment with good results in the oxidation of acetone.

Plasma and Superconductivity for the Sustainable Development of Energy and the Environment

The main aim of this review is to present the current state of the research and applications of superconductivity and plasma technologies in the field of energy and environmental protection. An additional goal is to attract the attention of specialists, university students and readers interested in the state of energy and the natural environment and in how to protect them and ensure their sustainable development. Modern energy systems and the natural environment do not develop in a sustainable manner, thus providing future generations with access to energy that is generated from renewable sources and that does not degrade the natural environment. Most of the energy technologies used today are based on non-renewable sources. Power contained in fuel is irretrievably lost, and the quality of the energy is lowered. It is accompanied by the emissions of fossil fuel combustion products into the atmosphere, which pollutes the natural environment. Environmental problems, such as the production of gaseous and solid pollutants and their emission into the atmosphere, climate change, ozone depletion and acid rains, are discussed. For the problem of air pollution, the effects of combustion products in the form of carbon oxides, sulfur and nitrogen compounds are analyzed. The plasma and superconductivity phenomena, as well as their most important parameters, properties and classifications, are reviewed. In the case of atmospheric pressure plasma generation, basic information about technological gas composition, pressure, discharge type, electromagnetic field specification, electrode geometry, voltage supply systems, etc., are presented. For the phenomenon of superconductivity, attention is mainly paid to the interdependencies between Tc, magnetic flux density Bc and current density Jc parameters. Plasma technologies and superconductivity can offer innovative and energy-saving solutions for power engineering and environmental problems through decreasing the effects of energy production, conversion and distribution for the environment and by reductions in power losses and counteracting energy quality degradation. This paper presents an overview of the application of technologies using plasma and superconductivity phenomena in power engineering and in environmental protection processes. This review of plasma technologies, related to reductions in greenhouse gas emissions and the transformation and valorization of industrial waste for applications in energy and environmental engineering, is carried out. In particular, the most plasma-based approaches for carbon oxides, sulfur and nitrogen compounds removal are discussed. The most common plasma reactors used in fuel reforming technologies, such as dielectric barrier discharge, microwave discharge and gliding-arc discharge, are described. The advantages of solid waste treatment using plasma arc techniques are introduced. Applications of superconductors for energy generation, conversion and transmission can be divided into two main groups with respect to the conducted current (DC and AC) and into three groups with respect to the employed property (zero resistivity, ideal magnetism/flux trapping and quench transition). Among the superconductivity applications of electrical machines, devices for improving energy quality and storage and high field generation are described. An example that combines the phenomena of hot plasma and superconductivity is thermonuclear fusion. It is a hope for solving the world’s energy problems and for creating a virtually inexhaustible, sustainable and waste-free source of energy for many future generations.

Vanadia-Zirconia and Vanadia-Hafnia Catalysts for Utilization of Volatile Organic Compound Emissions

Utilization is a sustainable and interesting alternative for the destructive treatment of volatile organic compounds due to avoided CO₂ emission. This work concentrates on the development of active and sulfur-tolerant catalysts for the utilization of contaminated methanol. Impregnated and sol-gel prepared vanadia-zirconia and vanadia-hafnia catalysts were thoroughly characterized by N₂ sorption, analytical (S)TEM, elemental analysis, XRD and Raman spectroscopy, and their performances were evaluated in formaldehyde production from methanol and methanethiol mixture. The results showed higher activity of the sol-gel prepared catalysts due to formation of mono- and polymeric vanadia species. Unfortunately, the most active vanadia sites were deactivated more easily than the metal-mixed oxide HfV₂O₇ and ZrV₂O₇ phases, as well as crystalline V₂O₅ observed in the impregnated catalysts. Metal-mixed oxide phases were formed in impregnated catalysts through formation of defects in HfO₂ and ZrO₂ structure during calcination at 600 °C, which was evidenced by Raman spectroscopy. The sol-gel prepared vanadia-zirconia and vanadia-hafnia catalysts were able to produce formaldehyde from contaminated methanol with high selectivity at temperature around 400 °C, while impregnated catalysts required 50-100 °C higher temperatures.

Bismuth as Smart Material and Its Application in the Ninth Principle of Sustainable Chemistry

This paper reports an overview of Green Chemistry and the concept of its twelve principles. This study focusses on the ninth principle of Green Chemistry, that is, catalysis. A report on catalysis, in line with its definition, background, classification, properties, and applications, is provided. The study also entails a green element called bismuth. Bismuth’s low toxicity and low cost have made researchers focus on its wide applications in catalysis. It exhibits smartness in all the catalytic activities with the highest catalytic performance among other metals.

Electronic structure and reactivity of Fe(iv)oxo species in metal-organic frameworks

We investigate the potential use of Fe(iv)oxo species supported on a metal-organic framework in the catalytic hydroxylation of methane to produce methanol. We use periodic density-functional theory calculations at the 6-31G**/B3LYP level of theory to study the electronic structure and chemical reactivity in the hydrogen abstraction reaction from methane in the presence of Fe(iv)O(oxo) supported on MOF-74. Our results indicate that the Fe(iv)O moiety in MOF-74 is characterised by a highly reactive (quintet) ground-state, with a distance between Fe(iv) and O(oxo) of 1.601 Å, consistent with other high-spin Fe(iv)O inorganic complexes in the gas phase and in aqueous solution. Similar to the latter systems, the highly electrophilic character (and thus the reactivity) of Fe(iv)O in MOF-74 is determined by the presence of a low-lying anti-bonding virtual orbital (3σ*), which acts as an electron acceptor in the early stages of the hydrogen atom abstraction from methane. We estimate an energy barrier for hydrogen abstraction of 50.77 kJ mol-1, which is comparable to the values estimated in other gas-phase and hydrated Fe(iv)O-based complexes with the ability to oxidise methane. Our findings therefore suggest that metal-organic frameworks can provide suitable supports to develop new solid-state catalysts for organic oxidation reactions.

Removal of VOCs from gas streams with double perovskite-type catalysts

Double perovskite-type catalysts including La₂CoMnO₆ and La₂CuMnO₆ are first evaluated for the effectiveness in removing volatile organic compounds (VOCs), and single perovskites (LaCoO₃, LaMnO₃, and LaCuO₃) are also tested for comparison. All perovskites are tested with the gas hourly space velocity (GHSV) of 30,000hr^-1, and the temperature range of 100-600°C for C₇H₈ removal. Experimental results indicate that double perovskites have better activity if compared with single perovskites. Especially, toluene (C₇H₈) can be completely oxidized to CO₂ at 300°C as La₂CoMnO₆ is applied. Characterization of catalysts indicates that double perovskites own unique surface properties and are of higher amounts of lattice oxygen, leading to higher activity. Additionally, apparent activation energy of 68kJ/mol is calculated using Mars-van Krevelen model for C₇H₈ oxidation with La₂CoMnO₆ as catalyst. For durability test, both La₂CoMnO₆ and La₂CuMnO₆ maintain high C₇H₈ removal efficiencies of 100% and 98%, respectively, at 300°C and 30,000hr^-1, and they also show good resistance to CO₂ (5%) and H₂O_(g) (5%) of the gas streams tested. For various VOCs including isopropyl alcohol (C₃H₈O), ethanal (C₂H₄O), and ethylene (C₂H₄) tested, as high as 100% efficiency could be achieved with double perovskite-type catalysts operated at 300-350°C, indicating that double perovskites are promising catalysts for VOCs removal.

Hexaphenylbenzene and hexabenzocoronene-based porous polymers for the adsorption of volatile organic compounds

Here we report the vapor adsorption properties of two novel hexaphenylbenzene and hexabenzocoronene-based porous polymers which display excellent affinity for organic compounds (up to 100 wt%) and selectivity over water (<1 wt%).