Toluene degradation in air/H2O DBD plasma: A reaction mechanism investigation based on detailed kinetic modeling and emission spectrum analysis

Scheelite Catalysts for Thermal Mineralization of Toluene: A Mechanistic Overview

Toluene, a highly stable aromatic hydrocarbon, is utilized as a benchmark molecule for thermal mineralization by the catalytic community. Mostly, the catalysts used for toluene mineralization either use platinum group metals (PGM) as catalysts or are regulated by a plasma incinerator. Though these catalysts/processes promise better efficiency and lower reaction temperature, they are neither cost-effective nor do they produce thermally stable byproducts. However, most of the metal-oxide catalysts used for toluene degradation are less efficient owing to incomplete mineralization and formation of stable intermediates, which results in higher mineralization temperature. The present work showcases tungsten- and molybdenum-based Scheelites [BaXO4 (X = W, Mo, and Mo0.5W0.5)], which have been utilized for toluene mineralization at ∼200 °C. The intermediates formed during adsorption and thermal reaction are deciphered as a function of temperature using in situ FT-IR studies including their kinetic behavior. These surface intermediates formed over the Scheelite catalysts under an oxidative/inert atmosphere elucidate the toluene mineralization mechanism as a function of temperature/time. The surface active sites for these oxide catalysts for both adsorption and formation of reaction intermediates are deciphered using detailed X-ray photoelectron spectroscopy (XPS) studies. It shows the effective role of the oxidation states of constituent oxides M-O (M = Mo/ W) in the reaction mechanism. Mineralization of toluene in a nonoxidative atmosphere shows a Mars and Van Krevelen (MVK) type of mechanism, suggesting participation of lattice oxygen for the catalytic reaction. To the best of our knowledge, this work represents one of the lowest temperatures achieved for toluene mineralization using oxide catalysts. The identification of reaction intermediates can guide further optimization efforts to minimize the mineralization temperature.

Optimal Conversion of Food Packaging Waste to Liquid Fuel via Nonthermal Plasma Treatment: A Model-Centric Approach

The efficiency of employing a multifactorial approach to enhance the nonthermal plasma (NTP) chemical conversion of solid waste food packaging materials into liquid petroleum hydrocarbons was assessed for the first time in this study. The researchers adopted a hybrid approach which integrated the zero-dimensional (0-D) and response surface model (RSM) techniques. After their application, the researchers noted that these strategies significantly enhanced the model prediction owing to their accurate electrochemical description. Here, the researchers solved a set of equations to identify the optimisation dynamics. They also established experimental circumstances to determine the quantitative correlation among all process variables contributing to food plastic packaging waste degradation and the production of liquid fuels. The findings of the study indicate a good agreement between the numerical and experimental values. It was also noted that the electrical variables of NTP significantly influenced the conversion yield (Yconv%) of solid plastic packaging waste to liquid hydrocarbons. Similarly, after analysing the data, it was seen that factors like the power discharge rate (x1 ), discharge interval (x2), power frequency (x3), and power intensity (x4) could significantly affect the product yield. After optimizing the variables, the researchers observed a maximal Yconv% of approximately 86%. The findings revealed that the proposed framework could effectively scale up the plasma synergistic pyrolysis technology for obtaining the highest Yconv% of solid packaging plastic wastes to produce an aromatics-enriched oil. The researchers subsequently employed the precision of the constructed framework to upgrade the laboratory-scale procedures to industrial-scale processes, which showed more than 95% efficiency. The extracted oil showed a calorific value of 43,570.5 J/g, indicating that the liquid hydrocarbons exhibited properties similar to commercial diesel.

Facet-Dependent Photocatalytic Behavior of Rutile TiO2 for the Degradation of Volatile Organic Compounds: In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy and Density Functional Theory Investigations

In this study, a custom rutile titanium dioxide (TiO2) photocatalyst with a single exposed surface was utilized to investigate the facet-dependent photocatalytic mechanism of toluene. The degradation of toluene was dynamically monitored using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technology coupled with theoretical calculations. The findings demonstrated that the photocatalytic degradation rate on the TiO2 (001) surface was nearly double that observed on the TiO2 (110) surface. This remarkable enhancement can be attributed to the heightened stability in the adsorption of toluene molecules and the concurrent reduction in the energy requirement for the ring-opening process of benzoic acid on the TiO2 (001) surface. Moreover, the TiO2 (001) surface generated a greater number of reactive oxygen species (ROS), thereby promoting the separation of photogenerated charge carriers and concurrently diminishing their recombination rates, amplifying the efficiency of photocatalysis. This research provides an innovative perspective for a more comprehensive understanding of the photocatalytic degradation mechanism of TiO2 and presents promising prospects for significant applications in environmental purification and energy fields.

Tar Formation in Gasification Systems: A Holistic Review of Remediation Approaches and Removal Methods

Gasification is an advanced thermochemical process that converts carbonaceous feedstock into syngas, a mixture of hydrogen, carbon monoxide, and other gases. However, the presence of tar in syngas, which is composed of higher molecular weight aromatic hydrocarbons, poses significant challenges for the downstream utilization of syngas. This Review offers a comprehensive overview of tar from gasification, encompassing gasifier chemistry and configuration that notably impact tar formation during gasification. It explores the concentration and composition of tar in the syngas and the purity of syngas required for the applications. Various tar removal methods are discussed, including mechanical, chemical/catalytic, and plasma technologies. The Review provides insights into the strengths, limitations, and challenges associated with each tar removal method. It also highlights the importance of integrating multiple techniques to enhance the tar removal efficiency and syngas quality. The selection of an appropriate tar removal strategy depends on factors such as tar composition, gasifier operating and design factors, economic considerations, and the extent of purity required at the downstream application. Future research should focus on developing cleaning strategies that consume less energy and cause a smaller environmental impact.

Materials Enabling Methane and Toluene Gas Treatment

This paper summarizes the latest research results on materials for the treatment of methane, an important greenhouse gas, and toluene, a volatile organic compound gas, as well as the utilization of these resources over the past two years. These materials include adsorption materials, catalytic oxidation materials, hydrogen-reforming catalytic materials and non-oxidative coupling catalytic materials for methane, and adsorption materials, catalytic oxidation materials, chemical cycle reforming catalytic materials, and degradation catalytic materials for toluene. This paper provides a comprehensive review of these research results from a general point of view and provides an outlook on the treatment of these two gases and materials for resource utilization.