Current progress on catalytic oxidation of toluene: a review

Constructing oxygen vacancies in Cu-doped MnO2 by a quenching strategy for boosting the catalytic oxidation of toluene

Here, a quenching strategy was developed to create oxygen vacancies in Cu doped α-MnO2. The evolutions of oxygen vacancies were directly followed by means of XRD refinement, EPR and XPS. In combination with DFT calculations and detailed characterizations, evidence is captured that oxygen vacancies not only act as direct sites for the adsorption and activation of gaseous oxygen and toluene, but also accelerate the consumption and replenishment cycle of lattice oxygen species by weakening the strength of metal-oxygen bonds. In situ DRIFTS study reveals that both adsorbed oxygen and lattice oxygen species directly participate in the oxidative decomposition of toluene, where adsorbed oxygen species play pivotal roles in the initial oxidation of toluene to benzoate, whereas the process of ring opening of benzoate relies on the activation of lattice oxygen. Benefiting from crucial contribution of oxygen vacancies in activating oxygen species, α-CuMnO2-500-Q obtained by the quenching method is capable of fully catalyzing the oxidation of toluene at 240 ℃, representing a reduction of about 80 ℃ compared to pristine α-CuMnO2-500. Furthermore, the toluene oxidation mechanism was proposed as well via in situ DRIFT spectra.

Numerical simulation and risk assessment of toluene tank leakage in petrochemical industries, China

Large-capacity toluene storage tank leakage accidents can lead to severe casualties and environmental damage. In this study, numerical simulation of the toluene leakage accidents is performed using PHAST and ALOHA softwares across 16 scenarios. The present research focuses on the dispersion of toluene lethal and toxicity clouds, as well as the associated risks from vapor cloud explosions and pool fires resulting from the large-capacity toluene storage tank leakage. Meanwhile, the effects of influential factors such as leakage height, wind speed, ambient temperature, and atmospheric stability on toluene leakage accidents are also discussed, and then the worst-case scenario of the toluene leakage accident is obtained. The effects of wind speed, ambient temperature, leakage height, and atmospheric stability on outcomes such as toxic clouds, vapor dispersion, explosions, and pool fires are also analyzed. The result reveals that toxic cloud dispersion increases with ambient temperature, while the impact of vapor cloud explosions and pool fires decreases with the increase of leak heights. Wind speed significantly affects pool fire spread. The influential factors related to maximizing hazard range including low leak heights, low wind speeds, high temperatures, and stable conditions are obtained. Risk analysis indicates that vapor cloud explosions significantly impact outdoor potential loss of life (PLLoutdoor) compared with other incidents. Scenario 4 within a directional range from 33.8 to 56.3° shows the highest incident frequencies, highlighting its importance for risk monitoring. These findings are crucial for enhancing emergency response strategies and safety protocols in industrial safety management.

An ionic Cu9Na4-phenylsilsesquioxane/bis(triphenylphosphine)iminium complex: synthesis, unique structure, and catalytic activity

The synthesis of a high nuclear (Cu9Na4) complex 1via the self-assembly of copper(II) phenylsilsesquioxane induced by complexation with bis(triphenylphosphine)iminium chloride (PPNCl) was successfully achieved. This complex, which includes two bis(triphenylphosphine)iminium PPN+ cations, represents the first example of a metallasilsesquioxane/phosphazene compound. The Cu9Na4-silsesquioxane cage demonstrates a nontrivial combination of two pairs of Si6-cyclic/Si4-acyclic silsesquioxane ligands and a fusion of two Si10Cu4Na2 fragments, combined via the central ninth copper ion. The catalytic efficacy of the copper(II) compound (1) was evaluated through the peroxidative oxidation of toluene using tert-butyl hydroperoxide (t-BuOOH) as the oxidant. The primary oxidation products were benzaldehyde (BAL), benzyl alcohol (BOL), and benzoic acid (BAC), with BAC being the predominant product, especially in acetonitrile (NCMe). The formation of cresols, indicating oxidation at the aromatic ring, was observed only in water and under microwave irradiation (MW) in NCMe. Remarkably, the highest total yield of 40.3% was achieved in water with an acidic additive at 80 °C, highlighting the crucial role of the acid additive in enhancing reaction efficiency and selectivity. This study underscores our copper(II) complex as a highly effective catalyst for toluene oxidation, demonstrating its significant potential for fine-tuning reaction parameters to optimize yields and selectivity. The unprecedented structure of the complex and its promising catalytic performance pave the way for further advancements in the fields of metallasilsesquioxane chemistry and catalysis.

Metal oxide-based photocatalysts for the efficient degradation of organic pollutants for a sustainable environment: a review

Photocatalytic degradation is a highly efficient technique for eliminating organic pollutants such as antibiotics, organic dyes, toluene, nitrobenzene, cyclohexane, and refinery oil from the environment. The effects of operating conditions, concentrations of contaminants and catalysts, and their impact on the rate of deterioration are the key focuses of this review. This method utilizes light-activated semiconductor catalysts to generate reactive oxygen species that break down contaminants. Modified photocatalysts, such as metal oxides, doped metal oxides, and composite materials, enhance the effectiveness of photocatalytic degradation by improving light absorption and charge separation. Furthermore, operational conditions such as pH, temperature, and light intensity also play a crucial role in enhancing the degradation process. The results indicated that both high pollutant and catalyst concentrations improve the degradation rate up to a threshold, beyond which no significant benefits are observed. The optimal operational conditions were found to significantly enhance photocatalytic efficiency, with a marked increase in degradation rates under ideal settings. Antibiotics and organic dyes generally follow intricate degradation pathways, resulting in the breakdown of these substances into smaller, less detrimental compounds. On the other hand, hydrocarbons such as toluene and cyclohexane, along with nitrobenzene, may necessitate many stages to achieve complete mineralization. Several factors that affect the efficiency of degradation are the characteristics of the photocatalyst, pollutant concentration, light intensity, and the existence of co-catalysts. This approach offers a sustainable alternative for minimizing the amount of organic pollutants present in the environment, contributing to cleaner air and water. Photocatalytic degradation hence holds tremendous potential for remediation of the environment.

Enhancement of Gaseous o-Xylene Elimination by Chlorosulfonic Acid-Modified H-Zeolite Socony Mobil-5

It is important to develop effective strategies for enhancing the removal capacity of aromatic volatile organic compounds (VOCs) by modifying conventional porous adsorbents. In this study, a novel HZSM-5 zeolite-supported sulfonic acid (ZSM-OSO3H) was prepared through ClSO3H modification in dichloromethane and employed for the elimination of gaseous o-xylene. The ClSO3H modification enables the bonding of -OSO3H groups onto the HZSM-5 support, achieving a loading of 8.25 mmol·g-1 and leading to a degradation in both crystallinity and textural structure. Within an active temperature range of 110-145 °C, ZSM-OSO3H can efficiently remove o-xylene through a novel reactive adsorption mechanism, exhibiting a removal rate exceeding 98% and reaching a maximum breakthrough adsorption capacity of 264.7 mg. The adsorbed o-xylene derivative is identified as 3,4-dimethylbenzenesulfonic acid. ZSM-OSO3H demonstrates superior adsorption performance for o-xylene along with excellent recyclability. These findings suggest that ClSO3H sulfonation offers a promising approach for modifying various types of zeolites to enhance both the elimination and resource conversion of aromatic VOCs.

Toluene Oxidation: CO2 vs Benzaldehyde: Current Status and Future Perspectives

Toluene is a common and significant volatile organic compound (VOC). Although it finds extensive application in various industrial processes (chemical manufacturing, paint and adhesive production, and as a solvent), it creates a huge environmental impact when emitted freely into the atmosphere. Two solutions were found to mitigate the emission of this pollutant: the total oxidation to CO2 and H2O and the selective oxidation into benzaldehyde. This review discusses the two main alternatives for tackling this problem: converting the toluene into carbon dioxide by total oxidation or into benzaldehyde by selective oxidation. It presents new catalytic advances, new trends, and the advantages and disadvantages of both methods.

Synthesis, Optical, Dielectric, SHG, Magnetic and Visible Light Driven Catalytic Studies on Compounds Belonging to the Swedenborgite Structure

A new compound, InBaZn3 GaO7 , with swedenborgite structure along with transition metal (TM) substituted variants have also been prepared. The structure contains layers of tetrahedral ions (Zn2+ /Ga3+ ) connected by octahedrally coordinated In3+ ion forming the three-dimensional structure with voids where the Ba2+ ions occupy. The TM substituted compounds form with new colors. The origin of the color was understood based on the ligand-field transitions. The near IR reflectivity studies indicate that the Ni - substituted compounds exhibit good near - IR reflectivity behavior, making them possible candidates for 'cool pigments'. The temperature dependent dielectric studies indicate that the InBaZn3 GaO7 compound undergoes a phase transition at ~360 °C. The compounds are active towards second harmonic generation (SHG). Magnetic studies show the compounds, InBaZn2 CoFeO7 and InBaZn2 CuFeO7 to be anti-ferromagnetic in nature. The copper containing compounds were found to be good catalysts, under visible light, for the oxidation of aromatic alkenes. The many properties observed in the swedenborgite structure-based compounds suggests that the mineral structure offers a fertile ground to investigate newer compounds and properties.

Electrocatalytic oxidation of gaseous toluene in an all-solid cell using a foam Ti/Sb-SnO2/β-PbO2 anode

Mineralization of benzene, toluene, and xylene (BTX) with high efficiency at room temperature is still a challenge for the purification of indoor air. In this work, a foam Ti/Sb-SnO2/β-PbO2 anode catalyst was prepared for electrocatalytically oxidizing gaseous toluene in an all-solid cell at ambient temperature. The complex Ti/Sb-SnO2/β-PbO2 anode, which was prepared by sequentially deposing Sb-SnO2 and β-PbO2 on a foam Ti substrate, shows high electrocatalytic oxidation efficiency of toluene (80%) at 7 hr of reaction and high CO2 selectivity (94.9%) under an optimized condition, i.e., a cell voltage of 2.0 V, relative humidity of 60% and a flow rate of 100 mL/min. The better catalytic performance can be ascribed to the high production rate of ⋅OH radicals from discharging adsorbed water and the inhibition of oxygen evolution on the surface of foam Ti/Sb-SnO2/β-PbO2 anode when compared with the foam Ti/Sb-SnO2 anode. Our results demonstrate that prepared complex electrodes can be potentially used for electrocatalytic removal of gaseous toluene at room temperature with a good performance.

Short- and long-term effects of chronic toluene exposure on spatial memory in adolescent and adult male Wistar rats

Addiction to toluene-containing volatile inhalants is of significant medical and social concern, particularly among youth. These concerns are underscored by the fact that the majority of adult abusers of toluene started as teenagers. Surprisingly, however, the lasting effects of chronic toluene exposure, especially in various age groups, have not been well investigated. Recently, we reported that adolescent and adult male Wistar rats show differential responses to chronic toluene exposure in recognition memory tasks. Since different cognitive functions may be differentially affected by drugs of abuse, we used the same model to evaluate the short- and long-term effects of chronic toluene on spatial learning and memory using Morris water maze. Daily exposure to toluene (2000 ppm) for 40 days (5 min/day) resulted in age-dependent behavioral changes. For example, only adolescent animals showed a decrease in time and distance travelled to find the hidden platform 24 h after the last toluene exposure. In contrast, only adult rats exhibited a decrease in acquisition time and distance travelled at 90 days' post toluene exposure. Our data provide further support for the contention that age-dependent responses should be taken into consideration in interventional attempts to overcome specific detrimental consequences of chronic toluene exposure.

Low-Temperature Toluene Oxidation on Fe-Containing Modified SBA-15 Materials

Transition metals as catalysts for total VOC oxidation at low temperatures (150-280 °C) are a big challenge nowadays. Therefore, iron-modified SBA-15, AlSBA-15, and ZrSBA-15 materials with 0.5 to 5.0 wt.% Fe loading were prepared and tested for toluene oxidation. It was found that increasing Fe loading significantly improved the rate of oxidation and lowered the temperature of achieving 100% removal of toluene from above 500 °C for the supports (AlSBA-15 and ZrSBA-15) to below 400 °C for 5FeZrSBA-15. The formation of finely dispersed iron oxide active sites with a particle size less than 5 nm was observed on all the SBA-15, AlSBA-15, and ZrSBA-15 supports. It was found that the surface properties of the mesoporous support due to the addition of Al or Zr predetermined the type of formed iron oxide species and their localization on the support surface. Fe-containing SBA-15 and AlSBA-15 showed activity in total toluene oxidation at higher temperatures (280-450 °C). However, 5 wt. % Fe-containing ZrSBA-15 showed excellent activity in the total oxidation of toluene as a model VOC at lower temperatures (150-380 °C) due to the synergistic effect of Fe-Zr and the presence of accessible and stable Fe²⁺/Fe³⁺ active sites.

Surface Modification by Amino Group Inducing for Highly Efficient Catalytic Oxidation of Toluene over a Pd/KIT-6 Catalyst

Toluene is one of the typical volatile organic compounds in industry, particularly in energy and fuels production processes, which is required to be eliminated effectively to protect the environment. Catalytic oxidation of toluene is widely studied for its high efficiency, and rational design and synthesis of metal catalysts are keys for toluene oxidation. In this study, an efficient catalyst was designed and synthesized by introducing -NH₂ groups on the ordered mesoporous silica (KIT-6) surface to anchor and disperse Pd species, leading to Pd nanoparticles being highly dispersed with uniform particle size distribution. Meanwhile, it was found that the introduction of -NH₂ made Pd centers present an electron-rich state, and the active Pd centers could activate O₂ molecules to generate more reactive oxygen species and promote the conversion of toluene, which was verified by in situ XPS and O₂-TPD characterization. Compared with the catalysts prepared by an impregnation method, the catalytic performance of the Pd/NH₂-KIT-6 (0.5 wt %) catalyst was significantly improved. A conversion of 90% for toluene (2400 ppm, 24,000 mL·g^-1·h^-1) was achieved at 171 °C, and the toluene conversion was maintained above 90% for 900 min, displaying the excellent activity and stability of the Pd/NH₂-KIT-6 catalyst.