It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

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Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

To elucidate the role of oxygen vacancy defects, various Mn-based oxides with oxygen vacancy defects are employed to the toluene oxidation, which are synthesized by adjusting solvent and double-complexation routes. The MnOx-ET catalyst shows the highest catalytic activity (T90 = 225 °C) for toluene oxidation. Compared with other Mn-based oxides, the as-prepared MnOx-ET catalyst has more surficial oxygen vacancies and good oxygen storage capacity (OSC), which is the reason on its remarkable activity for toluene oxidation. In addition, in situ DRIFTS study reveals that both lattice oxygen and adsorbed oxygen species can participate in the activation-oxidation process of toluene, which results in two reaction routes for the toluene oxidation. The rich oxygen-vacancy concentration of catalysts accelerates the key steps for the activation and generation of oxidized products. Quasi-in situ XPS results further confirm that enrich adsorbed-oxygen species as active oxygen and increasing Mn4+ concentration enhance the superior activity for toluene oxidation.

Highly efficient mesoporous MnO2 catalysts for the total toluene oxidation: Oxygen-Vacancy defect engineering and involved intermediates using in situ DRIFTS

Recent advances in hydrodeoxygenation of biomass-derived oxygenates over heterogeneous catalysts

A series of CeaMnOx hollow microsphere like arbutus with hierarchical structure are prepared by redox co-precipitation method and applied for catalytic toluene combustion. The Ce0.03MnOx shows a better catalytic performance for toluene combustion with high stability, water resistance, even under the condition of 5vol.% H2O. The results of XRF, XRD, Raman, N2 adsorption-desorption, SEM, TEM prove that the doping of Ce can affect the structure of CeaMnOx such as much smaller particle size and higher specific surface area. The characterizations of H2-TPR, O2-TPD, XPS certify the strong interaction between Ce and Mn oxides that leads to more surface adsorbed oxygen and Mn4+ species due to oxidation reduction cycle of Mn3+ + Ce4+ ↔ Mn4+ + Ce3+ after Ce addition. Meanwhile, the Toluene-TPD in different conditions confirms the introduction of water promoted the catalytic oxidation of toluene. In situ DRIFTS is used to investigate the reaction process of toluene oxidation. And the results reveal that the Ce0.03MnOx catalyst has much stronger ability to adsorb and activate toluene compared with MnOx catalyst, especially under with H2O. That may be the main reason that the Ce0.03MnOx catalyst exhibits the special catalytic activity for toluene combustion.

Synthesis of CeaMnOx hollow microsphere with hierarchical structure and its excellent catalytic performance for toluene combustion

The highly dispersed Pd nanoparticles supported UiO-66 catalysts were successfully prepared via ethylene glycol reduction method (Pd-U-EG). And their catalytic performances were evaluated by toluene degradation. A series of characterization methods were carried out to characterize the physicochemical properties of the samples. During the effect of high weight hourly space velocity, stability and reusability test, the catalytic activity of Pd-U-EG remains unchanged, which also indicated good catalytic performance. More importantly, water resistance test (10-20 vol.% water) indicated that Pd-U-EG had a great water resistance. The study of toluene-TPD, toluene-TPSR and in-situ DRIFTS at different temperatures under different conditions over Pd-U-EG indicated the role of H2O. The introduction of H2O at low temperature was conducive to the adsorption of toluene, but inhibited the degradation of toluene. Differently, the H2O presence at high temperature was favorable to toluene degradation. In addition, toluene degradation mechanism was also revealed.

Excellent catalytic activity and water resistance of UiO-66-supported highly dispersed Pd nanoparticles for toluene catalytic oxidation

Considering the harmful effects of volatile organic compounds (VOCs) on the atmosphere and public health, the search for proper catalytic materials for the effective catalytic elimination of VOCs remains one of the most pressing issues in the environmental field. In this study, a series of mesoporous Co3O4-n (n = 0.00, 0.0001, 0.01, 0.05, 0.10, 1.00, representing the concentration of HNO3 aqueous solution) catalysts were fabricated by the acid treatment of Co3O4 that was previously prepared via a hydroxycarbonate precipitation method (Co3O4-P). The catalytic performances of the prepared catalysts were evaluated for the model reaction of toluene oxidation. An obvious enhancement of catalytic activity in the reaction was achieved over the acid-treated Co3O4 catalysts using lower HNO3 concentrations, with Co3O4-0.01 exhibiting the optimum catalytic activity (T90 = 225 °C, 15 °C lower than that of Co3O4-P), excellent catalytic durability under dry conditions and a high regeneration capability under humid conditions. Benefitting from the dilute acid treatment, the Co3O4-n (n = 0.01, 0.05, 0.10) catalysts presented higher specific surface areas, more weak acidic sites and higher abundances of surface Co2+ and Oads species, which were regarded as the key factors responsible for their enhanced catalytic activities.

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Fabrication of mesoporous Co3O4 oxides by acid treatment and their catalytic performances for toluene oxidation

Zeolitic acidity as a promoter for the catalytic oxidation of toluene over MnOx/HZSM-5 catalysts

Insights into the size and structural effects of zeolitic supports on gaseous toluene oxidation over MnOx/HZSM-5 catalysts

Promotional effect of HZSM-5 on the catalytic oxidation of toluene over MnOx/HZSM-5 catalysts

The production of second-generation biodiesel with triglycerides or their derivatives through hydroprocessing is considered as a promising approach to make transportation fuels. In this study, a series of Ni-based catalysts supported on basic composite oxides (MO-Al2O3, M=Mg, Ca, Ni, Cu, Zn) were prepared for the catalytic deoxygenation of oleic acid in the presence of H-2. Ni/ZnO-Al2O3 exhibited the highest deoxygenation activity and alkane selectivity, which depended on its moderate basicity. Investigations of the reaction conditions, which include reaction time, reaction temperature, H-2 pressure, and Ni loading, suggested that n-heptadecane was the predominant product and its content increased with reaction temperature. The reaction temperature was more important than H-2 pressure in the catalytic deoxygenation of oleic acid. Additionally, the overall reaction pathways for the conversion of oleic acid were proposed based on the product distribution for different durations and reaction rates of stearic acid, 1-octadecanol, and stearyl stearate, in which the oxygen atoms in the oleic acid were mainly removed in the form of CO through a hydrogenation-dehydrogenation-decarbonylation reaction route. If glycerol trioleate was used instead of oleic acid, Ni/ZnO-Al2O3 exhibited a high hydrodecarbonylation activity and selectivity to n-heptadecane.

He Huang

Papers

Fabrication of mesoporous Co3O4 oxides by acid treatment and their catalytic performances for toluene oxidation

Zeolitic acidity as a promoter for the catalytic oxidation of toluene over MnOx/HZSM-5 catalysts

Insights into the size and structural effects of zeolitic supports on gaseous toluene oxidation over MnOx/HZSM-5 catalysts

Promotional effect of HZSM-5 on the catalytic oxidation of toluene over MnOx/HZSM-5 catalysts

Highly Selective Hydrodecarbonylation of Oleic Acid into n‐Heptadecane over a Supported Nickel/Zinc Oxide–Alumina Catalyst