Gaseous ozone decomposition over high silica zeolitic frameworks

Catalytic Ozonation of Toluene over Acidic Surface Transformed Natural Zeolite: A Dual-Site Reaction Mechanism and Kinetic Approach

Volatile organic compounds (VOCs) are responsible for damage to health due to their carcinogenic effects. Catalytic ozonation using zeolite appears as a valuable process to eliminate VOCs from industrial emissions at room temperature. For full-scale application of this new abatement technology, an intrinsic reaction rate equation is needed for an effective process design and scale-up. Results obtained here provide a mechanistic approach during the initial stage of catalytic ozonation of toluene using an acidic surface transformed natural zeolite. In particular, the contribution of Lewis and Brønsted acid sites on the surface reaction mechanism and overall kinetic rate are identified through experimental data. The least-squares non-linear regression method allows the rate-determining step to be established, following a Langmuir–Hinshelwood surface reaction approximation. Experimental evidence suggest that ozone is adsorbed and decomposed at Lewis acid sites, forming active atomic oxygen that leads to the oxidation of adsorbed toluene at Brønsted acid sites.

Deactivation and Regeneration of Zeolite Catalysts Used in Pyrolysis of Plastic Wastes—A Process and Analytical Review

In catalytic industrial processes, coke deposition remains a major drawback for solid catalysts use as it causes catalyst deactivation. Extensive study of this phenomenon over the last decades has provided a better understanding of coke behavior in a great number of processes. Among them, catalytic pyrolysis of plastics, which has been identified as a promising process for waste revalorization, is given particular attention in this paper. Combined economic and environmental concerns rose the necessity to restore catalytic activity by recovering deactivated catalysts. Consequently, various regeneration processes have been investigated over the years and development of an efficient and sustainable process remains an industrial challenge. Coke removal can be achieved via several chemical processes, such as oxidation, gasification, and hydrogenation. This review focuses on oxidative treatments for catalyst regeneration, covering the current progress of oxidation treatments and presenting advantages and drawbacks for each method. Molecular oxidation with oxygen and ozone, as well as advanced oxidation processes with the formation of OH radicals, are detailed to provide a deep understanding of the mechanisms and kinetics involved (direct and indirect oxidation, reaction rates and selectivity, diffusion, and mass transfer). Finally, this paper summarizes all relevant analytical techniques that can be used to characterize deactivated and regenerated solid catalysts: XRD, N2 adsorption-desorption, SEM, NH3-TPD, elemental analysis, IR. Analytical techniques are classified according to the type of information they provide, such as structural characteristics, elemental composition, or chemical properties. In function of the investigated property, this overall tool is useful and easy-to-use to determine the adequate analysis.

Recent advances in catalytic decomposition of ozone

Ozone (O₃), as a harmful air pollutant, has been of wide concern. Safe, efficient, and economical O₃ removal methods urgently need to be developed. Catalytic decomposition is the most promising method for O₃ removal, especially at room temperature or even subzero temperatures. Great efforts have been made to develop high-efficiency catalysts for O₃ decomposition that can operate at low temperatures, high space velocity and high humidity. First, this review describes the general reaction mechanism of O₃ decomposition on noble metal and transition metal oxide catalysts. Then, progress on the O₃ decomposition performance of various catalysts in the past 30 years is summarized in detail. The main focus is the O₃ decomposition performance of manganese oxides, which are divided into supported manganese oxides and non-supported manganese oxides. Methods to improve the activity, stability, and humidity resistance of manganese oxide catalysts for O₃ decomposition are also summarized. The deactivation mechanisms of manganese oxides under dry and humid conditions are discussed. The O₃ decomposition performance of monolithic catalysts is also summarized from the perspective of industrial applications. Finally, the future development directions and prospects of O₃ catalytic decomposition technology are put forward.

Aldehydes gas ozonation monitoring: Interest of SIFT/MS versus GC/FID

Two analytical techniques - online Gas Chromatography coupled with Flame Ionization Detector (often used method for VOCs monitoring) versus Selected Ion Flow Tube coupled with Mass Spectrometry (a more recent technique based on direct mass spectrometry) - were compared in association to an ozone-based gas treatment. Selecting aldehydes as the representative VOCs, their concentrations were monitored during ozonation experiments by both techniques in parallel. Contradictory results were obtained in the presence of ozone. Aldehydes were up to 90% removed due to a reaction with ozone according to GC/FID analysis, whereas with SIFT/MS, aldehydes concentration remained at the same level during the experiments regardless of the ozone presence. In addition, it was demonstrated that the apparent aldehydes removal was affected by GC injector temperature, varying from 90% (when it was at 250 °C) to 60% (at 100 °C). Meanwhile, even when the ozonation reactor was heated to 100 °C, no aldehydes conversion was evidenced by SIFT/MS, suggesting that the GC injector temperature was not the only interference-causing parameter. The ozone-aldehyde reaction is probably catalyzed by some material of GC injector and/or column. An ozone-GC interference was therefore confirmed, making unsuitable the use of GC/FID with silicone stationary phase to monitor aldehydes in presence of high concentrations of ozone (at least 50 ppmv). On the other hand, SIFT/MS was validated as a reliable technique, which can be employed in order to measure VOCs concentrations in ozonation processes.