Gaseous ozone decomposition over high silica zeolitic frameworks

Abstract

For several decades, it has been known that ozone emissions are harmful to humans, plants, and animals. Heterogeneous catalytic decomposition is an efficient process for removing ozone from air. This study examines the effect of the zeolite's framework and pore width on efficiency for decomposing gaseous ozone. Four highly hydrophobic zeolites are used: a large cavity zeolite (Faujasite/H-FAU), a medium pore zeolite with parallel channel (Mordenite/H-MOR), and two medium pore zeolites with interconnected channels (H-ZSM-5/H-MFI and Na-ZSM-5/Na-MFI). Experiments were conducted in fixed-bed flow reactors loaded with zeolite at ambient conditions (20 8C and 101 kPa). Zeolite surfaces were analyzed during the experiments in order to understand the influence of physical and chemical surface properties on the ozone decomposition mechanism. A higher amount of ozone is eliminated using H-MOR, compared with the zeolite samples H-FAU, H-MFI, and Na-MFI. Pore width and micropore framework size distribution (channel and cages) appear to be key factors. A narrow channel or cage, slightly larger than the ozone molecule size, seems to promote ozone interactions with Lewis acid sites. Fourier transform infrared spectroscopy shows that Lewis acid sites (LAS), located on the walls of zeolite pores, decompose ozone. This leads to the formation of atomic oxygen species that could react with another ozone molecule to form dioxygen. Hence, LAS are regenerated, ready to decompose another ozone molecule once more.

Effect of Rice Husk Particle Size on ZSM‐5 Physico‐Chemical Properties for Selective Formation of 1,3,5‐Trimethyl‐2‐Benzylbenzene (Pharmaceutical Intermediate)

“…100ZSM‐5 x‐y and 200ZSM‐5 x‐y showed three bands at 1440, 1490 and 1550 cm −1 for Lewis, Lewis+Brønsted and Brønsted acid site respectively. The band for Lewis acid appeared at a comparatively lower wavelength (1440 cm −1 ) which can be attributed to the presence of two types of Lewis acid site; one could be attributed to the presences of extra framework alumina or electronic defaults in the framework alumina [24,25] . This observation is in agreement with those proposed by Marques et al [26] .…”

“…This observation is in agreement with those proposed by Marques et al [26] . for Beta zeolite and Nicolas Brodu et al [24] . for ZSM‐5 zeolite.…”

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

“…IR evidence obtained here suggests that a surface reaction occurs between adsorbed toluene at Brønsted acid sites and active oxygen species generated after ozone adsorption and decomposition at Lewis acid sites. Such a surface reaction mechanism is in agreement with previous reports, that claim the adsorption of toluene molecules at Brønsted acid sites and the adsorption of ozone molecules at Lewis acid sites followed by its transformation into active oxygen species [32,48,[55][56][57]. After that, it has been indicated that active oxygen species interact with adsorbed toluene molecules, leading to the formation of toluene oxidation by-products, as reported elsewhere [58,59].…”

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

“…This type of degradation leads to the formation of adsorbed oxygenated species such as atomic oxygen, peroxide ions and hydroxyl radicals as described in a mechanism proposed by Li et al [141]. The use of ozone over a catalytic surface therefore produces a great variety of species from molecular gases to short lifetime radicals, which are available for coke oxidation [142,143]. The following set of equations describes ozone decomposition over metal oxides and zeolites.…”