Mechanisms of catalytic ozonation: An investigation into superoxide ion radical and hydrogen peroxide formation during catalytic ozonation on alumina and zeolites in water

A Ikhlaq, David R Brown, Barbara Kasprzyk-Hordern

Research output: Contribution to journalArticle

88 Citations (Scopus)

Abstract

This study aims to investigate mechanisms of ozonation in the presence of ZSM-5 zeolites and γ-alumina in water. Four ZSM-5 zeolites with varying silica to alumina ratios and with both hydrogen and sodium counter ions were used in the study (Z1000H:SiO2/Al2O3 = 1000, Z900Na:SiO2/Al2O3 = 900, Z25H:SiO2/Al2O3 = 25 and Z25Na:SiO2/Al2O3 = 25). The formation of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide ion radical (oO2−) was investigated during ozonation in the presence of ZSM-5 zeolites and alumina using amplex red and 4-chloro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-Cl) as probe molecules. To the authors’ knowledge, this is the first report utilising NBD-Cl and amplex red to study mechanisms of catalytic ozonation. The results showed that alumina promotes much higher formation of ROS in aqueous solutions when compared to ozonation alone and ozonation in the presence of ZSM-5 zeolites. The process was found to be pH dependent. Furthermore, alumina showed its highest activity at a pH close to its point of zero charge. The presence of tertiary butyl alcohol (TBA) and phosphates in the reaction solution did not have a significant effect on ROS production in the presence of ZSM-5 zeolites. However, in the case of alumina, the presence of phosphates significantly lowered ROS formation. This indicates the critical importance of surface hydroxyl groups of alumina in ozone decomposition and ROS formation. In contrast to H2O2 formation, TBA did not have a significant effect on oO2− production in the case of alumina. This suggests that oO2− plays a significant role in the formation of hydroxyl radicals. Furthermore, both zeolites and alumina were found to catalyse the removal of NBD-Cl from aqueous solution. Therefore, it is suggested that alumina operates through a radical mechanism leading to the production of ROS. On the other hand, zeolites serve as reservoirs of ozone and adsorbents of organic compounds, which interact via direct ozonation pathways. The activity of zeolites depends on the silica to alumina ratios of the zeolite and is independent of the nature of the zeolite counter ions.
Original languageEnglish
Pages (from-to)437-449
Number of pages13
JournalApplied Catalysis B: Environmental
Volume129
DOIs
Publication statusPublished - 7 Jan 2013

Fingerprint

Zeolites
Ozonization
Aluminum Oxide
Hydrogen peroxide
Superoxides
aluminum oxide
hydrogen peroxide
Hydrogen Peroxide
Alumina
Ions
ion
Water
Reactive Oxygen Species
Oxygen
water
tert-Butyl Alcohol
Radiation counters
Ozone
zeolite
Silicon Dioxide

Cite this

@article{7a206801692a42cd8b737876d59193c9,
title = "Mechanisms of catalytic ozonation: An investigation into superoxide ion radical and hydrogen peroxide formation during catalytic ozonation on alumina and zeolites in water",
abstract = "This study aims to investigate mechanisms of ozonation in the presence of ZSM-5 zeolites and γ-alumina in water. Four ZSM-5 zeolites with varying silica to alumina ratios and with both hydrogen and sodium counter ions were used in the study (Z1000H:SiO2/Al2O3 = 1000, Z900Na:SiO2/Al2O3 = 900, Z25H:SiO2/Al2O3 = 25 and Z25Na:SiO2/Al2O3 = 25). The formation of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide ion radical (oO2−) was investigated during ozonation in the presence of ZSM-5 zeolites and alumina using amplex red and 4-chloro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-Cl) as probe molecules. To the authors’ knowledge, this is the first report utilising NBD-Cl and amplex red to study mechanisms of catalytic ozonation. The results showed that alumina promotes much higher formation of ROS in aqueous solutions when compared to ozonation alone and ozonation in the presence of ZSM-5 zeolites. The process was found to be pH dependent. Furthermore, alumina showed its highest activity at a pH close to its point of zero charge. The presence of tertiary butyl alcohol (TBA) and phosphates in the reaction solution did not have a significant effect on ROS production in the presence of ZSM-5 zeolites. However, in the case of alumina, the presence of phosphates significantly lowered ROS formation. This indicates the critical importance of surface hydroxyl groups of alumina in ozone decomposition and ROS formation. In contrast to H2O2 formation, TBA did not have a significant effect on oO2− production in the case of alumina. This suggests that oO2− plays a significant role in the formation of hydroxyl radicals. Furthermore, both zeolites and alumina were found to catalyse the removal of NBD-Cl from aqueous solution. Therefore, it is suggested that alumina operates through a radical mechanism leading to the production of ROS. On the other hand, zeolites serve as reservoirs of ozone and adsorbents of organic compounds, which interact via direct ozonation pathways. The activity of zeolites depends on the silica to alumina ratios of the zeolite and is independent of the nature of the zeolite counter ions.",
author = "A Ikhlaq and Brown, {David R} and Barbara Kasprzyk-Hordern",
year = "2013",
month = "1",
day = "7",
doi = "10.1016/j.apcatb.2012.09.038",
language = "English",
volume = "129",
pages = "437--449",
journal = "Applied Catalysis B: Environmental",
issn = "0926-3373",
publisher = "Elsevier",

}

TY - JOUR

T1 - Mechanisms of catalytic ozonation: An investigation into superoxide ion radical and hydrogen peroxide formation during catalytic ozonation on alumina and zeolites in water

AU - Ikhlaq, A

AU - Brown, David R

AU - Kasprzyk-Hordern, Barbara

PY - 2013/1/7

Y1 - 2013/1/7

N2 - This study aims to investigate mechanisms of ozonation in the presence of ZSM-5 zeolites and γ-alumina in water. Four ZSM-5 zeolites with varying silica to alumina ratios and with both hydrogen and sodium counter ions were used in the study (Z1000H:SiO2/Al2O3 = 1000, Z900Na:SiO2/Al2O3 = 900, Z25H:SiO2/Al2O3 = 25 and Z25Na:SiO2/Al2O3 = 25). The formation of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide ion radical (oO2−) was investigated during ozonation in the presence of ZSM-5 zeolites and alumina using amplex red and 4-chloro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-Cl) as probe molecules. To the authors’ knowledge, this is the first report utilising NBD-Cl and amplex red to study mechanisms of catalytic ozonation. The results showed that alumina promotes much higher formation of ROS in aqueous solutions when compared to ozonation alone and ozonation in the presence of ZSM-5 zeolites. The process was found to be pH dependent. Furthermore, alumina showed its highest activity at a pH close to its point of zero charge. The presence of tertiary butyl alcohol (TBA) and phosphates in the reaction solution did not have a significant effect on ROS production in the presence of ZSM-5 zeolites. However, in the case of alumina, the presence of phosphates significantly lowered ROS formation. This indicates the critical importance of surface hydroxyl groups of alumina in ozone decomposition and ROS formation. In contrast to H2O2 formation, TBA did not have a significant effect on oO2− production in the case of alumina. This suggests that oO2− plays a significant role in the formation of hydroxyl radicals. Furthermore, both zeolites and alumina were found to catalyse the removal of NBD-Cl from aqueous solution. Therefore, it is suggested that alumina operates through a radical mechanism leading to the production of ROS. On the other hand, zeolites serve as reservoirs of ozone and adsorbents of organic compounds, which interact via direct ozonation pathways. The activity of zeolites depends on the silica to alumina ratios of the zeolite and is independent of the nature of the zeolite counter ions.

AB - This study aims to investigate mechanisms of ozonation in the presence of ZSM-5 zeolites and γ-alumina in water. Four ZSM-5 zeolites with varying silica to alumina ratios and with both hydrogen and sodium counter ions were used in the study (Z1000H:SiO2/Al2O3 = 1000, Z900Na:SiO2/Al2O3 = 900, Z25H:SiO2/Al2O3 = 25 and Z25Na:SiO2/Al2O3 = 25). The formation of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide ion radical (oO2−) was investigated during ozonation in the presence of ZSM-5 zeolites and alumina using amplex red and 4-chloro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-Cl) as probe molecules. To the authors’ knowledge, this is the first report utilising NBD-Cl and amplex red to study mechanisms of catalytic ozonation. The results showed that alumina promotes much higher formation of ROS in aqueous solutions when compared to ozonation alone and ozonation in the presence of ZSM-5 zeolites. The process was found to be pH dependent. Furthermore, alumina showed its highest activity at a pH close to its point of zero charge. The presence of tertiary butyl alcohol (TBA) and phosphates in the reaction solution did not have a significant effect on ROS production in the presence of ZSM-5 zeolites. However, in the case of alumina, the presence of phosphates significantly lowered ROS formation. This indicates the critical importance of surface hydroxyl groups of alumina in ozone decomposition and ROS formation. In contrast to H2O2 formation, TBA did not have a significant effect on oO2− production in the case of alumina. This suggests that oO2− plays a significant role in the formation of hydroxyl radicals. Furthermore, both zeolites and alumina were found to catalyse the removal of NBD-Cl from aqueous solution. Therefore, it is suggested that alumina operates through a radical mechanism leading to the production of ROS. On the other hand, zeolites serve as reservoirs of ozone and adsorbents of organic compounds, which interact via direct ozonation pathways. The activity of zeolites depends on the silica to alumina ratios of the zeolite and is independent of the nature of the zeolite counter ions.

UR - http://www.scopus.com/inward/record.url?scp=84868256889&partnerID=8YFLogxK

UR - http://dx.doi.org/10.1016/j.apcatb.2012.09.038

U2 - 10.1016/j.apcatb.2012.09.038

DO - 10.1016/j.apcatb.2012.09.038

M3 - Article

VL - 129

SP - 437

EP - 449

JO - Applied Catalysis B: Environmental

JF - Applied Catalysis B: Environmental

SN - 0926-3373

ER -