Abstract
Benzene, toluene and xylene (BTX) are a particular class of volatile organic compounds, which are highly toxic pollutants. In this study, samples of gallium-containing mesoporous silica (MS-Ga7% and MS-Ga11%) were synthesized and their catalytic activity in the oxidation of BTX was investigated. The physicochemical characterization shows that the inclusion of gallium in the mesoporous silica structure leads to an increase in the number of oxygen vacancies in the structure of the MS-Ga system, which can result in an increase in the total and surface oxygen mobility. The results show the highest conversion for benzene (65%), with > 40% for toluene and > 28% for o-xylene. The high catalytic activity observed was attributed to a combination of several factors including a higher number of active sites (gallium and gallium oxide) being exposed, with a greater mobility of the active oxygen species on the surface of the catalyst promoting the catalytic activity.
Highlights
IntroductionThe emission of high levels of volatile organic compounds (VOC) to the atmosphere during various industrial and commercial processes is considered detrimental to human health and the environment.[1,2,3,4,5,6] Benzene, toluene and xylene (BTX) are volatile organic compounds used as common solvents as well as raw materials in the production of other chemicals.[7,8,9] All three substances are known to be toxic.[10,11] Several VOC removal technologies, such as flame combustion, catalytic combustion, catalytic destruction using ozone and plasma, photocatalytic decomposition, adsorption processes and biological treatment, have been developed to eliminate VOCs.[2,6,12,13,14] Catalytic oxidation is considered to be the most effective approach, mainly due to its high efficiency in the degradation to carbon dioxide and water, even in effluents with low concentrations of VOCs, and low energy cost.[3,15] it is extremely difficult to achieve the complete combustion of VOCs at low temperatures
The Ga2O3 may increase the amount of oxygen vacancies and, in turn, the oxygen mobility and the catalytic activity. These vacancies are filled by the oxygen atoms that diffuse from the bulk to the surface of the catalyst, suggesting that the presence of crystalline defects enhances the mobility of the oxygen species, as confirmed by the results for the oxygen storage capacity (OSC)
The characterizations show that gallium doping led to an increase in the oxygen vacancies in the system
Summary
The emission of high levels of volatile organic compounds (VOC) to the atmosphere during various industrial and commercial processes is considered detrimental to human health and the environment.[1,2,3,4,5,6] Benzene, toluene and xylene (BTX) are volatile organic compounds used as common solvents as well as raw materials in the production of other chemicals.[7,8,9] All three substances are known to be toxic.[10,11] Several VOC removal technologies, such as flame combustion, catalytic combustion, catalytic destruction using ozone and plasma, photocatalytic decomposition, adsorption processes and biological treatment, have been developed to eliminate VOCs.[2,6,12,13,14] Catalytic oxidation is considered to be the most effective approach, mainly due to its high efficiency in the degradation to carbon dioxide and water, even in effluents with low concentrations of VOCs, and low energy cost.[3,15] it is extremely difficult to achieve the complete combustion of VOCs at low temperatures. Common catalyst supports include activated carbons, silica, alumina, polymers and zeolites. The aim of this study was to synthesize a galliumcontaining mesoporous silica (type MCM-41) catalyst with surface acidity, which can provide high catalytic efficiency for the complete oxidation of BTX without the formation of reaction by-products other than carbon dioxide and water
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