Abstract
HFC-134a, one of the representative hydrofluorocarbons (HFCs) used as a coolant gas, is a known greenhouse gas with high global warming potential. Catalytic decomposition is considered a promising technology for the removal of fluorinated hydrocarbons. However, systematic studies on the catalytic decomposition of HFC-134a are rare compared to those for other fluorinated hydrocarbon gases. In this study, Ga-Al2O3 and S/Ga-Al2O3 catalysts were prepared and the change in their properties post-acid treatment was investigated by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), temperature-programmed desorption of ammonia (NH3-TPD), in situ Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The S/Ga-Al2O3 catalyst achieved a much higher HFC-134a conversion than Ga-Al2O3, which was ascribed to the promotional effect of the sulfuric acid treatment on the Lewis acidity of the catalyst surface, as confirmed by NH3-TPD. Furthermore, the effect of hydrogen fluoride (HF) gas produced by HFC-134a decomposition on the catalyst was investigated. The S/Ga-Al2O3 maintained a more stable and higher HFC-134a conversion than Ga-Al2O3. Combining the results of the stability test and characterization, it was established that the sulfuric acid treatment not only increased the acidity of the catalyst but also preserved the partially reduced Ga species.
Highlights
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are two classes of coolants, which have been found to directly contribute to the destruction of the stratospheric ozone layer [1,2].The Montreal protocol in 1987 banned the use of these coolants, and hydrofluorocarbons (HFCs) were developed to replace them [1,2]
To investigate the effect of sulfuric acid treatment on catalysts for HFC-134a decomposition, Ga-Al2 O3 and S/Ga-Al2 O3 catalysts were prepared by co-precipitation and impregnation methods
S/Ga-Al2 O3 catalyst achieved a much higher HFC-134a conversion than Ga-Al2 O3, which was ascribed to the promotional effects of sulfuric acid treatment on catalytic activity, as reported in many earlier studies for the catalytic decomposition of other fluorinated hydrocarbons
Summary
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are two classes of coolants, which have been found to directly contribute to the destruction of the stratospheric ozone layer [1,2].The Montreal protocol in 1987 banned the use of these coolants, and hydrofluorocarbons (HFCs) were developed to replace them [1,2]. HFC-134a is one of the most commonly used HFC refrigerants today, and measures to remove it from the atmosphere are urgently required to prevent global warming [1]. Several technologies, such as thermal decomposition, plasma, and catalytic decomposition, have been investigated for HFC-134a removal [4,5,6,7,8,9]. Among these methods, catalytic decomposition is considered promising because it can be carried out at lower temperature than other methods [7,8,9]. Izuka et al experimentally compared thermal and catalytic decompositions [9]
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