This contribution studies partial oxidation of 2-chlorophenol on surfaces of neat silica at temperatures of 250, 350, and 400 °C; i.e., temperatures that frequently lead to catalytic formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) from their precursors. We have identified 2,6-dichlorophenol (2,6-DCPh), 2,4-dichlorophenol (2,4-DCPh), and 2,4,6-trichlorophenol (2,4,6-TriCPh), but have detected no chlorinated benzenes (CBzs). The detected chlorinated and nonchlorinated DD/Fs comprise dibenzo-p-dioxin (DD), 1- and 2-monochlorodibenzo-p-dioxin (1-, 2-MCDD), 1,6-, 1,9-, 1,3-dichlorodibenzo-p-dioxin (1,6-, 1,9-, 1,3-DCDD), 4-monochlorodibenzofuran (4-MCDF), and 4,6-dichlorodibenzofuran (4,6-DCDF) at the reaction temperatures of 350 and 400 °C. However, at a lower reaction temperature, 250 °C, we have detected no PCDD/Fs. We have demonstrated that neat silica surfaces catalyze the generation of PCDD/Fs from chlorophenols at the upper range of the catalytic formation temperature of PCDD/F. The present finding proves the generation of PCDD/Fs on particles of fly ash, even in the absence of transition metals.
Abstract2-chlorophenol (2-CPh) adsorption on the surface of silica, alumina, silica-and aluminasupported iron oxides at 30 °C and 250 °C was examined. The formation of a carbanion chlorophenolate/chlorophenoxy radical intermediate on the surface of silica and alumina surfaces is identified by in-situ FTIR analysis. The IR spectra of 2-CPh adsorbed on the supported iron oxide at 250 °C highlight significant differences in the adsorption complex between 2-CPh and the two supported iron oxides ( silica and alumina).Under conditions of low coverage of 2-CPh on the surface of these catalysts, FTIR analysis suggests that the adsorption of 2-CPh on the surface of silica-supported iron oxide commences with the formation of a chlorophenolate species, where in contrast 2-CPh creates a surface formate species on alumina-supported iron oxide. Moreover, stronger bonds of 2-CPh, and higher concentration of the carbonate species, are evident on the alumina surfaces, based on both FTIR and XPS analyses.
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