Formation of PCDD/Fs, PCBs and HCl during catalytic combustion of chlorobenzene over supported transition metal (Cr, V and Cu) oxide catalysts

As an efficient scheme, catalytic combustion can be used to eliminate chlorinated volatile organic compounds (CVOCs). To avoid the formation of more toxic by-products, it is essential to reveal the relationship between the chlorine-containing products and redox properties of catalyst. In the present study, the activity for chlorobenzene (CB) oxidation, HCl production, and formation of by-products polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs)were investigated over γ-Al2O3-supported transition metal (Cr, V and Cu) oxide catalysts. The results showed that the 10Cr-Al catalyst with relatively high specific surface areaand more oxygen absorbed than other catalysts exhibited higher catalytic oxidation activity for CB. The temperatures needed for 90% conversion of CB (T90) were 331, 353 and 386 °C for 10Cr-Al, 10V-Al and 10Cu-Al, respectively. The amount and type of acid sites on the surface of catalysts play an important role in the distribution of products and by-products. It was found that the increase of acid sites and the presence of Brønsted acid (B-acid) significantly improve the HCl selectivity of catalysts. More HCl was formed on the 10V-Al catalyst with B-acid sites. Meanwhile PCDD/Fs and PCBs detected in the by-products had a tight relationship with the acidity sites and redox performance of the catalyst. The yields of ∑PCDD/Fs and ∑PCBs were the largest on 10V-Al at T10, reaching 25.60, 66.93 mmol/mol CB, respectively. The obtained results provided theoretical support for the subsequent development of CVOCs catalytic oxidation catalysts and the control of toxic by-products.