Implication of operation time on low-temperature catalytic oxidation of chloroaromatic organics over VOx/TiO2 catalysts: Deactivation mechanism analysis

Three commercial granular catalysts were collected according to their operation time (fresh, two years, and three years, denoted as Cata-1, Cata-2, and Cata-3, respectively). The catalytic efficiency and CO2/CO/HCl selectivity of 1,2-dichlorobenzene (1,2-DCB) catalytic oxidation were investigated at low temperature (150-200 ?). The Cata-1 showed excellent catalytic activities with high conversion efficiency (CE, 76.12-85.94%), CO2/CO selectivity (77.56-82.47%), and HCl selectivity (63.74-72.54%). The irreversible deactivation distinctly reduced the catalytic activities of Cata-2 and Cata-3, caused the decrease of catalytic reaction rate (k) and increase of apparent activation energy (E-a) from Cata-1 (1.59-2.18 s(-1), 11.01 kJ/mol) to Cata-2 (0.12-0.38 s(-1), 34.44 kJ/ mol) and Cata-3 (0.007-0.125 s(-1), 92.70 kJ/mol), respectively. Based on the abundant characteristic results and their correlation coefficient (R-2) with 1/E-a, the S-poisoning was assigned as the major deactivation factor, while the implication factors also included alkali metals, heavy metals, HCl, fly ash, and the deposition substances formed with them. The deactivation pathways contained destroying surface porous structures and Bronsted acid sites, inhibiting the redox cycle of VOx, competing for surface reactive oxygen species, and blocking surface active sites. Based on these, two improvement suggestions were proposed to (1) develop new catalysts by reducing VOx content and introducing a second active component (eg., WOx, MoOx, CeOx, etc.); (2) develop new reactivated technologies. The former can impair the S-poisoning and improve the resistance for other implication factors and the redox ability of catalyst, and the latter was aim to sweep foreign residues, restore, or introduce surface reactive oxygen and available acid sites. The results provided essential basics for further improvement of granular catalyst and benefited the synergistic emission control of chloroaromatic organics and NOx from MSWI.