Structural characterizations of fluoride doped CeTi nanoparticles and its differently promotional mechanisms on ozonation for low-temperature removal of NOx (x = 1, 2)

Abstract

Nanostructured cerium and titanium mixed oxides (CeTi) as well as fluoride (F−) doped one (CeTiF) prepared by coprecipitation method were tested as ozonation catalysts for the low-temperature NOx (x=1, 2) removal. The CeTiF exhibits higher catalytic activities than CeTi, which are found to present linear relationship with the OH radical concentration. The F− is for the first time to be doped into CeTi as the ozonation catalyst. The doping of F− does not increase the density of surface –OH or surface areas, whereas it lowers the binding energies of surface –OH, promoting its reaction activities and thus the production of OH radicals. More importantly, the F− mainly substitutes the O2− in Ce–O–Ti linkage bonds (Ce–F−–Ti formation) rather than Ti–O–Ti or Ce–O–Ce, producing oxygen vacancies in the neighboring Ce–O–Ti. These vacancies benefit the adsorption of sufficient H2O to yield active surface –OH in the reaction process, promoting the adsorption of O3 and thus the production of OH radicals. The isotopic method is utilized to elaborate the catalytic mechanisms. The results show that the adsorption of H2O on oxygen vacancies plays a more critical role in the OH production, thus NOx (x=1, 2) removal.