Size effect of Pt nanoparticles in acid-assisted soot oxidation in the presence of NO

Pt/Al₂O₃ catalysts with mean Pt particle size ranged from 2.7 to 7.1 nm were synthesized by chemical reduction method, and the sulfated counterparts were prepared by impregnation of sulfuric acid. The turnover frequency of platinum for soot oxidation under loose contact conditions in a feed flow containing NO and O₂ are positively correlated with the size of platinum. The sulfated Pt/Al₂O₃ exhibits higher catalytic activity for soot oxidation in the presence of NO despite their reduced ability for NO₂ production. Such a contradiction is more significant for those catalysts with smaller platinum particles. Herein, the catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), inductive coupled plasma (ICP) emission spectrometry, CO chemisorption, thermogravimetric analysis (TGA), NH₃ temperature-programmed desorption (NH₃-TPD), NO temperature-programmed oxidation (TPO) and NO_x temperature-programmed desorption (TPD). Possible effect of Pt particle size for the catalytic oxidation of soot in the presence of NO was presented based primarily on the promoted NO₂ transfer efficiency onto the soot pushed by the acidic catalysts.