The promoting effect of Pt loaded with different redox supports on NO NO2 cycle-assisted soot combustion

Supports with different redox properties (Al2O3, Ce0.5Zr0.5O2-Al2O3, Ce0.5Zr0.5O2) and their corresponding Pt-based catalysts were prepared to investigate the effect of the suitability between Pt and different supports and the promotion of the NONO2 cycle on the catalytic activity of soot combustion. It is interesting that Pt-loaded nonredox support Al2O3 exhibited a poor catalytic activity for soot combustion in the absence of NO but an excellent catalytic activity in the presence of NO. However, unlike the Al2O3 support, Pt loaded Ce0.5Zr0.5O2-Al2O3 and Ce0.5Zr0.5O2 as redox supports showed an opposite result. N2 adsorption-desorption and XRD results indicated that Pt loading had no obvious effect on the texture properties of the supports. More zero-valent Pt (Pt0) on Pt/Al2O3 revealed by XRD, CO chemisorption and XPS was suggested as a major factor for promoting NO oxidizing cycles. Therefore, an amount of NO2 molecules produced on Pt0 is key to accelerate soot combustion under loose contact. The weak interaction between Pt and Al2O3 kept more Pt in the lower valence state. The Pt from Pt/Ce0.5Zr0.5O2-Al2O3 and Pt/Ce0.5Zr0.5O2 reduced the number of NONO2 cycles and further limited the assistance of NO2 in soot combustion due to a high-valence state of most of Pt. However, the preferable reducibility of the redox supports benefit soot combustion in O2/N2 because of the presence of active oxygen. This work would provide a new understanding for the further improvement of soot oxidation with the catalysts.