Soot combustion over CeO catalyst: the influence of biodiesel impurities (Na, K, Ca, P) on surface chemical properties.

This work assessed the impact of biodiesel impurities on CeO catalyst for soot combustion via soot-TPO experiments. The results showed that Na- and K-doped catalysts were assisted for soot combustion, while Ca- and P-doped catalysts had a negative effect. N adsorption-desorption and XRD results indicated that doping biodiesel impurities led to smaller surface area by blocking small pores. Surface chemical properties are suggested as major reasons for promoting soot combustion by means of XPS, H-TPR, and O-TPD. Na- and K-doped catalysts showed stronger redox ability and surface lattice oxygen mobility, poorly for Ca- and P-doped catalysts. Interestingly, a large number of surface oxygen species were observed on P-doped catalyst and it enhanced the ignition of bio soot. In the presence of NO, surface chemical properties including NO storage/release capacity and NO oxidation ability were characterized by NO-adsorption DRIFTS, NO-TPO and NO-desorption DRIFTS, alkali-doped catalyst with excellent NO storage capacity that can release active oxygen species and gaseous NO accelerate heterogeneous soot combustion, and the poor NO conversion ability to NO that weakens the promotion effect of soot combustion. Particularly in the existence of P, the promotion effect of soot elimination in NO + O was further weakened by the reason of poor NO storage capacity and NO oxidation ability.