Efficient purification of auto-exhaust carbon particles over non-noble metals (Fe, Co, Cu) decorated hexagonal NiO nanosheets

Abstract

The purification of carbon (soot) particles emitted from vehicle exhaust is strongly related to the modified surface characteristic of the catalysts. Herein, the hexagonal NiO nanosheet catalysts (M−NiO) decorated by non-noble metals (M: Fe, Co, Cu) were successfully synthesized by the hydrothermal method. The introduced heteroatoms substitute partial Ni atoms in surface [NiO6] octahedrons, and the formed cooperative effect between surface heteroatoms and adjacent Ni atoms can boost the formation of coordinatively unsaturated ions for activating reactants. Atomic M−NiO catalysts exhibited high activity for catalytic purification of carbon particles, and their activity is strongly dependent on the heteroatoms-NiO cooperative effect. Among three catalysts, Co-NiO catalyst performed the best catalytic performance and the lowest apparent activation energy (Ea), whose values of T50, SCO2m, TOF and Ea are 390 °C, 99.3 %, 0.785 h−1 and 78.2 kJ mol−1, respectively. With the aids of the characterizations and DFT calculation, the mechanism of M−NiO catalysts for soot purification is proposed: the cooperative effect between surface heteroatoms and adjacent Ni atoms boosts the rate-determining step of NO oxidation to NO2. It is meaningful for further development of high-efficient and low-cost catalysts for removal of auto-exhaust carbon particles.