Novel and active Bi2Zr1.9M0.1O7 (M = Mn, Fe, Co, Ni) catalysts for soot particle removal: Engineering surface with rich oxygen defects via partial substitution of Zr-site

To obtain more cost-effective, non-noble catalysts for soot particle combustion of diesel engine cars, Bi₂Zr_1.9M_0.1O₇ (M = Mn, Fe, Co, Ni) compounds with partial lattice substitution have been designed and synthesized. All the substituted catalysts show significantly promoted activity, in the order of Bi₂Zr₂O₇ < Bi₂Zr_1.9Ni_0.1O₇ < Bi₂Zr_1.9Co_0.1O₇ < Bi₂Zr_1.9Fe_0.1O₇ < Bi₂Zr_1.9Mn_0.1O₇. The presence of NO improves the activity of all the samples due to the generation of active surface nitrates/nitrites. It has been proven that all the modified catalysts possess weaker Zr–O bonds, which facilitates the generation of more surface defects. Density functional theory calculations have confirmed that a more defective catalyst has a lower vacancy formation energy and O₂ adsorption energy. Isotopic ¹⁸O₂ labeling has also substantiated that a more defective catalyst has a faster gaseous O₂ exchange rate, thus improving the generation of more abundant soot reactive oxygen sites. The weakening of Zr-O bonds is the inherent factor to improve the catalytic activity. Mn-substitution can lead to the weakest Zr-O bonds in Bi₂Zr_1.9Mn_0.1O₇, which thus shows the optimal catalytic activity. Notably, the complete soot combustion can be achieved even at 360°C on this catalyst.