Transition-metal‐doped ceria carried on two-dimensional vermiculite for selective catalytic reduction of NO with CO: Experiments and density functional theory

Selective catalytic reduction (SCR) reduces oxynitrides from power plant and vehicle emissions, and enhancements in efficiency would lessen pollution further. We prepared a series of transition metal (TM) doped CeO2 catalysts by impregnating them with vermiculite (VMT) as a carrier for reducing NOx by SCR with carbon monoxide (CO–SCR). The catalyst performance was in the following order: Zn < Cr < Fe < no dopant < Mn < Ni < Co < Cu. In other words, Mn, Ni, Co, and Cu greatly promoted NO conversion compared with Ce/VMT alone, whereas Zn, Cr, and Fe dopants hindered NO conversion. We applied density functional theory (DFT) by structural optimization and potential configuration analyses of CeO2 (1 1 1) and TM–CeO2 (1 1 1), which enabled us to propose the reaction pathway and the potential energy distribution of the transition state. Our DFT analyses are in accordance with the sequence of the NO + CO reaction. The performance of the Cu catalyst was superior to the others. The CeO2 (1 1 1) lattice plane is primarily in the cerium species, whereas the Cu–O–Ce interface forms in two phases, which indicates a complex interplay between the copper and cerium. Furthermore, the catalyst has numerous surface oxygen vacancies (Ovs) and active *O species, and exhibits an impressive reduction capacity: the NO conversion reaches 100% with a gas hourly space velocity of 102,000 h−1 at 300 °C. The CO–SCR reaction pathway on the Cu–CeO2 (1 1 1) surface is as follows: R1: CO + Olattice → Ov; R2: 2NO → *ONNO → N2O + *O; R3: N2O → N2 + *O; R4: *O + CO → CO2; R5: *O + Ov → Olattice. The synergy of the dopants on the CeO2 (1 1 1) surface modulated the distribution of active centers in the catalyst, which in turn modulated the catalyst performance. Our research will be useful for flue gas remediation.