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

Abstract

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 (111) and TM–CeO2 (111), 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 (111) 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 (111) 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 (111) 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.