Effects of Tb and Ba introduction on the reaction mechanism of direct NO decomposition over C-type cubic rare earth oxides based on Y2O3

Abstract

C-type cubic Y₂O₃, (Y_0.70Tb_0.30)₂O_3+δ, and (Y_0.99−xTb_xBa_0.01)₂O_2.99+δ (x = 0, 0.10, 0.20, 0.30, and 0.40) were prepared to investigate their catalytic performance for NO decomposition. In the direct NO decomposition process, NO is adsorbed on basic sites of the catalyst surface to form adsorbed nitrosyl, and the number of basic sites affects the NO decomposition activity. In particular, the negative effect of CO₂ presence on the catalytic activity is related to the number of the surface basic sites. Furthermore, it was evidenced from temperature programmed desorption (TPD) of NO and IR measurements that adsorbed nitrosyl reacts with gas-phase NO and decomposes to N₂. The effects of Ba²⁺ and Tb^3+/4+ introduction on the activity of the catalyst are discussed based on this NO reaction mechanism. It is concluded that the principal effects of Ba²⁺ doping are an increase in the number of basic sites and the generation of oxide anion vacancies in the lattice. In addition, we demonstrate that Tb^3+/4+ ions in the lattice facilitate O₂ desorption and act as NO adsorption sites, so that the catalytic activity is significantly enhanced by Tb^3+/4+ introduction, despite the small number of basic sites on the catalyst surface.