Unraveling the roles of Cu dopant on formaldehyde catalytic oxidation over La0.8Sr0.2Mn1-xCuxO3 perovskite: An experimental and theoretical study

Abstract

A serious of La0.8Sr0.2Mn1-xCuxO3 perovskite-type catalysts were prepared through sol-gel method and evaluated for formaldehyde (HCHO) catalytic oxidation. The experimental and density functional theory (DFT) studies were performed to uncover the role of Cu dopant on HCHO oxidation over La0.8Sr0.2Mn1-xCuxO3 catalysts and determine the optimal doping amount of Cu. The perovskite with Cu substitution content of 0.2 exhibited the best catalytic activity and good thermal stability for HCHO oxidation. The degree of Cu substitution significantly influenced the textural properties of the catalysts. La0.8Sr0.2Mn0.8Cu0.2O3 catalyst had the highest specific area, pore volume, and crystalline degree of perovskite, which enabled more active sites to be exposed for HCHO adsorption. The introduction of bivalent Cu2+ resulted in charge imbalance that was compensated by the increased Mn4+/Mn3+ ratio of perovskite. Partial substituting Mn by Cu cations enhanced the oxygen mobility of perovskites, which was ascribed to a synergy between surface Cu and Mn atoms. La0.8Sr0.2Mn0.8Cu0.2O3 catalyst presented excellent oxygen mobility and thus promoted HCHO catalytic oxidation. DFT calculation results indicated that the absolute value of HCHO adsorption energy on the surface Cu–O site is higher than that on the Mn–O site. The Cu dopant facilitated HCHO adsorption and promoted more electrons transferring from HCHO to the catalyst, which was beneficial for HCHO activation and subsequent oxidation. Finally, the in-situ FTIR measurement combined with DFT calculation was performed to reveal the reaction mechanism of HCHO oxidation on La0.8Sr0.2Mn1-xCuxO3 perovskite. The corresponding reaction cycle of HCHO oxidation was proposed based on the experimental and theoretical methods. The reaction cycle contained seven elementary reaction steps, in which O2 dissociation is identified as the rate determining step with the energy barrier of 1.47 eV.