Understanding A-site tuning effect on formaldehyde catalytic oxidation over La-Mn perovskite catalysts

A combination study of density functional theory (DFT) calculation and microkinetic analysis was carried out to investigate A-site tuning effect on formaldehyde (HCHO) oxidation over La-Mn perovskite catalysts (A = Sr, Ag, and Sn). The oxygen mobility of A-doped LaMnO₃ catalysts and reaction mechanism of HCHO oxidation on catalyst surfaces were investigated. The microkinetic simulation was performed to quantitatively determine the activity of catalysts toward the HCHO catalytic oxidation. The results indicated that A-site tuning weakens the binding energy of Mn-O bond of LaMnO₃ surface and facilitates the formation of surface oxygen vacancy. The presence of dopants can significantly reduce the activation energy of O₂ dissociation, which ascribes to the facilitation of electron transfer between oxygen species and catalyst surfaces. The reaction cycle of HCHO oxidation contains seven steps: HCHO adsorption, HCHO* dehydrogenation, CHO* dehydrogenation, CO₂ desorption, H₂O desorption, O₂ adsorption and oxygen vacancy recovery. The dopants promote HCHO adsorption and reduce the activation energy of HCHO oxidation. Two elementary steps control the overall reaction rate of HCHO oxidation. CHO* dehydrogenation step has the largest degree of rate control value at low temperature and O₂ adsorption step controls the whole reaction at high temperature.