Effect of elemental doping on the catalytic activity of ABO3 perovskite oxides during low-pressure gas nitriding

Abstract

In order to optimize the catalytic activity of the LaFeO3 oxide during low-pressures gas nitriding, the elemental doping by chromium, nickel and cerium was applied in the present work. The effects of doped LaFeO3 oxides on catalytic nitriding efficiency were systematically investigated. A new catalytic feature was proposed to explain the differences in catalytic activity among ABO3 oxides. The microstructure, phase composition and thickness of nitrided layers were characterized by the optical microscope, scanning electron microscope, X-ray diffraction and micro-hardness tester, respectively. The chemical bonds on nitrided surfaces were carefully investigated by X-ray photoelectron spectroscopy. The first-principles calculation was applied to reveal the inner diffusion behavior of nitrogen atoms. The results show that all ABO3 oxides exhibit an excellent catalytic activity in low-pressure gas nitriding. The LaFeO3 and (La0.5Ce0.5)FeO3 oxide show the enhanced catalytic activity as nitriding time prolonging while the LaCrO3 and LaNiO3 oxide present an opposite phenomenon. It depended on the state of active oxygen on nitrided surfaces, which is affected by the valence of doped elements. A critical ratio of adsorbed oxygen to hydroxyl on nitrided surfaces was proved to be 1.33. Beyond this value, ABO3 oxides have a remarkable improvement on catalytic nitriding.