Experimental and DFT studies on oxygen release and migration mechanisms of LaAl-type perovskites as catalyst supports in biomass-to-H2 conversion

Abstract

Perovskites are potential candidates for catalyst supports in biomass gasification to produce high-purity H₂ due to their excellent redox properties. However, the significant mechanism of lattice oxygen release and migration in perovskites has not been clearly understood. In this work, the characteristics of surface oxygen release and subsurface oxygen migration in various LaAl-type perovskites were investigated by experiments and density functional theory calculations. Results show that the oxygen release capacity of La_0.7Sr_0.3AlO_3−δ is considerable and that of Ni/La_0.7Sr_0.3AlO_3−δ decreases slightly compared to the difficult occurrence of oxygen release in LaAlO₃. Moreover, the rate-limiting step of oxygen release from pure LaAlO₃ is determined to be the formation of O₂ complex by two opposite O atoms. Sr doping reduces the charge of the outermost O atom, making oxygen release easy, and the desorption process of O₂ becomes the rate-limiting step. After Ni loading, the strength of the surrounding Al–O bond increases, which raises the energy barrier and blocks the release of oxygen to some extent.