Structural modification of LaCoO3 perovskite for oxidation reactions: The synergistic effect of Ca2+ and Mg2+ co-substitution on phase formation and catalytic performance

摘要

Ca2+ and/or Mg2+ modified LaCoO3 perovskites were synthesized via a continuous supercritical water (sc-H2O) route, followed by a suite of heat-treatment processes. Experimental results revealed that the introductions of Ca2+ and Mg2+ had profoundly hindered the crystal growths of La(OH)(3) and Co(OH)(2) crystallites in sc-H2O environment where the extra Mg(OH)(2) had provided a confined platform for their reaction, effectively facilitating the formation of phase pure LaCoO3 perovskite. The synergistic effect as induced by dual-site substitution of Ca2+ and Mg2+ was proven very beneficial for suprafacial oxidation process, which had reduced the apparent activation energy (Ea) of LaCoO3 to only 34 kJ/mol in toluene oxidation. This is comparable to some noble metal catalysts. However, the dual-site substitution had somehow deactivated the intrafacial reaction process as the co-substituted Ca2+ had inhibited the generation of surface lattice oxygen and decreased the reducibility of LaCoO3 perovskite. (C) 2015 Elsevier B.V. All rights reserved.