Structural modification of LaCoO sub(3) perovskite for oxidation reactions: The synergistic effect of Ca super(2+) and Mg super(2+) co-substitution on phase formation and catalytic performance

Ca super(2+) and/or Mg super(2+) modified LaCoO sub(3) perovskites were synthesized via a continuous supercritical water (sc-H sub(2)O) route, followed by a suite of heat-treatment processes. Experimental results revealed that the introductions of Ca super(2+) and Mg super(2+) had profoundly hindered the crystal growths of La(OH) sub(3) and Co(OH) sub(2) crystallites in sc-H sub(2)O environment where the extra Mg(OH) sub(2) had provided a confined platform for their reaction, effectively facilitating the formation of phase pure LaCoO sub(3) perovskite. The synergistic effect as induced by dual-site substitution of Ca super(2+) and Mg super(2+) was proven very beneficial for suprafacial oxidation process, which had reduced the apparent activation energy (Ea) of LaCoO sub(3) to only 34kJ/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 Ca super(2+) had inhibited the generation of surface lattice oxygen and decreased the reducibility of LaCoO sub(3) perovskite.