Ba-addition Induced Enhanced Surface Reducibility of SrTiO3: Implication on Catalytic Aspects
Surface reducibility engineering is one of the vital tools to enhance the catalytic activity of materials. A heavy redox treatment can be utilized to affect the structure and surface of the catalytic materials. Here, we choose SrTiO3 (STO) with a cubic perovskite structure as a system to induce oxygen vacancies by using nascent hydrogen from NaBH4 leading to a heavily-reduced version of SrTiO3 (RSTO). To further understand the surface reduction and its dependence on the foreign-ion (Ba) incorporation in SrTiO3 is studied by synthesizing Sr0.5Ba0.5TiO3 (SBTO) and BaTiO3 (BTO) using a facile hydrothermal method. Reduced version of the pristine and mixed oxide shows distinct optical absorptions, indicating oxygen vacancy-mediated reducibility engineering. Detailed CO oxidation experiments suggest the order of activity over the as-prepared and reduced supports as: STO>SBTO>BTO and RSBTO>RSTO>RBTO, respectively. The interesting observation of reversal of CO oxidation activity over STO and SBTO after reduction negates the assumption of similar intensity of reduction on the surfaces of these oxide supports. The fundamental aspect of surface reducibility is addressed using temperature programmed reduction/oxidation (TPR/TPO) and XPS.