Modification of titania having different crystallite sizes and their applications as supports for cobalt catalysts

Abstract

Ru-modified and Zr-modified titania supported cobalt catalysts with different crystallite sizes of TiO₂ (11-16 nm) were investigated in this study. The catalysts were prepared by impregnation of cobalt precursor onto the modified and unmodified titania. The catalysts were characterized by several techniques such as XRD, BET, SEM & EDX, TEM, TPR, CO chemisorption, and XPS. It was found that the size of cobalt oxides on the support was corresponding to the size of the support used. The TPR results showed that Ru and Zr caused changes in reduction behavior of the cobalt catalysts. The Ru modification on titania support resulted in lower reduction temperature due to the effect of H₂ spillover whereas in case of Zr modification, the reduction temperature was shifted to higher. It indicated that there were formation between cobalt oxides and the support, which was modified with Zr. The TiO₂_11 nm support exhibited more dispersion of Co oxides than the TiO₂_16 nm. It revealed on significant changes in binding energy for Ru-modified/ Zr-modified and unmodified catalysts from XPS results. Based on CO hydrogenation, it was found that the smaller crystallite size of TiO₂ (11 nm) exhibited the better catalytic activity than the larger crystallite size (16 nm) for both modified and unmodified supports. However, the modified supported catalysts resulted in lower C₂-C₄ hydrocarbon product under methanation condition. Ru and Zr modification of the TiO₂ had a significant impact on the properties of Co/TiO₂ catalysts, especially on the larger TiO₂ crystallite size.