Ind. Eng. Chem. Res. 2005, 44, 6599-6604
6599
Impact of Ti3+ Present in Titania on Characteristics and Catalytic Properties of the Co/TiO2 Catalyst Kongkiat Suriye, Piyasan Praserthdam,* and Bunjerd Jongsomjit Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Chulalongkorn University, Bangkok 10330, Thailand
This work investigated the effect of the defect structure referred to as Ti3+ present in titania support of supported titania on characteristics and activity of the Co/TiO2 catalyst. Titania supports were prepared by sol-gel and then calcined under N2 plus increasing the amount of O2 to change the surface defect concentration. The surface defect of titania support was increased by increasing the oxygen percent in feed during the calcination process. This defect was monitored using the CO2-temperature program reduction (CO2-TPD) and electron spin resonance (ESR). Cobalt was impregnated onto titania supports containing different defect structures. XRD, SEMEDX, TPR, and H2-chemisorption were used to characterize Co/TiO2. It was found that dispersion of cobalt and reducibility increased with the amount of surface defect present. Based on high dispersion and reducibility results this catalyst showed a high conversion for methanation without changing CH4 selectivity. 1. Introduction The hydrogenation of CO and related reactions on reducible oxide-supported noble metals are sensitive to metal-support interaction.1 As known, the Co/TiO2 catalyst is considered to have strong metal support interaction2-6 and shows high activities in CO hydrogenation. Co/TiO2 is known to give a distribution of FT products ranging from C1 to C18+ hydrocarbons with high selectivity for C2-C11.7 The interaction between a support and a metal oxide (catalyst) precursor is an important factor used to determine the dispersion of a metal catalyst and hence the behavior of a catalyst as well.7 In fact, the synthesis of highly dispersed cobalt catalysts requires the initial formation of very small CoO or Co3O4 crystallites. It was reported that the formation of small oxide clusters needs strong interactions between the support and the cobalt precursor. However, too strong an interaction would suppress reduction of these CoOx clusters8 resulting in low reducibilities. Moreover, strong interaction between Co and TiO2 can produce the suboxide at an interface that is more resistant to reduction than the other supports.9 The absence of bulk oxygen vacancy defects in the TiO2 markedly reduces the extent of interface chemistry leading to negligible reduction at the metal/TiO2 interface to form suboxide (Co/TiOx; x
