TiO2–supported catalysts for the steam reforming of ethanol

TiO2 was used as support for Ni, Co and Cu to prepare catalysts for the steam reforming of ethanol, due to its known tendency to form strong metal-support interaction (SMSI) with some metals. The samples were prepared following different procedures, tuning the reducibility of the active phase and its interaction with the support. The latter parameter showed pivotal to impart suitable catalytic activity and most of all stability towards coking. Indeed, the insurgence of SMSI may allow to keep the active phase dispersed, improving activity and inhibiting the formation of carbon filaments over the active phase. The comparison between different active phases (Ni, Co, Cu, 10 wt%) confirmed Ni as very active, although it has a higher tendency to form carbon filaments. This drawback may be at least partially controlled by favouring high Ni dispersion through the formation of a mixed oxide with the support. The calcination temperature, and in general the preparation procedure for the catalyst, showed of pivotal importance to establish SMSI. In particular, calcination at relatively low temperature (i.e. 500 °C) induced initially a higher dispersion of the active phase (mean Ni crystal size 7 nm), however not accompanied by sufficient stabilisation during activity testing (mean Ni crystal size increased to 44 nm). By contrast, calcination at higher temperature (i.e. 800 °C) favoured the instauration of a SMSI and the formation of a mixed oxide (NiTiO3), which, after activation, allowed the coexistence of smaller particles, more active and resistant to deactivation and sintering, together with the more sintered ones (mean Ni crystal size 27 nm before and after activity testing). Different characterisation data (XRD, FT-IR, TPR, TEM) allowed to conclude the need of calcination at high temperature to achieve sufficient activity and resistance of the catalyst for this application. Co and Cu proved more promising as for C balance, although their activity at low temperature was unsatisfactory, mainly due to poor activity for CC bond cleavage. The characterisation of the spent catalysts by XRD, TEM and Raman allowed to evidence the different types of C deposed and to check for active phase stability against sintering.