Ni-, Co- and Cu-TiO2 catalysts for the steam reforming of ethanol: how the preparation method affects catalytic performance

Concept A set of Ni-, Co-, Cu-based catalysts supported over TiO2 for the steam reforming of ethanol were prepared by different procedures. For most of them the support was prepared by precipitation and calcined at 500°C or 800°C. Other samples were prepared by flame pyrolysis (FP), aiming at high metal dispersion coupled with synthesis at high temperature, to impart a strong metal-support interaction, besides high thermal resistance. The samples were characterised by AAS, XRD, N2 adsorption-desorption, TPR, SEM, TEM and FT-IR. Activity testing for the steam reforming of ethanol was performed after activation at 500°C or 800°C in H2 flow on a continuous micropilot plant, by feeding a 3:1 (mol/mol) mixture of water/ethanol at 500°C for 8 h-on-stream. Motivations and Objectives Ni-based catalysts raised much interest for the present application [1-3]. Very high activity has been observed at high reaction temperature (>600°C), but it would be interesting to operate under milder conditions, in order to lower the energy input to the process and to improve H2 productivity by favoring the water gas shift reaction. The major inconvenient for Ni-based samples is usually ascribed to coking, often due to the formation of carbon filaments over the active phase. This phenomenon is correlated to catalyst deactivation and appearance of by-products. Indeed, if at high reaction temperature with excess steam carbon may be gasified, at operation at 500°C the C balance, often much lower than 100% evidences coke accumulation. Results and Discussion H2 productivity at 500°C seemed firmly dependent on the calcination and on activation temperature of the catalyst when Ni was supported over TiO2 prepared by impregnation. When the sample was calcined and activated at 500°C, no H2 production was observed due to poor ethanol conversion, with selectivity mostly to acetaldehyde and poor carbon balance. By contrast, calcination of the sample at 800°C induced very high H2 productivity, higher C balance and negligible byproducts formation except some CH4 These results were attributed to the formation of a mixed oxide between Ni and the support during synthesis at high temperature (both for Impregnation and FP), which keeps the metal well dispersed in spite of the high activation temperature. This leads to very small Ni particles after activation, which demonstrated to be more active and, most of all, more stable towards coking. C balance was in general much higher for the Co- and Cu-containing samples than for the Ni-based ones. One may conclude that for most of these samples there is no additional coking on the catalyst due to the active phase. However, they proved in general less active than Ni-based ones when tested at 500°C. References [1] I. Rossetti, A. Gallo, V. Dal Santo, C.L. Bianchi, V. Nichele, M. Signoretto, E. Finocchio, G. Ramis, G. Garbarino, A. Di Michele, ChemCatChem, 5 (2013) 294. [2] I. Rossetti, C. Biffi, C. Bianchi, V. Nichele, M. Signoretto, F. Menegazzo, E. Finocchio, G. Ramis, A. Di Michele, Appl. Catal. B, 117-118 (2012) 384. [3] E. Finocchio, I. Rossetti, G. Ramis, Int. J. Hydrogen Energy, 38 (2013) 3213.