Coking and sintering progress of a Ni supported catalyst in the steam reforming of biomass pyrolysis volatiles

Abstract

The valorization of biomass (pine wood) for hydrogen production has been studied in a two-step process, comprising pyrolysis and subsequent steam reforming of the volatiles produced in the first step. This work focuses on the deactivation of the Ni commercial catalyst used in the second step. Pyrolysis of biomass has been performed in a conical spouted bed reactor at 500 ºC, and the in-line catalytic steam reforming of the pyrolysis volatiles, in a fluidized bed reactor at 600 ºC. Deactivated catalyst samples were recovered at different values of time on stream, and analyzed by means of XRD, N2 adsorption-desorption, SEM and TEM microscopies, TPO, Raman and FTIR spectroscopies. The results show that the deactivation is mainly due to the encapsulation of Ni particles by coke, together with Ni sintering, to a lesser extent. The former is ascribed to the condensation of oxygenates (particularly phenols), and the latter is inevitable within the current conditions. As the fraction of uncovered Ni particles decreases with time on stream, the deposition of encapsulating coke is decreased, promoting the deposition of coke on the catalyst support, with a more carbonized structure and formed through the thermal decomposition of phenols in the reaction medium.