Effect of reaction conditions on the deactivation by coke of a NiAl2O4 spinel derived catalyst in the steam reforming of bio-oil

Abstract

The steam reforming of bio-oil is a promising and economically feasible technology for the sustainable H2 production, yet with the main challenge of designing highly active and stable catalysts. This work aimed to study the deactivation mechanism of a NiAl2O4 spinel derived catalyst, the role of Ni and alumina sites in this mechanism and the appropriate reaction conditions to attenuate deactivation. The reaction tests were carried out in a fluidized bed reactor with prior separation of the pyrolytic lignin. The fresh or used catalysts were characterized using X-ray diffraction, temperature-programmed oxidation, X-ray photoelectron spectroscopy, scanning electron microscopy combined with energy dispersive X-ray spectroscopy, and Raman spectroscopy. For steam/carbon ratios > 3.0, space time above 0.075 h and temperature between 600−700 °C, high initial hydrogen yield is obtained (in the 85–90 % range) with CO yield near 20 %, CH4 yield below 5 % and negligible initial yield of hydrocarbons. The catalyst is more stable at 600 °C, with coke formation preferentially located on Ni sites inside the catalyst particle. Increasing the temperature favors the coke development and consequent deposition on the alumina support, leading to a rapid catalyst deactivation because the limited availability of Ni and alumina sites. These results contribute to understand the phenomenon of catalyst deactivation in the steam reforming of bio-oil and set appropriate reaction conditions to mitigate this problem with a NiAl2O4 spinel derived catalyst.