Bio-oil steam reforming over a mining residue functionalized with Ni as catalyst: Ni-UGSO

Abstract

Bio-oil reforming is considered for syngas or H2 production. In this work, we studied the steam reforming (SR) of two raw bio-oils without adding external steam, using a recently-developed catalyst, Ni-UGSO. Experiments were performed at temperature (T) = 750–850 °C and weight hourly space velocity (WHSV) = 1.7–7.1 g/gcat/h to assess C conversion (XC) and product yields. The results show that, in all conditions and with both bio-oils tested, the catalyst is stable for the entire duration of the tests (~500 min) even when some C deposition occurred and that only at the highest WHSV tested there is a slight deactivation. In all tests, catalytic activity remained constant after a first, short, transient state, which corresponded to catalyst activation. The highest yields and conversions, with YH2, YCO and XC of 94%, 84% and 100%, respectively, were observed at temperatures above 800 °C and WHSV = 1.7 g/gcat/h. The amount of H2O in the bio-oils had a non-negligible effect on catalyst activity, impacting yH2, yCO and XC values. It was observed that, above a critical amount of H2O, the catalyst was not fully activated. However, higher H2O content led to the reduction of C deposits as well as lower yH2 and yCO and, through the water-gas-shift reaction, to higher YCO2 (CO2 selectivity). Fresh and spent catalysts were analyzed by physisorption (BET), X-ray diffraction, scanning electron microscopy and thermogravimetric analysis: the results reveal that, during the oils’ SR reaction, the initial spinel (Ni-Fe-Mg-Al) structures decreased over time-on-stream (TOS), while metallic Ni, Fe and their alloy phases appeared. Although significant sintering was observed in used catalysts, especially at high H2O/C ratio, the catalyst’s specific surface generally increased; the latter was attributed to the presence of nanometric metallic Ni and Ni-Fe alloy particles formed by reduction reactions. A small amount of C (4%) was formed at low H2O/C.