Syngas production from two-stage sorption-enhanced steam gasification of sewage sludge over bifunctional Ni-Ca catalyst

To further enhance the syngas production, the bifunctional Ni-CaO/Al2O3 catalyst was introduced into the two-stage sorption-enhanced catalytic steam gasification of sewage sludge (SS) in this study. Considering the high yield and purity of H2 at the first stage and CO at the second stage, 600 and 800 °C are determined as the optimal temperatures for the first and second stage, respectively. The Ni5Ca40/Al catalyst shows superior CO2 capture capacity, a high dispersion of Ni, and strong metal–support interaction over which the highest syngas production of 645.5 NmL/gdry ss was generated with a H2-rich gas stream at the first stage (396.9 NmL/gdry SS) and a CO-rich gas stream at the second stage (208.4 NmL/gdry SS). There is a synergistic effect of CaO and Ni on the enhancement in both yield and purity of H2 at the first stage, whereas the yield and purity of CO at the second stage are mainly affected by the CaO.