Influence of reaction conditions on the catalytic activity of a nickel during the supercritical water gasification of dewatered sewage sludge

Dewatered sewage sludge with different moisture contents was treated with a nickel catalyst in supercritical water in a batch quartz tube micro-reactor at different temperatures and reaction times. The catalytic activity of the nickel wire catalyst was investigated. Because of the gradual deactivation of the catalyst, the hydrogen yield decreased by 8–72% after five catalytic cycles. The temperature has the largest influence on the deactivation rate of the nickel catalyst. The decline rate of the hydrogen yield decreased from 67% to 8% when the temperature was increased from 400 °C to 500 °C. SEM, EDS and TPO were used to characterize the spent catalyst. The results showed that the deactivation of the nickel catalyst is caused by the deposition of char/coke on the catalyst surface. Finally, the relationship between the reaction conditions and catalyst deactivation was investigated from the viewpoint of the organic matter degradation pathway.