Catalytic performance of sewage sludge char and ash in the decomposition of NH3

Abstract

The present study was conducted to study the catalytic performance of sewage sludge char and ash on NH3 decomposition by using a fixed bed reactor. The results indicated that sewage sludge char exhibited strong activity towards NH3 decomposition, which was highly influenced by temperature and atmosphere. The influence of atmosphere on NH3 decomposition was investigated at 973 K, it showed that the char activity was greatly promoted with the presence of O2, and the major product of NH3 oxidation catalyzed by relatively fresh char was N2 rather than NO. In contrast, the NH3 decomposition was suppressed with H2O introducing, and there was a significant amount of NO being produced. Compared to char, the in-situ combusted ash showed relatively poor catalytic performance with respect to NH3 conversion. At 973 K, the NH3 conversion catalyzed by ash was dominated by the inhabitation effect of H2O with the presence of both O2 and H2O. However, when the temperature increased to 1128 K, O2 tends to take a dominant role to promote NH3 conversion. By XRD analysis of the fresh and spent char, it was proposed that iron phosphide (Fe2P) may be responsible for the high activities towards NH3 decomposition, following a cycle mechanism.