Effect of ammonia on gasification performances of phenol in supercritical water

•Effects of ammonia on the gasification pathways of phenol were analyzed.•Higher temperature promoted the hydrogen production and degradation of phenol.•The gasification efficiencies increased linearly in the first 10s, and then stabilize.•Ammonia prevented the gasification of phenol, especially at higher concentrations.•Stable nitrogen polycyclic compounds were generated for the mixture of phenol and ammonia.