Study on the detailed reaction pathway and catalytic mechanism of a Ni/ZrO2 catalyst for supercritical water gasification of diesel oil

•High temperature and long reaction time promoted the gasification of diesel in SCW.•The carbon gasification efficiency achieved 97.5% at 500 °C with Ni/ZrO2.•The reaction pathway of diesel was obtained by analyzing liquid intermediates.•The Ni/ZrO2 catalyst could enhance the steam reforming and pyrolysis reaction.•The Ni/ZrO2 catalyst could effectively inhibit the formation of tar or coke.