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/ZrO 2. • The reaction pathway of diesel was obtained by analyzing liquid intermediates. • The Ni/ZrO 2 catalyst could enhance the steam reforming and pyrolysis reaction. • The Ni/ZrO 2 catalyst could effectively inhibit the formation of tar or coke. Diesel oil, as a petroleum product, can be used as a model of oilfield wastewater to be gasified in supercritical water (SCW). This paper is aimed to obtain the gasification characteristics, detailed reaction pathway of diesel oil and the catalytic mechanism of a Ni/ZrO 2 catalyst in SCW, providing some guidance for supercritical water gasification (SCWG) of oilfield wastewater. The SCWG of 6.8 wt% diesel experiments were carried out in a quartz reactor system with different temperatures (460, 500, 540 °C), reaction time range of 0–90 min. The carbon gasification efficiency achieved 97.5% at 500 °C with the Ni/ZrO 2 catalyst, which was over 3 times higher than 27.6% under non-catalytic condition. The liquid intermediate was analyzed by gas chromatography-mass spectrometry, and naphthalene was the most difficulty intermediate to be gasified in diesel SCWG. A kinetic model was established to describe quantitatively the variation of gas yields with experimental conditions. The production and consumption of gases by SCWG of diesel oil under non-catalytic and catalytic conditions were analyzed in detail, and the mechanism of the Ni/ZrO 2 catalyst was proposed. The Ni/ZrO 2 catalyst effectively enhanced the steam reforming and pyrolysis reactions as well as inhibited the polymerization and aromatization reaction. [ABSTRACT FROM AUTHOR]