Structural effect of ZrO2 on supported Ni-based catalysts for supercritical water gasification of oil-containing wastewater

Supercritical water gasification (SCWG) is a promising technology to treat oil-containing wastewater. This study reports a Ni/ZrO2 catalyst with mixed phase of tetragonal ZrO2 and monoclinic ZrO2 synthesized by a one-step sol-gel method, which shows good catalytic activity and stability in SCWG of oil mixture. The evolution of particle size, crystal structure, and pore size caused by increasing calcination temperature is demonstrated by X-ray diffraction and transmission electron microscopy. When calcined at 700 degrees C, Ni/ZrO2 shows superior catalytic activity and stability in SCWG reaction, with a high carbon gasification efficiency of 91.3% at 500 degrees C. The characterizations of fresh and spent catalysts suggest that Ni/ZrO2 catalyst with the fraction of monoclinic ZrO2 around 75% would be highly active and stable in SCWG reaction. In addition, two sets of optimal gasification conditions of SCWG of oil are obtained by varying operating parameters, which provides guidance for different concentrations of oil-containing wastewater treatment. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

A Ni/ZrO2 catalyst with mixed phase of tetragonal ZrO2 and monoclinic ZrO2 shows high catalytic activity and stability in supercritical water gasification of oil mixture. Optimal gasification conditions for oil-containing wastewater treatment are obtained, providing guidance for different concentrations of oil-containing wastewater.