Ni/ZrO2 Catalysts Synthesized via Urea Combustion Method for CO2 Methanation

Abstract

A series of Ni/ZrO2 catalysts were synthesized by urea combustion method for CO2 methanation. The effects of zirconium precursors and urea dosage on the structure and catalytic performance of the catalysts were tested. Results showed that the Ni/ZrO2–O catalyst derived from zirconium oxynitrate hydrate exhibited better catalytic activity than the Ni/ZrO2 catalyst because of its higher Ni dispersion and smaller Ni particle size. In addition, the urea dosage significantly influenced the low-temperature activity of the catalysts by affecting the metal–support interaction, Ni dispersion, and Ni particle size. The Ni/ZrO2–O-0.4 catalyst with a urea-to-nitrate molar ratio of 0.4 exhibited the best catalytic activity owing to its moderate metal–support interaction, highest Ni dispersion, and smallest Ni particle size, achieving 69.2% CO2 conversion and 100% CH4 selectivity at 300 °C, 0.1 MPa, and a weight hour space velocity (WHSV) of 50,000 mL/(g·h). Moreover, the urea combustion method can lead to the entire phase transformation from monoclinic ZrO2 to tetragonal ZrO2 accompanied by the incorporation of oxygen vacancies in the ZrO2 lattice. This phenomenon can also be related to the high catalytic activity of the as-prepared catalysts.