Influence of Ni to Co ratio supported on ZrO₂ catalysts in phenol steam reforming for hydrogen production

In this work, catalytic steam reforming of phenol for hydrogen production was investigated. This study focuses on the effects of Ni to Co ratio supported on ZrO₂ catalysts. The Ni_xCo_y/ZrO₂ (x = 0, 1, 2, 3, 4 where x + y = 4) catalysts were prepared by impregnation method. Steam reforming activity was tested in a fixed bed reactor at 600 °C using a feed of phenol/water mixture at a molar ratio of 1:9 and a constant liquid feed rate of 0.36 ml/min. The catalysts were characterized by BET surface area, X-ray diffraction (XRD), transmission electron microscopy (TEM), NH₃ Temperature-Programmed Desorption (NH₃-TPD), CO₂ Temperature-Programmed Desorption (CO₂-TPD), H₂ Temperature-Programmed Reduction (H₂-TPR) and thermo-gravimetric analysis (TGA). The increase in the Co content from 0 to 4, caused a decrease in the crystal size, the t-ZrO₂ phase and the reducibility of the catalysts. However, it only slightly affected the total surface area. It was found that metallic Ni₄ and Co₄ catalysts have lower activity towards phenol steam reforming and deposit higher coke due to having higher acidity sites compare to bimetallic catalysts. In contrast, Ni₃Co₁ displayed a superior catalytic activity among all the catalysts, suggesting the presence of the highest basic site and high coking resistance. Phenol conversion of 53.5% and hydrogen yield of 50.4% were achieved with the Ni₃Co₁ catalyst, even though its activity decreased by increasing the cobalt content.