Deactivation of Pd/SiO2 catalyst in the continuous liquid-phase selective hydrogenation of an unsaturated ketone

In this paper, the deactivation causes of the Pd/SiO2 catalyst for continuous liquid-phase selective hydrogenation of 6,10,14-trimethylpentadeca-13-en-2-one in 2000 h of pilot plant test were systematically investigated by N-2 adsorption-desorption, thermogravimetric and differential thermal analyses, scanning electron microscope, transmission electron microscope, X-ray diffraction, X-ray fluorescence, experiments ofCOpoisoning and regeneration, and laboratory retests of the deactivated catalyst samples. The pore textures of Pd/SiO2 catalysts were not destructed during the pilot test, while there were no obvious carbonaceous deposits appearing on the deactivated catalyst samples. The sintering and crystallization of Pd metal nanoparticles were found, which could be partially accountable for the deactivation of Pd/SiO2 catalysts. Though Pd leaching did not take place in the pilot test, the Pd active phase could be slightly poisoned by sulfur impurities from feedstock hydrogen. Combining the results of CO poisoning and regeneration experiments with those of compositional analyses of fresh and circulating hydrogen in the pilot test, it could be concluded that CO poisoning should be another important reason for the deactivation of the Pd/SiO2 catalyst due to high concentration of CO in the reaction system of pilot test and relatively low reaction temperature in the middle and at the bottom of the catalyst bed. Fortunately, the CO poisoned Pd/SiO2 catalyst in the pilot test could be in situ regenerated by installing a purifier for CO elimination from the circulating hydrogen and increasing the temperature of the whole catalyst bed to slightly higher than 383 K.