Comparison of the catalytic benzene oxidation activity of mesoporous ceria prepared via hard-template and soft-template

Abstract

Mesoporous ceria samples were prepared both by nanocasting using SBA-15 mesoporous silica as hard-template and by evaporation-induced self-assembly using F127 triblock copolymer as soft-template. The samples were characterized by TEM, XRD, TPR, XPS and nitrogen adsorption. Ceria prepared with hard-template appeared as arrays of connected rods with high specific surface area and highly defective internal structure that facilitates bulk reduction by hydrogen at temperature as low as 400°C. The soft-template made sample exhibited morphology of three dimensionally linked filaments with low extent of internal defects. Hydrogen reduction of the soft-template made ceria was confined to the surface region for reduction temperature as high as 700°C. The hard-template made ceria was much more active than the soft-template made ceria for benzene oxidation at low temperature, giving a T50 at 257°C. The activity of the soft-template made ceria was greatly enhanced by etching with 2M NaOH at 80°C overnight. The high benzene oxidation activity of both the hard-template made and the sodium hydroxide treated soft-template made ceria were attributed to the generation of surface defects by the action of sodium hydroxide. The defect sites adsorb active oxygen that effect benzene oxidation below 300°C.