THE INFLUENCE OF WATER ON THE REDUCTION AND REOXIDATION OF CERIA

Two different samples of ceria have been characterized by temperature programmed reduction in carbon monoxide (CO-TPR), surface area determination and transmission electron microscopy (TEM). The much higher reducibility at temperatures below 550-degrees-C of a sample prepared by decomposition of cerium carbonate, compared to a commercial ceria, was attributed to the much lower crystallinity. When this ceria, in the partly reduced state, was brought in contact with water vapour, it was readily reoxidised with evolution of hydrogen. The oxygen storage capacity of this sample, determined in cycling experiments, was considerably lowered by the presence of water.