A composition and a process for producing the composition are disclosed. The composition comprises (1) repeat units derived from a carbonyl compound and a glycol and (2) one or more ultrafine metal oxides. The process can comprise (1) contacting, in the presence of a catalyst and optionally one or more ultrafine metal oxides, a carbonyl compound such as dicarboxylic acid with a glycol under a condition sufficient to produce polyester wherein the glycol can be pretreated with a metal oxide or (2) incorporating an ultrafine metal oxide into or onto polyester. Also disclosed is a process for substantially removing, or reducing the content of, an aldehyde in a glycol which comprises contacting the glycol with at least one metal oxide.