This investigation consisted of a study of the break-in behavior of a tungsten oxide on silica catalyst during propylene disproportionation. A catalyst of 10 percent WO3 on silica gel (223 square meters per gram B.E.T. surface area) was used in a microcatalytic reactor. During the initial contacting of freshly activated samples of this catalyst with propylene, significant increases in disproportionation activity were observed for periods of up to 20 hours. The object of this study was to investigate the phenomena responsible for this break-in. The rate of approach to steady-state activity data were obtained using catalyst samples which were first saturated with each of the three gases involved in this reaction (propylene, ethylene, and 2-butene) by pulsing at .94 and 2.7 atmospheres before.starting the propylene flow. Effects of each gas on the break-in behavior of the catalyst were determined. A material balance around the reactor was made for each gas by pulse reactor techniques.Ph. D.