A method of estimating the lifetime of surface reaction intermediates by moment analysis of TAP reactor pulse response curves has been developed. The average surface lifetime of the adsorbed reaction intermediate in the hydrogenation of benzene to cyclohexane over Pt/SiO2 at 140 degrees C and 92 kPa of hydrogen is 38 +/- 4 ms, as measured by a TAP pulse experiment. The steady-state turnover frequency for this reaction under the same conditions is 1.0 +/- 0.2 s(-1). This implies that the surface coverage of Pt by benzene is low under the steady-state conditions.