Abstract A technique for the application of temperature programmed desorption from high surface area solids has been developed using ultra-high vacuum procedures (UHV) and a sample preparation method that employs only microgram quantities of the adsorbent. The solid sample is highly dispersed to avoid interparticle mass and heat transport effects common in experiments with powders. The desorption spectrometer is designed for use in various types of studies of interest in catalysis. As an exploratory experiment, the adsorption behavior of ethylene on NaX-zeolite was reinvestigated. A model is proposed for the adsorption and subsequent diffusion of C 2H 4 into the zeolite pores. The desorption activation energy of 8.7 kcal mol and a saturation capacity of 1.8 × 10 14 C 2H 4 cm 2 are in excellent agreement with the values obtained by others, and the saturation capacity is as expected on geometrical grounds. Three C 2H 4 binding sites are discriminated on NaX-zeolite, with one being on the external surface of the nominally 1micrometer zeolite crystals, and the other two being due to adsorption inside the zeolite cages.