Preparation and Evaluation of a Synthetic Zeolite Catalyst An Undergraduate Chemistry Laboratory Experiment R. G. Copperthwaite, G. J. Hutchlngs, and M. van der Rlet University of the Witwatersrand, 1 Jan Smuts Avenue, Johannesburg 2001. Republic of South Africa As part nf an attempt to popularize certain aspects of practical sulid-state chemistry and, in particular, heterogeneous catalysis (see previous paper in THIS JOURNAL), we have developed an undergraduate teaching cxprriment in which the student nreoares the svnthetic zeolitc ZSM-5 ( 1 ) and then evaluates tl;e materialas a catalyst for a-xyleie isomerization. Such isomerization Drocesses have become (2). The synthetic industrially important in recent zeolite ZSM-5 is asolid strong acid and is characterized by a framework structure enclosing channels that restrict molecular diffusion and give the zeolite the property of shape selectivity; both of these features are demonstrated in the experiment described. The literature preparations of Z S M d currently available involve hydrothermal crystallization over extended periods (3) (10-14 days) and as such are not suitahle for undergraduate teaching experiments. We have modified these procedures to enable the experiment t o be completed by athird-year undergraduate student in three consecutive laboratory sessions, each of 3 hours' duration. Materials required are those that should be readily available in most teaching institutions. Background ZSM-5 has two types of intersecting channels (4) with pore "windows" of dimensions 5.4 X 5.6 A and 5.1 X 5.6 A. Due to slight differences in molecular shape. D-xvlene diffuses through the structure at a rate that is io4?as& than oor m-xylrnr, (5). Moreover, this zeolite contains strong acid sites that are able to catalyze hydrocarbon isomerizaiions. Indeed, the combination of acidity and shape selectivity allows the material to act as a n efficient isomerization catalyst for converting either a- or m-xylene (or mixtures of the two). to D-xvlene. a- andlor m-xvlene are obtained from oilrefining operations and can therefore be converted t o the more commerciallv valuable D-isomer. .D-Xvlene . is used extenaively in the petrochemical industry fur producing terephthaiatus, and 75% of world annual production now uses the zeolite catalyst ZSM-5 for xylrne isomerizatinn. Zeolite
