INFLUENCE OF PREPARATION VARIABLES ON THE DISPERSION OF PLATINUM ON ZEOLITE KL

Various preparation conditions were investigated to evaluate their eff ect on the dispersion of Pt on zeolite KL. The highest dispersion was obtained by calcining in O-2 at about 350 degrees C. Calcining in N-2 or H-2 resulted in lower dispersions. Irrespective of the gas atmosphe re, heating at 600 degrees C resulted in sintering of the Pt. The dura tion of calcination, whether at 350 degrees C or 600 degrees C, had li ttle effect on Pt dispersion. The rate at which the temperature was in creased up to the calcination temperature and the rate of the O-2 flow also had no effect. Subsequent to identical calcination procedures, r eduction with H-2 resulted in much higher Pt dispersions than reductio n with CO. Below 350 degrees C the temperature of the H, reduction did not have a marked effect on dispersion. At the 1.5% Pt level, differe nt loading techniques, viz., liquid ion exchange, solid-state ion exch ange, and incipient wetness impregnation, resulted in similar Pt dispe rsions. There was a good correlation between the percentage of Pt disp ersion and n-hexane conversion in the aromatization reaction. Pt dispe rsions were determined by CO chemisorption, and the observed trends we re confirmed by TEM. Hydrogen chemisorption was a less satisfactory me thod of measuring dispersion. (C) Elsevier Science Inc. 1997.