Sol-gel preparation and thermal stability of Pd/gamma-Al2O3 catalysts

A series of Pd/gamma-Al2O3 catalysts with a designed loading of 1 wt % were prepared by the set-gel method using boehmite (AlOOH) sols and various pal ladium compounds. These materials were developed for later use as inorganic membranes. The samples were calcined at 400 degrees C in flowing O-2 to de compose the Pd complex and change the phase of the support to gamma-Al2O3. Hp pulse chemisorption was used to determine the average Pd particle sizes, while particle size distributions were obtained from TEM micrographs. XRD was used to determine the crystallinity of the gamma-Al2O3 support after ex tended treatments at 650 degrees C in O-2 and H-2 atmospheres. The physical properties of the support were studied using nitrogen adsorption-desorptio n at 77 K. Initial BET surface areas were about 350 m(2)/g. Pore size distr ibutions were very narrow and centered at 3.6 nm, but broadened and became bimodal during the 650 degrees C treatments. An ion-exchanged sample prepar ed by traditional methods was used as a basis for comparison to the sol-gel samples. (C) 1999 Kluwer Academic Publishers.