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

摘要

A series of Pd/γ-Al2O3 catalysts with a designedloading of 1wt% were prepared by the sol-gel method usingboehmite (AlOOH) sols and various palladium compounds.These materials were developed for later use as inorganicmembranes. The samples were calcined at 400℃ in flowing O2to decompose the Pd complex and change the phase of thesupport to γ-Al2O3. H2 pulse chemisorption was used todetermine the average Pd particle sizes, while particle sizedistributions were obtained from TEM micrographs. XRD wasused to determine the crystallinity of theγ-Al2O3 support afterextended treatments at 650℃ in O2 and H2 atmospheres. Thephysical properties of the support were studied using nitrogenadsorption-desorption at 77K. Initial BET surface areas wereabout 350m2/g. Pore size distributions were very narrow andcentered at 3.6 nm, but broadened and became bimodal duringthe 650℃treatments. An ion-exchanged sample prepared bytraditional methods was used as a basis for comparison to the so-gel samples.