PLATINUM-PROMOTED AND UNPROMOTED SULFATED ZIRCONIA CATALYSTS PREPARED BY A ONE-STEP AEROGEL PROCEDURE .1. PHYSICO-CHEMICAL AND MORPHOLOGICAL CHARACTERIZATION

摘要

Through a one-step sol-gel synthetic method, several sulfated zirconia systems with different sulfate content and several Pt-promoted Sulfated zirconia systems with a fixed amount of sulfate and different amounts of Pt were prepared. S and Pt in the resulting catalysts were determined by analytical methods. Crystallographic and morphological features of the ZrO2 support and, where present, of the supported Pt were examined by XRD and TEM. The adsorptive capacity of Pt-promoted systems toward H-2 and O-2 was determined with a pulse-flow system, and toward CO both with a pulse-flow system and by FTIR spectroscopy. FTIR was also used to characterize the sulfate species present at the surface of the various systems, and to evaluate the resistance of surface sulfates toward vacuum thermal treatments and toward reductive treatments at various temperatures; the latter property was also determined by TPR-MS. The preparation method leads to catalysts that are either pure tetragonal or mainly monoclinic, depending on the amount of sulfuric acid. Reductive treatments deactivate (shield) the exposed Pt, whereas oxidative treatments reactivate it; the presence of Pt, which is known to improve the performance and the stability of sulfated ZrO2 systems, renders surface sulfates much easier to eliminate either by thermal treatment in vacuo or by reduction in H-2. (C) 1997 Academic Press [References: 48]