Sequential Saturating Reactions of ZrCl4 and H2O Vapors in the Modification of Silica and γ-Alumina with ZrO2

Zirconia-modified silica and alumina samples were prepared by the atomic layer epitaxy technique using successive saturating reactions of ZrCl 4 and H 2 O vapors. The growth of ZrO 2 was followed by X-ray diffraction, diffuse reflectance IR Fourier transform spectroscopy, and 1 H magic angle spinning NMR measurements. In addition, coverage of the silica surface was estimated by low-energy ion scattering (LEIS). At the reaction temperature of 300 °C the main reaction of ZrCl 4, on both supports, occurred with surface OH groups, leading to amorphous ZrCl x species. In addition, part of the molecules reacted to form ZrO 2 agglomerates while simultaneously chlorinating OH groups of the supports. Water treatment removed Cl from the ZrCl x surface species, leaving behind Zr−OH groups, and released the directly chlorinated OH groups. Both the reappearing OH groups of the support and the Zr−OH groups were then again available during the next ZrCl 4 treatment for both main reactions of ZrCl 4 . As the reaction cycles were repeated the concentration of amorphous Zr in the samples increased together with the amount of crystalline ZrO 2 and surface coverage. On silica, after five cycles of repeated reactions when an average surface density of 5 Zr/nm 2 had been achieved, 25% of the original accessible OH groups were still present on the surface. At that point, LEIS measurements showed 50% coverage. On the surface of both silica and alumina, ZrO x was present in the form of tetragonal agglomerates and an amorphous network phase. Two types of Zr−OH groups were identified.