Surface Characterization of Zirconia-Coated Alumina as Support for Pt Particles

Abstract

ZrO 2 /Al 2 O 3 samples were prepared by impregnation of the alumina powder with a solution of zirconium hydroxide in nitric acid, containing ZrO 2 in the range of 1-20 wt%. Platinum was impregnated by incipient wetness technique, using an aqueous solution of H 2 PtCl 6 . The surface coverage of zirconia on alumina, as probed by XPS and ISS, increased up to 10 wt% of ZrO 2 and above this concentration crystallites of zirconia nucleated, which decreases the BET surface area. XRD measurements indicated that the average size of these crystallites was about 1 nm. ISS data of Pt/ZrO 2 and Pt/10%ZrO 2 /Al 2 O 3 catalysts, after reduction at 773 K indicated an increase in the surface population of Zr atoms which are able to catch CO. This interaction was also probed by FTIR spectra of CO adsorbed on Pt/ZrO 2 catalyst, where an intense band at 2130 cm --1 , associated to CO adsorption on Pt-ZrO x interface, was observed.

The Interaction of Oxides of the Pd/Ce/Zr/Al2O3 Catalysts Prepared by Impregnation Over Alumina and Promoting Effects on Surface Properties

“…The values presented in this work are 0.6 eV smaller than that reported in the literature, which could indicate a change in the coordination number of zirconium due to the interactions with the other elements. Furthermore, XPS analyses of Pt/Zr system obtained by Souza et al [22] indicated similar behavior. These authors considered that it was only a surface phenomenon, restricted to the first atomic layer in the platinum neighboring.…”

Surface Modifications and Applications of Magnetic and Selective Nonmagnetic Nanoparticles

“…Similarly, there are different precursors that can be used in the formation of zirconia coating 88,[95][96][97][98][99] . The alkoxide form is still the popular choice, and zirconium propoxide and butoxide are among the commonly used 95,100 .…”

Interpretation of kinetic data with selected characterizations of active sites

“…For catalysts that kinetically inhibit excessive carbon deposition, like zirconia-containing catalysts described here, the surface concentration of carbon at the metal surface (in the form of CH x ) is at steady state and remains constant, i.e., the rate of CH x decomposition equals that for CH x reaction with CO 2 adsorbed species. Assuming two independent balances of sites, the reaction rate of methane was derived and presented good correlation with the experimental results [38].…”

“…The spectra showed a small band at 2178 cm À1 at 298 K, which was attributed to the linear adsorbed CO species on cationic sites (either Zr 4+ or Zr 3+ ). This adsorption involves the sdonation type to coordenatively unsatured surface cationic sites (cus), acting as Lewis acid centers, according to previous works [38]. The Pt/ZrO 2 catalyst reduced at 773 K showed also an intense band at 2130 cm À1 , which can be associated to CO adsorption on Pt-ZrO 2 interface, that means, on Pt sites interacting strongly with zirconia.…”

“…In conclusion, the interface Pt-Zr n+ and the Pt sites were observed using in situ techniques and support the mechanistic dual site model proposed for the reaction rate kinetics [38].…”