investigations for catalysts based on a variety of oxides, with Equilibrium adsorption was used to study the influence of some alumina being the most extensively investigated support.
parameters on the precursor formation of catalysts consisting of
For several years our laboratory has generally adopted zirconia-supported chromia (ZC) or molybdena (ZMo). Uptake the EA method to investigate zirconia-based catalysts. The capacities of zirconia treated at various temperatures before adzirconia support is prepared from so-called hydrous zirconia sorption (from 673 to 1023 K) showed little dependence on tem-(HZ) heated at selected temperatures in the range 673 to perature. The Me uptake (Me Γ
Cr or Mo) as a function of the 1123 K. HZ possesses ion exchange properties (2), but we equilibrium concentration of Me species in solution obeyed the have shown that even heat-treated HZ possesses exchange Langmuir law for limited ranges. The Langmuir plots therefore and adsorption properties (3) up to the highest temperature yielded saturation coverage values, n m , that depended on the concentration range. The meaning of ''monolayer coverage'' is dis-explored.
cussed. The n m value measured at a range of solution pH from 1
In this paper we report the results of a study of the influto 8 depended little on pH. The values ranged from 1.6 to 2 atoms ence of pH and solute concentration on the formation of nm 02 for Cr, and were around 3.6 atoms nm 02 for Mo. The adsorp-MoO 3 /ZrO 2 and CrO 3 /ZrO 2 with zirconia treated at various tion data suggested three adsorption regimes: (i) a strong, appartemperatures. We also explore the possible competing role ently irreversible adsorption, (ii) a partly reversible, direct adof NO 0 3 ions and analyze the uptake isotherms. The determisorbate-surface interaction, corresponding to the initial stage in nation and definition of the maximum coverage by a given the Langmuir plots, which eventually merges in (iii), a weaker metal is discussed. In addition to performing analytical and adsorption regime, showing an adsorbate-adsorbate interaction.
textural characterization, we examine some samples by XPS We compare our data with reported values for Cr and Mo equilibto highlight the state of Me dispersion. Finally, we compare rium adsorption on alumina.