Influence of chloride ions on the interaction of deuterium with Ce0.6Zr0.4O2 mixed oxide

F. C. GENNARI; T. MONTINI; P. FORNASIERO; M. GRAZIANI

Buenos Aires

Simposio; XV Symposium on Metastable, Amorphous and Nanostructured Materials, ISMANAM 2008; 2008

UBA-CONICET

Ceria-zirconia mixed oxide (CZ) is a key component in modern automotive three-way catalysts and a promising material for many important reactions involving production and purification of H . Although these materials are usually support for active metals, its interaction with small molecules such as H reveals unusual properties which directly influences thecatalytic processes. The reactivity of ceria is connected to its chemical reducibility, resulting in a high capability for storing oxygen under oxidizing conditions and realising it under reducing conditions. Ce0.6Zr0.4O2 (CZ60) was synthesized by a co-precipitation technique and chlorinated by impregnation with aqueous NH4Cl. The samples were characterized using techniques able to distinguish between bulk (XRD and Raman spectroscopy) and surface (FTIR spectroscopy of OH groups and of adsorbed methanol) compositions. Interaction of the samples with deuterium was investigated under flow conditions by Temperature Programmed Reduction and under static conditions by FTIR spectroscopy. The as-synthesized CZ60 exhibited conventional redox behaviour, comparable to single phase ceria-zirconia mixed oxides, which is discussed on the basis of the sample´s bulk compositional inhomogeneity, its surface cerium enrichment, and the presence of trace amounts of silicon. Redox cycling (TPR up to 1173 K and reoxidation at 700 K) resulted in surface cerium enrichment, which only moderately affected the interaction of the material with D . Addition of trace of chloride ions to the oxide surface promoted both H/D scrambling and vacancy creation. Chloride ion was found to coordinate preferentially with cerium sites, most likely through reorganization during calcination procedure after the impregnation step. It has been observed that chloride ion can both promote or deactivate H/D scrambling and vacancy creation. The intensity of these effects depends strongly on the adopted experimental conditions and the chloride loading.