R. Di Monte

An unusual promotion of the redox behaviour of CeO2-ZrO2 solid solutions upon sintering at high temperatures

The reduction behaviour of a high surface area CeO2-ZrO2 solid solution is compared with that of a high surface area CeO2. It is shown that, upon sintering induced by repetitive reduction/oxidation processes, the temperature of reduction of the solid solution decreases from 900 to 700 K. In contrast, the reduction at low temperatures of the CeO2 sample is strongly retarded after such treatments. The role of ZrO2 in promoting the reduction at low temperatures is discussed.

Effect of ZrO2 content on textural and structural properties of CeO2 / ZrO2 solid solutions made by citrate complexation route

Abstract Single phase homogeneous CeO 2 –ZrO 2 solid solutions with various compositions were synthesized using a citrate complexation route. Investigation of the sintering behaviour disclosed important modifications of the textural and, in particular, structural properties, which apparently create a strongly defective structure that could explain the unusual redox properties of these catalytic systems.

Oxygen storage and catalytic NO removal promoted by CeO2-containing mixed oxides

Abstract CeO 2 –ZrO 2 mixed oxides show improved redox properties as compared to CeO 2 which makes them important innovative materials for three-way catalysts. The origin of this effect and the structural/redox correlation are discussed. The influence of the improved redox capacities on the reduction of NO by CO catalyzed by Rh/CeO 2 –ZrO 2 catalysts is reported and evidence for an active role of the CeO 2 –ZrO 2 support in NO activation is presented.

NO reduction by CO over Pd/Ce0.6Zr0.4O2Al2O3 catalysts: in situ FT-IR studies of NO and CO adsorption

Abstract Adsorption of CO-, NO- and CO/NO-containing mixtures was investigated by in situ IR spectroscopy under flow conditions over Pd/δ-Al2O3 and Pd/Ce0.6Zr0.4O2/δ-Al2O3. The attention is focused on the effects of Ce0.6Zr0.4O2 addition to Pd/Al2O3 on the catalytic properties and reaction intermediates. Linearly bonded and bridged CO species adsorbed on palladium were clearly identified on Pd/Al2O3 while CO adsorption is inhibited under reaction conditions in the presence of Ce0.6Zr0.4O2. Addition of Ce0.6Zr0.4O2 affects the nature of the Pd sites by stabilizing oxidized dispersed Pd species. Evidence is obtained that the presence of the Ce0.6Zr0.4O2 solid solution modifies the adsorption properties of the supported Pd species and promotes the reduction of NO below 500 K via an alternative mechanism. This presumably involves reactive oxygen species at the Pd–Ce0.6Zr0.4O2 interface generated by the redox Ce4+/Ce3+ couple.

Promotion of reduction in Ce0.5Zr0.5O2: the pyrochlore structure as effect rather than cause?

Evidence is presented that the well-established phenomenon of promotion of Ce0.5Zr0.5O2 reduction by suitable treatment procedures may be controlled by adjusting the conditions; and that such reduction leads to the formation of the pyrochlore structure at extremely low temperature.

The CeO2-ZrO2 System: Redox Properties and Structural Relationships.

CeO 2 -ZrO 2 mixed oxides show improved oxygen storage property compared to CeO 2 due to the involvement of the bulk of the oxide in low temperature redox processes. In the present work we investigated the M-O local structure by means of EXAFS and Raman spectroscopy. Evidence is found that significant distortions of the oxygen sublattice are induced by introduction of Zr 4+ into the CeO 2 lattice. It is suggested that these distortions generate mobile oxygens which are responsible for the improved redox properties at moderate temperatures.

A comparative study of oxygen storage capacity over Ce0.6Zr0.4O2 mixed oxides investigated by temperature-programmed reduction and dynamic OSC measurements

The effects of redox-ageing on the temperature-programmed reduction and dynamic oxygen storage were investigated on two samples of Ce0.6Zr0.4O2 prepared under different synthesis conditions. It was observed that a high-temperature reduction/mild oxidation redox cycle can generate temperature-programmed reduction (TPR) profiles featuring a reduction peak at a temperature as low as 537 K. However, despite such favourable reduction behaviour, a strong deactivation of the oxygen storage is observed under dynamic conditions, indicating the limitations of the TPR method for investigation of oxygen storage.

NO Reduction by CO over Pd/CeO2-ZrO2-Al2O3 Catalysts.

Pd-loaded Ce 0.6 Zr 0.4 O 2 supported on Al 2 O 3 are investigated as catalysts for the reduction of NO by CO. The attention is focused on the role of the support and of the Pd dispersion on the catalytic activity. The system shows a very high activity below 500 K which is almost independent on the Pd dispersion. The high activity is attributed to a promoting effect of the Ce 0.6 Zr 0.4 O 2 on the NO conversion.

Thermal stability and oxygen storage capacity of noble metal/ceria-zirconia catalysts for the automotive converters with the on-board-diagnostics (OBD)

Reduction behaviour and oxygen storage capacity (OSC) of Rh-loaded and metal-free Ce0.5Zr0.5O2 mixed oxides is investigated. It is shown that use of different synthetic methods and the homogeneity of the solid solution strongly affect both the reduction behaviour and the total- OSC. Presence of supported noble metal (NM) minimises the differences between the different samples due to the ability of the NM to promote reduction of the Ce0.5Zr0.5O2 by activating hydrogen.

Reactivation of aged model Pd/Ce0.68Zr0.32O2 three-way catalyst by high temperature oxidising treatment

A deactivated (aged under redox-cycled model TWC feed-stream) Pd/Ce(0.68)Zr(0.32)O(2) catalyst is remarkably reactivated when subjected to a high temperature oxidising treatment whereas this effect is only marginal for Pd/Al(2)O(3), which indicates the key role of such treatment in restoring the Pd-Ce(0.68)Zr(0.32)O(2) interactions leading to highly active catalysts.