Alfonsina Pappacena

Ageing induced improvement of methane oxidation activity of Pd/YFeO3

The ageing characteristics of flame-made 2 wt% Pd supported on YFeO3 were analysed in comparison with a Pd/Al2O3–CeO2–ZrO2 three-way catalyst (TWC) with respect to structural changes and catalytic performance for methane oxidation under stoichiometric reaction conditions. Thermal treatment under lean conditions (air, 900 °C) resulted in slight decrease in the methane oxidation activity of the TWC. In marked contrast, YFeO3-supported Pd catalysts exhibit an increase in activity after such treatment. Activity enhancement is even higher when the treatment was performed under stoichiometric conditions (air–fuel equivalence ratio, λ = 1, 900 °C). To explain this observation, in-depth characterization (BET, STEM, OSCC, XAS, and CO chemisorption) of fresh and aged catalysts was performed. Both thermal and stoichiometric ageing cause a severe sintering of the support particles and the phase transformation from hexagonal to orthorhombic YFeO3. Despite the absence of a mixed Pd–YFeO3 phase, the growth of Pd particles appears to be limited under the λ = 1 atmosphere. In contrast to thermally aged catalysts where large PdO particles are formed, well-defined metallic Pd nanoparticles of 10–20 nm are present after stoichiometric ageing along with higher methane oxidation activity. Although it is tempting to conclude that metallic Pd is active for methane oxidation under the given conditions, reversible and periodic partial oxidation of the large metallic particles is observed in modulation excitation high energy X-ray diffraction (HXRD) experiments designed to simulate the oscillating redox conditions experienced during operation. These results indicate that large Pd particles exhibit improved methane oxidation activity but equally confirm that activity under stoichiometric conditions is the result of a delicate equilibrium dictated by the bulk-Pd/surface-PdO pair.

Development of a modified co-precipitation route for thermally resistant, high surface area ceria-zirconia based solid solutions

Abstract In this work a modified co-precipitation route for ceria-zirconia based material with a high surface area, high thermal stability and enhanced OSC properties has been developed and the importance of the addition of surfactants and H2O2 in order to promote the stability of these materials at high temperatures has been developed.

Water splitting reaction on Ce0.15Zr0.85O2 driven by surface heterogeneity

Ce0.15Zr0.85O2 was investigated in the two-step water splitting reaction. High-temperature treatment in N2 induced compositional and structural heterogeneities which contributed to a six-fold increase of H2 yield after the first cycle. Ceria surface enrichment and the formation of a ceria–zirconia oxynitride phase positively affected the reduction and oxidation steps.

Ceria Based Materials with Enhanced OSC Properties for H2 Production by Water Splitting Reaction

A novel surfactant-assisted synthesis method was developed in our laboratory to enhance the oxygen storage capacity (OSC) and the thermo stability of a TWC catalyst based on zirconia and rare earth oxides. The same procedure was used to prepare ceria-zirconia compositions with different amount of ceria, either undoped or doped with La and Nd. The potential use of these materials in a two steps solar thermochemical water splitting cycle for the production of H2 was investigated. For this proposal the O2 release of the materials was measured through thermogravimetric analysis in N2 at 1573K. Then all prepared compositions were subjected to an aging treatment at temperature above 1573K in air or in N2 flow and their activity in producing H2 via water splitting at 1073K was evaluated with respect their structural evolution. The results obtained highlight that the reactivity depends on the temperature and atmosphere of the treatments and on the composition. The best result was obtained for the ceria rich composition treated at 1573K in N2 and for the corresponding doped composition treated in air.

Catalysts and Processes in Solid Oxide Fuel Cells

This chapter describes the requirements necessary for the development of suitable solid oxide fuel cell electrodes. The materials and the chemical and electrochemical processes involved in the anode compartment are then specifically considered. Particular emphasis is given to the advances that have been achieved and the necessary improvements that are still needed in order to operate at intermediate temperature with renewable resources or light hydrocarbons. Moreover, the relationship between catalysis and electrocatalysis and the issues correlated with an integrated or direct oxidation will be introduced.