Structuration of Pd(2 wt %)/Fe−Al Oxide Catalysts on Ceramic and Metallic Monoliths: Physicochemical Characterization, Effect of the Nature of the Slurry, and Comparison with LaMnO3Catalysts

The main objective of this study has been twofold: (i) to investigate the effect of the nature of the slurry used to structurate a catalyst on monoliths; (ii) to study the influence of the nature of the monoliths on the physicochemical properties and on the catalytic activities in the combustion of methane. The slurry used in this work was made with an acidified solution of Pd(2 wt %)/Fe−Al oxide catalyst. This catalyst was prepared by the citrate method and deposited on ceramic and metallic monoliths according to a dip coating or an orbital stirring procedure. Both types of structured catalysts were studied using the following physicochemical techniques: specific surface area measurements (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The Pd(2 wt %)/Fe−Al oxide catalyst used for monolith coating does not undergo any textural or crystallinity modification during the deposition procedure. Catalytic activities obtained for powder and monolithic catalysts are compared. The surface of the support plays an important role in the structuration of catalysts. The amount of deposited catalyst has an influence on the catalytic activity. The amount of deposited catalysts depends on the nature of the monolith, on the coating technique, and on the nature of the slurry. Comparisons between structured Pd(2 wt %)/Fe−Al oxide and structured LaMnO 3 on ceramic and metallic monoliths (previous work) were made to clarify the influence of the nature of the slurry on the amount of deposited catalysts. The amount of deposited catalysts on ceramic monolith using Pd(2 wt %)/Fe−Al oxide catalyst is lower than that deposited using LaMnO 3 . In the case of metallic monoliths, the difference is less significant. The influence of a diffusion limitation of the reaction rate in structured catalysts with Pd(2 wt %)/Fe−Al oxide seems to be less important than with LaMnO 3 . Higher catalytic activities were observed for Pd(2 wt %)/Fe−Al oxide on the ceramic monoliths at high temperature. Coating on the metallic monoliths led to a better activity at low temperature compared to the corresponding powder catalyst.