The influence of water vapor on methane catalytic combustion was studied over a Pd@CeO2/Si-Al2O3 catalyst, carefully designed to maximize Pd-CeO2 interaction and prevent metal sintering and compared to a conventional impregnated catalyst with identical chemical composition. Although the nanostructured Pd@CeO2/Si-Al2O3 catalyst is thermally stable, the addition of water to the reaction feed leads to a transient deactivation at low temperatures, consistent with the well documented competitive adsorption. In addition to this, the hierarchically structured catalyst exhibits an additional severe deactivation after methane oxidation in the presence of water vapor at 600°C that can be reversed only by heating the catalyst above 700°C. The presence of water in the reaction feed deactivates the conventional impregnated catalyst less severely and the activity largely returns upon water removal. Catalytic FTIR and CO-chemisorption data indicate that this severe deactivation process in the hierarchical catalyst is due to the formation of stable OH groups on the surface of the ceria nanoparticles. These hydroxyl groups are suggested to significantly inhibit the oxygen spillover from the CeO2 nanoparticles to Pd, preventing its efficient re-oxidation, as observed by operando X-ray absorption near edge spectroscopy (XANES) experiments. At the same time, their presence can contribute to limit the gas phase accessibility of Pd, as indicated by the decrease of CO chemisorption capability. The presence of hydroxyls plays a minor role on the deactivation of the conventional catalyst at 600°C.
|Original language||English (US)|
|Number of pages||9|
|State||Published - Oct 30 2014|
Bibliographical noteKAUST Repository Item: Exported on 2021-07-06
Acknowledgements: Dr. Matteo Cargnello (UPenn, Philadelphia) is acknowledged for discussions. M.M., T.M. and P.F. acknowledge financial support from University of Trieste trough the grant FRA2013 “Advanced core-shell based catalysts for methane catalytic combustion”, the EU for the grant FP7-NMP-2012-SMALL-6 (project ID 310651) and MIUR (Rome) for the grant HI-PHUTURE (protocol 2010N3T9M4). C.C., and R.J.G. were supported by the Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division, Grant No. DE-FG02-13ER16380. We acknowledge SOLEIL for provision of synchrotron radiation facilities and we would like to thank V. Briois and G. Alizon for assistance in using beamline SAMBA.
ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry
- Organic Chemistry