Decomposition of Al2O3-Supported PdSO4 and Al2(SO4)3 in the Regeneration of Methane Combustion Catalyst: A Model Catalyst Study
Department of Chemistry, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland
Dinex Finland Oy, Global Catalyst Competence Centre, P.O. Box 20, FI-41331 Vihtavuori, Finland
Shoreham Technical Centre, Ricardo UK Ltd., Shoreham-by-Sea, West Sussex BN43 5FG, UK
Author to whom correspondence should be addressed.
Catalysts 2019, 9(5), 427; https://doi.org/10.3390/catal9050427
Received: 22 March 2019 / Revised: 30 April 2019 / Accepted: 3 May 2019 / Published: 8 May 2019
(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)
Exhaust gas aftertreatment systems play a key role in controlling transportation greenhouse gas emissions. Modern aftertreatment systems, often based on Pd metal supported on aluminum oxide, provide high catalytic activity but are vulnerable to sulfur poisoning due to formation of inactive sulfate species. This paper focuses on regeneration of Pd-based catalyst via the decomposition of alumina-supported aluminum and palladium sulfates existing both individually and in combination. Decomposition experiments were carried out under hydrogen (10% H2/Ar), helium (He), low oxygen (0.1% O2/He), and excess oxygen (10% O2/He). The structure and composition of the model catalysts were examined before and after the decomposition reactions via powder X-ray diffraction and elemental sulfur analysis. The study revealed that individual alumina-supported aluminum sulfate decomposed at a higher temperature compared to individual alumina-supported palladium sulfate. The simultaneous presence of aluminum and palladium sulfates on the alumina support decreased their decomposition temperatures and led to a higher amount of metallic palladium than in the corresponding case of individual supported palladium sulfate. From a fundamental point of view, the lowest decomposition temperature was achieved in the presence of hydrogen gas, which is the optimal decomposition atmosphere among the studied conditions. In summary, aluminum sulfate has a two-fold role in the regeneration of a catalyst—it decreases the Pd sulfate decomposition temperature and hinders re-oxidation of less-active metallic palladium to active palladium oxide.