Fundamentals of Sulfate Species in Methane Combustion Catalyst Operation and Regeneration—A Simulated Exhaust Gas Study

Abstract

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. The main question for methane operating vehicles is the durability of the palladium-rich aftertreatment system. To improve the durability of the catalysts, a regeneration method involving an efficient removal of sulfur species needs to be developed and implemented on the vehicle. This paper tackles the topic and its issues from a fundamental point of view. This study showed that Al2(SO4)3 over Al2O3 support material inhibits re-oxidation of Pd to PdO, and thus hinders the formation of the low-temperature active phase, PdOx. The presence of Al2(SO4)3 increases light-off temperature, which may be due to a blocking of active sites. Overall, this study showed that research should also focus on support material development, not only active phase inspection. An active catalyst can always be developed, but the catalyst should have the ability to be regenerated.

Understanding sulfur poisoning of bimetallic Pd-Pt methane oxidation catalysts and their regeneration

“…For instance, Honkanen et al [50] report that remaining Al2(SO4)3 has an even stronger effect on the catalyst performance than the oxidation state of Pd/PdO as spillover of sulfur species to the noble metal leads to re-poisoning. These findings are further supported by Kinnunen et al [94], who claim that the presence of aluminum sulfate hinders palladium reoxidation after a reductive regeneration treatment. In this regard usage of CZ as support material seems to be the better choice compared to alumina.…”

Decomposition of Al2O3-Supported PdSO4 and Al2(SO4)3 in the Regeneration of Methane Combustion Catalyst: A Model Catalyst Study

“…Temperature-programmed desorption (TPD) and oxidation (TPO) with low oxygen are relevant techniques to enhance the fundamental understanding of the catalyst decomposition and structure under these conditions. Lean operation conditions are restored at Point (4), which re-oxidizes and recovers the active form of the catalyst at Point 5, as discussed in our previous work [25].…”

Catalyst Deactivation, Poisoning and Regeneration

“…The complexity of catalyst poisoning obviously increases along with the increasing use of biomass/waste-derived/residual feedstocks [2,3] and with requirements for cleaner and novel sustainable processes, such as those implementing a catalytic assisted chemical looping approach [4,5].This Special Issue provides insight for several specific scientific and technical aspects of catalyst poisoning and deactivation, proposing more tolerant catalyst formulations and exploring possible regeneration strategies. In particular, 14 research articles focus on heterogeneous catalysts by investigating thermal [6-8], physical [9,10] and chemical [11][12][13][14][15][16][17][18][19] deactivation phenomena, and also exploring less conventional poisons related to the increasing use of bio-fuels [17]. Some regeneration strategies [11,16], together with solutions to prevent or limit deactivation phenomena [7,9,11,16], are also discussed.…”

“…The individual and combined decomposition of aluminum and palladium sulphates, components of DOC, TWC and MOC, is presented in [12]. The same authors also address the role of sulphates formed on the support in restoring the Pd active species under different atmospheres and under simulated exhaust gas [13]. The deactivating effect of SO 2 and the formation of undesired by-products during the NH 3 SCR over a MnFe/TiO 2 catalyst for low-medium temperature is analyzed in [14] by investigating the mechanism of the main and side reactions occurring during the SCR process.…”