- Title
- Understanding Structure-Function Relationships in Zeolite-Supported Pd Catalysts for Oxidation of Ventilation Air Methane
- Creator
- Hosseiniamoli, Hadi; Bryant, Glenn; Kennedy, Eric M.; Mathisen, Karina; Nicholson, David; Sankar, Gopinathan; Setiawan, Adi; Stockenhuber, Michael
- Relation
- ACS Catalysis Vol. 8, Issue 7, p. 5852-5863
- Publisher Link
- http://dx.doi.org/10.1021/acscatal.7b04462
- Publisher
- American Chemical Society (ACS)
- Resource Type
- journal article
- Date
- 2018
- Description
- Catalytic combustion of ventilation air methane (VAM) is a potential solution for abatement of this greenhouse gas. In this study, we evaluate the combustion of VAM (with methane concentrations below 1%) spanning over 100 h time on stream (TOS) during reaction over a Pd/HZSM-5 catalyst. The aim is to understand the structural changes that lead to catalyst deactivation. We observe the formation of carbonaceous deposits even under oxygen-rich conditions, which are an important contributor to deactivation. X-ray absorption spectroscopic (XAS) investigation shows that, in addition to carbon deposits, the growth of Pd oxide clusters leads to a reduced number of accessible sites and in turn intrinsic activity. STEM-EDS analysis disclosed the presence of the carbonaceous deposit on the surface of the used catalyst, and TGA confirmed the presence of different carbon species on the used catalyst under very lean conditions. Structural changes show that Pd–O/acid–base interactions have a significant influence on the structure of the active site. This assertion is consistent with findings from acid–base characterization experiments. Although the catalyst displayed a high level of stability over the first 10 h of VAM combustion, long-term reaction, in the presence of water vapor, is associated with partial rearrangement of the zeolite, accompanied by a gradual deactivation of the catalyst. This rearrangement is associated with a decrease in surface area and pore volume, which is consistent with the significant changes observed in the Al-X-ray absorption near-edge spectroscopic (XANES) analysis. A comparison of the NH3-TPD of fresh and used Pd/HZSM-5 catalysts shows that the strengths of the acid sites are significantly reduced. This is a consequence of the changing nature of transition metal interaction with the zeolite, which is accompanied by the dealumination of the zeolite support, thereby enhancing Pd agglomeration and the emergence of two low index surface orientation facet planes identified as PdO(101) and PdO(100). A higher turnover frequency (TOF) (0.031 s–1) for reactivated Pd/HZSM-5 after removing all carbonaceous material compared to the TOF (0.024 s–1) for used Pd/HZSM-5 was observed. The catalyst regained 75% of its initial catalytic activity after removing carbonaceous compound from the used catalyst. We propose the formation of a palladium carbonaceous complex manifesting itself in carbonate and a carbonyl group observed in used Pd/HZSM-5. These species act as an important contributor to catalyst deactivation and cause partial reversible deactivation during long-term VAM combustion.
- Subject
- VAM; Pd/HZSM-5; XAFS; Pd-Pd; Pd-O-Pd; agglomeration
- Identifier
- http://hdl.handle.net/1959.13/1443575
- Identifier
- uon:42039
- Identifier
- ISSN:2155-5435
- Language
- eng
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