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- Title
X-Ray Imaging of SAPO-34 Molecular Sieves at the Nanoscale: Influence of Steaming on the Methanol-to-Hydrocarbons Reaction.
- Authors
Aramburo, Luis R.; Ruiz ‐ Martínez, Javier; Sommer, Linn; Arstad, Bjørnar; Buitrago ‐ Sierra, Robison; Sepúlveda ‐ Escribano, Antonio; ZandbergEN, HENny W.; Olsbye, Unni; de Groot, Frank M. F.; WeckhuysEN, Bert M.
- Abstract
The effect of a severe steaming treatment on the physicochemical properties and catalytic performance of H-SAPO-34 molecular sieves during the methanol-to-hydrocarbons (MTH) reaction has been investigated with a combination of scanning transmission X-ray microscopy (STXM), catalytic testing, and bulk characterization techniques, including ammonia temperature programmed desorption and 27Al and 29Si magic angle spinning nuclear magnetic resonance. For this purpose, two samples, namely a calcined and a steamed H-SAPO-34 catalyst powder, have been compared. It has been found that calcined H-SAPO-34 displays a high selectivity towards light olefins, yet shows a poor stability as compared to a zeolite H-ZSM-5 catalyst. Moreover, in situ STXM at the carbon K-edge during the MTH reaction allows construction of nanoscale chemical maps of the hydrocarbon species formed within the H-SAPO-34 aggregates as a function of reaction time and steam post-treatment. It was found that there is an initial preferential formation of coke precursor species within the core of the H-SAPO-34 aggregates. For longer times on stream the formation of the coke precursor species is extended to the outer regions, progressively filling the entire H-SAPO-34 catalyst particle. In contrast, the hydrothermally treated H-SAPO-34 showed similar reaction selectivity, but decreased activity and catalyst stability with respect to its calcined counterpart. These variations in MTH performance are related to a faster and more homogeneous formation of coke precursor species filling up the entire steamed H-SAPO-34 catalyst particle. Finally, the chemical imaging capabilities of the STXM method at the Al and Si K-edge are illustrated by visualizing the silicon islands at the nanoscale before and after steaming H-SAPO-34.
- Subjects
MOLECULAR sieves; CATALYTIC activity; METHANOL; HYDROCARBONS; X-ray imaging; DESORPTION; CATALYSTS
- Publication
ChemCatChem, 2013, Vol 5, Issue 6, p1386
- ISSN
1867-3880
- Publication type
Article
- DOI
10.1002/cctc.201200670