Aramburo, Luis R., Ruiz Martínez, Javier, Sommer, Linn, Arstad, Bjørnar, Buitrago Sierra, Robison, Sepúlveda-Escribano, Antonio, Zandbergen, Henny W., Olsbye, Unni, Groot, Frank M.F. de, Weckhuysen, Bert M.
X-Ray Imaging of SAPO-34 Molecular Sieves at the Nanoscale: Influence of Steaming on the Methanol-to-Hydrocarbons Reaction
ChemCatChem. 2013, 5(6): 1386-1394. doi:10.1002/cctc.201200670
URI: http://hdl.handle.net/10045/39544
DOI: 10.1002/cctc.201200670
ISSN: 1867-3880 (Print)
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.
Keywords:Carbon, Hydrocarbons, Hydrothermal treatment, Molecular sieves, X-ray absorption
Wiley-VCH Verlag GmbH & Co. KGaA
info:eu-repo/semantics/article