Understanding the spatial distribution of coke deposition within bimodal micro-/mesoporous catalysts using a novel sorption method in combination with pulsed-gradient spin-echo NMR

• Published in: Journal of catalysis Vol. 286; pp. 260 - 265
• Main Authors: Chua, Li Min, Hitchcock, Iain, Fletcher, Robin S., Holt, Elizabeth M., Lowe, John, Rigby, Sean P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.02.2012; Elsevier; Elsevier BV
• Subjects: Adsorption; alkylation; aluminum; benzene; Catalysis; Catalysts; Chemisorption; Chemistry; Coke; Colloidal state and disperse state; Deactivation; Diffusion; ethane; Exact sciences and technology; General and physical chemistry; Ion-exchange; mass transfer; micropores; NMR; Nonane; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; platinum; Pore network; Porous materials; silicon; Sorption; surface area; Surface physical chemistry; temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolite; Zeolites: preparations and properties; Chemisorption; NMR; Nonane; Deactivation; Adsorption; Coke; Pore network; Zeolite; Diffusion; Micropore; Acidic site; NMR spectrometry; Porous material; Molecular sieve; Alkylation; Solid; Platinum; Gradient; Acidity; Spin echo; Coke deposition; Ethane; Mesoporosity; Sorption; Heterogeneous catalysis; Microporosity; Spatial distribution; Pore; Benzene; Distribution; Surface area; Catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2011.11.012

Determination of the spatial location of metal surface area within bidisperse, MFI zeolite-based catalysts. [Display omitted] ► Novel method for the determination of the spatial distribution of active metal surface area. ► PGSE NMR studies of mass transport within bimodal Pt-ZSM-5 catalysts. ► Benzene alkylation with ethane studied. ► New method used to explain different coking behaviour in different catalysts. A new method for the determination of the spatial distribution of metal surface area within bimodal micro-/mesoporous solids has been developed. This novel technique involves incorporating a nonane pre-adsorption stage between two successive chemisorption experiments. This method has been used to probe the distribution of platinum amongst the micropores and mesopores of a range of bi-functional PtH-MFI catalysts, each possessing differing surface acidities, which have been used for benzene alkylation with ethane. It has been found that the catalyst with the lowest Si/Al ratio, and thus highest number of acid sites, also possessed the largest metal surface area within its microporosity. This catalyst was also the one that deactivated most rapidly, with coke being deposited predominantly within the micropore network. This was attributed to the bi-functional mechanism for coke formation at higher temperatures. Pulsed-gradient spin-echo NMR has also been used to show that a combination of higher mesopore platinum concentration and higher mass transport rates facilitated greater coke deposition within the mesoporosity.