Abstract
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.
Highlights
Alkylation of benzene with ethene is currently used to synthesise ethylbenzene, a vital intermediate in the manufacture of polystyrene
It was found that coke was predominantly deposited in different locations, depending on the Si/Al ratio, with more losses of surface area due to coke arising within the microporosity at lower values of the ratio, and in the mesopore network at higher values
The micropore pore size distribution obtained from nitrogen adsorption and the metal surface area obtained from chemisorption could be combined to obtain more detailed information on the spatial distribution of metal
Summary
Alkylation of benzene with ethene is currently used to synthesise ethylbenzene, a vital intermediate in the manufacture of polystyrene. A potential alternative is the direct alkylation of benzene with ethane using a bi-functional catalyst that performs both the dehydrogenation and alkylation steps. Platinum on MFI zeolite has been proposed as a potential catalyst, and the reaction studied in detail [1]. In previous work [1] it was shown that zeolites with differing Si/Al ratios gave rise to differing coking behaviour. The reasons for the particular coke distribution in different catalysts will be explored. It will be shown that the spatial distribution of platinum and the mass transfer rates contribute to the coke location. A novel method for determining the spatial distribution of platinum within the catalyst has been developed based upon the nonane pre-adsorption method, previously used to assess microporosity [2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
