Benzene alkylation with ethane in ethylbenzene over a PtH-MFI catalyst: Kinetic and IR investigation of the catalyst deactivation

This study demonstrates that the deactivation of the highly acidic PtH-MFI catalyst in the reaction of benzene alkylation with ethane in ethylbenzene (EB) proceeds in two modes. The first mode corresponds to the selective deactivation of the Pt sites, which are highly active in the hydrogenolysis reactions. This deactivation occurs during the first ∼4 h of the catalyst operation and results in the significant improvement of the catalyst selectivity toward EB. The second, much slower, deactivation process is observed during tens of hours and is responsible for the deactivation of Pt and acid sites with similar rates. This deactivation mode leads to the re-distribution of the reaction products in a way that is very similar to the effect of contact time on the product distribution. The analysis of the IR spectra of the fresh and coked catalyst samples reveals that coke species are formed both inside and outside of the zeolite channels. It is shown that these coke species block the catalyst Brønsted acid sites directly but do not block the zeolite channels up to the coke content of 5-6 wt.% in the catalyst. The coke located on the external surface has a major effect on the large Pt particles (∼10 nm) present in the catalyst, as follows from the IR study of the CO adsorption. Our work also indicates that there are at least two different Pt sites in the Pt particles, possibly responsible for the different reaction types, namely dehydrogenation and hydrogenolysis. These two different Pt sites are affected by coke deposits differently, and therefore, their deactivation can explain the observed two modes of the catalyst deactivation.