Evolution of carbonaceous deposits on H-mordenite and Pt-doped H-mordenite during n-butane conversion

Simultaneous coking and dealumination of zeolite H-ZSM-5 during the transformation of chloromethane into olefins

“…The relative ratio of the IR intensities of -CH 3 and -CH 2 groups is almost constant, indicating that there is no significant variation in the length of the aliphatic chains in coke with increasing TOS. Evolution of coke content with the total number of acid sites and acid strength of the spent catalyst at different reaction temperatures and different TOS (450 °C).UV-Vis absorption spectroscopy is sensitive to the electronic transitions of different aromatic species and it is a suitable technique for the analysis of the formation and growth of coke in different reactions, such as cracking of polyolefins,35,36 bio-oil cracking,34,44 aromatization of paraffins and olefins,45 dehydrogenation of paraffins,46,47 as well as the MTO condensed aromatic compounds are observed, such as two and three ring aromatic carbocations from naphthalene, anthracene and phenanthrene,45,50 more condensed species are observed at 565-635 nm, such as aromatic carbocation species with four and five rings, Evolution of the intensities of the FT-IR spectrum vibration bands with time on stream corresponding to functional groups of coke on the spent catalyst at 450 °C.…”

Butane Isomerization as a Diagnostic Tool in the Rational Design of Solid Acid Catalysts

“…Though the WO x /ZrO 2 system had a much higher initial isobutane yield (10 mol%) than the zeolite Y (5 mol%), the zeolite Y remained stable over 5 h. In contrast the isobutane yield for the WO X /ZrO 2 system rapidly decreased, achieving just 2 mol% isobutane yields after 3 h. This stability emphasizes how important acid strength is in forming olefinic precursors to the butyl carbenium intermediates in both monomolecular and bimolecular pathways. While olefinic species are vital species in this reaction, they are also known to have a deactivating role in isomerization [76][77][78][79][80]. Thus, the effect is twofold; high acidic strength promotes high concentrations of olefinic species via a high carbocation concentration, which in turn promotes a high reaction rate.…”

“…As Engelhardt notes, the side reactions of cracking and disproportionation are influenced far more by the carbocation concentration than the rates of isobutane formation [79]. However high olefinic concentrations promote a high rate of coking side reactions resulting in a high deactivation rate [77,[79][80][81]. Specifically, this is due to the selective deactivation of active sites through polyolefin coking products, preventing further carbocation formation through blockage of the active site.…”

“…This subsequently reduced the observed conversion rate as the bimolecular mechanism was suppressed as a result. Wulfers et al demonstrate that by including H 2 in the reaction feed, olefinic concentrations are reduced, though reaction rate is lowered [77]. By replacing H 2 with He, reaction rates increased with olefin concentrations, although the deactivation rate likewise increased.…”

“…Wulfers and Jentoft demonstrate that when studying mordenite activity with a purified butane feed, isomerization activity is enhanced by the addition of a miniscule 18 ppm feed of butene [76]. Further work by Wulfers et al found that introducing butene in a time on stream experiment cause the rapid increase in the rate of isobutane rate formation, although this mainly triggered a rapid deactivation [77]. Findings from Fogash et al supported this finding, by showing that complete removal of olefinic impurities from the feed eliminated isomerization activity in mordenite [78].…”