English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

4851 of dry air a t 550 OC, conditions which would result in extensive dehydroxylation of the zeolite. According to the dehydroxylation model of Kiih133 and others34 cationic A1 species are formed as the framework is dealuminated. In fact, N M R results have shown that extensive dealumination can occur at temperatures as low as 500 O C. j 5 In the work presented here dehydroxylation and concomitant dealumination were avoided as was shown by the unit cell size of the catalyst after reaction. This is consistent with N M R results of Bosacek et aL3I which showed that upon deammination at 400 OC under "shallow-bed" conditions only about 3 Al/uc were removed from the framework. Although the acid strength of different types of zeolites may differ considerably because of changes in bond angle, bond length, etc., it is interesting to compare the specific activity for hexane cracking over a dealuminated Y sample and HZSM-5 having Si/A1 = 26. The activities of 350 O C were 11.4 and 8.5 Mmol/ (g.min), respectively. Considering the differences in the zeolites the activities are quite similar. For cumene dealkylation the HZSM-5 catalyst was about twice as active as a comparable dealuminated Y, and for methanol dehydration the HZSM-5 was about 4 times as active.Is Thus, the relative activity depends very much on the probe reaction. Conclusions Hexane cracking is essentially a linear function of the lattice A1 content over a range of Si/Al ratios from 4.6 to 255. To the extent that hexane cracking is a measure of strong acidity, the acid strength is constant over this range of Si/Al ratios. It is postulated that protons associated with isolated framework aluminum in the 4-rings give rise to the strong acidity which characterizes this material. The presence of aluminum in second-neighbor positions significantly decreases the acidity of a site. This is essentially the Dempsey-Mikovsky-Marshall (DMM) model of strong Consistent with this model, a normal H-Y zeolite, which has only a small amount of isolated tetrahedral aluminum, is relatively inactive for hexane cracking. Moreover, as described in part 1 l 5 the H-Y zeolite is relatively inactive for methanol dehydration, which requires only weak acid sites. This suggests that test reactions to characterize acid sites in zeolites need to be used with caution since a few strong acid sites may dominate the activity, even when a less-demanding reaction is employed. Iron pentacarbonyl adsorbed on dry …

Characterization of a new iron-on-zeolite Y Fischer-Tropsch catalyst