Zeolite acidity distribution, estimation

To summarize, industrial processes in which zeolites are used are mostly reactions catalysed by acid sites [14-26]. In other words, acidity with a controlled distribution of acid sites strengths is probably the most important property observed in the zeolite catalyst. Therefore, the estimation of features related to acidity is evidently crucial for understanding the reactivity of zeolites. The understanding of zeolites acidity comprises knowledge of related concepts ... 

Adsorption microcalorimetry allows an accurate determination of amount, strength and strength distribution of surface sites, based on the heats of adsorption of appropriate probe molecules and differential heats as a function of surface coverage. Following text discuss the applicability of adsorption microcalorimetry for the determination of zeolites acidity, and the estimation of different factors that can influence this important property. 

The strategy for estimation of zeolites acidity comprises (includes) the adsorption and subsequent desorption of chosen probe molecules both events can be studied by different physical methods. From the obtained results, the facts about acidic sites (such as the strength, strength distribution...) can be derived. As it has been already discussed (Chap. 3), the characteristics of probe molecule (its nature and size), as well as the temperature dependence of the heats of adsorption have to be considered during the estimation of zeolite acidity. However, additional parameters that are related to zeolite of interest might influence its acidity, and have to be taken into consideration. Here, the influence of ... 

Recently, we investigated the associative alkylation reaction of toluene with methanol catalyzed by an acidic Mordenite (see Figures 13 and 14) by means of periodic ab initio calculations." We observed that for this reaction some transition selectivity occurred, and induced sufficiently large differences in activation energies to explain the small changes in the para/meta/ortho distribution experimentally observed on large pore zeolites. Thepara isomer is the more valuable product as it is an important intermediate for terphthalic acid, an important polymer monomer." The steric constraints obtained for the transition state structures could be estimated from local intermediates for which the orientations of the toluene molecule were similar as the ones observed for the transition states (see Figure 14). 

We also studied the effect of ion exchange with on the catalytic activity of acid-treated Bent (H -Bent ), sometimes called activated clay. The results are given in Table IV. H" -Bent is virtually the same as H -Bent in catalytic activity. However, the catalytic activity of Ti -Bent for methanol conversion to hydrocarbons is much higher than that of Ti -Bent. The hydrocarbon yield reaches 90%, and the products, in addition to methane, are primarily olefins lower than Ce. The selectivity for olefin formation is estimated to be 90% or higher based on C2 and C3 hydrocarbon product distribution. Ti -Bent appears to surpass the phosphorus compound-modified zeolite proposed by Kaeding and Butter (31) in selective activity for olefin formation, and has the potential to exceed H-Fe-silicate (32) and Ni-SAPO-34 (33), proposed recently by Inui et al. 

---