Catalytic activity correlations

Isopropylation over HY, HL and Other Zeolites - The catalysis over HY and HL was quite different from that over HM.61 63 The further isopropylation of IPN and DIPN isomers was quite rapid in spite of the higher number of bulky isopropyl groups. The yield of IPN had a maximum value during the initial stage of the reaction, and then decreased with reaction time. At longer periods, the product amounts decreased as follows DIPN > IPN > TrIPN. Because the catalytic activities correlate well with the pore surface areas of the zeolite, the isopropylation occurs predominantly inside the pores. These results indicate that HY and HL have enough space for the isopropylation of naphthalene inside their pores. Naphthalene and its alkylates can easily enter into and diffuse out of the pores. 

In every case the catalytic activity correlated linearly with the percent of Na+ substituted by H+ in the lattice (Figure 3). The protonic sites created by introducing Ca2+ in the lattice were more active than those produced by leaching out some of the Na+ from the zeolite. 

Preliminary data on the reactivity of these materials in a typical Knoevenagel reaction (cyclohexanone and ethyl cyanoacetate) indicates a general trend towards higher activity with increasing water content in the material preparation system. This is complicated by some irregularities in the data from the samples prepared from solvents with roughly comparable water ethanol volume ratios. While many systems have been described where the catalytic activity correlates with changes in textural properties[9], the trends in activity found in this study correlate best with an increase in framework mesopore diameter, and do not follow the... 

The influence of the heteroatom on the acid strength is shown, for example, in Fig. 28. Here the rates of alkylation of 1,3,5-trimethylbenzene and the decomposition of cyclohexyl acetate catalyzed by the acid forms of several 12-tungstates are plotted against the negative charge of polyanion for solid heteropolyacids (63, 183). The catalytic activities correlate well with the acid strength in solution (Fig. 14). This correlation indicates that the acid strength of... 

Other paraffins have also been used for measuring acidity. Neopentane is an attractive compound since protonation of a C-C bond is the preferred primary step for cracking. Corma and coworkers and Guisnet and coworkers used n-heptane in studies of H-Y. Klyachko et al. used octane to characterize the acidities of mordenites and ZSM-5 zeolites. The catalytic activity correlated well with their acidities as determined by calorimetric measurements of the heats of adsorption of ammonia. Higher paraffins such as hexadecane have also been used, but their utility is questionable due to the increased number of secondary reactions that can occur. ... 

In some instances, there still exist conflicting reports about the surface acidity-catalytic activity correlation. These differences may arise not only from the use of different reaction conditions and different approaches to preparing or modifying the catalysts but also from a poor characterization of the materials employed. Indeed, the detailed physicochemical characterization of the catalytic materials, as well as the study of their interaction with reagents and products, still represents well-recognized problems in the use of heterogeneous catalysis for organic syntheses. 

The influence of adsorbed Si, P, S, and Cl on the medium-pressure cyclotrimerization of acetylene to benzene over Pd(l 11), (100), and (110) has been studied by Logan et al. (113). Whereas both sulfur and chlorine decrease the activity, silicon increases the activity. The effect of phosphorous depends on the crystal face. According to their work function measurements, sulfur withdraws electron density from the Pd surface (as is also expected for chlorine), whereas Si donates electron density, and P has the least effect on the work function. Thus, the qualitative influences on catalytic activities correlate with the influences of the additives on the electronic character of the surface. In addition, Si decreases the carbon coverage seen in postreaction AES from —82 to —70% of a monolayer, whereas sulfur and chlorine increase the amount of carbonaceous residue. The authors interpreted these results by suggesting that the electron-donating ligands keep the Pd surface cleaner for the desirable reaction by... 

Benzaldehyde undergoes Tischtschenko type reaction to produce benzylbezoate over alkaline earth oxides[30]. The catalytic activity correlates well with the amount of basic sites, and the basic sites are believed to be active sites. The reaction proceeds as follows. The slow step of the reaction is H- transfer from (I) to (II) In this reaction, not only basic sites (0 ions) but also acidic sites (metal cations) are participating as shown above. 

The first-order rate constant of the esterification of anhydrous phthalic acid catalyzed by nickel sulfates mounted on alumina and some other solid acids is shown in Table IV, together with the acidity of the catalysts measured by using p-dimethylaminoazobenezene as an indicator and the acidity calculated from the rate constants (cf. Section II). The catalytic activity correlates better with the acidity obtained by the latter method. The acidities measured by both methods coincide in the case of nickel sulfate, but do not in the case of silica-alumina. This is considered, according to Tarama et al., to be due to the fact that the Lewis acid sites which are assumed to be included in silica-alumina do not show catalytic activity. However, this might also be interpreted as due to the differences in acid strength and selectivity. 

Thlocarbonyls and Thlophosphates - A variety of substances with C=S or P=S functionalities. Including dlethyldithlocarbamate and parathion, inactivate cytochrome P-450 and result in microsomal heme loss when catalytically acted upon by the enzyme,The most informative mechanistic data is that obtained for parathion which suggests that several sulfur atoms are covalently bound but actual loss of catalytic activity correlates with loss of the prosthetic heme group.It has been postulated that catalytically-released sulfur atoms react with protein sulfhydryl groups to give hydrodisulfides, one of which subsequently reacts with the heme group. This postulate is supported by the demonstration that benzyl hydrodisulfide destroys cytochrome P-450 and its prosthetic group without a requirement for catalytic turnover of the enzyme but the nature of the products formed in the reaction is not known. 

The results of catalytic activity correlate very well with the free metal surface area (dispersion) obtained by hydrogen-oxygen titration cycles HOTC method. 

The investigations discussed earlier clearly demonstrate that the reactant itself should be used as a probe molecule in order to obtain reliable surface structure-catalytic activity correlations. A controlled chemisorption of the reactant... 

In another study [138], authors presented evidence that heats of adsorption of ammonia on three different kinds of zeolite structure (Y, mordenite, ZSM-5) can be used to obtain the correlation plots that describe relationships between acidic and catalytic properties of these catalysts. Catalytic properties were tested in simple carbonium ion reactions. An approach to search acidity-catalytic activity correlations was based on the straightforward concept which implies that the heat of adsorption of the base is directly related to the energy needed for the protonation of hydrocarbon molecules leading to the carbocation formation. For example it was... 

---