Catalysts H mordenite

This chapter compares the reaction of gas-phase methylation of phenol with methanol in basic and in acid catalysis, with the aim of investigating how the transformations occurring on methanol affect the catalytic performance and the reaction mechanism. It is proposed that with the basic catalyst, Mg/Fe/0, the tme alkylating agent is formaldehyde, obtained by dehydrogenation of methanol. Formaldehyde reacts with phenol to yield salicyl alcohol, which rapidly dehydrogenates to salicyladehyde. The latter was isolated in tests made by feeding directly a formalin/phenol aqueous solution. Salicylaldehyde then transforms to o-cresol, the main product of the basic-catalyzed methylation of phenol, likely by means of an intramolecular H-transfer with formaldehyde. With an acid catalyst, H-mordenite, the main products were anisole and cresols moreover, methanol was transformed to alkylaromatics. 

Figure 44.3. Conversion of methanol (O), yields of alkylaromaties (A) and yields to light componnds (CO + CO2 + CH4) (O) as functions of temperature. Feed composition (molar fractions) methanol 0.12, nitrogen 0.88. Catalyst H-mordenite.

Figure 44.5. Conversion of phenol ( ), molar selectivity to anisole (X), o-cresol (O), p-cresol (A), 2,6-xylenol (O), salicylaldehyde ( ) and polyalkylated phenols ( ) as functions of temperature. Catalyst H-mordenite. Feed composition N2 89.3%, formaldehyde 1.7%, phenol 0.46%, methanol 0.03% and water 8.5%.

Figure 1. Catechol conversion and selectivity to guaiacol, o-cresol, phenol, p-cresol and 3-methylcatechol as functions of temperature. Catalyst H-mordenite. Feed catechol and methanol (1/10 molar feed ratio).

For cumene production (from benzene and propene) a new process has been developed in which H-mordenite (with high Si/Al) serves as the catalyst. Here the... 

Selective synthesis of ethylenediamine from ethanolamine over modified H-mordenite catalyst... 

The results in Table 3 show that H-mordenite has a high selectivity and activity for dehydration of methanol to dimethylether. At 150°C, 1.66 mol/kg catal/hr or 95% of the methanol had been converted to dimethylether. This rate is consistent with that foimd by Bandiera and Naccache [10] for dehydration of methanol only over H-mordenite, 1.4 mol/kg catal/hr, when extrt lat to 150°C. At the same time, only 0.076 mol/kg catal/hr or 4% of the isobutanol present has been converted. In contrast, over the HZSM-5 zeolite, both methanol and isobutanol are converted. In fact, at 175 X, isobutanol conversion was higher than methanol conversion over HZSM-5. This presents a seemingly paradoxical case of shape selectivity. H-Mordenite, the zeolite with the larger channels, selectively dehydrates the smaller alcohol in the 1/1 methanol/ isobutanol mixture. HZSM-5, with smaller diameter pores, shows no such selectivity. In the absence of methanol, under the same conditions at 15(fC, isobutanol reacted over H-mordenite at the rate of 0.13 mol/kg catal/hr, higher than in the presence of methanol, but still far less than over H M-5 or other catalysts in this study. 

Conclusive evidence has been presented that surface-catalyzed coupling of alcohols to ethers proceeds predominantly the S 2 pathway, in which product composition, oxygen retention, and chiral inversion is controlled 1 "competitive double parkir of reactant alcohols or by transition state shape selectivity. These two features afforded by the use of solid add catalysts result in selectivities that are superior to solution reactions. High resolution XPS data demonstrate that Brpnsted add centers activate the alcohols for ether synthesis over sulfonic add resins, and the reaction conditions in zeolites indicate that Brpnsted adds are active centers therein, too. Two different shape-selectivity effects on the alcohol coupling pathway were observed herein transition-state constraint in HZSM-5 and reactant approach constraint in H-mordenite. None of these effects is a molecular sieving of the reactant molecules in the main zeolite channels, as both methanol and isobutanol have dimensions smaller than the main channel diameters in ZSM-S and mordenite. 

Figures 44.1 and 44.2 report the performance in the gas-phase phenol methylation of the H-mordenite and of the Mg/Fe/O catalyst, respectively. The differences between the two catalysts concerned both the transformations occurring on methanol and the type of phenolic products obtained. The H-mordenite was very active at 350°C the conversion of phenol was 80%. A further increase of temperature led to a decrease of conversion. This can be attributed to a progressive deactivation of the catalyst, due to...

The three-function model introduced in the preceding section has been established on an H-mordenite (HMOR) supported cobalt—palladium catalyst [12], For the sake of demonstration, model catalysts with a unique function, i.e. FI, F2 or F3, (Figure 5.1), were prepared to separately give evidence of the major role of each active site (Figure 5.1). Let us note that three functions does not necessarily mean three different active sites, but in the case of CoPd/HMOR material, three different sites were identified. 

DRIFT spectroscopy was used to determine Av0h shifts, induced by adsorption of N2 and hexane for zeolite H-ZSM-5 (ZSM-a and ZSM-b, Si/Al=15.5 and 26), H-mordenite (Mor-a and Mor-b, Si/AI— 6.8 and 10) and H-Y (Y-a and Y-b, Si/Al=2.5 and 10.4) samples. Catalysts were activated in 02 flow at 773 K in situ in the DRIFTS cell and contacted than with N2 at pressures up to 9 bar at 298 K or with 6.1% hexane/He mixture at 553 K, i.e., under reaction conditions. Catalytic activities of the solids were measured in a flow-through microreactor and kapp was obtained as slope of -ln(l-X0) vs. W/F plots. The concentration of Bronsted acid sites was determined by measuring the NH4+ ion-exchange capacity of the zeolite. The site specific apparent rate constant, TOFBapp, was obtained as the ratio of kapp and the concentration of Bronsted acid sites. 

Karge and Ladebeck (90) studied the alkylation of benzene with olefins over aluminum-deficient, beryllium exchanged mordenite and found a considerable extension of the lifetime of the catalyst, as compared to H-mordenite. The authors were able to carry out quite efficiently the alkylation reaction as well as the transalkylation of ethylbenzene at relatively low temperatures. 

Another thermal analysis method available for catalyst characterization is microcalorimetiy, which is based on the measurement of the heat generated or consumed when a gas adsorbs and reacts on the surface of a solid [66-68], This information can be used, for instance, to determine the relative stability among different phases of a solid [69], Microcalorimetiy is also applicable in the measurement of the strengths and distribution of acidic or basic sites as well as for the characterization of metal-based catalysts [66-68], For instance, Figure 1.10 presents microcalorimetry data for ammonia adsorption on H-ZSM-5 and H-mordenite zeolites [70], clearly illustrating the differences in both acid strength (indicated by the different initial adsorption heats) and total number of acidic sites (measured by the total ammonia uptake) between the two catalysts. 

Figure 1.10 Differential heats of adsorption as a function of coverage for ammonia on H-ZSM-5 (o) and H-mordenite ( ) zeolites [70], In both cases, the heats decrease with the extent of NH3 uptake, indicating that the strengths of the individual acidic sites on each catalyst are not uniform. On the other hand, the H-ZSM-5 sample has a smaller total number of acidic sites. Also, the H-mordenite sample has a few very strong sites, as manifested by the high initial adsorption heat at low ammonia coverage. These data point to a significant difference in acidity between the two zeolites. That may account for their different catalytic performance. (Reproduced with permission from Elsevier.)...

To test this hypothesis a Pt/mordenite catalyst was prepared from H-mordenite by exchanging a small amount of Pt and reducing at low temperature, so that Pt-H adducts could be formed and most Pt atoms were located in the side pockets of the... 

Kumar, N., Villegas, J.I., Salmi, T., Murzin, D.Y., and Heikkila, T. (2005) Isomerization of n-butane to isobutane over Pt-SAPO-5, SAPO-5, Pt-H-morden-ite and H-mordenite catalysts. Catal. Today, 100, 355-361. 

As observed above, in order to quench HMF produced in situ, dealuminated H-form mordenites were investigated in a water/MIBK mixture (1/5) [84, 85]. In this case, a maximum conversion of fructose of 54% (along with 90% selectivity to HMF) was obtained over an H-mordenite with a Si/Al ratio of 11. HMF was continuously extracted with a flow of MIBK circulating in a countercurrent way through a catalytic heterogeneous reactor containing the H-mordenite zeolite. On the continuation of their efforts, the same authors then set up a new continuous solid-liquid-liquid reactor where the zeolite was now in suspension in the aqueous phase while the HMF was continuously extracted with MIBK in a countercurrent way to the aqueous phase and catalyst feed. 

Scheme 5 Xylose can be dehydrated to produce furfural. The reaction has been reported using several different catalysts including zeolites, sulfonic acid functionalized MCM-41 and immobilized heteropolyacids. The best selectivity towards furfural was achieved using zeolite H-mordenite, although at low conversion of xylose.Overall, the best yield of furfural was obtained using sulfonic acid functionalized MCM-41.

With zeolites as the solid acid catalyst, the best results for HMF synthesis were obtained by Moreau et al. who tested acidic mordenites with different Si/Al ratios in batch experiments and reported that dealuminated H-Mordenite with Si/Al ratio of 11 exhibited the highest selectivity and even so at reasonably high fructose conversion (91% selectivity at 76% conversion after 60 min. at 165 °C using water/methyl isobutyl ketone as the reaction media).Other zeolites, H-Y, H-Beta and H-ZSM-5 were also tested for the reaction, however, none of these catalysts were as selective as H-mordenite. ... 

Hardacre et al. report the Friedel-Crafts benzoylation of anisole with benzoic anhydride to yield 4-methoxybenzophenone with various ILs and zeolite catalysts (USY, HZSM-5, H-beta, and H-mordenite). The rates of reaction were found to be significantly higher using ionic liquids compared with organic solvents.Continuous-flow studies of successful ionic liquid systems indicate that the bulk of the catalysis is due to the formation of an acid via the ion exchange of the cation with the protons of the zeolite as shown in the following reaction. Scheme 8. 

The following catalysts were used for reactivity tests (a) H-mordenite zeolite, H-MOR40, shaped in extrudates, supplied by Sud-Chemie AG, and having Si02/Al203 ratio equal to 40. (b) AIF3, supplied by Aldrich, (c) AFP/0, prepared following the... 

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