Isopropanol dehydration

Dumesic and co-workers studied the activity of isopropanol dehydration (247) on a series of silica-supported oxide catalysts as well as the acidic properties of these materials using IR spectroscopy and TGA of adsorbed pyridine (59) and adsorption microcalorimetry of pyridine at 473 K (18,104). Samples that showed only Lewis acidity were at least one to two orders of magnitude less active than the samples that displayed Brpnsted acidity. The activity of the latter samples increased in the order Sc < Ga < Al + This is the same order found for differential heats of pyridine adsorption on the Brpnsted acid sites, and a good correlation between the heats and the activity was found. No correlation was found with the initial heats or for the samples that had only Lewis acidity. 

In order to assess the effect of various synthesis parameters and the presence of a second oxide (Ti02 or Zr02> at different concentrations on the AI2O3 structure, the corresponding samples were prepared by low-temperature sol-gel method. The oxides were characterized by N2 physisorption, XRD and Al MAS-NMR. In all samples calcined at Tc 973 K four-, five- and six-coordinated aluminum were detected. A pseudospinel model was used to evaluate the structural changes in the different oxides. The sol-gel AI2O3 calcined at 1173 K (Al /Al" -5.7, no metastable pentahedral aluminum) was the material that better fitted the proposed model. AI2O3 oxides calcined at different temperatures were studied in the isopropanol dehydration in order to correlate their performance to the amounts of Al. ... 

In this work, we investigated the effect of some parameters (type of synthesis additive and calcination temperature) as well as the presence of a second cation (Ti" or Zr ) on the formation of five-coordinated aluminum and the consequential structure modification in sol-gel alumina-based supports. The samples prepared were characterized by N2 physisorption. X-ray diffraction and Al MAS-NMR. The isopropanol dehydration over... 

Isopropanol dehydration over AI2O3 calcined at different temperatures was studied in a pyrex glass steady state system. The fixed bed (50 mg) tubular reactor was operated at differential regime (% conversion<10), in the 423temperature range and atmospheric pressure. The feed was composed of a N2 (Praxair) stream saturated with isopropanol at room temperature. The analysis of effluents from the reactor was carried out by gas chromatography with a Gow-Mac Series 750 apparatus equipped with a thermal conductivity detector and a Porapak Q packed column. 

AI2O3 calcined at different temperatures was studied in the isopropanol dehydration (propylene only product), the results at Tr=473 K being shown in Fig 6. For both series (AlA and AlC) the trends were similar both on per weight and per surface area basis (not shown). Conversely to other authors [4], there was no correlation between the dehydrating activity and the AP amount in the oxides (Table 2), the latter often related to Lewis acid... 

Fig. 6. Isopropanol dehydration rate of sol-gel AI2O3 prepared with different additives (per weight basis), Tr=473 K.

P-06 - Acidity characterization of dealuminated H-ZSM-5 zeolites by isopropanol dehydration... 

A series of dealuminated ZSM-5 zeolites with various framework Si/Al ratios were prepared by different methods (HCl, ammonium hexafluorosilicate, steaming). The number of acid sites that correspond to the high-temperature desorption peak of the ammonia-TPD spectra of all the dealuminated samples is in 1 1 mole analogy to the framework Al (FAl), irrespective the degree and the type of dealumination method. The catalytic activity of the H-ZSM-5 zeolites for isopropanol dehydration is linearly related to the number of acid sites that correspond to the FAl-content (Bronsted acidity). The Si-Al amorphous phase that is formed in the high-temperature steamed samples affects activity and induces different product selectivity for propene and diisopropyl ether. 

Degradation, polyethylene Degradation, polymers, catalytic Dehydration, Cd-FAU Dehydration, clinoptilolite Dehydration, isopropanol Dehydration, K-LSX Dehydration, MOR Dehydrocyclodimerisation, butadiene Dehydrogenation, ethylbenzene Dehydrogenation, methanol Dehydroisomerisation, n-butane Dehydroxylation, phenol Delaminated zeolites De novo simulation DeNOx catalyst... 

Ionic conduction, lithium silicate 09-0-05 Isopropanol dehydration 29-P-06... 

Only a few years after the existence of active centers was first postulated, Dohse and coworkers in 1930 ( ) determined the site density by what amounts to determining the number of chemisorbed reactant molecules when the reaction is zero order. For isopropanol dehydration over alumina they found a site density— asji min their alumina had a normal surface area—of about 10 cm. In 1937 Kubokawa ( ) used a poisoning method, measuring the amount of mercuric ion which inhibited > 2 decomposition over platinum black. Balandin and Vasser i rg obtained in 1946 ( ) a site density of the order of 10 cm for the dehydration of isopropanol over a mixed oxide of zinc and alumina. 

The chemisorption of isopropanol at 313 K leads to the coverage of the heteropolyacids with a stable monolayer of adsorbed isopropoxy species and avoids further surface reaction. These adsorbed intermediate-reactive alkoxy species further react and desorb as propylene (or other product depending on the nature of the site) upon controlled heating during the TPSR experiment. Therefore, the quantification of the desorbed product is proportional to the total number of acid sites active on isopropanol dehydration towards propylene. 

Younes M K, Ghorbel A, Rives A, Hubaut R (2000) Study of acidity of aerogels Zr02-S04 by isopropanol dehydration reaction, surface potential and X-ray photoelectron spectroscopy. J Sol Gel SciTechn 19 817-819... 

The catalysts based on silica fiberglass materials can be efficiently used in many gas-phase and Hquid-phase catalytic processes such as acid-catalyzed isopropanol dehydration reactions. To date, the acid-base properties of fiberglass materials, including the Brpnsted acidity, were not studied in detail. The lack of detailed studies could be due to the low specific surface area of fiber-... 

Although materials prepared by post-aliunination procedures did not feature acid sites stronger than those obtained by direct synthesis, the catalytic activity of the former (evaluated for ciunene cracking [115,116], isopropanol dehydration [120,121] or aldehyde condensation [117]) was found systematically higher than that of the latter. Such a result must be attributed to a better accessibility of the acid sites in the case of post-aluminated materials. This fact was actually shown by CoUart et al. [118,119] in the case of [Si]-MCM-48s treated with Al(acac)3. The munber of acid sites titrated by ammonia amounted to 100% and 68% of the total number of aliuninum atoms deposited in samples containing 1.2wt% (Si/Al = 37) and 5.1 wt% (Si/Al = 17) Al, respectively. 

The activity toward isopropanol dehydration is also used to characterize the acidity of HPA compounds since the product distribution depends on the nature of surface active sites (and bulk active sites considering the pseudo-liquid behavior of heteropoly compounds). Strong surface Brpnsted (H+) and Lewis acid sites catalyze the dehydration of isopropanol to propylene (di-isopropyl ether for weak Lewis acid sites) and redox/basic sites lead to the dehydrogenation of the alcohol to acetone. 

Table 5.4 Solid properties and relative activity for the isopropanol dehydration...

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