Zeolite adsorbate phenol

The limiting step of benzene to phenol transformation is suggested to be the reaction between zeolite adsorbed N2O and catalyst active sites bound with phenol... 

The products of the reaction are the following /-butyl-phenyl-ether (TBPE), p-/-butyl-phenol (p-TBP), o-/-butyl-phenol (o-TBP) and 2,4-di-/-butyl-phenol (2,4-DTBP). Compounds adsorbed on the external surface were recovered in methylene chloride (CH2C12) by a soxhlet treatment for 24 hours of the deactivated zeolite sample. The content of the compounds inside the zeolite (coke) was determined after dissolution, in 40 % HF at room temperature, of the catalyst recoved after 5 min, 45 min, 5h and 7.5 h extraction by CH2C12 then followed. The composition of soluble coke was investigated by analysis GC-MS. The procedure is reported in detail elsewhere [10]. 

In agreement with this, the analysis of the products forming during the alkylation over MCM-22 samples at different reaction time showed that about 80-90 wt. % of the recovered material is adsorbed on the external surface (phenol, o-TBP and p-TBP), whereas only about 10-20 wt.% is formed inside the zeolite ( coke constituted by p-TBP, naphthalenes, 9,10-dihydro-phenanthrene and acenaphthylene). Coke molecules could be formed in both supercages and sinusoidal channels. However, in the large supercages they would be converted into bulkier compounds, which is not the case. Therefore they are most likely located in the sinusoidal channels. 

The strength of articles based on phenolic compositions and solidified without additional pressure and heat supply is 2-4 times lower than the strength of thermally solidified resins this limits their applications as engineering materials. One of the primary causes of material strength decrease is pore formation due to volatilization of water and formaldehyde during polycondensation. Different water adsorbents (calcium carbonate, clay, silicates, methasilicates, zeolites, etc.) should be... 

A Rideal type mechanism in which phenol from the gas phase reacts with methanol adsorbed on acid sites was proposed for O- and C-methylation of phenol over acid zeolites (46) ... 

Wedge-shaped crystals, mp 247-248°. Slightly sol in water. alcohol, pyridine. Insoluble in ether and in aq acid soin, but Completely sol in aq alkaline soin. Possesses two acidic groups, one a phenolic and the other a carboxyl having pK values of 9.75 and 5.50. respectively. Characteristic blue fluorescence, max at pH 3 to 4. The fluorescence disappears on reduction with hydrosulfite and is restored to the original intensity with HjO.. Is adsorbed on zeolite from aq solns at pH 4 to 5 and can be eluted with 25% KCI butanol extracts of neutral eluates also show characteristic blue fluorescence which is increased by a trace of acetic acid. Stable to boiling with di) alkali (lJV> but upon being heated with 0.5N add for a few minutes it is converted to the lactone. 

Beutel et al. (2001) studied the interactions of phenol with zeolite NaX using solid-state H and Si MAS and Si CP-MAS NMR spectroscopy. The H MAS NMR spectrum of NaX degassed at 400°C included peaks at 5h= 1.24,2.05,4.05, and 5.11 ppm. The signal at 2.05 ppm is characteristic of silanol protons at the external surface of the zeolite. On NaY zeolite (Si/Al=2.4), a peak at 5h= 1.6 ppm was found after pretreatment in air and in vacuum at 400°C and assigned to traces of water adsorbed on cations. Therefore, the peak at 8h=1.24 ppm was attributed to free hydroxyl protons of water molecules strongly adsorbed on Na+ ions. The peaks at great 8h values could be attributed to water bound to different active sites. 

The effect of surface acidity on the behavior of Fe-MFI zeolite catalysts with different Si/Al and Si/Fe ratios for benzene hydroxylation to phenol has been studied by Selli et al. [190] using FTIR and microcalorimetric analysis of adsorbed pyridine. The behavior of the catalysts in terms of activity and deactivation rate is discussed in relation to the nature, concentration and strength of the surface acid sites. Surface acidity, though not involved directly in the hydroxylation reaction, plays a major role in determining the lifetime of the catalyst. 

For all processes that involve the adsorption step, such as physical processes of separation or catalytic transformations, the usage of solid materials with optimised activity as adsorbents and catalysts is necessary. Various solids, such as porous materials (zeolites—molecular sieves with hierarchical porosities and natural clays), activated carbons, mesoporous silica-based materials, pillared clays and metal oxides, have shown the ability to act as adsorbents or as catalysts for the conversions of previously mentioned atmospheric pollutants. Solid materials are also used for the removal of pollutants that can be found in wastewaters. The possibilities to remove polyaromatic hydrocarbons (PAHs) and heavy metal particles using the adsorptive characteristics of activated carbon and porous materials from wastewaters have been proven [15-17]. The same classes of solids are used for the elimination of organic pollutants form wastewaters by heterogeneous catalytic oxidation processes one of the most important tasks is to eliminate phenolic compounds [13]. 

Figure 10.10 shows the profiles of differential heats revealed as a function of the amounts of aqueous solution of nicotine adsorbed on different solids. Based on the values and profile of differential heats, it can be concluded that adsorption capabilities of P-zeolites are comparable with that of activated carbon, solid known to be effective adsorbent for remediation of wastewaters. There is evidence in the literature on the studies of other water pollutants adsorption, such as phenol, aldehydes and the ketones, done by the application of microcalorimetry [40]. 

Often, there is a correlation between acidic/basic or red-ox properties of some solid material and its ability to adsorb or catalytically convert certain pollutant. For example, acidity of different zeolites and mesoporous materials is important for their ability to adsorb aldehydes and ketones (from the gas phase) or phenol and nicotine (from the aqueous phase) [40, 43]. Red-ox properties are often correlated with catalysts efficiency for example, red-ox features of ceria-based mixed oxides are of importance for their ability to catalyse direct conversion of methane to synthesis gas, and they can be affected by incorporation of Zr02 [44]. The oxidability of mixed oxides is an important feature, which determines the possibility of their use as catalysts for combustion reactions and it can be also determined using TPR-TPO techniques [45]. 

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