Zeolite adsorbate nitriles

An in situ infrared investigation has been conducted of the reduction of NO by CH4 over Co-ZSM-5. In the presence of O2, NO2 is formed via the oxidation of NO. Adsorbed NO2 then reacts with CH4. Nitrile species are observed and found to react very rapidly with NO2, and at a somewhat slower rate with NO and O2. The dynamics of the disappearance of CN species suggests that they are reactive intermediates, and that N2 and CO2 are produced by the reaction of CN species with NO2. While isocyanate species are also observed, these species are associated with A1 atoms in the zeolite lattice and do not act as reaction intermediates. A mechanism for NO reduction is proposed that explains why O2 facilitates the reduction of NO by CH4, and why NO facilitates the oxidation of CH4 by O2. 

The cyclocondensation of l,3-amino alcohols with carboxylic acid derivatives is a method often applied for the synthesis of 5,6-dihydro-4/7-l,3-oxazines <1996CHEC-II(6)301 >. Ebsorb-4, a weakly acidic zeolite-type adsorbent with 4 A pore size, proved an efficient catalyst of the cyclization of benzoic acid and 3-aminopropanol <2002TL3985>. In the presence of zinc chloride as a catalyst, the expulsion of ammonia drove the reactions of 3-aminopropanol with nitriles to completion, affording 2-substituted 5,6-dihydro-47f-l,3-oxazines in good yields... 

Infrared spectra of nitriles adsorbed on zeolites have been reported by Angell and Howell (252), by Karge (238), by Ratov et al. (237), and by Butler and Poles (253). Some Raman spectra are also available (254, 255). Besides H-bond-ing, the nitriles appear to interact primarily with the exchangeable cations. Acetonitrile, CH3CN, has been used frequently. However, assignment of the v2 mode (C=N stretch) in coordination compounds is quite confused due to the occurrence of Fermi resonance between the v2 mode and the (v3 + i>4) combination mode. This problem has recently been dealt with by Knozinger and Krietenbrink (255). 

The external surfaces of H-FER [143-145], H-MFl [146, 147] and H-MOR [147, 148] have been studied by IR spectroscopy of adsorbed hindered aliphatic nitriles, pyridine [145, 146], lutidine and aromatic hydrocarbons [149]. Terminal silanols and Lewis acid sites exist at the external surface of H-FER, H-MFl and H-MOR. Interestingly, the acidity of the external silanol OH groups of zeolites can be enhanced with respect to those of silica, appearing similar to those of SA. The very... 

The external versus internal surface has also been investigated in the case of Co-H-zeolites active in the selective catalytic reduction of NO by methane [20]. The highly hindered nitrile, ortho-toluonitrile (oTN) has been used, co-adsorbed with CO and NO. The pre-adsorption of oTN poisons the external cationic sites of Co-H-ZSM5. Successive adsorption of CO shows that some of the Co ions are on the inner surface and some on the outer surface. The coadsorption of oTN and NO shows that trivalent Co ions are actually located in the internal cavity surface of Co-H-ZSM-5 while divalent Co ions distribute almost equally in the internal and external surface. 

Similarly, Co ions at the external surface of Co-H-FER and Co-H-MOR have been detected. Similar experiments with hindered nitriles show the location of alkali ions at the external surface ofalkali-MOR zeolites [160]. CO mainly adsorbs at the external surface of the small pore zeolite 3A (K-LTA) while it enters the cavities of zeolite 4A (Na-LTA) [161]. 

The use of CO and nitriles as probes also reveal the possibility of interactions of adsorbed molecules with other cations in zeolite channels [162, 163],... 

Hydrogen cyanide, acrylonitrile, and acetonitrile adsorption on NaX and HY have been observed (20). Stronger interactions occur on the zeolite than on silica since the frequency shifts are greater. The nitriles interact with the cations in NaX and with the hydroxyl groups and dehydroxylated sites on HY zeolite. Acetonitrile, acetonitrile-d3, and benzonitrile have been adsorbed on various cation and HY zeolites (4). For acetonitrile, the C=N bond frequency is higher than that of the liquid phase and varies with cation, indicating that the adsorption of molecules is associated with the cation. A linear correlation is found between the cation electrostatic field and the CN bond frequency. 

The methyl disproportionation reaction appeared to occur at the higher temperatures. Hydrogen-rich species—methane and hydrogen— were observed in the gaseous products. In the absence of carbon monoxide or other multiple-bonded gaseous molecules, it may be assumed that an amine or nitrogenous species was the hydride donor, and that hydrogen-deficient moieties (nitriles, polyunsaturates, etc.) remained as adsorbed coke (0.2 wt % N, 2.2 wt % C) on the zeolite surface. 

Sikdar et al. (2000) developed adsorbent-filled PV membranes for removing VOCs from waste water. These membranes were prepared by dispersing at least one hydrophobic adsorbent uniformly into a polymer matrix. Polymeric membrane was made of rubbery polymer selected from the group consisting of PDMSs, PTMSP, PUs, polycarbonates (PCs), PE-block-polyamides, silicon PCs, styrene butadiene rubber, nitrile butadiene rubber, and ethane-propene terpolymer. The hydrophobic adsorbent was selected from the group consisting of hydrophobic zeolites, hydrophobic molecular sieves, activated carbon, hydrophobic polymer resin adsorbents, and mixtures thereof. 

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