Exchanged zeolites mordenite

Preparation, characterization, and photoreactivity of titanium (IV) oxide encapsulated inside sodium or ammonium exchanged zeolite, mordenite, or potassium zeolites were described 111... 

Barrer showed these hydrogen zeolites, mordenite and chabazite, to be crystalline using x-ray diffraction, and stated, Hydrogen zeolites are effectively crystalline aluminosilicic acids, the salts of which are their diverse cation exchange products." Szymanski, Stamires, and Lynch (13) used simple thermal decomposition of an ammonium zeolite X in an attempt to prepare the hydrogen zeolite... 

The ability of water molecules to promote a reaction depends on many factors. In most cases, zeolites with monovalent cations have low activity. However, the addition of water molecules to X and Y zeolites with monovalent ions increased the isomerization of cyclopropane (63). De-cationized zeolites can be promoted readily with water, and the process is reversible (2, 60, 64). It was shown (2) that the promoting ability of water molecules in faujasites is less when the Si02/Al203 increases. Dealu-minated faujasites are even more difficult to promote. For erionite and mordenite the maximum effect of water was observed only after treatment with liquid water and subsequent heating (2). The effect of water on zeolites saturated with polyvalent cations is less pronounced (65, 66, 67). However, the presence of multivalent cations stabilizes the catalytic activity. Water and alcohols were reported to promote ion exchanged zeolites for n-pentane isomerization (68) and n-hexadecane hydrocracking (69). 

Other examples of the use of natural zeolites in catalysis has been the use of Cd-exchanged chabazite, clinoptilolite, erionite, and mordenite as catalysts in the hydration of acetylene to acetaldehyde [26], and a Cu-exchanged natural mordenite, which was studied as a catalyst for the selective reduction of NO with NH3 [27],... 

The hydronium exchanged synthetic mordenite does have a band, as shown in spectrum 10 in Figure 1. The iron substituted mordenite samples (spectra 8 and 9) do not show the presence of the band it was "removed" as a result of the substitution reaction. An absorption band at 950 cm- is normally attributed to an Si-OH stretch vibration (14, 15), and is typically observed in some acid or hydrothermally treated zeolites. 

Paetow and Riekert (28, 29) in a careful study have compared the relative activities of Cu2 +-exchanged zeolite T and mordenite with various copper-containing compounds. On the basis of turnover numbers per CO chemisorption site the Cu2 +-exchanged zeolites are 2-4 orders of magnitude less active than CuO, CuMn204, and CuCr204. This was considered to be consistent with the involvement of lattice oxygen as an intermediate which is easier to remove in oxides than zeolites. 

These results are consistent with the generalized reaction scheme, initially presented by Rabo et al., in which both NH +- and H30+-exchanged zeolites decompose to produce an Br-form that upon further heating becomes a decationized zeolite. This behavior is similar to that reported earlier for calcined ion-exchanged synthetic mordenites, where two distinct sources of acidity were found in the NH4+-form but not in the H30+-form. 

Emission Spectra. The emission spectra of the uranyl acetate dihydrate in solution and in the solid state are shown in Figure 1. The fine structure in the solid state spectrum is not observed in solution. The corresponding emission spectra of uranyl-exchanged zeolites. A, Y, mordenite and ZSM-5 are shown in Figures 2-4. Excitation is carried out at 366 nm. The emission spectra have been scanned in all cases between 450 nm and at least 630 nm. 

The emission spectra for uranyl-exchanged zeolites Y, mordenite and X all have differences but do show some fine structure and therefore resemble the solid state spectrum of uranyl acetate dihydrate. In fact, the spectrum of uranyl ions exchanged into sodium mordenite is very similar to that of the uranyl acetate dihydrate solid spectrum shown in Figure 1. Further support for our belief that some zeolites have a solution like environment and others have a solid like environment comes from the correlation between the crystallinity of these uranyl-exchanged zeolites and the appearance of some fine structure in the emission spectrum. We find no apparent correlation between this fine structure and the concentration of the uranyl ion in the zeolites even with a ten-fold change in the concentration of the uranyl ion. 

Since the work of Lee et al. [37], zeolite mordenite continues to play an extraordinary role as a shape selective catalyst for the isopropylation of biphenyl. A high degree of dealumination [37, 38] and high pressure of propylene [39] seem to be advantageous to achieve high selectivities for 4,4 -diisopropylbiphenyl. Also, selective poisoning of the external sites with tributylphosphite [40] and the use of cerium exchanged sodium mordenites [41] are reported to suppress an undesired consecutive isomerization of 4,4 -diisopropylbiphenyl once formed in the pores. 

In this paper we describe the surface chemistry of adsorption of thiophene on acidic (HZSM5, H-Mordenite (HMOR)) and non-acidic (NaY) zeolites, as well as on their partially nickel or cobalt exchanged forms. The thiophene HDS activity of Ni or Co exchanged zeolites was studied and connection was established between the adsorption and the catalytic properties. 

Selective catalytic reduction (SCR) of NO, by hydrocarbons is under investigation as an alternative NO, removal technology. NO reduction by NHj is presently the commercial state-of-the-art technology available for reducing NO, from stationary sources and from the exhausts of lean-bum gasoline and diesel engines. A number of catalysts for the selective reduction of NO by hydrocarbons have been examined in previous studies [1-18], Transition metal ion-exchang zeolite catalysts such as mordenite and ZSM-5 are the most effective SCR catalysts. 

Cation Exchange in Mordenite. Until 1974 there had been few systematic studies of ion exchange in mordenite and only Rees had determined isotherms. Peculiarities were found which had not been observed in A, X, and Y zeolites or in chabazite, in that only limited exchange of divalent ions could be achieved. Using a natural mordenite from Harbourville, Nova Scotia, Rees found for... 

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