Zeolite substrate

Figure 5.32 Formation of the neutral metal complex 59 covalently bonded to the zeolite substrate through the ligand via basic surface sites [191].

The current synthesis of ethyl alcohol eliminates sulfuric acid and uses phosphoric acid suspended on zeolite substrates. Zeohtes are porous aluminosilicate crystalline minerals. The use of phosphoric acid as a catalyst allows the direct hydrolysis of ethylene into ethyl alcohol C2H4 + H20 —> C2H5OH. Industrial alcohol is rendered inconsumable by adding a small amount of a poisonous substance such as methanol or acetone to it. Alcohol unfit for consumption because of a poisonous additive is termed denatured alcohol. 

In general, adsorption isotherms obtained with this and other zeolitic substrates are of Brunauer s Type I, the simple hyperbolic form also known as the Langmuir isotherm. Consequently, the asymptotic limit of adsorption is used instead of the value of Vm normally derived from the BET evaluation of specific surface area. It is, of course, not possible to define exact monolayer or multilayer adsorption in these three-dimensional interconnected pore systems. 

Another aspect to zeohte catalytic activity, briefly mentioned earlier, is the use of ion-exchange modification to introduce elements of known catalytic propensity into the zeolite promoter. Examples of this are in Table 31. There has been a considerable amount of work devoted to the investigation of the dispersion of metal particles (e.g. Ni and Fe) on zeolite substrates to enhance specific organic reactions. 

In order to confirm that the novel stability of Nff is peculiar to the zeolite substrate, a 7-alumina loaded with 5 wt. % of NiCl2 was treated with sodium vapour at 575°C for 1 h in vacuum. The brown product gave a Ni° e.s.r. signal but no Nff signal. 

Catalyst Characterization. Chemical analyses, x-ray diifraction analyses, and gas adsorption procedures were used to characterize the composition, crystallographic character, and surface structure of the nickel and cobalt zeolite catalyst preparations. The chemical and x-ray procedures were standard methods with the latter described elsewhere 11). Carbon monoxide chemisorption measurements provide useful estimates of the surface covered by nickel atoms from the zeolite substrate 10). 

Chemisorption measurements of either CO or hydrogen on transition metals mounted on zeolite substrates require considerable care for adequate interpretation. The zeolite lattices after high-temperature evacuation can adsorb large amounts of hydrogen, and divalent cations such as calcium can adsorb large amounts of CO. 

Zeolite Substrate Diagnostic IR vibrations Probable nature of interaction Ref. 

Amide hydrolysis is a key step in the widespread strategy of protection/deprotection of amino groups for synthetic purposes, usually carried out in homogeneous phase with mineral acids. It is shown here that under mild conditions (batch reactor, liquid phase, 75°C) large pore zeolites (HY, HBeta, HMOR) can catalyse the hydrolysis of various aromatic amides. The best results are obtained over HY zeolite samples with Si/Al ratios of 16 and 30 e.g. complete and selective hydrolysis of 2-nitroacetanilide after 2-4 hours reaction for a zeolite/substrate ratio of 0.5 g/mmol. For similar values of the Si/Al ratio HBeta and rather all HMOR samples are much less active than HY samples, which is probably related to diffusion limitations. 

The decomposition of methanol or ethanol on an iron-cobalt catalyst deposited on a zeolite substrate represents a transition to the CVD methods (Section 3.3.1.5). Here as well, SWNTs of high purity are obtained. The yields can be up to 800% with reference to the catalyst employed (or 40% relative to the starting material). 

Furthermore, we employed a CO molecule adsorbed at the on-top site of the cluster Ir4 to probe changes in its electronic structure induced by the support. When the zeolite substrate is described by the most realistic Z-Na model, the... 

The adsorption of NO on in-situ synthesized CuZSM-5/cordierite monolithic catalysts of different Si/Al ratios was studied by diffuse reflectance FTIR spectroscopy at different NO partial pressures from 500 ppm to 2000 ppm and temperatures from 298 K to 773 K. At room temperature, Cu mostly exists in oxidized Cu form. A lot of N2O species were observed on the surface even at room temperature. A band at 2133 cm is attributed to NO -Oiattice and only related to the number of lattice A1 in the zeolite. There may exist a copper-zeolite-substrate interaction on such as synthesized monolithic catalysts. 

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