Gallium-containing zeolites

The gallium containing zeolites analclme and nepheline hydrate II have also been described (18). Only the silicon NMR of gallium thomsonite (-82.9 ppm (7) c.f. thomsonite, -83.5 ppm (3)) has, to our knowledge, been previously described. 

High resolution SI NMR spectra of galloslllcates with the faujaslte structure exhibit relative peak Intensities similar to faujaslte Indicating similar distributions of T atoms. However, the peaks In the gallium containing zeolites are deshielded by an amount nearly proportional to the number of gallium atoms In the first neighbor shell. 

Raichle, A. Moser, S. Traa, Y. Hunger, M. and Weitkamp, J., Gallium-containing zeolites as valuable catalysts for the conversion of cycloalkanes into a premium synthetic steam-cracker feedstock, Catalysis Communications 2(1), 23-29 (2001). 

Aromatization activity of gallium containing MEl and TON zeolite catalysts in n-butane conversion effects of gallium and reaction conditions. Appl. Catal. A, 316, 61-67. 

The isomorphous substitution of silicon within the zeolitic framework is an important problem and a challenge for elements different from aluminium. Although the introduction of boron, gallium, or iron is relatively easy and well documented [1], few studies are devoted to the introduction of Co(II) into the framework of zeolites [2]. As both the framework and the extraframework Co-species seem to be active in catalysis [3], it is of paramount importance to synthesize and well characterize Co-containing zeolites [4],... 

Li, J., et al., 2015. Maximizing carbon efficiency of petrochemical production from catalytic co-pyrolysis of biomass and plastics using gallium-containing MFI zeolites. Applied Catalysis B Environmental 172—173 (0), 154—164. 

Other framework structures based on zeolites have also been synthesized which contain atoms other than aluminium and silicon, such as boron, gallium, germanium, and phosphorus, which are tetrahedrally coordinated by oxygen. Such compounds are known as zeotypes. Pure aluminium phosphate, commonly called ALPO, and its derivatives, can take the same structural forms as some of the zeolites such as sodalite (SOD), faujasite (FAU), and chabazite (CHA) (e.g., ALPO-20 is isostructural... 

A completely new approach for BTX production has emerged in recent years. It converts C2 to C6 paraffins into aromatics using a modified ZSM-5 zeolite catalyst which contains gallium (19). An example of this approach, the Cydar process, has been in commercial operation by British Petroleum at Grangemouth, Scodand since August 1990 (20). It uses C3 C4 feed and employs UOP s CCR technology to compensate for rapid catalyst coking. 

Difluorobenzenes are isomerized under gas-phase conditions in the presence of metallosilicates, containing the structure of pentasil zeolites with isomorphic substitution of some silicon atoms by aluminum, gallium, or iron.4 A German patent describes the isomerization of l-bromo-2,4-difluorobenzene to l-bromo-3,5-difluorobenzene in pentasil-type zeolites in an autoclave at 320 C and 25 x 105 Pa for 1 h, giving 29% conversion and 73% selectivity.5... 

The products of the reactions of silanetriols with gallium [41] and indium alkyls [42] are very similar to those obtained from aluminum alkyls described above. The interest in Ga containing siloxanes stems from the known catalytic activity of Ga-doped zeolites in the dehydrogenation reactions of alkanes. The reactions of silanetriols 15 and 16 with GaMej or InMes in refluxing hexane/1,4-dioxane lead to the cubic Ga/In siloxanes [RSi03M-THF]4 (M = Ga 38, 39 In 40, 41), respectively. In the resulting products, the Ga and In centers are coordinated to a dioxane solvent molecule These compounds have a very similar structure to that of aluminosiloxanes 30-33 shown in Scheme 7. 

There is considerable interest in isomorphous substitution of aluminium in the zeolite framework by other elements and some papers have described the synthesis of MFI zeolites containing boron, gallium, titanium and iron as lattice elements (ref.1-3). The replacement of Al ions with the ions of another element can modify both the acidity and pore size features of the zeolite (ref.4, 5), resulting in modification of the catalytic property of zeolite catalysts (ref.6-8). 

Recently, there has been considerable interest in the isomorphous substitution of tetrahedral aluminium in zeolite frameworks with catalytically active elements such as iron, gallium and boron. These materials have acidities Afferent from the corresponding aluminosilicates leading to altered activity, selectivity and stability. Mdssbauer spectroscopy has been used to study the iron incorporated into zeolites during synthesis. Fe(III) can be present on tetrahedral framework sites as Fe " cations acting as counterions and as Fe(III) oxides precipitated in or on the zeolite crystals. The most common iron oxide is a-Fe203 which contains iron only in octahedral coordination. 

Microporous silicates synthesised with isomorphous substitution of elements such as boron and gallium for silicon show similar demetallation behaviour, where the heteroatoms leave the structure more readily than aluminium atoms. In particular, the behaviour upon calcination of boron-containing solids has been examined by and Si MAS NMR. Boron is observed to move from tetrahedral to trigonal coordination upon the formation of the protonic boro-silicate form, and studies on the protonated form of zeolite B-Beta have shown that the boron may be removed from the framework stepwise by hydrolysis of Si-O-B bonds, ultimately giving boric acid. This is lost from the structure if put into contact with aqueous solution. 

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