Titanium-containing zeolites

Some of these shortcomings may be overcome by a new type of oxidation catalyst similar to zeolites titanium-containing silicates (TS-1) were synthesized by Taramasso, Perego, and Notari in 1983. These catalysts demonstrated very selective oxidation using hydrogen peroxide as the oxidant. According to Notari (79),... 

G. Hourdin, The catalysis of the Ruff oxidative degradation of aldonic acids by titanium-containing zeolites, Catal. Lett., 69 (2000) 241-244. 

Titanium-containing zeolite was an efficient catalyst for oxidation of benzene with hydrogen peroxide in a microwave field, affording phenol with high selectivity. It was reported that microwaves had a strong effect on the selectivity of the reaction. 

The advantages of shape selective catalysis are alreacfy ejq)loited in a number of industrial processes [11-14]. Astonishingly, virtually all these processes rely on a single structural type of catalyst, viz. zeolite ZSM-5 in various modifications, or its titanium containing analogue TS-1 [15]. It is, moreover, noteworthy that many of these processes convert and/or produce mononuclear aromatic compounds. It is not surprising, therefore, that a vast scientific literature exists on shape selective reactions of benzene derivatives in zeolite ZSM-5. 

The authors suggest that the new method could be of some value for titanium containing zeolites with structures different from silicalite, for instance large pore zeolites which could be useful in the oxidation of large molecules which cannot be oxidized with TS-1. 

Since the first synthesis of TS-1 in 1983 [1], considerable efforts have been devoted to the synthesis of titanium-containing zeolites [2, 3]. Recently, Ti-beta, a large-pore molecular sieve, has been extensively studied [4, 5]. Owing to its unique large-pore channel system, Ti-beta seems to be more active than the medium-pore TS-1 catalyst for the oxidation of cyclic and branched alkenes with aqueous hydrogen peroxide. Under the usual synthesis conditions, however, Ti-beta crystallizes with some Al as a framework constituent [4], This leads to the presence of acid centers, which may have a detrimental effect on the activity or selectivity of this type of catalyst. Since 1992, the discovery of a new family of mesoporous molecular sieves has received much attention [6,7], Because of their mesoporous nature (20-100A), the Ti-MCM-41 zeolites may be useful as oxidation catalysts for larger molecules [8], In this... 

The Direct Enantioselective Synthesis of Diols from Olefins using Hybrid Catalysts of Chiral Salen Cobalt Complexes Immobilized on MCM-41 and Titanium-containing Mesoporous Zeolite... 

The synthesis of titanium-containing beta zeolite has been carried out by direct hydrothermal synthesis and by secondary synthesis. In the direct synthesis with aluminum salts and titanium and silicon alkoxides, it is necessary to operate in the absence of alkalies, since these cause the formation of an amorphous precipitate containing Ti02 and Si02. Evidence for the substitution... 

The synthesis of these titanium-containing materials by treatment of the corresponding preformed zeolites with (NH4)2TiF6 at 348—368 K has been claimed (Skeels et al, 1989 Skeels, 1993). No evidence for Tilv incorporation has been provided. 

Acidity in crystalline titanium silicates has been observed only when a titanium-containing zeolite interacts with H2C>2, but this is due to the formation of peroxo compounds, as discussed below. 

Post-synthesis modifications have been successful in preparing titanium-containing molecular sieves active in oxidation. The method employed for the post-synthesis incorporation of Ti to the zeolite beta was also applied to the incorporation of Ti into MOR and FAU [60]. 

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