Vanadium-containing zeotype materials

Table 1.2 Synthesis of vanadium-containing zeotype and ordered mesoporous materials... 

In this section, the catalytic chemistry of selected framework metal-containing zeotype materials is reviewed, with an emphasis on commercial applications. The catalytic activities of framework metal-containing zeotype materials, especially those containing titanium, vanadium, or tin, have been investigated extensively. The enormous interest in these materials is attributed to their remarkable catalytic activities and especially their selectivities in oxidation reactions. Because hydrogen peroxide is generally used as the oxidant, water is formed as a by-product. Hence, oxidation reactions carried out with these catalysts can be considered environmentally clean processes. Several review articles have been published that summarize the catalytic reactions (2a,3b-d,89). In this section, the focus is on selected industrially relevant reactions. 

The activation of phenol is much easier than that of benzene because of the high aromaticity of benzene and the corresponding charge delocalization. TS-1 has been used primarily as the catalyst for phenol hydroxylation, and the conditions have been thoroughly optimized (215). TS-2 (216) and Ti-MCM-41 (217) were also evaluated, but they do not perform as well as TS-1. Ramaswamy et al. (52) compared various framework metal-containing zeotype materials with MEL structure for phenol hydroxylation the incorporated metals were aluminum, tin, titanium, and vanadium. The... 

The syntheses of VS-1 (49), VS-2 (51), V-BEA (61), V-MTW (54), V-MCM-22 (143), V-MCM-41 (57,144), and V-UTD-1 (145) have been reported, and these materials have been characterized. The chemical nature and the reactivity of these fiamework vanadium-containing silicates depend on the valence and coordination environment of the vanadium species in the framework structure. Theory-based calculations (142,146) have indicated that vanadium(V) is stabilized in zeotype frameworks in two different tetrahedral coordinations one is characterized by a highly stable vanadyl (V=0)... 

Zeotype materials containing metal cations, for example ions of titanium, vanadium, chromium, iron, or tin, in the tetrahedral positions of their frameworks have been explored as solid Lewis acid catalysts (Ig). Such materials have been shown to be active in the Meerwein—Pormdorfr-Verley reduction of carbonyl compounds (151,233), and the BV oxidation (also called BV rearrangement) (234). 

---