Metal framework-containing zeotype

Figure 1.1 The principal synthesis routes used to prepare metal framework-containing zeotype materials. The four major components are a silicon source, a metal source, a template, and a mineralizing agent. These give the overall reagent mixture that then undergoes crystallization under hydrothermal conditions to produce the desired zeotype material.

Further metal framework-containing zeotype or ordered mesoporous materials... 

Table 1.10 List of processes for propylene oxide manufacture with metal framework-containing zeotype or other porous materials as catalysts...

Framework metal-containing zeotype materials Classification... 

This review is focused on the science and technology of framework metal-containing zeotype materials, a critical and increasingly important class of catalyst. In the following paragraphs, first the structural characteristics of zeo-Htes, which are close and well investigated relatives of zeotype materials, will be briefly summarized. Then the role of the framework metal for the structural and surface chemistry of zeolite and zeotype materials will be introduced. 

The framework metal-containing zeotype materials that are the focus of this review do not contain aluminum and thus do not classify as zeolites. Zeotype materials are characterized by properties that make them alike to... 

Significance of framework metal-containing zeotype materials... 

This chapter focuses on the application of framework metal-containing zeotype materials as catalysts and is a report of the state of the associated science, presenting a summary of current and future challenges. The chapter is organized as follows First, the general synthesis procedures of framework... 

The success of syntheses designed to incorporate gallium into zeotype frameworks depends on the synthesis conditions, as is true for other framework metal-containing zeotype materials. Several researchers have claimed gaUium incorporation into the frameworks of zeotype structures (5b, 166). 

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. 

A review of the extensive Hterature indicates a diverse array of reactions catalyzed by framework metal-containing zeotype materials. The key reactions are illustrated in Figure 1.4. 

The principal reactions for each of the framework metal-containing zeotype materials are the following ... 

In the commercially relevant reports of benzene oxidation catalyzed by framework metal-containing zeotype materials hydrogen peroxide or nitrous oxide (N2O) are used as oxidants. Thus phenol is produced without major by-product formation. 

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... 

TS-1 (230) and TS-2 (231) have been tested as catalysts for the vapor phase Beckman rearrangement of cyclohexanone oxime to 8-caprolactam. However, as these framework metal-containing zeotypes are outperformed by metal-free high silica MFI (232), this catalytic chemistry is not reviewed further. 

In this section, the commercial applications involving framework metal-containing zeotype catalysts are summarized. Notwithstanding the intriguing properties, only a limited number of framework metal-containing zeotype materials, among them TS-1, Ga-MFI, and some mesoporous catalysts, are currendy used for commercial applications. Framework metal-containing catalysts are no different than other catalysts in that the activity, stability, lifetime, manufacturability, and catalyst cost must meet certain requirements for a new catalytic process to be implemented. 

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