Mesoporous materials, Beckmann

Zeolites and other mesoporous materials are excellent catalysts for industrial and laboratory applications. Favourable characteristics are their capacity to immobihze homogenous catalysts rendering them heterogeneous, their thermal stability, and the ease of separation from the reaction products and reuse in hquid- and gas-phase conditions. The pore size and Brpnsted and Lewis acidic properties are determinant for their use as catalyst in the Beckmann rearrangement. Recently, a review on the use of zeolites and mesoporous materials in the Beckmann rearrangement was published. ... 

The Beckmann rearrangement of cyclohexanone oxime in the gas phase has been investigated over siliceous MCM-41- and MCM-48-type materials. At 275°C complete conversion occurs for several hours with selectivities for s-caprolactam up to 65 %, until the catalysts deactivate rapidly. The deactivation of the mesoporous catalysts is considerably reduced as compared to that obtained over an amorphous silica gel. MCM-48 exhibits the highest catalyst lifetime which, for MCM-41-type materials, is longer with larger pore diameter. With an aluminum-containing H-MCM-41 catalyst an increased e-caprolactam selectivity is achieved. 

Beckmann rearrangement of cyclohexanone oxime over mesoporous MCM-41 and MCM-48 type materials... 

Crosslinked TS-1 zeohte materials are among the best catalysts for the gas-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam [156]. Crosshnking of the zeolite particles resulted in the additional mesoporosity and as a result, in an increased activity in the title reaction. Note that the deactivation of the catalysts is significantly decreased. The increased activity correlates with the newly created mesopore surface area. 

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