Shallow-bed CAVERN device

One of the drawbacks of this CAVERN device is the occurrence of a nonuniform distribution of reactant on catalysts because adsorption occurs on a deep bed of catalyst packed in a MAS rotor. To overcome this problem, we developed several shallow-bed CAVERN devices (95), and Fig. 10 shows a version of one such design. A thin layer of catalyst is supported on a glass trapdoor, and the device is evacuated. A furnace is clamped in place so that the catalyst can be activated if necessary. The catalyst is cooled with a cryogen bath, and a controlled amount of adsorbate is introduced from the vacuum line. The trapdoor is raised, the loaded catalyst falls into the MAS rotor, and the seal is driven into place. Finally the cold, sealed rotor is manually transferred into the cold MAS probe. The added advantages of the shallow-bed CAVERN is that all manipulations can be carried out without using a glovebox in any step. 

An ultra-shallow-bed CAVERN device (Fig. 11) was developed to accommodate occasions where an extremely homogeneous distribution of adsorbates is required. Here the same amount of catalyst is loaded onto a much larger surface. After catalyst activation, reactants are introduced onto an ultrathin layer of catalyst bed (<0.5 mm) to achieve a homogeneous distribution of adsorbates on catalyst. 

A shallow-bed CAVERN design was developed by the same group allowing the catalysts to be activated under shallow-bed conditions at temperatures up to at least 500 C prior to adsorption, eliminating the need to handle activated catalysts in a glove box in order to transfer it into the MAS rotor (86). The new device was illustrated by MAS NMR... 

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