Zeolite Beta: characterization and passivation of the external surface acidity

The external surface acidity of zeolite Beta can be selectively passivated by means of an amorphous silica layer. This coating is permeable, thus leaving the inner pore system accessible to reactants. For the coating to be effective, a Beta preparation giving relatively large, well-formed crystallites needs to be used, the microcrystalline mass afforded by the Wadlinger procedure giving poor results. The catalytic properties of the silica-coated Beta macrocrystals were investigated for two different reactions. The coated zeolite Beta material can be regenerated several times without destroying the inert shell. (C) 1997 Elsevier Science B.V.