A tailor-made silicalite-1 membrane encapsulated catalyst with a size in millimeters has been directly synthesized over the activated-carbon supported Rh catalyst pellet to form a core-shell structure (S1/Rh/A.C.) by a hydrothermal synthesis method. For the reaction of hydroformylation of 1-hexene, the encapsulated catalysts present perfect catalytic performance for both the conversion and the normal to iso ratio of the aldehyde products. Increasing in the thickness of the silicalite-1 membrane can improve the selectivity of the normal products, but the reaction conversion decreases significantly. However, the modification of the encapsulated catalyst by tetraethyl orthosilicate (TEOS) can reduce the zeolite crystalline gaps to improve the normal aldehyde selectivity and to keep the similar 1-hexene conversion compared with that of the S1/Rh/A.C. catalyst. This encapsulated catalyst is efficient to produce and separate the aimed product from the multiple products in one-step with the spatial confined structure of the catalytic-inert silicalite-1 membrane. (C) 2009 Elsevier B.V. All rights reserved