Efficient surface functionalization of zeolites via esterification

A new class of hybrid organic/inorganic materials was obtained via esterification of surface hydroxyl groups of various zeolites of Y and ZSM-5 types. For comparison, amorphous silica gel was used. The objective of this study was the development of a new method for the surface functionalization of zeolites, i.e., materials that have two distinct surface types (internal and external). The coexistence of functionalized external catalytic sites and unmodified internal acidic sites allows for the possibility of bifunctional catalysis, e.g., hydrogenation at the external sites and isomerization or alkylation at the internal sites. Furthermore, the relatively low concentration of the surface hydroxyl groups compared to other materials may be ideal for the heterogenization of organometallic complexes, since steric hindrance of the heterogenized complexes is not affecting the catalytic activity. Some complexes are sensitive towards hydroxyl groups at the surface and thus, using zeolites may increase their expected catalytic activity. In this work phenylbutanol was chosen as a test substrate, since it resembles in bulk various homogeneous organometallic complexes that are used as catalysts (e.g., Pd(II) complexes possessing catalytic activity in cross-coupling reactions). The presented method is intended to be a general approach for the functionalization of zeolites. The main result of our study is that ZSM-5 has the highest potential for surface functionalization.