Catalyst Site Requirements for Olefin Etherification over H-Beta Zeolites

We report site requirements for H-Beta zeolites for the etherification of hydrophobic long-chain olefins with hydrophilic alcohols in a triphasic system using 1-dodecene and ethylene glycol as model reactants. Olefin etherification rates normalized by total Al monotonically increased as the Si/Al molar ratio increased up to 75 (Al content decreased), suggesting that a large portion of Al does not contribute to etherification activity for H-Beta zeolites with a low Si/Al ratio. The olefin consumption rate per Al correlated well with the surface hydrophobicity of the H-Beta zeolites. Thus, we hypothesized that the impact of Si/Al on long-chain olefin etherification activity for H-Beta zeolites under these reaction conditions was caused by the increasing hydrophobicity of the zeolites with decreasing Al content (increasing the Si/Al ratio). We found that when titrating an H-Beta zeolite with basic molecules that could enter the zeolite’s micropores (0.77 × 0.66 and 0.56 × 0.56 nm), no etherification activity was observed, indicating that long-chain olefin etherification occurs inside the microporous channels. From titrating with 2,6-ditert-butyl-pyridine, we inferred that Lewis acidic Al sites within the micropores of H-Beta have little contribution to long-chain olefin etherification because 2,6-ditert-butyl-pyridine can enter the micropores of H-Beta and bind only to Brønsted acid sites. In summary, we demonstrate that Brønsted acid sites inside the micropores of H-Beta within a hydrophobic environment are required for the etherification of long-chain hydrophobic olefins with hydrophilic alcohols.