Controllable transformation of biomass-derived diols over ammonia-modified H-Beta zeolite

For the controllable transformation of C_3–6 diols in ethylene glycol (EG), H-Beta zeolite catalyst was modified with NH₃ via incomplete desorption. 60.8% of acid sites on the zeolite were deactivated, but the ratio of strong acid sites was obviously increased. With 1,2-pentanediol (PDO) as a representative large-carbon-number diol, the undesirable acetalization and oligomerization reactions of EG were suppressed in the EG-PDO reaction system over the modified catalyst due to their dependency on total acid sites. NH3-TPD and FTIR results proved that Lewis acid sites on the modified zeolite were eliminated after modification, resulting in the suppression of acetalization and oligomerization reactions. In contrast, a portion of strong Brønsted acid sites still remained, ensuring the catalytic transformation of PDO. Only 8.2% of EG was consumed after 8-h reaction, and the conversion of PDO could reach 84.3%. The loading of NH₃ on the surface of zeolite pores led to diffusion resistance, slightly decreasing the reaction rate of PDO without affecting the reaction selectivity. The catalytic reactions of other C3–6 diols in EG followed similar principles, and the selectivity to aldehydes or ketone was improved over this modified catalyst. Non-diol biomass hydrogenation products such as glycerol had negative influence on the selectivity, so these components should be isolated before the reactions. This catalyst could be reused at least 5 times, and the conversion of PDO slightly decreased. This work sheds light on the relationships between acid properties of catalyst and different reactions of diols.