Ion-exchange modification of zeolite for the controllable catalytic transformation of diols and selective conversion of 1,2-butanediol to butanal

Abstract

For the controllable transformation of 1,2-propanediol (PDO) and 1,2-butanediol (BDO) in ethylene glycol (EG), the acidity of H-Beta zeolite was modified via ion exchange with NaH2PO4 and Na2HPO4. After the modification, the separation factors for PDO and BDO reached 7.7 and 11.6 (vs 3 on the parent H-Beta). The selectivity to butanal-derived acetal declined to 4% (vs 42% on the parent H-Beta). Therefore, EG consumption was greatly reduced. Lower temperatures were favorable to the formation of acetone, butanone, and 1,3-butadiene, while higher temperatures promoted the acetalization and oligomerization reactions. The ion-exchange treatment increased the stability of zeolite crystalline structure. Microcalorimetry and NH3-TPD results indicated that the strong and moderate acid sites with NH3 adsorption heat ≥140–160 kJ/mol and of 100–110 kJ/mol were responsible for the dehydration and butanal-related acetalization reactions, respectively. In contrast, the propanal-related acetalization reactions were less sensitive to the strength and type of acid sites. On the other hand, butanal can be selectively synthesized from BDO with this catalyst. The acidity of zeolite catalysts can be modulated with this simple approach for the improvement of selectivity to desirable products.