In situ DRIFTS for the mechanistic studies of 1,4-butanediol dehydration over Yb/Zr catalysts

To study the effect of acid-base properties of catalysts on 1,4-butanediol (BDO) dehydration to 3-buten-1-ol (BTO), Yb/Zr catalysts with different Yb content were synthesized by a wet impregnation method. The texture property, crystalline form and surface properties of the catalysts were characterized by N 2 physisorption, XRD, NH 3 -TPD, CO 2 -TPD and in situ DRIFTS. The catalytic performance of BDO dehydration was also tested in a fixed-bed reactor. The experimental results showed that the activity of BDO dehydration and the selectivity of by-product tetrahydrofuran (THF) decreased with the increased Yb content, while the selectivity of the main product BTO gradually increased. The yield of BTO maximized at 64.5% when the Yb content reached 15%, which showed the best catalytic performance. Comprehensive analysis of experimental results showed that the activity of BDO dehydration and the selectivity to the by-product THF were manipulated by the acid sites of the catalysts, while BTO selectivity was tuned by both acid and basic sites of the catalysts. A higher density ratio of basic/acid sites favored the BTO formation and inhibited the formation of by-products THF. The in situ DRIFTS study of BDO dehydration over m -ZrO 2 and Yb 2 O 3 elucidated that the hydroxyl groups of BDO molecules first interacted with acid sites to form several types of butoxides. Further abstraction of β-H by basic oxygen anion could convert these butoxides into aldehyde species, which finally reacted to form BTO. The DRIFTS results were consistent with the experimental conclusions that the acid sites of the catalysts could interact with hydroxyl groups and basic sites facilitate the β-H abstraction of BDO and thereby enhancing the formation of BTO.