Abstract:

Modified ZrO₂ catalysts were prepared by doping with alkaline earth metal oxides (CaO, SrO, or BaO) in a wet impregnation method. The catalysts were characterized by N₂ physisorption, X-ray diffraction, and temperature-programmed desorption (TPD) with NH₃ and CO₂. Their catalytic performance in the vapor-phase selective dehydration of 1,4-butanediol (BDO) to 3-buten-1-ol (BTO) was investigated. The results showed that the alkaline earth metal can change the acid-base properties on the catalyst surface and thus affect BDO conversion and BTO product selectivity. For ZrO₂ catalyst modified by CaO, Ca²⁺ entered the ZrO₂ crystal lattice and formed Ca?O?Zr hetero-linkages. These allowed the CaO/ZrO₂ catalyst to maintain a high acid density and generate a large number of basic sites when compared with unmodified ZrO₂. In contrast, SrO and BaO reacted with ZrO₂ to generate the corresponding zirconates, which resulted in decreased acid density on the catalyst surface. Of the catalysts tested, CaO/ZrO₂ showed the best catalytic performance. The highest yield of BTO was 60.5% and was achieved at 350℃ over CaO/ZrO₂ catalyst. The key point for highly selective dehydration of BDO to BTO resided in the synergistic effect between acid and base sites on the catalyst surface.

Key words: 1,4-Butanediol, 3-Buten-1-ol, Alkaline earth metal oxide, Zirconia, Acid-base concerted site