Vapor-phase catalytic dehydration of 1,4-butanediol (1,4-BDO) was investigated over modified ZrO2 catalysts. In the dehydration of 1,4-BDO over monoclinic ZrO2 (m-ZrO2), an unsaturated alcohol, 3-buten-1-ol (3B1OL), was produced together with tetrahydrofuranand-gamma-butyrolactone. Among alkaline earth metal oxide modifiers, CaO with an appropriate content significantly enhanced the 3B1OL selectivity of m-ZrO2. The modification of CaO was more efficient over m-ZrO2 than tetragonal ZrO2. CO2-TPD measurements reveal that CaO supported on m-ZrO2 calcined at 800 degrees C or higher generated new basic sites, which are attributed from Ca-O-Zr hetero-linkages, for the effective formation of 3B1OL from 1,4-BDO. In order to create more Ca-O-Zr hetero-linkages on the m-ZrO2 surface efficiently, additional ZrO2 was loaded on m-ZrO2 together with CaO via a co-impregnation method. At an appropriate weight ratio of CaO/ZrO2 = 7/2 loaded on m-ZrO2, both the 1,4-BDO conversion and the 3B1OL selectivity were enhanced greatly. Especially, the 3B1OL selectivity exceeded 90% at 350 degrees C. (C) 2017 Elsevier B.V. All rights reserved.