Dehydration of 1,4-butanediol was investigated over ZrO2 at temperatures of 325-375 degrees C. Modification of ZrO2 with a small amount of sodium hydroxide greatly enhanced the selectivity to 3-buten-1-ol. Temperature-programmed desorption of adsorbed NH3 and CO2 elucidated acidity and basicity of the catalysts, respectively. The number of acidic sites on the ZrO2 decreased with increasing Na content, and disappeared at Na content of 1.0 mol%, whereas the number of basic sites increased with increasing Na content. In the relationship between Na content and the selectivity to products, selectivities to tetrahydrofuran and gamma-butyrolactone simply increased with the number of acidic and basic sites, respectively. However, the selectivity to 3-buten-1-ol was maximized at an appropriate Na content. 3-Butan-1-ol is possibly formed by acid-base-concerted catalysis of monoclinic ZrO2 in the dehydration of 1,4-butanediol. (c) 2005 Elsevier B.V. All rights reserved.