Vapor-phase dehydration of 3-methyl-1,3-butanediol to 3-methyl-3-buten-l-ol was investigated over carbon-modified alumina, C/Al2O3, which was prepared by depositing carbonaceous species, i.e. coke, on Al2O3 with contacting Al2O3 surface with 3-methyl-1,3-butanediol vapor at 250 C. Temperature-programmed desorption of adsorbed NH3 revealed that the strength of acid sites of fresh Al2O3 was weakened by the coke deposition. It was found that the selectivity to 3-methyl-3-buten-1-01 was increased by the coke deposition over Al2O3 catalysts in the dehydration of 3-methyl-1,3-butanediol at 200 C. Generation of the main by-products such as isobutylene and 4,4-dimethy1-1,3-dioxane were prohibited by the acid sites weakened by the coke deposition. The 13C NMR and IR measurement elucidated that the deposited coke had C=C, C=O, COO, CH2, CH3, and OH groups, which indicates that the coke consisted of polymeric unsaturated alcohol. The coke content that is effective in inhibiting the decomposition of 3-methyl-1,3-butanediol into isobutylene was ca. 15 wt.% of C/Al2O3. (C) 2014 Elsevier B.V. All rights reserved.