The liquid product of the gas-phase amination of 2,6-diisopropylphenol (2,6-DIPP) to prepare 2,6-diisopropylaniline (2,6-DIPA) was analyzed using gas chromatography-mass spectrometry. Besides 2,6-DIPP and 2,6-DIPA, there are by-products such as water, 1,3-diisopropylbenzene, 2,6-diisopropylcyclohexamine in the liquid product, in which 2,6-diisopropylcyclohexamine is a major constitute by-product. The ratio of 2,6-diisopropylcyclohexamine to 2,6-DIPA is low when the reaction proceeds more completely at lower reaction space velocity, but this ratio increases when the reaction proceeds incompletely at higher space velocity. So that 2,6-diisopropylcyclohexamine is suggested to be the intermediate product of gas-phase amination of 2,6-DIPP. The reaction mechanism of gas-phase amination of 2,6-DIPP on the bifunctional palladium-lanthanum supported catalyst was proposed. This reaction was synergistically catalyzed by the Pd metal active sites that facilitated hydrogenation and dehydrogenation reactions and the acid sites on the catalyst support that accelerated isomerization and amination reactions. (C) 2003 Elsevier B.V. All rights reserved.