The catalytic conversion of the C4 fraction from a fluid catalytic cracking (FCC) unit over a commercial FCC equilibrium catalyst was investigated using a confined fluidized bed reactor system. Butenes were easier to convert than butanes, and 1-butene was the easiest to convert among the butene isomers. The ethene and propene yields increased with increased reaction temperature and decreased with increased weight hourly space velocity (WHSV). The formation of propene involved two successive steps: butene dimerization and large hydrocarbon cracking. Aromatics were formed by the aromatization of the intermediate large olefins. A mechanism parameter RcA was proposed to describe the relative function of the cracking reaction to the aromatization reaction. Rok increased with increased reaction temperature and decreased with increased WHSV. The cracking reaction predominates on the aromatization reaction at high reaction temperatures. (C) 2013 Elsevier B.V. All rights reserved.