The selectivity in ring opening of cyclohexane and methylcyclopentane over a nickel-alumina catalyst

Abstract

Ring opening of cyclohexane and methylcyclopentane (MCP) catalyzed by a nickel-alumina catalyst was investigated at a hydrogen pressure of 10 atm, in the temperature range from 230 to 320 °C. MCP can react at a temperature some 50 °C lower than cyclohexane. At lower temperatures, the major products of either reaction are hexane isomers which consist of n-hexane (HEX), 2-methylpentane (2MP), and 3-methylpentane (3MP). The composition of hexane isomers obtained from cyclohexane depends on the reaction temperature, and the relative molar proportions can be expressed as HEX:2MP:3MP = 2–6:1:1. The composition of hexane isomers obtained from MCP is almost unchanged over the temperature range and expressed as HEX:2MP:3MP = 1:5:5. It is found that ring opening of cyclohexane proceeds along two different paths: (a) isomerization to MCP with subsequent conversion to hexane isomers, (b) direct opening of the cyclohexane ring to form n-hexane. The difference in reactivities between cyclohexane and MCP is discussed in terms of the specific modes of their adsorption on the catalyst.