The partial gas‐phase hydrogenation of benzene to cyclohexene on supported and coated ruthenium catalysts

The conversion of benzene to useful products such as cyclohexene is of industrial interest because of the expected surplus of benzene due to its substitution in gasoline by other non‐polluting components in the next years. Therefore, the partial gas‐phase hydrogenation of benzene to cyclohexene at atmospheric pressure was performed in order to develop catalysts as an alternative to those used in liquid‐phase hydrogenation. Two types of ruthenium‐containing catalysts were investigated, viz. supported catalysts with different support materials and coated catalysts with electrolytically formed alumina as support. In order to yield the desired cyclohexene the presence of methanol as a reaction modifier was necessary in the gas phase during the reaction. The hydrogenation on supported Ru catalysts gave selectivities of about 35%, while on coated Ru catalysts selectivities up to 45% were obtained at conversion degrees of 5%. Improved catalyst performance, especially higher selectivity and yield, was obtained at increased partial pressure of methanol and hydrogen and by addition of copper as second metal in the oxide layer of the coated catalysts.