Abstract
Three types of catalysts, (A) chemically mixed catalyst activated in hydrogen after calcination, (B) chemically mixed catalyst activated in hydrogen without calcination, and (C) impregnated catalyst activated in hydrogen without calcination, were prepared. Their properties were investigated and compared, so as to elucidate the reasons why type (B) catalyst is the most effective for the formation of cyclohexene in the partial hydrogenation of benzene.
Measurements of TGA, FT-IR, XRD, EM, hydrogen and carbon monoxide adsorptions indicated differences among the three types of the ruthenium catalysts : (1) type (B) catalyst contains diols used in its preparation, (2) active components (Ru, Cu) in the type (B) catalyst are highly dispersed compared with the other two catalysts, (3) the hydrogen absorption capacity of type (B) catalyst is much lower than its carbon monoxide absorption capacity, and (4) the carbon monoxide absorption capacity of type (C) catalyst is essentially the same as its hydrogen absorption capacity.
From these findings, the diols remaining in type (B) catalyst following activation are considered to help prevent active components from aggregating by linking them to a support (Si) as a bridging ligand and to depress the formation of cyclohexane by reducing the hydrogen absorption capacity of ruthenium through coordination of the hydroxy groups. Type (B) catalyst is thus concluded to give high activity and cyclohexene yield in the partial hydrogenation of benzene.
