Transformation of cyclohexanone on PtHZSM5 catalysts — reaction scheme

The transformation of cyclohexanone was carried out on PtHZSM5 catalysts under the following conditions: flow reactor, 473 K, pressures of cyclohexanone and hydrogen equal to 0.25 and 0.75 bar respectively. Six families of products were identified by GC or GC-MS analysis: C₆ cyclic hydrocarbons 1, C₁₂ bicyclic hydrocarbons 2 (e.g., cyclohexylcyclohexene), cyclohexenylcyclohexanone 3, cyclohexylcyclohexanone 4, phenylcyclohexanone 5, tricyclic ketones 6 (e.g., biscyclohexenylcyclohexanone). A reaction scheme is proposed to explain the formation of these products. Compounds 1 would result from the following steps: hydrogenation of cyclohexanone (probably in the enol form) on Pt sites, dehydration of cyclohexanol on the acid sites, hydrogenation or dehydrogenation of cyclohexene on Pt sites. Compounds 2 are mainly formed through successive transformations of 4: hydrogenation, dehydration…; 3 results from aldolisation of cyclohexanone followed by dehydration of the resulting alcohol, 4 from hydrogenation of 3, 5 from dehydrogenation of 3. The compounds 6 result from aldolisation of 3 with cyclohexanone followed by dehydration, hydrogenation and dehydrogenation steps. The dehydration of alcohols is much more rapid than aldolisation and hydrogenation—dehydrogenation steps. On a 0.2 PtHZSM5 catalyst with a platinum dispersion greater than 70%, aldolisation is slower than hydrogenation—dehydrogenation steps. The deactivation of the catalyst affects more the acid sites than the metallic ones.