Liquid-phase benzene isopropylation using alumina solid Lewis superacid-supported platinum catalyst

Supporting platinum on alumina solid Lewis superacid (AmLSA; J. C. S,, Chem . Commun., 635 (1989)) was prepared by using of the in situ CVD technique a t 773 K with Ar--sputtered platinum fine particles and dry chlorine, follow ed by reduction with hydrogen at 673 K. The AmLSA-supported platinum cataly st (Pt/AmLSA) was applied to isopropylation of benzene with propene in the hydrogen stream at ambient temperature, using a semibatch reactor. Products were mono-, di-, tri-, and tetra-isopropylbenzenes. Conversion of propene to propane was below 1%, and a trace amount of cyclohexane from benzene was also observed. Deactivation of AmLSA due to strong adsorption of poly-subs tituted benzenes and/or propene oligomers was remarkably depressed by suppo rting platinum and supplying hydrogen into the propene stream. Consequently , the activity of Pt/AmLSA catalyst had increased almost 1.5 times that of AmLSA. At the same level of benzene conversion, the product distribution of isopropyl-substituted benzenes obtained on Pt/AmLSA was identical to that on AmLSA, and had shifted slightly into the mono-substituted benzene side c ompared with the result on AmLSA in the absence of hydrogen. In the isoprop ylation of benzene with 2-chloropropane, the results quite similar to those described above were obtained. From the above observations, synergetic eff ects of platinum supporting and hydrogen supplying were considered to be du e to the presence of hydrogen atoms spilled over from the platinum surface to the strong Lewis acid sites.