One-pot synthesis of olefins from aromatic ketones via tandem consecutive hydrogenation–dehydration reactions

In this work, the synthesis of aromatic olefins from the corresponding ketones via tandem consecutive hydrogenation–dehydration reactions was studied. The conversion of acetophenone (AP) to styrene (STY) was used as model reaction. Initially, the liquid-phase hydrogenation of AP to 1-phenylethanol (PHE), using cyclohexane as solvent, was investigated at 363 K and 10 bar over Ni, Co, Cu, Pd and Pt supported on SiO2. Cu/SiO2 was the most selective catalyst yielding 100% PHE. Then, the consecutive dehydration of PHE to STY was studied at 363 K and 2 bar over mesoporous solid acids (Al2O3, SiO2–Al2O3, Al-MCM-41, HPA/SiO2) and acid zeolites (HY, HBEA, HZSM-5). Zeolite HZSM-5 was the most selective catalyst, yielding 96% STY. On the basis of the former results, a mixture of Cu/SiO2 and HZSM-5 was used to investigate the feasibility of performing the one-pot synthesis of STY from AP, by promoting tandem consecutive AP hydrogenation–PHE dehydration reactions. A maximum STY selectivity of about 72% was achieved in a two-step catalytic run: the first step was carried out at 323 K and 20 bar and the second step at 353 K and 1 bar.