Ring-shift isomerization of sym-octahydrophenanthrene into sym-octahydroanthracene. Effects of zeolite catalysts and equilibrium compositions

The effects of zeolite catalysts and reaction conditions on the ring-shift isomerization of sym-OHP into sym-OHA were studied through experiments at 200-300°C under an initial pressure of 0.79 MPa N₂ or H₂. Eight catalysts were examined, including three hydrogen mordenites, two noble metal loaded mordenites, and three Y-zeolites. Among the three mordenites, the catalyst with lower acidity (HML8) displayed the best selectivity to sym-OHA but the lowest activity. Among the three Y-zeolites, best selectivity to sym-OHA was achieved with NiHY, which has lower acidity and lower content of stronger acid sites. The activity for sym-OHP conversion is: Pd/HM30A > Pt/HM30A > HY ≈ LaHY > HM20A > HM30A > HML8 > NiHY. The selectivity to sym-OHA decreases almost linearly with increasing conversion beyond the pseudo-equilibrium stage (about 50% conversion). The desirable condition over HML8 is 250°C for 0.5 h. The other catalysts with higher acidity (HM20A, HM30A, and HY) are promising catalysts at 200°C. Molecular mechanics calculations were performed to establish the upper limit of the catalytic conversion. The calculations and experimental results indicate that reaction temperature has a moderate effect on the equilibrium yield of sym-OHA, whose formation is favored at lower temperature. However, the experimentally determined equilibrium ratios of sym-OHA to sym-OHP (close to 1.3) are lower than the calculated values (2-2.6). The occurrence of simultaneous side reactions probably contributes to the shift of the equilibrium state of sym-OHA and sym-OHP.