title: A computational investigation of ring-shift isomerization of sym-octahydrophenanthrene to sym-octahydroanthracene catalyzed by acidic zeolites.
abstract: The ring-shift isomerization of sym-octahydrophenanthrene (sym-OHP) to sym-octahydroanthracene (sym-OHA) catalyzed by acidic zeolites (Mordenite (MOR) and Faujasite (FAU)) was investigated by the ONIOM(DFT:UFF) and DFT approaches. A "five-membered ring" mechanism through carbocation rearrangement via 1-2 migration was proved to be kinetically favored over a "six-membered ring" mechanism through Friedel-Crafts reactions. Computational studies based on the "five-membered ring" mechanism demonstrate that a decreasing Brønsted acid site strength from Al-H-MOR to Ga-H-MOR to B-H-MOR reduces the catalytic activity. The catalyst acid site strength would thereby impact the yield of sym-OHA. The isomerization barrier increases when using an Al-H-FAU catalyst that has a similar Brønsted acid site strength as Al-H-MOR but considerably bigger cages, indicating that apart from the desired density and strength of acid sites, optimal zeolite catalysts should have a pore size that better fits the intermediates and transition states. DFT calculations on Gibbs free energy were performed to evaluate the equilibrium ratios of sym-OHA to sym-OHP at specific reaction temperatures from 175 to 325 °C. The results indicate that reaction temperature has a moderate impact on the equilibrium yield of sym-OHA, whose formation is relatively favorable at a lower temperature under experimental conditions.
authors.affiliation: State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian, 116012, China.
authors.forename: Xiaowa
authors.initials: X
authors.lastname: Nie
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Janik
authors.forename: Xinwen
authors.initials: X
authors.lastname: Guo
authors.forename: Chunshan
authors.initials: C
authors.lastname: Song
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D000873:Anthracenes / Q000737:chemistry*; D002384:Catalysis; D007536:Isomerism; D008958:Models, Molecular; D010616:Phenanthrenes / Q000737:chemistry*; D017641:Zeolites / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D000873:Anthracenes; D010616:Phenanthrenes; C539489:faujasite; C048397:mordenite; D017641:Zeolites