Zeolite HBEA catalyzes hydrogenation of aromatic hydrocarbons—methyl-substituted benzenes (benzene and toluene), alkenyl-substituted benzenes (styrene), and polycyclics (naphthalene)—in presence of excess H2 at high-temperatures (573–748 K) with rates that depend linearly on aromatic and H2 pressures. The observed kinetic behavior can be rationalized based on a sequence of elementary steps where the first hydrogenation step of the adsorbed benzenic intermediate is rate-determining while subsequent hydrogenation and desorption steps are quasi-equilibrated and H+ is the most abundant surface species. Styrene hydrogenation exhibits the highest rates among the aromatics considered and results exclusively in ethylbenzene synthesis; in contrast, benzene/toluene and naphthalene hydrogenation results in formation of their triply-hydrogenated five-membered ring and doubly-hydrogenated ring open analogs, respectively. Based on independent studies involving co-reaction of cyclohexene and 1-methyl-1-cyclopentene with H2, we infer their facile interconversion and hydrogenation to methylcyclopentane implying that conversion of benzene to methylcyclopentane likely occurs via intervening formation of both five- and six-membered ring intermediates. Taken together, these studies demonstrate feasibility of aromatics hydrogenation and propensity of benzenic rings in these hydrocarbons to undergo ring reduction or ring opening during their activation with H2 on Brønsted acid zeolites.
Bibliographical noteFunding Information:
We acknowledge (i) Dow through the University Partnership Initiative and the National Science Foundation (CBET 1701534) for financial support, (ii) Dr. Andrzej Malek, Dr. Davy L. S. Nieskens, and Dr. Joseph DeWilde from Dow for helpful technical discussions, (iii) Dr. Nicholas Seaton from the University of Minnesota Characterization Facility, which receives partial support from the National Science Foundation through the Materials Research Science and Engineering Centers program, for providing the SEM-EDS measurements and SEM images of the HBEA sample, (iv) Mr. Xinyu Li from the University of Minnesota for providing the X-ray diffractogram and pyridine IR spectra of the HBEA sample, and (v) Ms. Zhichen Shi from the University of Minnesota for providing the NH 3 TPD data of the HBEA sample.
- Aromatics hydrogenation
- Brønsted acid zeolites
- Methanol to hydrocarbons
- Ring opening
- Ring reduction