Effects of Acidity on the Conversion of the Model Bio-oil Ketone Cyclopentanone on H−Y Zeolites
journal contributionposted on 24.09.2009, 00:00 by Jun Huang, Wei Long, Pradeep K. Agrawal, Christopher W. Jones
Deoxygenation of bio-oils on acidic zeolites is a potential method for upgrading bio-oils into energy-dense liquid fuels. One of the factors affecting the viability of zeolite-catalyzed dehydration/deoxygenation is minimization of coke formation. Here, cyclopentanone, a ketone commonly found in bio-oils, is utilized as a prototypical bio-oil ketone and its reactivity is evaluated over commercial H−Y zeolites with different acidities. 1H, 13C, and 27Al NMR studies of acidic H−Y zeolites contacted with cyclopentanone suggest that the nature of the zeolite acidity significantly affects the organic reactivity and coke formation. The conversion of cyclopentanone is shown to be preferentially initiated at lower temperatures on the zeolite with lower acid strength, higher Brønsted acid site density, and larger concentration of extraframework aluminum species (H−Y/5.2, 27.1 SiOHSupAl/uc, 12.05 EFA/uc) than over the zeolite with higher acid strength but lower acid site density (H−Y/30, 8.4 SiOHSupAl/uc, and 0.28 EFA/uc). The H−Y/5.2 initiates the three-step condensation of cyclopentanone to trindane with essentially complete deoxygenation at room temperature. In contrast, on H−Y/30, the main reaction at room temperature is a one-step condensation to produce dimer with 50% deoxygenation. These observations suggest that relatively weak Brønsted acid sites are able to initiate the conversion of cyclopentanone and that a large density of accessible acid sites may promote the reactions. The results suggest that hydride transfer, double-bond migration, and cracking reactions occur at relatively low reaction temperatures on H−Y/5.2. At temperatures higher than 400 °C, heavy coke is generated, as evidenced by 13C NMR spectra, and local strain in the zeolite framework at strong acid sites (SiOHAl), as observed in the 29Si MAS NMR spectrum.