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      Methyldecalin hydrocracking over palladium/zeolite-X

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      Author(s)
      Sayan, S.
      Demirel, B.
      Paul, J.
      Date
      2000
      Source Title
      Fuel
      Print ISSN
      0016-2361
      Publisher
      Elsevier Science Ltd, Exeter, United Kingdom
      Volume
      79
      Issue
      11
      Pages
      1395 - 1404
      Language
      English
      Type
      Article
      Item Usage Stats
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      Abstract
      Hydrocracking of methyldecalin over Pd/REX has been studied with surface sensitive techniques in the critical temperature range 325– 3508C. Results from in situ characterization of adsorbed species, and post-reaction analysis of the catalyst surface by infrared and photoemission spectroscopies, were related to product distributions. The results are discussed in light of quantum chemical calculations of free and catalyst bound intermediates, following ring-opening reactions. Liquid and gaseous products were detected by infrared and UV/Vis spectroscopies. Apparent activation energies of product formation hydrogen consumption, over a broader temperature range, were derived from previous autoclave experiments. An increase in temperature, 325–3508C, results in a shift from preferred cracking products to aromatics, an enhanced level of light hydrocarbon off-gases, and a higher coverage of carbonaceous residues. The increased level of carbonaceous residues is accompanied by a lowered coverage of the reactant, at the surface. The altered product distribution can be characterized by apparent single activation energies, valid from 300 to 4508C. Methane and aromatics show a similar rapid increase with temperature, hydrogen consumption a more timid increase, indicating a reaction limited by diffusion, and cycloalkane production a modest inverse temperature dependence. Fully hydrogenated ring-opening products represent valuable fuel components, but hydrogen deficiency can instead lead to chemisorbed precursors to coke. Our calculations show that cyclohexane, 1,2-diethyl, 3-methyl has a lower heat of formation than the corresponding surface intermediates, but a small enthalpy advantage can easily be countered by entropy effects at higher temperatures. This balance is critical to the formation of preferred products, instead of catalyst deactivation and aromatics. The theoretical results further show that surface intermediates, where the terminating hydrogen is replaced by a C–O bond, have distinct vibrations around 1150 cm21. q2000 Elsevier Science Ltd. All rights reserved.
      Keywords
      Aromatic hydrocarbons
      Catalysts
      Crude petroleum
      Emission spectroscopy
      Infrared spectroscopy
      Palladium
      Photoemission
      Temperature
      Ultraviolet spectroscopy
      Zeolites
      Methyldecalin
      Rare earth exchange
      Surface sensitive measurement
      Hydrocracking
      Permalink
      http://hdl.handle.net/11693/25009
      Published Version (Please cite this version)
      http://dx.doi.org/10.1016/S0016-2361(99)00276-8
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