|dc.description.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
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