The formation of high energy density fuel via the hydrogenation of naphthalene over Ni catalyst: The combined DFT and microkinetic analysis

Abstract

Decalin is the major ingredients of High-energy-density jet fuel JP-900, in which cis-decalin possesses more excellent combustion performance than trans-decalin. The various coordination environments on metal catalysts are crucial to evaluate activity of catalyst and selectivity of cis-decalin, the density functional theory and microkinetic modeling are applied to investigate the effect of various active sites on the process of naphthalene hydrogenation. Active sites with generalized coordination numbers of 7.50, 6.67, 5.57, and 5.50 from four Ni surfaces including Ni(1 1 1), Ni(1 0 0), Ni(1 1 0) and Ni(2 1 1) are built, respectively. To screen surfaces with preferable selectivity to cis-configuration, the four reaction paths are firstly considered including desorption of NA8H, direct hydrogenation of NA8H to cis- or trans-NA9H, and NA8H to trans-NA9H by hydrogen transfer on four surfaces. And the Ni(1 0 0) and Ni(1 1 1) surfaces exhibit optimal selectivity to cis-decalin by comparing energy barrier of the four paths and calculating the energy barrier gap between direct hydrogenation to cis- and H transfer to trans- configuration, which is the result of 9th C atom receiving more electrons in the process of generating trans-decalin. In addition, reaction mechanism of the whole reaction process from naphthalene hydrogenation to decalin was explored and finding that the rate-determining step of reaction lies in the process of the second-ring hydrogenation. Furthermore, the activity of the Ni(1 0 0) surface is not worse than that of Ni(1 1 1) by comparing the energy barrier of the rate-determining step, which is consistent with the analysis of the d-band-center for different surfaces and the adsorption energy for naphthalene. Microkinetic analysis shows that the temperature between 473 K and 553 K favors the selectivity to cis-decalin for metal Ni catalyst. Therefore, this study provides guide for screening surfaces with different coordination numbers with high activity of naphthalene hydrogenation and high selectivity to cis-decalin.