Catalytic partial oxidation of propylene on metal surfaces by means of quantum chemical methods

Kızılkaya, Ali Can
Direct, gas phase propylene epoxidation reactions are carried out on model slabs representing Ru-Cu(111) bimetallic and Cu(111) metallic catalyst surfaces with periodic Density Functional Theory (DFT) calculations. Ru-Cu(111) surface is modelled as a Cu(111) monolayer totally covering the surface of Ru(0001) surface underneath. The catalytic activity is evaluated following the generally accepted oxametallacycle mechanism. It is shown that the Ru-Cu(111) surface has a lower energy barrier (0.48 eV) for the stripping of the allylic hydrogen of propylene and a higher energy barrier (0.92 eV) towards propylene oxametallacycle (OMMP) formation compared to 0.75 eV barrier for OMMP formation and 0.83 eV barrier for allylic hydrogen stripping on Cu(111), and thus ineffective for propylene oxide production based on the investigated models and mechanism. In order to analyze the observed inability of the Ru-Cu(111) surface to selectively catalyze propylene oxide formation, a Lewis acid probe, SO2, was adsorbed on the oxygenated Cu(111) and Ru-Cu(111) surfaces and the binding energies, a measure of the basicity of the chemisorbed oxygen on the surfaces, on two systems are compared. As a conclusion, the reason behind this ineffectiveness of the Ru-Cu(111) surface for selectively catalyzing propylene epoxidation is related to the higher basicity of the atomic oxygen adsorbed on Ru-Cu(111) compared to the oxygen on Cu(111). The results are consistent both with recent publications about propylene epoxidation and previous studies performed about the structure of Ru-Cu catalysts.


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Citation Formats
A. C. Kızılkaya, “Catalytic partial oxidation of propylene on metal surfaces by means of quantum chemical methods,” M.S. - Master of Science, Middle East Technical University, 2010.