Journal
JOURNAL OF CATALYSIS
Volume 364, Issue -, Pages 216-227Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2018.05.020
Keywords
Heterogeneous catalysis; Gold; Nanoporous gold; Au(310); Stepped surface; Dioxygen activation; Methanol; Selective oxidation; Low-coordinated sites; DFT; Microkinetic modeling
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Funding
- German Research Foundation (DFG) [BA 1710/29-1, KL 1175/14-1, MO 1863/5-1]
- DFG [INST 184/108-1 FUGG, INST 184/157-1 FUGG]
- Ministry of Science and Culture of the Lower Saxony State
- North-German Supercomputing Alliance (HLRN) [nic00026]
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This work establishes a comprehensive analysis of the role of steps and kinks of the Au(3 1 0) surface in the generation of active oxygen species and elucidates the reaction pathway for methanol oxidation to formaldehyde. We have considered two possibilities for the O-O bond splitting in molecular O-2: via a dissociative O-2 adsorption or a direct reaction of O-2 with methanol. Both reaction pathways more favorably take place on the step edges of Au(3 1 0) than on flat Au(1 1 1). Depending on the adsorption positions of O-2, different dissociation pathways are possible, where the most favored path shows a substantially lower activation barrier compared to the flat gold surface. Atomic oxygen generated on the surface, prefers to build O-Au-O fragments with stronger binding to the surface than individually adsorbed O. The reaction pathways for methanol reaction with O and O-2 have been analyzed and compared. The direct reaction of methanol with molecular oxygen (an associative mechanism) proceeds via a formation of the OOH intermediate and its further dissociation to O and OH. This reaction sequence has low activation barriers of 0.3-0.4 eV and therefore should be preferred over O-2 dissociation to atomic O and the following reaction of O with methanol. By analogy, O-2 can react with water generating OOH with similarly low activation barriers. We have supported the proposed associative mechanism by microkinetic modeling. (C) 2018 Elsevier Inc. All rights reserved.
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