Interactive network of the dehydrogenation of alkanes, alkenes and alkynes – surface carbon hydrogenative coupling on Ru(111). Issue 1 (17th November 2020)

• Record Type: Journal Article
• Authors: Jiao, Yueyue; Ma, Huan; Wang, Hui; Li, Yong-Wang; Wen, Xiao-Dong; Jiao, Haijun
• Is Part Of: Catalysis science & technology. Volume 11:Issue 1(2021)
• Page Start: 191
• Page End: 210
• Publication Date: 2020-11-17
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/d0cy02055a
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : The reaction mechanisms of the dehydrogenation and retrosynthesis of alkanes, the consecutive dissociation of methane, ethane, ethene and ethyne, as well as propane, propene and propyne, on the fcc Ru(111) surface has been computed. Abstract : To understand the reaction mechanisms of the dehydrogenation and retrosynthesis of alkanes, the consecutive dissociation of methane, ethane, ethene and ethyne, as well as propane, propene and propyne, on the fcc Ru(111) surface has been investigated using periodic density functional theory computations (rPBE). Methane dissociation has the energy minimum path of → → → CH* → C*. Although ethane dissociation does not have ethene and ethyne as intermediates, they have the same final surface species with the minimum energy paths for ethane [ → → CH3 CH* → CH3 C* → → HC*C* → HC* + C*], ethene [ → → → HC*C* → HC* + C*] and ethyne [CH*CH* → HC*C* → HC* + C*]. Propane dissociation has the competitive routes of n -propyl [ → CH3 CH2 CH* → CH3 CH2 C* → CH3 CH*C* → CH3 C*C* → CH3 C* + C* →→ HC* + C*] and isopropyl with propyne as an intermediate [CH3 CH*CH3 → CH3 C*CH3 → → CH3 C*CH* → CH3 C*C* →→ HC* + C*], and the n -propyl route has propene as an intermediate for dissociation [ → CH3 C*CH2 */CH3 CH*CH* → CH3 CH*C*/CH3 C*CH* → CH3 C*C* →→ HC* + C*]. In these reactions, the most stable surface intermediates are HC*, CH3 C* and CH3 CH2 C* as homologs, as found experimentally on other metal surfaces. Our results rationalized the experimentally observed interconversion between + H* and CH3 C* as well as surface HC*C* and CH3 C*C* as key intermediates for the first C–C bond dissociation [HC*C* → HC* + C*; CH3 C*C* → CH3 C* + C*]. On the basis of surface C* and H2 gas, the retrosynthesis of methane, ethane and propane has increasing apparent barriers of 1.08, 1.51 and 1.66 eV, respectively, at 490 K and 1 atm H2 and 0.83, 1.14 and 1.15 eV, respectively, at 19.7 atm H2 . Surface carbon coverage changes the formation of alkanes from endergonic to exergonic. This pressure- and coverage-dependency is very important for understanding the reaction mechanism and selectivity. Surface alkynyl groups should be the intermediates for C–C coupling. The computed vibrational frequencies of CH*, CH3 C*, CH2 C*, HC*C* and agree with the experiments. The comparison in adsorption energies and reaction barriers and energies shows that the fcc Ru(111) surface is more active than the hcp Ru(0001) surface despite their very similar surface structures.