Competitive Paths for Methanol Decomposition on Ruthenium: A DFT Study

Abstract

Methanol decomposition is one of the key reactions in direct methanol fuel cell (DMFC) state-of-the-art technology, research, and development. However, its mechanism still presents many uncertainties, which, if answered, would permit us to refine the manufacture of DMFCs. The mechanism of methanol decomposition on ruthenium surfaces was investigated using density functional theory and a periodic supercell approach. The possible pathways, involving either initial C–H, C–O or O–H scission, were defined from experimental evidence regarding the methanol decomposition on ruthenium and other metallic surfaces. The study yielded the O–H scission pathway as having both the most favorable energetics and kinetics. The computational data, which present a remarkable closeness with the experimental results, also indicate methanol adsorption, the starting point in all possible pathways, to be of weak nature, implying a considerable rate of methanol desorption from the ruthenium, compromising the reaction.

Effects of Lattice Motion on Dissociative Chemisorption: Toward a Rigorous Comparison of Theory with Molecular Beam Experiments

“…Several dissociation pathways are possible, with scission of a C−H bond or O−H bond being most likely. 90,91 We speculate that S 0 for C−H bond breaking is likely to display a stronger variation with T, similar to CH 4 , while the O−H scission should exhibit a weaker variation, similar to what our models predict for H 2 O.…”

Ruthenium–Platinum Catalysts and Direct Methanol Fuel Cells (DMFC): A Review of Theoretical and Experimental Breakthroughs

“…Moura et al studied four possible pathways from three initial bond scissions (either an initial C-H, C-O, or an O-H bond scission) in the clean ruthenium surface, and initial O-H scission was considered as likely as the methanol decomposition pathway since: (a) it included the experimentally detected methoxy; (b) apart from the initial step of O-H bond scission, the pathway steps consistently presents the most energetically favorable route; (c) the energetics of the route explain both methoxy experimental detection and formaldehyde absence of detection; and, finally, (d) it is the most kinetically favorable pathway, namely, for temperatures of 220 and 340 K [73]. Nevertheless, in a certain temperature range, another pathway, with initial C-H bond breaking, might also be active as a minority pathway, and energetics of after H 2 formation from methanol decomposition indicates that this formation is likely possible as well [73]. Computational results also indicate a weak initial methanol adsorption, either in platinum or ruthenium surface, which could compromise effective methanol decomposition [69,72].…”

Methanol activation catalyzed by Pt7, Pt3Cu4, and Cu7 clusters: A density functional theory investigation

“…In order to clarity, all the calculated activation barriers ( Ea ) for the methanol dehydrogenation are shown in Figure and summarized in Table . For the first step of methanol dehydrogenation, there are three pathways such as O‐H, C‐H and C‐O bond scission . The pathway of C‐O bond scission is unfavorable owing to the high energy requirement .…”