Impact of the degree of dehydrogenation in ethanol C–C bond cleavage on Ir(100)

Abstract

A lack of comprehensive studies of the C–C bond cleavage in organic molecules hampers the rational design of catalysts for many applications, such as in fuel cells and steam reforming technologies. Employing ethanol on Ir(100) as an example, we studied 14 C–C bond cleavages of various species involved in the ethanol oxidation reaction using density functional theory calculations and used the degree of dehydrogenation (DoDH) of the reactant species as a variable to correlate the C–C bond cleavage barrier and reaction energy. This correlation method was also applied to the dehydrogenation reactions of ethanol on various catalysts, and great insight was obtained. The results show that the C–C cleavage barrier generally decreases with DoDH, with a local minimum around 33.3% DoDH. For reactants having more than 50% DoDH, the C–C cleavage is more ready to take place than the dehydrogenation and can occur at room temperature. Furthermore, the O atom in the reactive species plays a critical role in lowering the C–C bond cleavage barrier. The results provide necessary inputs for kinetic studies of ethanol reactions under operando conditions, where a reaction network beyond the minimum energy pathway is needed. The results will also serve as a benchmark for future studies of the ethanol C–C cleavage on other facets of Ir catalysts or on different catalysts. Furthermore, this work demonstrates that the proposed method opens up a new and effective way of correlating catalytic activities for the C–C bond cleavage involving long-chain alkanes and alcohols.

Role of Oxygen Species toward the C–C Bond Cleavage in Steam Reforming of C2+ Alkanes: DFT Studies of Ethane on Ir(100)

“…(s + p)-PDOS plots for C 1 and C 2 in (a) CH 2 C, (b) CH 2 CO, (c) CH 2 COH, (d) CHCH, (e) CHCHO, (f) CHCHOH, (g) CC, (h) CCO, and (i) CCOH. Data except for CHCH was taken from ref .…”

“…The bottom two layers were fixed in optimization calculations, and the bottom three layers were fixed in frequency calculations. The same model catalysts were used in our previous studies. , …”

“…Therefore, a positive reaction energy indicates an endothermic reaction. All of the computational techniques being employed in this work were also used in our previous DFT studies of ethanol oxidation reaction on Ir(100). , …”

“…As such, finding methods to correlate the vast number of elementary reactions in a meaningful way to assist our understanding and catalyst selection is of utmost importance. In the previous work, to effectively evaluate the catalytic performance for ethanol oxidation reaction, we defined the degree of dehydrogenation (DoDH) of a reactive species as a variable to correlate the activation energy and reaction energy of the C–C, C–H, and C–O bond cleavages and used it to identify the change of reaction type along the minimum energy pathway. We also compared the performance of different catalysts along the minimum energy pathway.…”

Insights and Activation Energy Surface of the Dehydrogenation of C2HxO Species in Ethanol Oxidation Reaction on Ir(100)

“…The above model catalyst and the computational techniques are the same as those used in our studies of the other 18 dehydrogenation reactions of EOR. [40,70,76,82] We summarize below the numerical details of the DFT calculations.…”