A Density Functional Theory Study on the Mechanism of Complete Ethanol Oxidation on Ir(100): Surface Diffusion-Controlled C–C Bond Cleavage

Abstract

Effective C−C bond cleavage is a critical concern in the applications of ethanol technologies. The lack of catalytic efficiency toward complete ethanol oxidation reaction (EOR) has hindered the development of direct ethanol fuel cells. Ir-based catalysts have recently shown promise in the complete EOR. However, its catalytic mechanism remains unclear, which impedes the development of better Ir-based catalysts. Herein, we report a comprehensive reaction network of complete ethanol decomposition on Ir(100) based on the extensive density functional theory calculations. Our results show that decomposition of ethanol on Ir(100) consists of four sequential dehydrogenation steps that lead to the generation of CH 2 CO species then follows two competitive reaction pathways, namely, the C−O bond cleavage that leads to the formation of poisonous CHC species and the diffusion of CH 2 CO leading to complete oxidation:Furthermore, the formation of acetic acid is not favored on Ir(100). This work highlights the essential roles of adsorption structure and diffusion of CH 2 CO in ethanol decomposition and will serve as a benchmark for future investigation of the complete EOR, such as exploring the electric and solvent effects on EOR.

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

“…A C–C bond cleavage in ethane decomposition without the presence of any other reactants can take place through one of the 10 elementary reactions summarized in Table S1. Among them, the C–C bond cleavages of CH 2 C, CHC, and CC species were studied on Ir(100) previously . In this work, we performed DFT calculations for the seven remaining reactions on Ir(100).…”

“…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). , …”

Electrochemical Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy Insights into CO Adsorption and Oxidation on Iridium Surface

“…Iridium (Ir) has attracted much attention recently due to its important role in the surface-sensitive electrocatalytic reactions such as alcohol oxidation, − ammonia oxidation, − oxygen evolution reaction, and so forth. , Specifically, ethanol oxidation reaction (EOR), serving as the anodic half-reaction of direct ethanol fuel cells which could be a promising sustainable portable power source, needs to promote its efficiency. Also, it has been demonstrated to benefit the catalysis performance through the addition or decoration of the Ir metallic component. ,, In detail, it was found that Ir could display excellent ability in breaking the C–C bond , and the C–H bond of ethanol molecule to form the so-called C1 intermediates (CO ad and CH x species), which could follow the so-called C1 reaction pathway and eventually result in the considerable conversion of ethanol into CO 2 . ,, Along this line, some Ir-based or Ir-contained EOR catalysts were reported either in acidic or alkaline media, such as PtIr–SnO 2 , IrSn/SnO 2 , and IrPd/C . Note that the pristine Ir itself can hardly exhibit EOR catalytic activity, which could be due to the poisoning effect from the as-generated CO ad and/or CH x species on the Ir surface.…”

“…Also, it has been demonstrated to benefit the catalysis performance through the addition or decoration of the Ir metallic component. 3,10,11 In detail, it was found that Ir could display excellent ability in breaking the C−C bond 3,12 and the C−H bond of ethanol molecule 13 to form the so-called C1 intermediates (CO ad and CH x species), which could follow the so-called C1 reaction pathway and eventually result in the considerable conversion of ethanol into CO 2 . 1,10,13 Along this line, some Ir-based or Ir-contained EOR catalysts were reported either in acidic or alkaline media, such as PtIr− SnO 2 , 3 IrSn/SnO 2 , 14 and IrPd/C.…”