DFT studies on the key competing reaction steps towards complete ethanol oxidation on transition metal catalysts

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

“…This result is consistent with our previous calculation on Ir(100) . This superior property of avoiding the formation of acetic acid can only be matched by Ni catalysts. , Rather, the previous experimental investigations on Ir-based and Ir alloy catalysts demonstrated that the formation of acetic acid is found over Ir-containing catalysts. ,, Combining the previous experimental results with our calculations, we propose two possible explanations: (i) the generation of acetic acid might be attributed to the other types of exposed surfaces, e.g., Ir(111), Ir(110), and Ir(211); (ii) acetic acid could be formed via the C–O coupling of hydroxyl and CH x CO ( x = 1 or 2). Finally, we note that this reaction in basic solutions probably does not need any catalysts in a homogeneous condition as it should be a thermal reaction with very low or no barrier, which is different from the heterogeneous reaction being described here.…”

“…This adsorption configuration of CH 3 CO, named η 1 (C2)-η 1 (O) here, will give rise to the generation of the Ir1-O2-C2-O1-Ir2 moiety in the TS, as shown in Figure a. This M-O-C2-O-M moiety was also observed in the TSs of the CH 3 COOH formation over other transition-metal catalysts (e.g., Ru, Rh, and Ni), which all possess high activation barriers for the CH 3 COOH formation via the C–O coupling between CH 3 CO and OH groups.…”

“…44 This superior property of avoiding the formation of acetic acid can only be matched by Ni catalysts. 49,73 Rather, the previous experimental investigations on Ir-based and Ir alloy catalysts demonstrated that the formation of acetic acid is found over Ircontaining catalysts. 42,50,51 Combining the previous experimental results with our calculations, we propose two possible explanations: (i) the generation of acetic acid might be attributed to the other types of exposed surfaces, e.g., Ir(111), Ir(110), and Ir(211); (ii) acetic acid could be formed via the C−O coupling of hydroxyl and CH x CO (x = 1 or 2).…”

“…This adsorption configuration of CH 3 CO, named η 1 (C2)-η 1 (O) here, will give rise to the generation of the Ir1-O2-C2-O1-Ir2 moiety in the TS, as shown in Figure 5a. This M-O-C2-O-M moiety was also observed in the TSs of the CH 3 COOH formation over other transition-metal catalysts (e.g., Ru, Rh, and Ni), 49 which all possess high activation barriers for the To explore the origin of the bond cleavage over the hollow and bridge sites, we calculated the Bader charges for hollowand bridge-site CH 2 CO. As displayed in Figure 4c, hollow-site CH 2 CO changed the surface structure of Ir(100). More precisely, the distance between Ir atoms around the hollow site was elongated from 2.769 to 2.833 Å.…”

“…Unlike the Pt and Pd catalysts, the most studied EOR catalysts that had detailed mechanistic studies, − there are no comprehensive mechanistic studies for Ir-catalyzed EOR. Even though various investigations on Ir-containing catalysts have been carried out, ,− ,− the reaction mechanism of EOR on Ir catalysts is still unclear. Additionally, questions such as poisoning of C 1 intermediates and the formation of by-products (e.g., acetaldehyde and ethyl acetate) remain.…”