Mechanistic Insights Evaluating Ag, Pb, and Ni as Electrocatalysts for Furfural Reduction from First-Principles Methods

Abstract

Electrochemical reduction of furfural (ECRFF) emerges as an efficient and sustainable means to obtain high-value chemicals and biofuels with the activity and product selectivity being sensitive to cathode materials. In this work, elementary steps describing furfuryl alcohol (FA) and 2-methylfuran (MF) production routes in ECRFF are studied by using periodic density functional theory on Ag, Pb, and Ni, as alternative cathode materials. The established Brønsted−Evans−Polanyi (BEP) relationship has been proven to be reliable to estimate energy barriers of C−O bond cleavage. The intrinsic characters of Ag, Pb, and Ni are then summarized in free energy diagrams to reflect the FA and MF production trends as future guidelines to evaluate ECRFF activity and selectivity on these metals. On all metal surfaces, at both terrace and stepped sites, the first C−H or O−H hydrogenation step, producing respective mh6 or mh7 intermediates, influences overall FA production. On Ag and Pb, pathways involving the mh6 intermediate are thermodynamically and kinetically favored, whereas on Ni, both mh6 and mh7 routes are competitive due to strong interactions between the furan ring and the substrate. In addition, these partially hydrogenated intermediates can also undergo C−O bond cleavage with reduced energy barriers (compared to direct C−O bond cleavage in furfural), which opens potential paths for parallel MF production. Conversion of FA into MF catalyzed by these metallic cathodes was considered as well, although the high C−O bond cleavage energy barrier is likely to hinder this process.

Controlling Competitive Side Reactions in the Electrochemical Upgrading of Furfural to Biofuel

“…According to previous reports, two reaction pathways for the ECH of FF exist as depicted in Scheme a: a direct and an indirect reaction for the production of MF from FF. The Li group showed direct conversion of FF to MF at low applied potential (−0.55 V vs. RHE) on Cu, having negligible conversion of FA to MF.…”

“…Accordingt op revious reports, two reaction pathways for the ECH of FF exist [7b, 8,10] as depicted in Scheme 1a:adirect and an indirect reaction for the production of MF from FF. TheL ig roup showedd irect conversion of FF to MF at low applied potential (À0.55V vs.R HE)o nC u, [7b] having negligible conversion of FA to MF.O nt he otherh and, the Huber group showed the conversion of FF to FA first, then FA conversion to further reduced furanic compounds as the magnitude of the applied potential increasedo nP t/C and Pd/C.…”

“…The reaction pathway for the ECH of FF is shown in Scheme a. Both direct and indirect reaction pathways for the production of MF are included, with the direct path recently being identified as probable both experimentally and computationally …”

“…direct path recently being identified as probable both experimentally [7b] and computationally. [8] Studies of both the ECH of FF and of HMF in acidic electrolytes showed that Cu electrodes were best for achieving significant production of MF and DMF. [6a, 7b,d] Also,p rotonabundant acidic solutions were required for the production of MF from FF, [7] DMFf rom HMF, [7a] or more reduced furanic derivatives than MF and DMF.…”

Guidelines to Achieving High Selectivity for the Hydrogenation of α,β-Unsaturated Aldehydes with Bimetallic and Dilute Alloy Catalysts: A Review

“…Here, the initial and the final state may refer to: (i) an adsorption process, from gas phase to the adsorbed state, to provide adsorption phase diagrams from ab initio thermodynamics, as done for acrolein; 165,166 or (ii) an activation process, from the initial state to the transition state, to provide free energy diagrams of the elementary reaction steps, as done for crotonaldehyde 31,160 and furfural. [167][168][169]…”