Integrated catalytic and electrocatalytic conversion of substituted phenols and diaryl ethers

Abstract

Electrocatalytic hydrogenation and catalytic thermal hydrogenation of substituted phenols and diaryl ethers were studied on carbon-supported Rh. The rates of electrocatalytic hydrogenation increase with increasingly negative potentials, which have been related with the coverage of adsorbed hydrogen. The lowest and highest negative potentials in electrocatalytic hydrogenation correspond to the onset of H 2 evolution and to the onset of reactions involving the electrolyte, respectively. For electrocatalytic and catalytic thermal hydrogen addition reactions, the dominant reaction pathway is hydrogenation to cyclic alcohols and cycloalkyl ethers. The presence of substituting methyl or methoxy groups led to lower rates compared to unsubstituted phenol or diphenyl ether. Methoxy or benzyloxy groups, however, undergo CO bond cleavage via hydrogenolysis and hydrolysis (minor pathway). The surface chemical potential of hydrogen can be increased also by generating a H 2 atmosphere above the reaction media, supporting the conclusion that thermal and electrochemical routes share the same reaction pathways.

Structure Sensitivity in Hydrogenation Reactions on Pt/C in Aqueous‐phase

“…The hydrogenation rates increased with increasing cathodic potentials on all Pt/C catalysts as reported for Rh/C. [24] However, varying cathodic potential did not influence the product selectivity ( Figure S4). The hydrogenation of phenol on the metal is hypothesized to proceed as a Langmuir Hinshelwood type mechanism with the reaction of surface hydrogen atoms with the aromatic ring being the rate determining step (Scheme 1).…”

“…Thus, the dependence of TOF on fractional exposure shows a marked particle size effect on aromatic ring hydrogenation under the conditions explored. The hydrogenation rates increased with increasing cathodic potentials on all Pt/C catalysts as reported for Rh/C . However, varying cathodic potential did not influence the product selectivity (Figure S4).…”

Electrocatalytic Upgrading of Lignin‐Derived Bio‐Oil Based on Surface‐Engineered PtNiB Nanostructure

“…During ECH, the adsorbed hydrogen (H ads ) is electrochemically generated in situ on the electrode surface rather than through the dissociation of molecular H 2 . However, phenols are more resistant to hydrogenation compared to other bio‐oil components, such as aldehydes and ketones, due to the high energy requirements for CO bond cleavage in carbonyl groups and hydrogenation of the aromatic ring . Therefore, the large‐scale application of bio‐oil upgrading requires the development of powerful ECH electrocatalysts.…”

Electrochemical Hydrogenation of Acetone to Produce Isopropanol Using a Polymer Electrolyte Membrane Reactor

“…Electrochemical hydrogenation (ECH) provides a more energy efficient and environment-friendly method of upgrading organics, by integrating both the electrochemical and catalytic methods [7]. The overall reaction mechanism of ECH of an unsaturated organic molecule is suggested as the following Equations (1)- (5) [8][9][10][11][12][13].…”

“…ECH has been widely used to upgrade unsaturated compounds to corresponding saturated chemicals, such as furfural [14][15][16][17][18][19][20], aromatic compounds [7,13,[21][22][23][24][25][26][27][28][29], soybean oil [30], edible oil [31,32], levulinic acid [33][34][35], lactic acid [36], acetaldehyde [37], ethanol [37], acetylene [38], bio-oil [39,40], cyclohexane [9], glucose [41], and lignin [42]. In all those cases, reactions take place under mild conditions with temperatures below 100 • C and atmospheric pressure.…”