On the Mechanism of Catalytic Decarboxylation of Carboxylic Acids on Carbon-Supported Palladium Hydride

Abstract

The high chemical stability of aliphatic carboxylic acid makes catalytic decarboxylation at low temperatures challenging. We show that arylaliphatic acids (Ar-C n H 2n -COOH, n ≥ 1) decarboxylate on carbon-supported Pd nanoparticles (Pd/C) at 90 °C with 100% selectivity. In situ XANES during decarboxylation of preadsorbed substrates indicates that the active phase is α-phase palladium hydride (α-PdH x ). The reaction rate is enhanced by one order of magnitude when hydrogen is preadsorbed. Tracing deuterium labeling positions, it is concluded that carboxylic acid (Ar-C n H 2n -COOH) undergoes an α-C−H bond dissociation on the Pd surface to the Ar-(CH 2 ) n−1 -CH*-COO* intermediate in the first step, followed by the C−COO scission, and finally, Ar-(CH 2 ) n−1 -CH* reacts with two sorbed H to produce Ar-(CH 2 ) n−1 -CH 3 . The high rates are related to the concentration of hydride present on the catalyst particles to complete the catalytic cycle in a Mars−van Krevelen-type mechanism and the rate of H/D exchange at the α-C− H position.

Selectivity of reaction pathways for green diesel production towards biojet fuel applications

“…Furthermore, the intermediate underwent C–COO bond cleavage resulting in R(C n −1 )–CH* and reacted with two adsorbed H to produce R(C n −1 )–CH 3 . 59 A similar explanation can be seen in other studies. 60,61…”

“…The C-H bond of carboxylic acid was cleaved on the surface of Pd creating intermediate R(C n−1 )-CH*-COO*. Furthermore, the intermediate underwent C-COO bond cleavage resulting in R(C n−1 )-CH* and reacted with two adsorbed H to produce R(C n−1 )-CH 3 59. A similar explanation can be seen in other studies 60,61.…”

Electronic Structure Optimization of PdZn-Graphitic Carbon Nitride Nanocomposites as Electrocatalysts for Selective CO2 to CO Conversion

“… 27 Besides, the shifting of photon energies of PdZnGCN to higher values in both C and N spectra indicates electron transfer occurred from g-C 3 N 4 to PdZn. 28 Figure 2 c,d shows two characteristic peaks from metallic Pd at around 24 360 and 24 383 eV, 29 while metallic zinc showed a peak at 9662 eV. 30 Slight decreases in peak intensities were observed in the spectrum of PdZnGCN due to interactions between PdZn and g-C 3 N 4 .…”

Transformation of triolein to biogasoline by photo-chemo-biocatalysis

“…Traditional chemical decarboxylation of fatty acids to prepare hydrocarbons usually suffered from harsh conditions, toxic or expensive catalysts, and undesired side products. [61][62][63] Therefore, alternative ways of decarboxylation under ambient conditions are highly desired. Recently, Beisson and co-workers reported a fatty acid photodecarboxylase from Chlorella variabilis NC64A (CvFAP) that could efficiently convert long-chain fatty acids into the corresponding (n − 1) hydrocarbons under the irradiation of blue light at room temperature.…”