Enhanced Fatty Acid Photodecarboxylation over Bimetallic Au–Pd Core–Shell Nanoparticles Deposited on TiO₂

Abstract

Photodecarboxylation of biomass-derived fatty acids to alkanes offers significant potential to obtain hydrocarbons and economic benefits due to the mild conditions and high activity. Herein, the photodecarboxylation of hexanoic acid into alkanes using TiO 2 -supported monometallic Au or Pd and bimetallic Au−Pd catalysts is reported. It was found that bimetallic Au−Pd catalysts, featuring a core−shell structure evidenced by EDX-mapping and element line profile, show better photocatalytic performance, achieving 94.7% conversion of hexanoic acid and nearly 100% selectivity to pentane under UV−vis irradiation in the absence of H 2 than the monometallic Au analogue. This remarkable enhancement in activity compared to its TiO 2 supported monometallic Au or Pd analogues can be attributed to the synergistic effect between Au and Pd within the nanostructured Au(core)-Pd(shell) alloy for achieving more efficient charge-separation efficiency upon visible light excitation. This photocatalyst exhibits a wide scope converting multiple fatty acids into hydrocarbons. Moreover, it can even photocatalyze the conversion of raw bio-oils into alkanes directly. No obvious activity loss was observed during the reusability tests, demonstrating the good stability of the present catalyst. Density functional theory (DFT) calculations indicate that oxidation of carboxylates on TiO 2 leads to alkyl radicals that become bound to metal nanoparticles. The superior catalytic performance of Au(core)-Pd(shell)/TiO 2 is derived from the weaker adsorption for H on the alloy and the lower hydrogen evolution reaction overpotential. Our research can result in an efficient bio-oil upgrading, resulting in the synthesis of biofuels from biomass under mild conditions.

Metal–organic framework heterojunctions for photocatalysis

“…103 Most organic compounds undergo photochemical degradative reactions, leading to their transformation and decomposition. Particularly aromatic carboxylic acids, the common ligands in MOFs, can undergo photodecarboxylation 104 leading to the generation of structural defects in the material. However, when the organic linker undergoes photoexcitation, favourable interaction with the metal nodes results in a fast deactivation pathway in most of the cases, leading to photoinduced ligand-to-metal charge separation, and this process acts as the quenching mechanism of the organic ligand decomposition process.…”

Combined Hydrogen and Alkane Production by Photocatalytic Decarboxylative C–C Homocoupling of Fatty Acid by Constructing a Hydrogen-Deficient Catalytic Interface

“…At present, various catalytic methods have been developed to convert fatty acids to the corresponding alkanes via hydrodeoxygenation reactions. However, most thermocatalytic systems require high-temperature and high-pressure conditions. − Photocatalysis provides a gentler method for biomass hydrodeoxygenation upgrading. − For instance, Wang et al achieved highly selective generation of C n –1 alkanes from long-chain fatty acids using Pt/TiO 2 catalysts and low-pressure hydrogen (0.2 MPa) by decarboxylative hydrogenation . Although it is a great improvement, it is still inevitable that excess hydrogen is needed to suppress the free radical side reactions.…”