Synthetic Fuels from Biomass: Photocatalytic Hydrodecarboxylation of Octanoic Acid by Ni Nanoparticles Deposited on TiO₂

Abstract

Decarboxylation of low‐value fatty acids from biomass is a simple process to produce synthetic fuels suitable to be blended with gasoline or diesel. The present study reports the photocatalytic decarboxylation of octanoic acid in the presence of H2 by a series of modified TiO2 to form mixtures of n‐heptane and tetradecane as major products in variable proportions, depending on the photocatalyst and the reaction conditions. It was found that the photocatalytic activity increases upon an optimal reductive NaBH4 treatment, presumably by generation of surface oxygen vacancies and by the deposition of Ni nanoparticles in the appropriate loading. Under the optimized conditions, an almost complete octanoic acid conversion and a combined selectivity to n‐heptane and tetradecane over 80 % were reached at 10 h of UV/Vis light irradiation with a 300 W Xe lamp. No changes in the photocatalytic performance were observed for six consecutive runs. The present results illustrate the possibility that photocatalytic decarboxylation offers for the transformation of biomass into synthetic fuels under mild conditions.

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

“…28 Recently, Hu et al employed a 10% Ni/TiO 2 photocatalyst for the decarboxylative hydrogenation of n-octanoic acid, resulting in the production of up to 20% of the coupling product under a hydrogen pressure of 0.2 MPa. 19 It has been established that through the decarboxylation process on TiO 2 , fatty acids can be transformed into active alkyl radicals, 29−31 to hydrogenation, coupling, disproportionation, or oxidation reactions, leading to a series of byproducts. 10,32−36 Manley et al studied the homocoupling of free radicals after photocatalytic decarboxylation of carboxylic acids and found that the yield was greatly affected by the substrate, indicating that the reactivity of free radical species in this system is uncontrollable.…”

Photocatalytic Hydrodecarboxylation of Fatty Acids for Drop‐in Biofuels Production

“…Among the options to avoid the harsh conditions applied by conventional routes to produce biofuels, photocatalytic hydrodecarboxylation of bioderived fatty acids has emerged as a viable alternative to afford hydrocarbons chemically compatible with drop‐in biofuels under mild reaction conditions. For example, alkanes in the range of synthetic fuels were obtained from fatty acids in high yields and high selectivity via photodecarboxylation using Pt/TiO 2 or Ni/TiO 2 as the photoredox catalyst system under UV light irradiation [18,19] . Although a major improvement to traditional protocols, the developed conditions still rely on the use of an atmosphere of hydrogen gas to promote the efficient termination of the active alkyl radical, rendering this approach less appealing.…”

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

“…Carboxylic acid photodecarboxylation requires the development of efficient photocatalysts, and considerable research has been conducted in this area trying to find more suitable materials. ,, In a semiconducting photocatalyst, photon absorption promotes electrons from the valence band to the conduction band, generating an electron hole in the valence band. This elementary process generates a transient charge separated state with negative electrons (e – ) and positive holes (h + ) pairs .…”

“…TiO 2 , having a bandgap of about 3.4 eV, absorbs photons of wavelength shorter than 380 nm, but other semiconductors with narrower bandgap can be excited by visible light. , TiO 2 possesses several advantages, including high activity under UV irradiation, high chemical and photochemical stability against photocorrosion, high relative abundance, low toxicity, and large scale affordability. These advantages have motivated the interest for TiO 2 in photocatalytic processes such as solar fuels production, , environmental remediation, , and photodecarboxylation. , …”

“…These advantages have motivated the interest for TiO 2 in photocatalytic processes such as solar fuels production, 19,20 environmental remediation, 21,22 and photodecarboxylation. 7,15 The photocatalytic activity of TiO 2 is known to increase with deposition on its surface of metal and metal oxide nanoparticles, acting as cocatalysts. 23,24 Although there is ample evidence that these metal nanoparticles can increase the photocatalytic activity of TiO 2 , the current data is mostly limited to monometallic nanoparticles, bimetallic nanoparticles having been considerably much less studied.…”