Developing a cost-effective catalyst for the selective tandem conversion of furfural (FFA) to ethyl levulinate (EL) is important for synthesizing biofuels and fine chemicals from biomass. However, traditional catalysts prefer the hydrogenation-dehydration-hydrolysis pathway and are slow due to high activation energy requirement. Herein, a NiCoP/LaPO 4 catalyst was prepared via calcination of layered double hydroxide (LDH) precursor, followed by hydrogen reduction, and phosphating. When applied to the tandem of FFA for EL production, it exhibited a high selectivity of 90.1% at 160 °C under ethanol and water via acetalization–hydrogenolysis–hydrolysis route. Catalytic mechanism investigation indicated that in situ hydrogen spillover from NiCoP nanoparticles to the LaPO 4 support, leading to the formation of H + –H − pairs. These H + –H − pairs not only provide Brønsted acid sites to drive FFA acetalization and 2-ethoxymethyl furan (EMF) hydrolysis but also activate the C–O bonds of the key intermediate 2-diethoxymethyl furan (DEMF) via the S N 2 mechanism, markedly accelerating the hydrogenolysis step. Moreover, the NiCoP/LaPO 4 catalyst shows remarkable catalytic versatility for the synthesis of different alkyl levulinates from a range of alcohols (i.e., methanol, propanol, isopropanol, butanol and benzyl alcohol). This study presents an efficient bifunctional catalysis approach for complex tandem reaction pathways aimed at synthesizing alkyl levulinate by hydrogen spillover to generate transient H + –H − pairs.
The production of 5-hydroxymethylfurfural (5-HMF) from saccharide conversion has fallen short of industrial expectations due to low reaction efficiency and high costs. Herein, we fabricated a series of LaPO4 catalysts with controlled crystal structures and tuned acidity via a facile hydrothermal method. The hexagonal LaPO4-120 catalyst exhibited a high glucose conversion of 99.9% and a remarkable 5-HMF yield of 90.1% at 150 °C for 60 min. Additionally, the hexagonal LaPO4-120 catalyst showed promising activities in converting various saccharides including fructose, glucose, cellobiose, sucrose, and inulin. A series of characterization studies and DFT calculations revealed that the hexagonal LaPO4-120 catalyst possessed low-coordination La sites and abundant zeolitic water stored in the open and oxygen-lined channels, which provided Lewis acid sites and a dynamically local Brønsted acid environment to respectively facilitate glucose isomerization and the subsequent dehydration. A plausible reaction mechanism involving a synergetic proton transfer via hydrogen bonding is proposed. This study offers insights for the design of low-cost and heterogeneous catalysts with finely tuned Lewis and Brønsted acid sites for 5-HMF production.
The behavior of nanoparticles in media of different refractive index has received considerable theoretical and experimental investigation. However, the behavior of larger particles, of micron size, has not been established. We have chosen Eu 3+ as a marker of environmental changes. Dilution of this ion into LaPO 4 gives a simple, fingerprint emission spectrum which has been studied via its luminescent lifetime, the R 2 (( 5 D 0 → 7 F 2 )/( 5 D 0 → 7 F 1 ) intensity ratio) and the electric dipole:magnetic dipole intensity ratio, (ED:MD), of spectral features. Measurements of micron-sized particles of LaPO 4 :Eu 3+ synthesized by several methods have been made for dispersions in alcohols, in compressed glass discs, in melted glass discs, in phosphor in glass (PiG) and in melted PiG. The experimental results are discussed and rationalized. The Eu 3+ 5 D 0 emission lifetime is reasonably constant in the bulk powders, powders dispersed in alcohols or compressed discs but is smaller in PiGs and melted glass discs. In the PiGs the structural integrity of LaPO 4 :Eu 3+ is maintained until they are melted at higher temperature. The change in lifetime, when varying the composition of the PiG, follows the Virtual Cavity Model. For dispersal of the particles in solvents there is a cut-off particle size below 1 μm where the electronic spectra of the moiety become insensitive to the environment and the properties are determined by refractive index. The remarkable change in R 2 ratio in the different systems considered – by a factor of nearly 600 % - and the corresponding decrease in 5 D 0 lifetime – by a factor of nearly 60 % - illustrates the versatility of the lanthanide ion.
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