Sammanfattning
For the first time, a tandem catalytic material, 5 wt % Pd/NbOPO 4, was utilized in the depolymerization of wood in supercritical ethanol under hydrogen atmosphere. The experiments were conducted under various conditions, with fresh, and acetone extracted birch. A comprehensive analysis was performed to elucidate the dissolution efficiency and achieved product distribution. The results indicated that with fresh birch, 34 wt % of lignin monomer yield with 84 wt % delignification efficiency were obtained while with extracted wood, 35 wt % of lignin monomer yield with 78 wt % delignification efficiency were achieved. The total lignin monomer content extracted from the fresh birch is composed of 76.9 wt % of dimethoxyphenols and 16.5 wt % with the guaiacol structure. Major lignin monomer product was homosyringaldehyde (61.9 wt %). With extracted wood, 93.2 wt % of dimethoxyphenols (63.6 wt % homosyringaldehyde) and 6.8 wt % of guaiacol-monomers were achieved. It was concluded that the depolymerization occurred via breaking of the ether bonds in lignin, including ether hydrolysis by Lewis acid sites over the solid acid catalyst and with subsequent deoxygenation of monophenols over Pd. In addition, an extraction process was proposed to extract the aromatic fraction from the obtained biocrude.
| Originalspråk | Engelska |
|---|---|
| Artikelnummer | 121148 |
| Antal sidor | 12 |
| Tidskrift | Renewable Energy |
| Volym | 233 |
| DOI | |
| Status | Publicerad - okt. 2024 |
| MoE-publikationstyp | A1 Tidskriftsartikel-refererad |
Finansiering
The results found in literature concerning wood liquefaction over different bifunctional catalysts (Table 1) revealed that noble metal-based catalysts, such as Pd and Ru, are active in depolymerization of lignin and hydrogenation of lignin-derived hydroxyl-containing molecules and therefore could enhance the monomer yield [34]. The main products were 4-n-propylguaiacol and 4-n-propylsyringol in the primary alcohol medium, i.e., methanol [34,37,38,40] and ethanol [36] under relatively high hydrogen pressures. The depolymerization of lignin in woody biomass was also demonstrated in the absence of an external hydrogen source, utilizing methanol/water as a co-solvent, at 230 \u00B0C and over Pt/\u03B3-Al2O3 catalyst under an inert atmosphere. Where hydrogen was generated from the methanol/water medium [35]. Furthermore, the results in Ref. [41] showed that \u03B3-Al2O3 as a support for Pt was not stable under hydrothermal conditions. Under limited hydrogen initial pressure, the deconstruction of wood in ethanol over a Br\u00F8nsted acid catalyst, Fe-Beta-H-150 at 243 \u00B0C was directed towards the formation of isoeugenol as the main component via dehydration and demethoxylation of sinapyl alcohol [9].B.E.T. isotherms of supported and unsupported catalysts do not show any N2 adsorption-desorption plateau at high P/P0. This behaviour is distinctly visible over Pd/NbP. According to IUPAC, the hysteresis loop H3 shows similar characteristics, which relates to the presence of wedge-shaped pores on the niobium support. The B.E.T. specific surface area, mean pore volume, pore diameter, and Pd particle size are reported in Table 3.The transmission electron microscopy (TEM, JEOL 1230, works at 80 kV) was used to determine the surface morphology of the catalyst. The TEM images of Pd/NbP are presented in Fig. S1. The histogram of Pd particle size distribution is also presented in the supporting information. The average Pd particle size was about 11 nm. The TEM image confirms the presence of loaded Pd nanoparticles over NbP support which could not be observed in the XRD due to detection limits. The absence of large Pd clusters and relatively uniform particle size, is due to point that Pd shows strong metal-support interaction between Pd and niobium support, thereby overcoming the electrostatic interaction between the interparticle Pd clusters which materializes them together. TEM images indicated that Pd particles were homogeneously deposited on the NbP support. Close observation at the TEM image of the niobium support shows the presence of wedge-type pores in which Pd nanoparticles are deposited. This microscopic image of the niobium support correlates with the wedge-type pores characteristic of the catalyst obtained from the B.E.T isotherm. The catalyst surface morphology and particle distribution of Nb and P were investigated by a field-emission scanning electron microscopy (FESEM, Carl Zeiss Merlin GmbH) (Fig. S2, Table S1), and EDS microelement mapping (SEM-EDS) was performed (Fig. 2).The SEM image of the Pd/NbP shows increased surface disorders compared to the bare niobium support. This further supports the argument in the aggregation of niobium support during catalyst synthesis, which resulted in decreased crystallinity of the final Pd/NbP catalyst. In NbP, curiously the ratio Nb/P was equal to one (supporting information). EDS microelement mapping images of NbP and Pd/NbP showed that Pd particles were uniformly distributed on NbP support. The Pd loading appeared to be relatively smaller compared to the initial loading of 5 wt % (3.6 wt % confirmed by SEM-EDS, Table S1). However, the deviation is well within the experimental errors. Undoubtedly, the immobilized Pd nanoparticles are shown to be homogeneously distributed over the NbP support. Detailed information on catalyst characterization results can be seen in Table 3 [52]. NbP has a higher amount of Br\u00F8nsted acid sites than Lewis acid sites; however, Pd doped on NbP blocks Br\u00F8nsted acid sites, as a result, the amount of Lewis acid sites of the catalyst became higher than Br\u00F8nsted acid sites.The authors would like to acknowledge the funding from Fortum Foundation (Project no: 20190066), Finland. This work is part of the activities of the Johan Gadolin Process Chemistry Centre - PCC at \u00C5bo Akademi University (Finland). In Sweden, the Bio4Energy program and the Wallenberg Wood Science Center are acknowledged. This work is also partially financed by the TANDEM FOREST VALUE grant TFV 2018-0031 under the auspicious of the Royal Swedish Academy of Agriculture and Forestry, KSLA. Partially supported by Alfred Kordelin Foundation (Grant no: 20207), Finland. The authors would like to acknowledge the funding from Fortum Foundation (Project no: 20190066), Finland. This work is part of the activities of the Johan Gadolin Process Chemistry Centre at \u00C5bo Akademi University (Finland). In Sweden, the Bio4Energy program and the Wallenberg Wood Science Center are acknowledged. This work is also partially financed by the TANDEM FOREST VALUE grant TFV 2018-0031 under the auspicious of the Royal Swedish Academy of Agriculture and Forestry, KSLA. Partially supported by Alfred Kordelinin Foundation (Grant no: 200207), Finland.
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