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Synergy in Lignin Upgrading by a Combination of Cu-BasedMixed Oxide and Ni-Phosphide Catalysts in Supercritical Ethanol

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ABSTRACT

The depolymerizationof lignin to bioaromatics usually requiresa hydrodeoxygenation (HDO) step to lower the oxygen content.A mixed Cu–Mg–Al oxide (CuMgAlOx) is an effective catalyst for the depolymerization of ligninin supercritical ethanol. We explored the use of Ni-based cocatalysts,i.e. Ni/SiO2, Ni2P/SiO2, and Ni/ASA(ASA = amorphous silica alumina), with the aim of combining lignindepolymerization and HDO in a single reaction step. While the silica-supportedcatalysts were themselves hardly active in lignin upgrading, Ni/ASAdisplayed comparable lignin monomer yield as CuMgAlOx. A drawback of using an acidic support is extensive dehydrationof the ethanol solvent. Instead, combining CuMgAlOx with Ni/SiO2 and especially Ni2P/SiO2 proved to be effective in increasing the lignin monomer yield,while at the same time reducing the oxygen content of the products.With Ni2P/SiO2, the lignin monomer yield was53 wt %, leading to nearly complete deoxygenation of the aromaticproducts.

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XRD patterns of (a) Ni/SiO2, (b) Ni/ASA, and (c) Ni2P/SiO2 catalysts (* metallic Ni; # Ni2P).
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fig1: XRD patterns of (a) Ni/SiO2, (b) Ni/ASA, and (c) Ni2P/SiO2 catalysts (* metallic Ni; # Ni2P).

Mentions: Figure 1 shows theXRD patterns of the reduced Ni catalysts. Reduction of NiO-P/SiO2 leads to phase-pure Ni2P/SiO2, whilemetallic Ni catalysts were obtained by reducing NiO/SiO2 and NiO/ASA. The nominal Ni loading of these catalysts is around10 wt %. The textural properties of the Ni-based and the CuMgAlOx catalyst are collected in Table 1. These catalysts were usedin different combinations to convert soda lignin in ethanol undersupercritical conditions. The reaction temperature was 340 °C,and the reaction time was 4 h. Hydrogen was not added to those reactionexperiments that involved the use of CuMgAlOx, as this catalyst produced in situ hydrogen by reforming ofethanol.13,37 When only supported Ni was used as the catalyst,the autoclave was pressurized by 30 bar H2 atmosphere.Another experiment involved the use of Ni2P/SiO2 in 10 bar N2 atmosphere. The results of these eight reactionexperiments are shown in Table 2.


Synergy in Lignin Upgrading by a Combination of Cu-BasedMixed Oxide and Ni-Phosphide Catalysts in Supercritical Ethanol
XRD patterns of (a) Ni/SiO2, (b) Ni/ASA, and (c) Ni2P/SiO2 catalysts (* metallic Ni; # Ni2P).
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getmorefigures.php?uid=PMC5384481&req=5

fig1: XRD patterns of (a) Ni/SiO2, (b) Ni/ASA, and (c) Ni2P/SiO2 catalysts (* metallic Ni; # Ni2P).
Mentions: Figure 1 shows theXRD patterns of the reduced Ni catalysts. Reduction of NiO-P/SiO2 leads to phase-pure Ni2P/SiO2, whilemetallic Ni catalysts were obtained by reducing NiO/SiO2 and NiO/ASA. The nominal Ni loading of these catalysts is around10 wt %. The textural properties of the Ni-based and the CuMgAlOx catalyst are collected in Table 1. These catalysts were usedin different combinations to convert soda lignin in ethanol undersupercritical conditions. The reaction temperature was 340 °C,and the reaction time was 4 h. Hydrogen was not added to those reactionexperiments that involved the use of CuMgAlOx, as this catalyst produced in situ hydrogen by reforming ofethanol.13,37 When only supported Ni was used as the catalyst,the autoclave was pressurized by 30 bar H2 atmosphere.Another experiment involved the use of Ni2P/SiO2 in 10 bar N2 atmosphere. The results of these eight reactionexperiments are shown in Table 2.

View Article: PubMed Central - PubMed

ABSTRACT

The depolymerizationof lignin to bioaromatics usually requiresa hydrodeoxygenation (HDO) step to lower the oxygen content.A mixed Cu–Mg–Al oxide (CuMgAlOx) is an effective catalyst for the depolymerization of ligninin supercritical ethanol. We explored the use of Ni-based cocatalysts,i.e. Ni/SiO2, Ni2P/SiO2, and Ni/ASA(ASA = amorphous silica alumina), with the aim of combining lignindepolymerization and HDO in a single reaction step. While the silica-supportedcatalysts were themselves hardly active in lignin upgrading, Ni/ASAdisplayed comparable lignin monomer yield as CuMgAlOx. A drawback of using an acidic support is extensive dehydrationof the ethanol solvent. Instead, combining CuMgAlOx with Ni/SiO2 and especially Ni2P/SiO2 proved to be effective in increasing the lignin monomer yield,while at the same time reducing the oxygen content of the products.With Ni2P/SiO2, the lignin monomer yield was53 wt %, leading to nearly complete deoxygenation of the aromaticproducts.

No MeSH data available.