Highly Efficient, Easily Recoverable, and Recyclable Re–SiO₂–Fe₃O₄ Catalyst for the Fragmentation of Lignin

Abstract

A series of Fe 3 O 4 @SiO 2 @Re catalysts were prepared by deposition of rhenium by means of the precipitation−deposition and impregnation procedures. Characterization of the catalysts confirmed that the deposition of silica protected the magnetite nanoparticles, resulting in a stable SiO 2 @Fe 3 O 4 composite, which was not affected by the treatments during the further deposition of rhenium. Rhenium was silent in XRD over the range of concentrations, at which it was deposited. Furthermore, XPS detected rhenium, only in the impregnation series; this may confirm that dispersion was high. As expected, rhenium was not reduced to the metallic state and generated weakly acidic Brønsted-type centers as detected by NH 3 -TPD. H 2 -TPD and chemisorption experiments demonstrate the capacity of these catalysts to chemisorb hydrogen. In line with these properties, rhenium catalyzed both C−C hydrogenolysis and C−O hydrolysis in successive steps. The performance of these catalysts was checked for a series of lignins of different origin and by means of different separation procedures. A very important finding is that these catalysts were highly stable and easy to recover.

Catalytic Transfer Hydrogenolysis Reactions for Lignin Valorization to Fuels and Chemicals

“…Along these lines and in addition to the more classical hydrogenation catalysts, e.g., noble or transition metals on carbon, zeolites, silica, etc., more "sophisticated" multifunctional catalytic formulation have been recently reported, as described in the sections above, including TiN-Ni and TiO 2 -Ni, FeNiB alloys, Cu based materials such as Cu 20 La 20 PMO (porous metal oxides) and CuMgAlO x , Fe on Rh/La 2 O 3 /CeO 2 -ZrO 2 , β-CaP 2 O 6 and CoP 2 O 6 , and others. With regard to catalyst recovery from batch reactor systems, new magneticcatalytic formulations with weakly acidic Brønsted-type centers, such as Fe 3 O 4 @SiO 2 @Re and Co@Nb 2 O 5 @Fe 3 O 4 which exhibited promising behavior in the reductive depolymerization of lignin using gaseous H 2 , could be also effectively used in catalytic transfer hdyrogenolysis reactions [143,144].…”

Catalytic Processes For Lignin Valorization into Fuels and Chemicals (Aromatics)

“…Pyrolysis of alkaline lignin catalyzed by proton zeolites with different pore size (i.e. H-BETA, H-ZSM-5 and H-USY), was studied by van Bokhoven et al [101][102]. These catalysts possess mainly Brönsted-type acid sites that play a dual role participating in lignin depolymerization but also stabilizing monomers to prevent re-polymerizing.…”

Ag2CO3 containing magnetic nanocomposite as a powerful and recoverable catalyst for Knoevenagel condensation

“…Moreover, the abundant silanol groups on the silica surface provide suitable conditions for different types of modification 10 , 25 – 28 . Some of recently developed magnetic nanostructures with silica shells are Fe 3 O 4 @BOS@SB/In 29 , Fe 3 O 4 @SiO 2 @PMO 30 , Re–SiO 2 –Fe 3 O 4 31 , Mag@Ti-NOS 32 , Fe 3 O 4 @RF@void@PMO(IL)/Cu 33 , Fe 3 O 4 @SiO 2 @propyl‐ANDSA 34 and Fe 3 O 4 @Au@mSiO 2 -dsDNA/DOX 35 . The MNPs with silica shell can be used as electrode 36 , adsorbent 37 , sensor 38 , catalyst support 10 , 29 , 32 – 34 , 39 , 40 , ion exchanger 41 and so on.…”