| Lignin consists of a large number of aromatic rings cross-linked by C-C and CO-C bonds to form a three-dimensional reticulated macromolecule,which is a natural aromatic polymer abundant in nature.Therefore,lignin can be used as a raw material for the production of liquid fuels and aromatic chemicals.Currently,the depolymerisation of lignin into liquid fuels rich in phenolic monomers is considered to be one of the most efficient ways of integrated use.However,challenges such as the complex structure of lignin,its stubborn resistance to erosion,and the low expected yield and selectivity of target products due to the easy polymerisation of lignin fragments and highly reactive intermediates during lignin depolymerisation.In this paper,we address these challenges in lignin depolymerisation by preparing lowcost green catalysts using natural seafoam(SEP)as a carrier and Mo and Mn as active metals for the preparation of phenolic-rich liquid fuels from lignin depolymerisation by catalysts in supercritical ethanol systems.Details of the study and its findings are as follows:(1)A series of Mo-Mn/SEP catalysts were designed and prepared and applied to the catalytic depolymerisation of lignin(LCD).Various analytical characterisations revealed that the Mn/Mo ratio could regulate the particle size of the metal oxides,the concentration of oxygen vacancies(OV)and surface acidic sites on the catalyst surface.At a Mn/Mo ratio of 3/1,3Mn1Mo/SEP has a moderate OV concentration and a reasonable distribution of Lewis and Br?nsted acid sites,which facilitates the adsorption of oxygen-containing intermediates and further hydrogenation and deoxygenation reactions.As a result,100% lignin conversion and 45.70% liquid product yield were achieved with 3Mn1Mo/SEP at 290°C reaction temperature,0.5MPa initial nitrogen pressure and 4h reaction in ethanol medium.Further analysis of the liquid product showed that the calorific value of the liquid product reached 32.31MJ/kg and the selectivity of the phenolic monomers was increased to 85.61%.In addition,the good cycling stability of 3Mn1Mo/SEP was found in five cycles,which demonstrates that the addition of Mn can effectively improve the cycling stability of the catalyst.(2)In order to further investigate the mechanism of catalytic depolymerization of lignin,2-phenoxy-1-phenylethanol(PP)was chosen as a model lignin β-O-4 bonding material to investigate the bond breaking mechanism of the catalyst.The experimental results of catalytic depolymerisation of PP revealed that compared with other catalysts,3Mn1Mo/SEP could achieve 98.8% conversion of PP and 44.6% and 47.3%selectivity for phenol and phenylethanol(the main products of PP breaking β-O-4),respectively.This is good evidence that a Mo/Mn ratio of 3/1 can significantly promote the selective breaking of β-O-4 bonds and that the addition of Mn effectively inhibits the alkylation of intermediates.Figure [21] Table [7] Reference [117]... |
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