Construction Of Pd/defective Carbon Catalyst And Study On Catalytic Hydrodeoxygenation Of Bio-models

Hydrodeoxygenation（HDO）is one of the effective ways to convert renewable bio-oils into biofuels and chemicals,and its development and utilization are of great significance for solving current energy and environmental problems.However,the traditional bio-oil hydrodeoxygenation process has harsh reaction conditions（high temperature and high pressure H₂）,and the product yield needs to be improved.Therefore,the construction of high-performance catalysts and reaction systems is of great significance for realizing the hydrodeoxygenation and upgrading of bio-oil and its model compounds under mild conditions.In this paper,a series of low-loaded Pd/defective carbon catalysts were constructed by the strategy of atomic doping and structural modification to explore the"structure-effect"relationship during the mild hydrodeoxygenation of bio-oil model compounds.The main research contents are as follows:（1）A series of N-doped carbon-supported Pd catalysts for vanillin hydrodeoxidation were synthesized using an in-situ N-doping strategy with 3-aminophenol as the nitrogen source and carbon source and a post-treatment N-doping strategy with urea as the nitrogen source.The effects of different nitrogen doping methods on the structure and performance of the catalysts were investigated.According to TEM,Raman,XPS and other characterization analysis,it is found that the in-situ N-doped catalyst（Pd/CAFR）has a high content of pyridine nitrogen,which can increase the defect content on the support.Meanwhile,the defect of carbon carrier is involved in the anchoring of Pd NPs and its reduction to Pd⁰species.Compared with the post-treated N-doped carbon supported Pd-based catalyst（Pd/NCFR）,the in-situ N-doped Pd/CAFR catalyst showed better HDO performance of vanillin,and the yield of 2-methoxy-4-methylphenol（MMP）reached more than 98%under mild reaction conditions（70℃,1 h）.The mechanism study showed that the synergistic effect of abundant defect sites and highly dispersed Pd NPs on Pd/N-doped carbon catalyst promoted the mild HDO of vanillin.（2）Based on in-situ N doping,Pd/defective carbon catalyst（Pd/CAFRS-X-Y）with S/N co-doping was further synthesized by introducing in-situ coated trithiocyanic acid as sulfur source.The effects of calcination temperature（X=700,800,900）and S/N co-doping ratio（Y=0.5,1,1.5）on the performance of the catalyst were investigated,which can effectively control the defect degree of the carrier.According to Raman and XPS,the doping of S contributes to the formation of the unique electronic structure in the carbon material,which strengthens the electron transfer between the carbon-based support and the Pd NPs,thurs increasing the content of Pd⁰active species on the catalyst.Pd/CAFRS-800-1catalyst with calcination temperature of 800℃and S/N co-doping ratio of 1 realizes the directional conversion of vanillin to 2-methoxy-4-methylphenol at 50℃for 3 h,in which the MMP yield is close to 99%.Mechanistic studies show that the synergistic effect of S/N co-doping enriches the degree of support defects and effectively modulates the electronic structure of Pd species,which improves the HDO performance of the catalyst.In addition,the S/N co-doped Pd/defective carbon catalyst showed excellent stability and generality for the HDO reaction process of biomass model compounds.（3）The N-doped Pd/HCAFR-X hollow carbon catalyst（Pd/HCAFR-X）was further synthesized by adjusting the structure of the catalyst.The effects of carbon support cavity effect and nitrogen source doping amount（X=0.3,0.6,0.9）on HDO performance of biogenic model compound（acetophenone）were investigated.According to TEM,Raman,BET,and XPS characterizations,it was found that the hollow support promotes the formation of the hierarchical porous structure,which is responsible for the exposure of active sites and the transport of species on the Pd/HCAFR-X catalyst.Furthermore,the nitrogen source doping amount can adjust the defect degree of the hollow carbon support and optimize the catalyst surface microenvironment,which is beneficial to the anchoring of Pd NPs.The Pd/HCAFR-0.6 catalyst with 0.6 g of nitrogen source doping exhibited excellent catalytic performance for the acetophenone HDO at 50℃for 3 h,and the yield of ethylbenzene was close to 99%.Mechanistic studies reveals that the synergistic effect between the hollow structural supports and defect-anchored Pd NPs on N-doped Pd/hollow carbon catalysts promotes the hydrodeoxygenation of acetophenone.In addition,the hollow-structured Pd/HCAFR-0.6 catalyst shows good catalytic performance for acetophenone HDO after 5 cycles.