Preparation Of Nitrogen-doped Carbon-loaded Palladium Catalysts And Their Catalytic Performance In The Hydrodeoxygenation Of Vanillin

With the increasing shortage of fossil energy and environmental pollution problems,the efficient conversion and utilization of biomass resources and their derivatives have become the focus of research,and the development of high performance biomass hydrodeoxygenation（HDO）catalysts is the key to solve these problems.Among many catalysts,metal/heteroatom-doped carbon catalysts stand out due to their tunable surface chemistry and pore structure.In this paper,a series of Pd/nitrogen-doped carbon catalysts were prepared for the upgrading of biomass derivatives（vanillin）hydrodeoxygenation under mild conditions using a one-pot hydrothermal method and a domain-limited pyrolysis method by adjusting the temperature and time of carbonization.The research work is as follows.First,silica@3-aminophenol-formaldehyde resin spheres（Si O₂@CAFR）were synthesized using a one-pot hydrothermal method,and a class of Pd/Si O₂@nitrogen-doped carbon catalysts（Pd/Si O₂@CAFR-T,T=700,800,900°C）were prepared for the hydrodeoxygenation of vanillin（VL）under mild conditions by varying the carbonization temperature.The characterization by XRD,Raman and XPS revealed that the content of pyrrole nitrogen and pyridine nitrogen in the catalysts changed significantly with the increase of carbonization temperature.The experimental results showed that the Pd/Si O₂@CAFR-800 prepared by carbonization treatment at 800℃had the most excellent vanillin hydrodeoxygenation performance,and 96.9%vanillin conversion and 27.9%2-methoxy-4-methylphenol（MMP）selectivity could be obtained under the reaction conditions of 25℃and 1 h.It was found that high pyrrole and pyridine nitrogen contents affected the Pd0 content,the degree of defects and the acidity level of the carriers.the good catalytic activity of the Pd/Si O₂@CAFR catalysts might result from the pooling effect caused by the high pyrrole and pyridine nitrogen doping.Secondly,a class of Pd/Si O₂@nitrogen-doped carbon@Si O₂catalysts（Pd/Si O₂@CAFR@Si O₂-T-H,T=700,800,900°C,H=2,5,8.11 h）were prepared by adjusting the temperature and time of carbonization using a class of sandwich-limited pyrolysis strategy with 3-aminophenol-formaldehyde resin as the intermediate template and silica as the cladding layer,11 h)for the hydrodeoxygenation of vanillin under mild conditions.It was found that adjusting the carbonization temperature and time had important effects on the pore structure,acidity,surface Pd0 content,pyridine and pyrrole nitrogen content and pyridine and pyrrole nitrogen ratio of the samples,and the Pd/Si O₂@CAFR@Si O₂-800-8h produced by carbonization at 800℃for 8 h had the highest pyrrole and pyridine nitrogen content（84.9%）and pyridine and pyrrole nitrogen ratio（80.6%）,thus the catalysts exhibit excellent activity and stability.Under the reaction conditions of 25℃and 1 h,the conversion of vanillin and the selectivity of MMP on the Pd/Si O₂@CAFR@Si O₂-800-8h catalyst could reach 97.1%and 35.3%,and the excellent performance was maintained after five cycles.