Study On Facile Preparation And Properties Of High Dispersed Carbon Supported Catalysts

Due to the excellent properties including acid and alkali resistance,thermal stability,high porosity and large specific surface area,carbon materials are widely used as supporter to prepar supported catalysts.Which is an effective method to improve the dispersion of the catalyst active components,resulting in more active sites can be provided to catalytic reactions,thus enhancing the catalytic performance.However,the loading of active components is limited to avoid the serious agglomeration of active components.Therefore,it is meaningful to prepare the catalyst with a high loading and a high dispersion of active components.In this thesis,one of renewable biomass‘polysaccharide-carrageenan’was used as carbon source to synthesis the carbon supported catalyst with high-dispersion active components.In the process of preparing,the active components was restricted to mobile through the chemical“anchoring”between carrageenan functional groups and active component ions and the“fixing”of carrageenan polymerized gel.And carbon-supported catalytic materials with honeycomb structure or nano-fibrous structure were fabricated successfully.The specific research work as follows:In this work,the polymer colloid of carrageenan was obtained through the formation of intermolecular bridge by the ionic bonding and electrostatic interaction between metal ions and carrageenan.Simultaneously,the metal ions were anchored in the carrageenan double helix structures to achieve a high dispersion.And the porous carbon-supported catalytic materials with high dispersion were obtained after drying and calcination of mixed gel precursor.The research work was focused on the effects of freeze-drying methods,inorganic salt hard templates,types and amounts of metal active component precursors on the structure of the prepared carbon materials.The obtained results indicating:（1）Slow freezing by the refrigerator is conducive to the gelation process of carrageenan;（2）The porosity and porous structure can be improved by using inorganic salt with a high melting point as hard template,the solubility of inorganic salt make it to be possible to removal by water washing,thus this process is eco-friend and recycled;（3）The prepared carbon material with a ultra-high loading shows a high dispersion;（4）Due to the generation of the reductive gas of CO during the process of the calcination in inert atmosphere,some metal ions can be reduced thoroughly to metal,thereby preparing a highly dispersed metal-supported catalytic material by one step.The properties of solvent have a strong effect on the structure of prepared carrageenan xerogel.Considering the agglomeration of carrageenan driven by a strong surface tension,resulting in the collapse of pores structure during the freeze-drying process,the tert-butanol with a smaller surface tension was choose to use as solvent to further investigate the effect of solvent on the structure.And the parameters of the organic solvent content,freezing method and calcination conditions were evaluated,respectively.The results indicating:（1）A fibrous precursor structure was successfully obtained after freeze-drying by using t-butanol as solvent,indicting the solvent has strong effect on the material structure;（2）The freezing method does no display an obvious effect on the structure of xerogel precursor;（3）Fibrous structure of xerogel precursor is easily fractured during the process of calcination in inert atmosphere,and the introducing of toluenesulfonic acid into the system is favorable to keep the carbon nano-fibrous structure.Finally,the selective hydrogenation of cinnamaldehyde was choosen as a probe reaction to investigate the catalytic performance of the prepared porous carbon-supported catalysts.Under the conditions:reaction temperature 120℃,2 H₂MPa,the conversion of cinnamaldehyde is 79.7%,and the main product selectivity of hydrogenated cinnamaldehyde is 60%after reaction for 2 h.