Application Of Carboxylated Carbon Materials In Acid-catalyzed Reaction

Exploration and application of metal-free catalyst,as a supplement and alternative to metal-based catalyst,are of great importance.Among various metal-free catalysts,acidic carbocatalyst attracts lots of attention from both academic and industrial fields as it is compatible with variety of acid sites and tunable with the surface hydrophility-hydrophobicity to control the adsorption-desorption behavior of intermediates as well as has amazing potential in the modification of carbon skeleton and facility for recycling and degradation in a more environment friendly way.The acid sites located on the surface of carbon materials also play vital roles in support metal particles.Therefore deep understanding of carboxylic groups would shed light on preparing carbon supported metal catalysts and the perception of interaction between metal and carbon support.This work aims for the application of carboxylated carbocatalysts(especially carbon nanotubes)in the acid-catalyzed reaction.We attempted to optimize the functionalization method of carboxylic groups,explore the influence of chemical environment to the structure-performance relationship of carboxylic sites and characterize the composition of oxidative carbon debris to figure out the chemical nature of carbocatalysts surface.The main conclusions are summarized as follow:(1)A new oxidation method based on our patented equipment for autoclaved oxidation of carbon materials with HNO3 vapor,which could dramatically reduce the usage of nitric acid,has been developed.The oxidative functionalization process could be more effective via increasing the oxidation temperature beyond the boiling point of nitric acid in the gas phase.The desorption of carbon debris generated by the oxidative etching could be suppressed without direct contact with liquid phase,thus continuous etching could be limited.The average catalytic activity of single carboxylic group increased with the overall number of oxygen-containing groups.The electron-withdrawing effect between nitro groups and carboxylic groups as well as between carboxyls themselves was postulated to explain the enhanced acid strength of carboxylic groups(2)Based on the kinetic study of the ring-opening reaction,a protocol for measuring the kinetic factors(normalized initial reaction rate,Ea,reaction order,and pre-exponential factor)and the fitted pKa value of' acidic carbon materials was developed.The carboxylic group and nitro group located on the carbocatalysts exhibit distinct thermal stability and IR features,which is speculated to be induced by the different intimacy between these groups.(3)The clear attribution of DRIFT feature peaks to the carboxylic groups,nitro groups,lactones and anhydrides on carbon materials was firstly reported based on a series of in-situ heating DRIFT spectra.The decomposition of these functional groups as well as the conversion of' carboxylic groups to lactones and anhydrides was also observed under in-situ conditions.We hope this work could shed light on the application of carboxylated carbocatalysts in acid-catalyzed reaction and provide a promising guideline for optimizing the chemical environment of acid sites according to the specific requirement of certain reaction based on the structure-performance relationship between acid strength and catalytic activity.