Study On Oxidative Condensation/Oxidation Esterification Of Aromatic Heterocyclic Aldehydes Under Oxygen

In recent years,biomass resources have attracted extensive attentions of researchers due to its advantages such as sustainability,non-pollution,abundance and low carbon-emission.In particular,biomass and biomass-based platform compounds can be directly converted into liquid fuels or refined products through chemical reactions.Among them,furfural is one of the most common platform compounds from the biomass feedstocks.In addition,structure of 3-pyridinecarboxaldehyde(3-PCA)should be very similar to that of furfural as an important chemical intermediate and raw material.Due to being typical aromatic heterocyclic aldehydes,both of them contain active aldehyde group and can be employed to synthesize high value-added chemicals through condensation,esterification,and hydrogenation etc..So,the investigation of the selective conversion of aromatic heterocyclic aldehydes is of significance on theoretical science and the industrial application value.In this thesis,different Au-supported solid catalysts were initially prepared by the colloidal immobilization method,and were further used for the oxidative condensation process of furfural with ethanol in the presence of molecular oxygen.The experimental results indicated that the conversion rate and the selectivity in terms of furfural and product furan-2-acrolein were 85.9% and 81.8% respectively with the catalyst,Au@CaO under no any base additive conditions.Furthermore,the effects with respect to reaction time,temperature and amount of catalyst on the oxidative condensation reaction were investigated in detail.Therein,the conditions are optimized.On the other hand,the effects of calcination temperature and protective reagent amount during the catalyst preparation were also discussed.In addition,the catalyst was characterized by XRD,BET,SEM,TEM,XPS,etc..Particularly,the basic strength and basicity of the catalyst were measured by the Hammett indicator method.It has been concluded that the synergistic effect between the gold nanoparticles and CaO plays a crucial role on oxidative condensation reaction.Finally,a possible catalytic mechanism was proposed based on the experimental results and catalytic principle.Moreover,different palladium-containing catalysts were further synthesized that include Pd-Te/C,Pd-Sb/C,Pd-Sn/C,Pd-Ga/C,Pd-Bi/C.The prepared catalysts were then employed in the selective oxidation reaction of furfural(or 3-PCA)with ethanol.As a result,it is found that oxidative condensation reactions are dominant for the furfural and ethanol,while oxidative esterification reactions mainly occurred betweenthe 3-PCA and ethanol in the presence of molecular oxygen.For instance,using the Pd-Te/C as the heterogeneous catalyst,the conversion of furfural and the selectivity of main product furan-2-acrolein was respectively 83.6% and 91.3% at 140 ? for 4 h under 0.3 MPaof dioxygen.Relatively,a 99% conversion of 3-PCA with 88.3%selectivity of main product ethyl 3-pyridinecarboxylate was attained under the similar conditions.In addition,the physical property of catalyst was characterized by general XRD,BET,TEM,TPD,and XPS techniques.By comparing the physical and chemical adsorption properties of the catalyst and the microstructure of the catalyst,it was found that the electronic properties of the corresponding catalytic components Pd and Te should be responsible for these above catalytic reactions in the ethanol solvent.Finally,the study on the recycling of catalyst was performed successfully,it is found that the catalyst remained high catalytic activity even after being reused for five times.