The Influences Of Exposed Facet Of Noble Metal Nanoparticles And Structure Of Ceria Based Supports On Catalytic Performance For Aerobic Oxidation Of HMF

With the development of social productivity,energy problem is becoming one of the most urgent problems for mankind.Biomass resources have a widely distribution,low cost,green renewability,in addition,it’s the only one renewable energy resources to provide alternative to fossil resources in production of carbon-based chemical products.In biomass resources,5-Hydroxymethylfurfural（HMF）is an important biological platform compounds,it can be produced from the basic carbohydrates,such as cellulose,glucose,fructose etc.HMF can be further utilized by oxidation,hydrogenation,polymerization to product variety high-value chemicals.Of these high-value chemical products,2,5-Furandicarboxylic acid（FDCA）which is an oxidative product of HMF can be used in polyester polymer materials synthesis process and has well-promising application ability.The reaction conditions in the aqueous phase using molecular oxygen as the oxidant is one of green chemical path for the catalytic oxidation of HMF to produce FDCA and becomes a hot topic research.This reaction is one of the representative model reaction of catalytic oxidation alcohol toward carboxylic acid in aqueous phase,it can be used as an entry point studies on the mechanism of same category catalytic reaction.Firstly,thesis is focused on influence of the face-effect and size-effect in HMF catalytic oxidation.This thesis synthesized different particle size of the octahedral shaped Pd nano single-crystal（Pd-NOs）and cube shaped Pd nano single-crystal（Pd-NCs）,HRTEM and XPS were used to study the morphology and surface chemical state analysis of single crystal nanoparticles.These synthetic single-crystal Pd nanoparticles were used in HMF catalytic oxidation reaction to study the face-effect and size-effect.It was found that the size of the Pd nano single-crystal grain size is mainly functioning by the proportion of surface Pd atom in this work.By controlling surface Pd molar,same morphology with different size showed similar catalytical performance,but different morphology which exposed different crystal face had different influence on HMF oxidation.Compared with{100}exposed by Pd-NC,{111}exposed by Pd-NOs had obvious catalytic activity in the HMF oxidation.It was found by the simulation results of reaction dynamics conducted by MATLAB that Pd-NOs showed better catalytic performance in the second step alcohol oxidation process of HMF catalytic oxidation reaction（from HMFCA to FFCA）,meanwhile Pd-NCs had poorer alcohol oxidation catalytic activity.It was proved that the Pd-NOs and Pd-NCs have different rate control steps.Based on the density functional theory,Pd（111）had a lower activation energy barrier in the alcohol oxidation step（from HMFCA to FFCA）than the Pd（100）.In addition,Pd（111）had high selectivity for O₂ hydrogenation reaction,which can promote to the production of hydrogen peroxide and remove excess electrons from the Pd surface to complete the catalytic cycle.On the anther hand,Pd（100）tended to dissociate the adsorbed O₂.The second part of this thesis discussed the influence oxygen vacancy of cerium oxide on the mechanism of catalytical enhancement supported Pt.This thesis used Bi³⁺,La³⁺and Mn²⁺doping in three-dimensional ordered macroporous structure cerium oxide materials to invest the influence of doping element on oxygen vacancy and oxygen activation capacity.Furthermore,the charge transfer capacity and HMF catalytic oxidation performance on the catalyst metal-support was also studied.A series of characterization of the synthsis 3D-Ce_1-xBi_x O_2-δsolid solution materials were performed,we proposed Bi³⁺ion doping in solid solution material can form the asymmetric structure of Bi-□（-Ce）₃ oxygen vacancy site.Compared with symmetrical oxygen vacancies（Ce-）₂?（-Ce）₂,on the one hand,oxygen molecules preferred to adsorb on Bi-□（-Ce）₃ to form stable 8-coordinated structure of Ce⁴⁺due to fluorite structure characteristics of cerium oxide.On the another hand,the Bi³⁺tends to form the six coordinated structure（similar to theδ-Bi₂O₃ structure）,so it is very easy to desorb the oxygen anion.Therefore,compared with the oxygen vacancy site of symmetric structure,the asymmetric oxygen vacancy site has stronger oxygen activation ability.And this oxygen activation process will continue to consume electrons,resulting in the electron transfer of Pt nanoparticles to the support.It would product Pt^δ+species which beneficial to the adsorption of the reactants and hydroxide ions,so that the catalyst can show significant catalytic activity in the HMF oxidation reaction.The synthesized Pt/Ce_0.8Bi_0.2O_2-δwas the most excellent catalyst.When La³⁺and Mn²⁺were used to combine with cerium oxide and form solid solution material,because of the different oxygen coordination number of La³⁺and Mn²⁺,and crystal structure of solid solution material was significant different from CeO₂ fluorite structure,so the impact on the crystalline structure of the CeO₂ is more significant.When La,Mn doping amount was 10%,3D-Ce_1-xLa_xO_2-δand 3D-Ce_1-xMn_xO_2-δhad higher oxygen vacancy and more than 3D-Ce_0.8Bi_0.2O_2-δ,but the catalytic activity was lower than of catalyst Bi doping.It may due to lack of asymmetric oxygen vacancy M-□（-Ce）₃.