The Accurate Regulation Of Coordination Structure And Its Catalytic Mechanism For Alcohol Selective Oxidation Catalyst

The selective oxidation reaction of alcohols is an important way for the conversion of oxygen-containing functional groups to pruduce the high-valueadded aldehydes,ketones and carboxylic acids products,which are widely used in the fields of pharmaceuticals,dyes,foods,and perfume-grade organic synthesis.In recent years,the heterogeneous catalytic oxidation method using molecular oxygen as the oxygen source has gradually become the development direction in the field of selective oxidation due to its advantages such as atomic economy,environmental friendliness and easy separation.The selective oxidation of alcohols involves the conversion of a variety of chemical bonds and functional groups including C-O bonds,C=O bonds,C-H bonds,and C-C bonds.The precise construction of catalyst active sites is used to selectively activate specific chemical bond types,which is also the key to achieve highefficiency directional conversion of alcohol selective oxidation reaction.By adjusting the coordination mode of the atoms on the catalyst surface,the geometrical and electronical structure of the metal and the supports can be effectively controlled leading to the enhancement of of the selective alcohols oxidation performance.This dissertation focused on conversion of alcohol molecules to the high value-added products in the fine chemical industry,using the selective oxidation of glycerol and octanol as probe molecules.Through the control of the crystal plane of the catalyst supports and the adjustment of the metal active component site,as well as the virious characterization methods,we studied the following 3 aspects to deepen the understanding of the structure-perfermance relationship.First,the role of the coordination structure of the supports on the adsorption of reactant or intermedieates was investigated to gain the intrinsic crystal-plane effect.Second,the role of the coordination structure of the supports on the formation of supported Pt active sites as well as the synergetic effect of activation extent of the adsorbed reactant or intermedieates are studied to achieve the enhancement of the oxidation performance.Third,the influence of the degree of continuity of active metal Pt on the adsorption and activation of reactants/intermediates are studied to identify the nature of the most active Pt sites for the each step in the whole oxidation reaction pathway.We also got the intrinsic relationship from the molecular/atomic view of the structure of active sites and its catalytic performance on the activation of hydroxyl and ?-C-H bond as well as the type of the aldehyde adsorption.The enhanced catalytic performance of alcohols is further achieved by the design and the synthesize of the specific active sites based on the differences of the characters of the various function groups.(1)The effect of the coordination structure of the catalyst support on the catalytic reaction performance was studied by adjusting the ratio of(001)crystal plane exposure of TiO2.It shows that the crystal plane of the support has an obvious effect on the selective oxidation depth of glycerol primary hydroxyl groups.The joint action of O and Ti atoms in the O2c-Ti5c coordination unsaturated site on the(001)crystal plane makes the aldehyde C=O bond adsorb and highly dissociate in the form of bidentate species.In addition,the O2c-Ti5c coordination unsaturated structure has a strong interaction with the Au active components in the AuPt bimetallic nanoparticles,forming a large number of Ti5c-O2c-Au?+ interface sites,which promotes the elimination of ?-C-H bond of the adsorbed bidentate aldehyde species,leading to a lower energy barrier for further oxidation of glyceraldehyde.This is the fundamental relationship for the crystal face effect of the catalyst and the catalytic performance.Therefore,the coordinated unsaturated sites of the carrier can effectively adjust the activation of the adsorption mode of the reactant molecules,which is the key to realize the high-efficiency and targeted conversion of glycerol molecules to glyceric acid products.(2)By adjusting the treatment conditions of the catalyst,the effect of the coordination structure of the crystal plane on the coordination structure of the supported active metal Pt atom as well as its synergistic mechanism of the reactant/intermediate product was studied in different treatment atmospheres.It shows that under air calcination conditions,the coordinated unsaturated O2cTi5c-O2c sites on the(001)crystal plane have strong interactions with metal Pt atoms and makes the formation of low-coordinated Pt clusters,resulting in an achievement of a large number of Pt coordination unsaturated active site.The selective oxidation reaction of octanol also has obvious crystal face effect,and each catalyst has significant differences in both catalytic activity and selectivity.The low-coordination Pt clusters can not only effectively activate the hard-toactivate OH functional groups in the octanol molecule to improve the ability to deprotonate the hydroxyl groups of the long-chain alcohol molecules under the base-free condition,but also promote the activation and elimination of the ?-CH bond.The rate of each step in the selective oxidation of octanol is matched,thereby increasing the rate of selective oxidation of octanol.In addition,the coordinated unsaturated O2c-Ti5c-O2 sites on the support(001)crystal plane can make the aldehyde group highly dissociated in the form of bidentate adsorption,and the low-coordination Pt clusters can further activate the C-H bond in the aldehyde group,which promote the generation of geminal diol intermediate species to a higher selectivity of caprylic acid.Therefore,the coordination unsaturated structure of the support can not only promote the efficient activation of the intermediate product octanal in the form of bidentate adsorbed species,but also have the obvious interaction with the metal Pt atom to promote the change of the metal coordination.Therefore,the synergistic enhancement of the both the structure of supports and the supported acitive metals is achieved for the enhancement of selective oxidation performance of octanol.(3)A two-step reduction deposition method was used to deposit different numbers of Pt atoms on the surface of Au nanoparticles.By directly adjusting the continuity of the metal Pt active sites of the catalyst and its coordination structure,the influence of the active metal Pt atoms with different continuity and the coordination structure on the adsorption and activation of reactant/intermediate molecule was further studied.It shows that the series of Au147Ptn bimetallic nanoparticles prepared by the two-step reduction deposition method are belong to quasi-random alloys with obvious core-shell structure.As the Pt atomic ratio gradually increases,the Pt atoms located in the outer layer gradually contact each other,and the continuity of the active sites gradually increases.In addition,there is a strong electron transfer from Au to Pt atoms,and Pt atoms located in the core are more likely to accept electrons to form Pt?species.The predominant active sites of each step in the glycerol selective oxidation reaction network are different.The continuous Pt sites increase the length of the ?-C-H bond,thereby promoting the activation of the C-H bond and subsequent dissociation and ?-H elimination.Pt?-species promote the activation of the ?-C-H bond on the aldehyde group,which is beneficial to the subsequent geminal glycol dehydration step,promoting the further oxidation of glyceraldehyde to glyceric acid.Further,by combining single metal Pt nanoparticles which has the continuous Pt sites and Au147Pt6 and Au147Pt12 quasi-random alloys which has a higher Pt?-species content on the same TiO2 support,,it promotes the further development of glyceraldehyde while maintaining high catalytic activity.And hence the the synergistic enhancement of the selective oxidation reaction of glycerol by the two active sites is achieved.Therefore,by studying the essential relationship between metal atoms with different continuity and the performance of the catalytic reaction,a variety of advantageous active sites can be selectively constructed according to the differences in the properties of each functional group.Hence,the synergistic activation of hydroxyl groups,aldehyde groups and their ?-C-H bonds can be achieved,resulting a efficient targeted transformation of glycerol molecules.