| Hydrogenation of unsaturated hydrocarbons is one of the important processes in the modern petrochemical industry.The synthesis of polymers and fine chemicals,such as the production of polyolefins,requires the removal of traces of alkynes from the olefinic feedstock because the alkyne deactivates the olefin to polymerize the catalyst and reduce the degree of polymerization.For efficient polymerization,a high selectivity catalyst for reducing the alkyne content to the ppm level in the olefin feed is highly desirable.For the development and use of Pd metal catalysts,Lindlar catalysts have a high selectivity for hydrogenation due to their high content.Sex is the most widely used.When a Lindlar catalyst is used,the lead complex is used to inactivate the metal Pd moiety.One disadvantage of Lindlar catalysts is the need for toxic additives for selective hydrogenation resulting in hazardous waste generation.Modification of Pd-based catalysts and metal alloying with less toxicity are recent research trends in these years,and these modified catalysts have proven to be highly selective.Lactic acid is a recognized biobased platform molecule that is usually produced by fermentation.Propylene glycol is a valuable commodity chemical with many chemical applications in food and consumer products.If a suitable catalyst is found,converting lactic acid to hydroxyl groups produces 1,2-propanediol,which is an economically viable route.Although noble metals such as Pt,Pd and Ru have exhibited high hydrogenation activity as excellent catalysts,their high price and low natural abundance cannot satisfy the industry's increasing demand for it.In order to overcome this limitation,a strategy is to minimize the use of precious metals while maintaining the overall catalytic efficiency of noble metals and their high stability.Due to the recent development of sub-nanometer measurements and single-metal atomic catalyst research,highly efficient traces of precious metals are not Homogeneous catalysts may be feasible in practical applications.When the size of the metal catalyst is reduced,the ratio of surface atoms to total atoms is different from that of the bulk catalyst.The surface atoms of the nano-sized metal catalyst provide significant catalytic energy for many important reactions in an unsaturated coordination environment.Especially when the size of the metal catalyst is reduced to a single atom or sub-nanometer cluster,most of the metal atoms are exposed to the catalytic reaction.Single atom catalysts(SACs)are a kind of metal atom atom dispersed or anchored on the surface of the carrier,A new frontier for heterogeneous catalysis.As a single metal atom has a higher surface energy than the corresponding metal cluster nanoparticles,the atoms are highly mobile and tend to form a polymerization during the synthesis.Keeping the metal loaded at very low levels to minimize agglomeration is a common practice to solve the problem.Another strategy is to anchor a single atom to a support with a stronger metal support interaction.Due to the powerful Electronic Metal Support Interoperability(EMSI),their electronic structure can be significant and easily modified,which can further provide specific catalytic behavior.TiO2 acts as a support to provide an electron-to-load metal catalyst,which is well suited for altering the electronic structure in heterogeneous catalysis.In this paper,TiO2 was synthesized by nucleation and crystallization method.Compared with commercially available titanium dioxide,the surface of Ti02 synthesized by this method is rich in high concentration of oxygen defects and Ti3+ defects.The noble metal is anchored by the defect surface rich in the surface of the carrier,the dispersion degree of the precious metal is improved,and the atomic utilization rate of the precious metal is greatly improved.The precious metal and the carrier titanium dioxide undergo a strong SMSI effect at a certain reduction temperature,and the electrons of the carrier titanium dioxide are transferred to the metal to modify the electronic structure of the surface of the noble metal.(1)The noble metal Pd is supported on the TiO2 carrier synthesized by the nucleation and crystallizing isolation method by impregnation and hydrogen reduction.It can be obtained by Ti2p Ols XPS,EPR,PL characterization.The concentration of Ti3+ and oxygen defects on the surface of Ti02 synthesized by nucleation and crystallization is much larger than that of commercially available Tio2.Moreover,as the metal loading increases,the concentration of Ti3+and oxygen defects in the catalyst decreases in turn.It is indicated that the defect sites anchor the metal Pd atoms,and a structure of Pd?--Ov-Ti3+is formed on the surface of the carrier TiO2.The noble metal on the surface of the catalyst 0.2 wt%Pd/Ti02 was observed by STEM-HAADP characterization as a cluster of atoms,and the monoatomic Pd occupied a large proportion.The dispersion of Pd measured by CO pulse is as high as 70%.The synthesized catalyst is used for the selective hydrogenation reaction of phenylacetylene.Under the reaction conditions of room temperature and atmospheric pressure,the activity of the reaction reaches 99%and the selectivity to styrene reaches 99%.In the reaction,metal palladium and Ti3+ occur.Synergistically,the TOF value of the catalyst is much larger than reported in the literature.(2)A 0.5 wt%Ru/TiO2 catalyst was synthesized in the same manner as in the first system.The effect of hydrogenation of lactic acid on the 0.5 wt%Ru/TiO2 catalyst in the aqueous phase was evaluated.At 140?,4Mp pressure,its reactivity reached 80%and the selectivity to 1,2-PDO reached 72%.During the reaction,a small amount of by-products such as propionic acid and 1-propanol were produced.,2-propanol,ethanol.Compared with the literature,it has higher reactivity under the same reaction conditions.The characterization shows that the synthesized 0.5wt%Ru/TiO2 has higher dispersion,indicating the universality of the carrier. |
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