Control Preparation And Catalytic Performance Of Single Atom Palladium Metal Catalysts

Supported noble metal catalysts have high activity and selectivity,and are widely used in many important chemical processes.In order to increase the utilization efficiency,the researcher usually disperse precious metals in the form of nanoparticles on a carrier with a high specific surface area.Monoatomic catalysts can theoretically achieve about 100%utilization efficiency of metal atoms.Research on the preparation,characterization and performance of single-atom metal catalysts has become a hot topic of concern recently.However,highly dispersed monoatomic metals have very high surface energy and are thermodynamically unstable.Therefore,the establishment of stable monoatomic metal catalysts has become one of the most challenging and important goals in the field of catalysis.In this dissertation,LDH-like materials were used for the laminar characteristics.The ZnCr-LDH and NiFe-LDH NiFe-LDH as support materials were used as carrier materials respectively.The photodeposition reduction method was used to prepare single atom Pd with 0.1%loading.Catalyst materials,and characterized by a variety of characterization techniques,such as HRTEM,XPS,spherical aberration-corrected scanning transmission electron microscopy-high angle dark field(STEM-HAADF),characterized the morphology,structure,and valence of monoatomic Pd catalysts.The properties were compared with the prepared nanoparticle Pd catalyst contrast samples.At the same time,the preparation mechanism of monoatomic catalysts was speculated.Finally,the monoatomic Pd catalysts prepared fr-om ZnCr-LDH and NiFe-LDH were applied to the selective hydrogenation of phenylacetylene and the electrocatalytic oxidation of ethanol,respectively,and the catalytic performance of monoatomic Pd catalysts was investigated.The main research contents and results are as follows:(1)A single atom Pd catalyst material was prepared by photodeposition method using nitrate-zinc-chromium hydrotalcite ZnCr-LDH intercalated as nitrate.After hydrogen reduction at 500 ?,there was no aggregation of single atom Pd.After photoreduction treatment with carbonate ions intercalated with ZnCr-LDH as carrier material,Pd was supported on the hydrotalcite support surface in the form of nanoparticles.(2)The single atom Pd catalyst material prepared from the ZnCr-LDH support was applied to the selective hydrogenation of phenylacetylene.It was found that the single atom Pd catalyst has significantly improved phenylacetylene conversion compared to the Pd nanoparticle catalyst.Rate and styrene selectivity,TOF value of Pd nanoparticle catalyst five times;After 500 degrees hydr-ogen reduction,the catalytic activity of single atom catalyst has significantly improved,TOF value of Pd nanoparticle catalyst 10 times.The single atom catalyst catalyzes the styrene selectivity to be higher than 90%.It is speculated that monoatomic catalysts reduce the formation of secondary surface hydrogen(?-PdH)in the reaction,inhibit the adsorption of styrene,avoid over-hydrogenation,and increase styrene selectivity.(3)At the same time,the single atom Pd catalyst material was prepared by photodeposition and reduction method using nickel iron hydrotalcite NiFe-LDH as carrier material.After 300-degree hydrogen reduction,Pd is still limited to a single atom in the nickel-iron alloy/nickel-iron composite oxide matrix.(4)The single atom Pd catalyst prepared from NiFe-LDH was used in the electrocatalytic oxidation of ethanol.It was found that the peak current density of the single atom catalyst was about 5 times that of the NiFe-LDH support.The electrocatalytic oxidation activity of the single atom Pd catalyst after 300 ? hydrogen reduction was significantly improved,and the peak current density was about 1.5 times that of the unreduced sample.