Catalytic Selective Aldehyde Hydrogenation And Oxidation Of Alcohol Over Highly Dispersed Platinum And Gold Nanoparticles

Noble metal catalysts are widely used in catalytic oxidation or hydrogenation of aldol for producing high value-added fine chemicals.The aggregation and deactivation of highly dispersed metal nanoparticles are the important factors that affect the economy.This work is devoted to prepare highly stable and well-dispersed noble metal catalysts and study its catalytic properties in the typical Redox reactions.By selecting spinel oxides as carriers which have similar lattice structure to Pt and Au,we prepared highly stable Pt/MgAl₂O₄ and Au/MgGa₂O₄ catalysts.Compared with the conventional catalysts,active components in these catalysts are not easy to fall off and aggregate because it can be stabilized in nano,sub-nano and single atomic scale due to the strong interaction with the carrier.In addition,MgAl₂O₄ and MgGa₂O₄ both have acid sites and basic sites and the acidity and basicity is adjustable at the same time,facilitating the selective adsorption of specific functional group on the substrate.We used multiple analytical techniques including XRD,BET,HAADF-STEM,ACTEM,ICP,NH3-TPD and CO2-TPD to characterize the composition,morphology,structure and the acidity and basisity of the catalysts.And we explored the structure-function relationship of the highly dispersed noble metal catalysts for selective hydrogenation of cinnamaldehyde,hydrogenation of benzaldehyde and oxidative dehydrogenation of ethanol which are typical probe reactions for production of high value-added fine chemicals.The main researches were as follows:?1?Pt single atoms in the Pt/MgAl₂O₄ have higher C=O double hydrogenation selectivity than Pt nanoparticles.We prepared MgAl₂O₄ supported Pt nanoparticles,amorphous aggregates and single atoms and evaluated their capability in the catalytic hydrogenation of benzaldehyde.By using N₂ adsorption,X-ray diffraction,aberration corrected transmission electron microscope,CO chemisorption and in-situ FTIR of chemisorbed CO,and inductively coupled plasma atomic emission spectroscopy,the Pt species were characterized as isolated or neighboring single atoms on MgAl₂O₄ support and Pt amorphous aggregates and then nano-crystallites with the increase of Pt loading.Pt single atoms on MgAl₂O₄ support are highly active for the selective catalytic hydrogenation of benzaldehyde to benzyl alcohol and the terrace atoms on Pt particles are more active but less selective presumably due to the ability of forming bridged carbonyl adsorbate.MgAl₂O₄ supported Pt single atom catalyst represents as a novel catalyst with high precious atom efficiency and excellent selectively catalytic hydrogenation ability.?2?Pt single atoms in the Pt/MgAl₂O₄ have higher catalytic performance on the selective oxidation of ethanol than Pt nanoparticles.Pt nanoparticles,Pt amorphous aggregation and Pt single atoms all showed similar product selectivity in the catalytic selective ethanol oxidation reaction.When the reaction temperature is below 100 oC,the selectivity to acetaldehyde can be up to 100%.The intrinsic catalytic activity of Pt single atoms?turnover frequency,TOF?is much higher than Pt nanoparticles in the Pt/MgAl₂O₄?100 oC,10.2 s-1 vs 7.2 s-1?.The apparent activation energy of Pt single atoms is slightly larger than that of Pt nanoparticles?26.1 vs.25.2 kJ/mol?,and the pre-exponential factor is also a little bit larger?lnA: 10.7 vs.10.1?.Since the Pt single-atom catalyst has higher Pt atom utilization?92.5% vs 53.2%?than Pt nano-catalyst,it has the potential to be developed as a commercial catalyst.?3?Au/MgGa₂O₄ is highly active on the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.The liquid-phase selective hydrogenation of cinnamaldehyde?CAL?to cinnamyl alcohol?COL?over gold nanoparticles?Au NPs?supported on a solid base of spinel?MgGa₂O₄?was investigated.The supported Au catalysts were prepared by a facile impregnation method and characterized by different analytical techniques like XRD,BET,STEM,ICP,NH3-TPD and CO2-TPD.The prepared Au/MgGa₂O₄ catalyst exhibited excellent catalytic performance for the selective hydrogenation of CAL with high conversion and selectivity of 93.6% and 81.6%,respectively.The influence of calcination temperature on the characteristics of the catalyst was systematically analyzed.The reaction conditions such as temperature,pressure,reaction time and type of the solvent were found to have profound effect on the performance of the chosen reaction.The role of acid-base properties of the support on catalytic activity was elucidated in addition to the characteristics of Au nanoparticles.