Study On The Structure-property Relationship Of Carbon Supported Ruthenium Based Catalysts In Ketones' Carbonyl Hydrogenation

Hydrogenation of the carbonyl group is one of the most useful and widely applicable reaction routes and important initial step for organic synthesis.Thus to design and develop an efficient catalyst used in carbonyl hydrogenaiton has the great practical potentiality.Moreover,revealing the structure-property relationship of the heterogeneous catalyst used in carbonyl hydrogenation is of great theoretical significance,such relationship between the catalysts' structure and its catalytic properties can provide the very important basic theoretical guidance to the rational designation of the efficient catalyst used in many other carbonyl compounds' hydrogenation.Herein,using ketones hydrogenation as the probe reactions?i.e.acetone hydrogenation to isopropanol,3-pentanone hydrogenation to 3-pentanol,4-heptanone hydrogenation to 4-heptanol?,carbon supported Ruthenium based catalysts were chosen as the main catalysis research object for hydrogenation of the carbonyl group.The catalytic performance of carbonyl hydrogenation can be controlly adjusted and well optimized through the construction of the multiple surface/interface active sites in catalyst and the fabrication of structural transformation per active sites.This study mainly focused on revealing the structure-property relationship of the catalysts used in carbonyl hydrogenation,which could provide the fundamental understanding for the heterogeneous catalytic hydrogenation of carbonyl group and could assist the rational design of the catalyst used in the hydrogenation of many other carbonyl compounds.The main research results are as follows:1.Carbon black supported ruthenium catalysts?Ru/C?with different Ru particle sizes and varying fractions of surficial RuO₂ are prepared and studied for acetone hydrogenation.The size of Ru particles and the surficial RuO₂ species on the Ru particles are found to affect the acetone conversion.We found a significant size effect of Ru metal particle on ketones hydrogenation whose TOF increases monodirectionally as the Ru particle size increases.This structure sensitivity is because that the relatively large metal particle has less proportion of highly unsaturated surface sites,which results in relatively weak interaction between the reactants and metal surface and more balanced coverage between the two reactants on metal surface,and thus facile ketones catalytic hydrogenation.Moreover,we also found that the synergetic effect between Ru02 and metallic Ru could be either positive or negative on the catalytic hydrogenation,depending on the size of the Ru nanoparticles.RuO₂ has the capability for the carbonyl activation,metallic Ru has the capability for the hydrogen dissociation,theoretically their synergy for the different adsorbates activation in catalysis is beneficial to the activity enhancement of acetone hydrogenation.However,in this study,introduction of surface Ru02 on the relatively small Ru particles could enhance the catalytic activity whereas those on the relatively large Ru particles decrease the catalytic activity.Such a size-dependent synergetic effect on the catalytic hydrogenation originates from the relative coverages of the two reactants on the catalyst surface according to the Langmuir-Hinshelwood mechanism.The size-dependent synergetic effect?either positive or negative on the catalytic hydrogenation,depending on the size of the Ru particles?that was found in this study,to the best of our knowledge,is a new finding in heterogeneous catalysis.2.A series of Carbon black supported PtRu alloy catalysts were synthesized and their catalytic properties of carbonyl hydrogenation were studied.Remarkable efficient and highly selective acetone hydrogenation at room temperature has been achieved via heterogeneous catalytic process in the presence of carbon supported Pt-Ru nano-alloy particles.The surface composition can be adjusted by adding the different proportion of the respective precursor quantity of Pt and Ru in the synthesis.Both the activity and selectivity can be controllably regulated and well optimized by adjusting the atomic scale distribution of surface Pt and Ru sites,a proper ratio between Pt atom and Ru atom on the catalyst surface can bring the optimal activity and selectivity?1.5Pt1.5Ru/C?.Annealing treatment of the Pt-Ru nano-alloy catalyst were found to influence the catalytic performance significantly.Higher annealing temperature can bring the higher TOF due to the particle diameter increase,particles with larger size favor the selectivity to isopropanol due to the less highly unsaturated surface defect sites than smaller ones.Oxidation treatment can lead to the construction of new sites on the surface,the resultant electropositive atoms?oxidized metal species?on the NPs surface can act as electrophilic or lewis acid sites for the adsorption and activation of carbonyl and the metallic surface sites can produce the dissociative hydrogen species,such synergy facilitate the catalytic activity enhancement.Isopropyl ether generation is related to the Pt atoms located at the highly unsaturated defect sites and its proportion on the surface,which can be covered by oxidized metal species though surface oxidation treatment and bring the resultant catalytic selectivity?isopropanol?increase.The samples annealed in N2 demonstrated most superior catalytic performance is related to the intimate interfacial contact between the metal particles and the carbon support,the resultant interfacial active sites could act as electrophilic sites in carbonyl activation.All the types of reactive sites in catalyst were finally summarized and discussed?Three types of active sits were existed in the PtRu/C samples.Type ?:surface metallic alloy sites.Type ?:surface metal oxide sites.Type ?:metal-carbon interface sites?.The remarkable catalytic performance of the samples annealed in N2 shown in this study is due to the significant trans-regional multiple synergetic behavior between the NPs surface region and the metal-carbon interface region,indicating the positive effect and the necessity of surface/interface multiple sites construction on the catalytic activity enhancement.Our study provides fundamental understanding for the heterogeneous catalytic hydrogenation of ketones and could assist the rational design of the catalyst used in the hydrogenation of carbonyl compounds including the esters,carboxylic acid,aldehydes,and etc.