Surface Coordination Chemistry And Catalytic Properties Of Atomically Dispersed Metal Catalysts

The atomic scale coordination structure and the electronic state of the active sites play crucial roles in heterogeneous catalysis.As a bridge between the homogeneous and heterogeneous catalysts,the atomically dispersed metal catalysts have been extensively explored in the recent decade.The relatively "homogeneous" active center and high metal usage make them superior to conventional metal particles.Besides,the atomically dispersed metal catalysts also provide ideal platforms to study the relationship between coordinative structure and catalytic performance at the atomic scale.Chapter 1,we summarize kinds of "effect" that affect the catalytic performance in the view of surface coordinative chemistry and discuss their relationship with the atomic scale catalysis mechanism.Chapter 2,we reveal that the highly active atomically dispersed Ru on ?-Al2O3 is stabilized from sintering during the catalytic hydrogenation carried out at high pressure and high temperature.Theoretical calculations and experimental evidence demonstrate that the Columbic interaction between the alkali ions and hydrogen species facilitates the heterolytic activation of H2 but inhibits the reduction and aggregation of Ru.By contrast,without the assistance of alkali ions,metallic Ru nanoparticles and oxygen vacancies are formed following dehydration of surface(hydr)oxygen species and the reduction of Ru during catalytic hydrogenation.In catalytic hydrogenation,with the involved ionic resonance,inverse equilibrium isotopic effect(iEIE)accompanying with low reaction barriers are revealed over the alkali ions promoted atomically dispersed Ru(?)catalysts.By contrast,normal kinetic isotopic effect(KIE)and high reaction barrier are observed over the metallic Ru.In addition,the alkali ions stabilized atomically dispersed Ru catalysts exhibit outstanding performance in catalytic hydrogenation of many unsaturated substrates as compared with the supported Ru nanoparticles.Chapter 3,The direct allylic alkylation of nucleophiles using allylic alcohols is realized by supported atomically dispersed Pdi/TiO2-EG under the mild neutral condition without using any additives.The distinct performance is attributed to the hydrogen-bonding assisted removing of-OH at the organic-inorganic interface.Chapter 4,As reveal by both DFT calculations and experiments in this chapter,coordinative unsaturated ultra-small Pd clusters display sluggish activity for hydrogenation due to the strong binding of hydrogen and catalytic intermediate thereon.However,when electron-withdrawing molecules,such as CO,are introduced to tune the electronic structure of Pd clusters,their hydrogenation activity is significantly boosted.Experimentally,supported Pd2CO catalysts are fabricated by depositing pre-established[Pd2(?-CO)2Cl4]2-clusters on oxides and demonstrated as an outstanding catalyst for the hydrogenation due to the presence of CO.Chapter 5,By means of oprando X-ray adsorption study,we find that the TiO2 supported Pd catalysts can dynamically evolve from supported Pd nanocluster to atomically dispersed Pd with the presence of chlorine ions at room temperature under different atmosphere.It is revealed that chlorine ions bind to the cation of oxide under reductive atomosphere,and bind to Pd under oxidative atomosphere.When the binding energy of Cl-on oxide cation is smaller than the binding energy of oxgene on oxide cation,the redispersion of Pd becomes thermodynamically favorable.