Synthesis Of Pd,Pt-Based Sub-Nano Catalysts And Their Performance On Organocatalysis

Compared with the traditional nanoparticle-based catalysts,sub-nano（single atoms and clusters）catalysts have the advantages of high atom utilization,unsaturated coordination environment,and unique electronic structure.All of these features of the sub-nano catalysts have attracted extensive scientific attention and have become a hot topic in the catalysis field.In this thesis,Pd clusters and Pt single atoms catalysts were prepared on two different oxide supports（yttrium oxide and bismuth molybdate）by 1)defect engineering strategy and strong metal support interaction strategy and 2)ion exchange strategy and wet chemistry strategy,respectively.Both catalysts have successfully applied to Heck coupling and alcohol oxidation reactions,respectively,and excellent catalytic efficacy was demonstrated.The main contents are listed as follows:（1）The defect engineering strategy was used to create abundant Y³⁺vacancies on the surface of Y₂O₃,which was favorable for stabilizing Pd species during the impregnation process to prepare palladium cluster catalyst（ICP=0.67 wt%）.The existence of Pd clusters was proved by high angle ring dark field scanning electron microscopy and extended X-ray absorption fine structure.The catalyst showed outstanding catalytic efficacy in the Heck coupling reaction of iodobenzene and methyl acrylate to yield methyl cinnamate(conversion:99%;selectivity:99%;TOF:2904 h^-1),along with strong substrate tolerance ability.This work provides experimental insights to fabricate metal cluster catalysts at the atomic scale with high catalytic performance.（2）An anion exchange method was used to prepare Bi₂MoO₆ nanosheets before platinum single atoms were deposited over Bi₂MoO₆ by wet impregnation.The existence of isolated platinum atoms was preliminarily confirmed by high-angle annular dark field scanning transmission electron microscopy.This catalyst can efficiently catalyze the oxidation reaction of cinnamyl alcohol to cinnamaldehyde under mild conditions（1 atm O₂,85℃）,with TOF up to 8337 h^-1 and both conversion and selectivity are higher than 99%.In addition,the catalytic activity of the catalyst remained almost unchanged after 8 cycles,suggesting its excellent stability.This work shed light on the preparation of efficient single atom catalysts for organic transformations.