浸渍法制备尺寸均一可调的贵金属纳米团簇及其尺寸依赖的催化性质

Size-engineered noble metal nanoclusters synthesized by impregnation for size-dependent catalysis

贵金属纳米团簇作为原子和纳米颗粒的中间形态,表现出特殊的电子结构和优异的催化性能.目前,这类纳米团簇通常通过湿化学法合成,其表面常被配体所钝化,而通过浸渍法合成的贵金属纳米团簇通常表现出较宽的尺寸分布.本研究以钯为例,发展了基于浸渍法精准合成尺寸介于0.9和2.9 nm、无表面配体的贵金属纳米团簇的新范式.该方法关键在于采用二氧化硅纳米胶囊为纳米反应器并引入非贵金属竞争吸附离子,从而达到严格控制贵金属纳米团簇成核和生长的目的,因此具有操作便利、合成可放大及纳米团簇尺寸精准可调等优势.钯纳米团簇在醇氧化-Knoevenagel缩合连续反应中表现出显著的尺寸效应,其中1.3 nm的钯纳米团簇具有最优的催化活性.这一新颖的合成策略为贵金属纳米团簇型催化剂的开发提供了新思路,为实验室级高品质纳米团簇催化剂的规模应用提供了可行方案.

Noble metal nanoclusters,as a bridge between atoms and nanoparticles,show extraordinary catalytic activities because of their unique electronic structures.Such nanoclusters are usually synthesized by a wet chemical approach through unfavorable surface passivation by ligands and have not been obtained by an impregnation approach with satisfactory size uniformity.Herein,we report highly uniform ligand-free noble metal nanoclusters,such as Pd nanoclusters,synthesized each in a silica capsule by an impregnation strategy,with their size accurately engineerable in the range of 0.9–2.9 nm.The key is to ensure the impregnation synthesis with strict control over the nucleation and growth of noble metal nanoclusters by involving hollow silica nanoreactors and non-noble metal competitor ions,thereby showing unprecedented advantages of operational simplicity,scalability,and excellent size controllability.These Pd nanoclusters exhibit a strong size effect on catalysis exemplified by the alcohol oxidation-Knoevenagel condensation sequential reaction,with those of 1.3 nm exhibiting the highest catalytic activity.We believe this novel strategy opens new opportunities for rationally designing efficient noble metal nanocluster-type catalysts for a broad range of important reactions and bringing laboratory-quality nanoclusters into large-scale applications.