Kidambi Srividhya, Dai Jinhua, Li Jin, Bruening Merlin L
Department of Chemistry, Michigan Sate University, East Lansing, Michigan 48824, USA.
J Am Chem Soc. 2004 Mar 10;126(9):2658-9. doi: 10.1021/ja038804c.
Alternating adsorption of poly(acrylic acid) and a polyethylenimine-Pd(II) complex on alumina and subsequent reduction of Pd(II) by NaBH4 yield catalytic Pd nanoparticles embedded in multilayer polyelectrolyte films. The polyelectrolytes limit aggregation of the particles and impart catalytic selectivity in the hydrogenation of alpha-substituted unsaturated alcohols by restricting access to catalytic sites. Hydrogenation of allyl alcohol by encapsulated Pd(0) nanoparticles can occur as much as 24-fold faster than hydrogenation of 3-methyl-1-penten-3-ol. Additionally, the nanoparticle/polyelectrolyte system suppresses unwanted substrate isomerization, when compared to a commercial palladium catalyst. Selective diffusion through poly(acrylic acid)/polyethlyenimine membranes suggests that hydrogenation selectivities are due to different rates of diffusion to nanoparticle catalysts. First-order kinetics are also consistent with a diffusion-limited mechanism. Further exploitation of the versatility of polyelectrolyte films should increase selectivity in hydrogenation as well as other reactions.
聚丙烯酸和聚乙烯亚胺-Pd(II)络合物在氧化铝上交替吸附，随后用硼氢化钠还原Pd(II)，得到嵌入多层聚电解质膜中的催化钯纳米颗粒。聚电解质限制了颗粒的聚集，并通过限制对催化位点的可达性，在α-取代不饱和醇的氢化反应中赋予催化选择性。与3-甲基-1-戊烯-3-醇的氢化相比，被封装的Pd(0)纳米颗粒对烯丙醇的氢化速度快24倍。此外，与商业钯催化剂相比，纳米颗粒/聚电解质体系抑制了不需要的底物异构化。通过聚丙烯酸/聚乙烯亚胺膜的选择性扩散表明，氢化选择性是由于向纳米颗粒催化剂扩散的速率不同。一级动力学也与扩散限制机制一致。进一步利用聚电解质膜的多功能性应会提高氢化以及其他反应中的选择性。
