摘要
本文继采用含硫配体(-SH,-SR)对高分子保护金属胶体的配位俘获之后,采用锚联在SiO_2表面的较含硫配体配位能力弱的P,N配体分别与聚乙烯吡咯烷酮(PVP)保护的胶体钯在室温下反应,在P/Pd大于3.5,N/Pd大于7时,可以实施对保护金属胶体的配位俘获,证实了配位俘获法是一种具有普遍意义的方法,经原子吸收光谱分析,溶液中残留的金属钯的量小于0.36 ppm(P/Pd=3.5)。经电子能谱证实,锚联膦胺配体与金属钯之间存在配位作用,这是实施保护胶体负载化的关键。透射电镜分析表明,在整个配位俘获的过程中,无论是在载体上或是在溶液中,胶体钯的颗粒大小与分布均保持不变。因此,配位俘获法是一种能控制多相催化剂中金属颗粒大小与分布的有效方法。由此合成的钯催化剂具有很高的催化活性,良好的选择性和稳定性,在对Cis,Cis-1,3-环辛二烯的选择性加氢中,其活性仅比均相的PVP-Pd胶体催化剂稍低,选择性达100％。在周转数达12,000次/个钯原子后,其催化活性仍保持不变,随着P/Pd比的增大,催化活性迅速下降。
Immobilization of poly (N-vinyl-2-pyrrolidone)-protected palladium colloids via coordination capture with phosphine-or amine- containing ligands anchored on silica gel can be achieved in molar ratio of P : Pd≥3. 5 or N : Pd≥7 respectively, resulting in well dispersed metallic catalysts. This demonstrates that the coordination capture is a universal method for catalyst preparation by immobilization of polymer-protected metal colloids with anchored ligands. AAS determination reveals that the remaining palladium content in solution after immobilization is less than 0. 36 ppm at P/Pd= 3. 5. XPS data illustrate that a covalent bond exists between the colloidal metal particles and the phosphorus atoms of the ligands, this is a prime driving force promoting the occurrence of coordination capture. TEM observations exhibit that no aggregation takes place during the immobilization, and the distribution and dimension of the palladium particle size remain constant no matter the colloidal Pd is in the solution or on the surface of the supports. Thus, this new method for catalyst preparation by immobilization of metal colloids affords an approach of controlling or adjusting the size of metal particles within 1-10 nm. The catalysts prepared by this method show excellent activity, selectivity as well as stability. For the partial hydrogenation of cis, cis-1, 3-cyclooctadiene, the immobilized catalyst has an activity only slightly less than that of the homogeneous PVP-Pd colloid catalyst. The selectivity of cyclooctene is -100% , and the activity keeps constant until reaching the total turnover numbers of 12,000 cycle/Pd atom.
出处
《分子催化》
EI
CAS
CSCD
1992年第1期8-14,共7页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金资助项目
北京中关村地区联合分析测试中心资助
关键词
胶体金属
配位俘获
Immobilization of polymer-protected metal colloids, Coordination capture, Selective catalytic hydrogenation
