摘要
本文综述了过渡金属、过渡金属络合物和金属氧化物催化作用中结构化学问题研究的某些重要进展。内容包括过渡金属和过渡金属原子簇上化学吸附和催化作用的结构敏感性问题,过渡金属络合物催化的不对称合成的最新进展及其高对映体选择性的一般机理,和金属复氧化物催化剂体系中的相间结构匹配,以及低碳烃选择氧化中的基元步骤对催化剂晶面的选择性等。
In this article, some of the more important advances in the studies of structural-chemical problems in catalysis by transition metals, transition-metal complexes, and metal oxides are reviewed.Ⅰ . Structural Sensitivity in Chemisorption and Catalysis on Transition Metals and Clusters. A typical example of structurally sensitive types of metal-catalyzed reactions is ammonia synthesis over iron catalysts, for which the least densely packed a-Fe (111) surface is catalytically about two orders of magnitude more active than the most densely packed a-Fe (110) surface, and about one order of magnitude more active than the next most densely packed a-Fe (100) surface (Somorjai et al. , 1982) . C7 sites, Fe7-site, and probable modes of multinuclear coordination activation of N2, have been proposed by some investigators. Recently, Somorjai et al. found that a-Fe (211) surface is also very active, about 80% as active as the (111) surface, and the importance of C7 sites was again stressed. Interpretation based on multinuclear coordination activation of N2 mainly on Fe3 sites has also been proposed. However, electronic factor must also be considered. Results of approximate quan-tumchemical calculations by Zhou et al. indicate that densities of energy levels, as well as rf-levels alone , around the EF of α-Fe surfaces decrease in the following order: (111) > (100) > (110), and that at the (111) surface layer , the dxz and dYz, orbitals near the EF are most densely populated. In the case of chemisorption of such small molecules as N2 and H2 on transition-metal clusters (Fen, Nbn, Con) or cluster cations (e.g. , Nbn+, Con+), interesting seesaw variations of chemisorption rates with cluster sizes . n, for small clusters or cluster cations have been observed. Correlation With variations in ionization potentials of the clusters, or with variations in desorption energies has been suggested. Conceivably, the basic cause of these unusual variations may be found from a study of the vari ations in geometric and electronic structures o
