HOMO- AND COPOLYMERIZATION OF ETHYLENE CATALYZED BY ANSA-METALLOCENES WITH DOUBLY HETERO-BRIDGES

Three ansa-metallocenes(Me_2C)(Me_2Si)Cp_2TiCl_2(1),[(CH_2)_5C](Me_2Si)Cp_2TiCl_2 (2)and (Me_2C)(Me_2Si)Cp_2ZrCl_2 (3)with larger dihedral angles and longer distance from metal to the center of Cp planes were synthesized and used as catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO).In the case of ethylene polymerization,compared the feature structures of unbridged metallocenes, singly bridged metallocenes and doubly bridged metallocenes 1,2,3,there exhibit the relationship bet...

Direct imaging and mechanism study of C_(6)α-olefin adsorption on faujasite and Linde Type A zeolites

Linearα-olefins are important chemical raw materials.To purifyα-olefins from a high-temperature Fischer–Tropsch synthetic oil,it is necessary to separate theα-olefins from the paraffins,which is challenging.Adsorption separation by zeolites is a promising alternative to energy-intensive distillation forα-olefin/paraffin separation.An integrated differential phase-contrast scanning transmission electron microscopy(iDPC-STEM)technique is used in combination with density functional theory(DFT)simulations and batch adsorption experiments to study the adsorption behavior of C_(6)α-olefins and the mechanism of selective adsorption of C_(6)α-olefin/paraffin.Direct electron microscopy real-space imaging of the atomic frameworks of the faujasite(FAU)and Linde Type A(LTA)zeolites and the C_(6)α-olefin-adsorption positions on their lattices is achieved through iDPC-STEM.The images provide direct evidence that C_(6)α-olefins preferentially adsorb at the edges of the FAU and LTA zeolite cavities.DFT calculations further reveal the relationship between host–guest interactions and different molecular orientations.Calculated and experimental results also show that the presence of calcium cations can enhance the selectivity of zeolites forα-olefin/paraffin adsorption.This work provides a means to investigate the behavior of guest molecules and the host–guest interactions in the adsorption or catalytic process of nanoporous materials.

Solid catalysts for the dehydrogenation of long-chain alkanes:lessons from the dehydrogenation of light alkanes and homogeneous molecular catalysis

Long-chain alkanes are abundant feedstocks supplied by natural resources and chemical industry. Specially, normal long-chain alkanes are primary products from Fischer-Tropsch synthesis(FTS) process, which is an important route for the utilization of coal in China. Facing a shift of energy nexus towards sustainable society, the conversion of long-chain alkanes derived from coal into value-added products(such as alkenes and oxygenates) is of great importance for securing China’s energy supply and the role transition of the commercial FTS plants from fuel makers to chemical suppliers. Among the potential transformation routes,the direct dehydrogenation of long-chain alkanes into alkenes is an attractive and practical route, due to the broad applications of long-chain alkenes(especially the linear α-olefins). In this review, we will summary the key insights obtained from the literature on the dehydrogenation of light alkanes based on supported metal catalysts and the dehydrogenation of alkanes with homogeneous molecular catalysts and then discuss how to translate these lessons into the development of efficient catalysts and processes for the dehydrogenation of long-chain alkanes into long-chain alkenes.