Synthesis of Azafluorenones using Zeolites.

A convenient method for the synthesis of various azafluorenones (2a-f & 4a-d) by cyclization of substituted arylpyridines (1a-f & 3a-d) using zeolites are described.     

Characterization of Extra-framework Cations in Zeolites. A temperature-programmed desorption (TPD) study

We have investigated the interaction of a few 5-ring organic compounds (cyclopentane, cyclopentene, furan, 2-methylfuran, 2,5-dihydrofuran and tetrahydrofuran) with alkali-metal cation-exchanged faujasites (LSX, X and Y types) by means of temperature-programmed desorption (TPD). The desorption behavior at higher temperatures of all probe molecules on the sodium ion containing faujasites with different Si/Al ratios reflects the higher cation content of zeolites with greater aluminum content. Only the desorption profiles of tetrahydrofuran and 2,5-dihydrofuran show, depending on the kind of cation, additional desorption features at higher temperatures. Using a regularization method, desorption energy distribution functions for furan and tetrahydrofuran were calculated. The calculated desorption energy distributions clearly illustrate the very different adsorption behavior of furan and tetrahydrofuran which leads to large differences in the binding energies between the corresponding adsorption complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of Sorption,Desorption, and Diffusion in Zeolites

Sorption and desorption in zeolites (molecular sieves) have to be considered as complex processes, involving simultaneous diffusion in zeolite crystals, mass transfer in the intercrystalline void of a pellet, and heat transfer between the zeolitic sorbent and its surroundings. The kinetics of sorption and desorption, respectively, of n-C₄H₁₀ in zeolite X and of CO₂ in zeolite A have been investigated: only the initial rates of uptake or release of the sorbet are controlled by mass transfer alone whereas ultimately they also depend on the rate of heat transfer from the sorbent to its surroundings or vice versa. Diffusivities of the sorbate in the zeolite crystals can be obtained from the kinetics of mass transfer, provided the resistance due to viscous or Knudsen flow between the crystals of the zeolitic sorbent can be eliminated. A sample consisting of a monolayer of single crystals had to be used for this purpose in the n-butane/zeolite X system; the intracrystalline diffusivity obtained in this way is not in conflict with data obtained by NMR spectroscopy. The intracrystalline diffusivities obtained in this way—taking into account the coupling of several processes during sorption — are higher than values reported in the literature.     

用XPS研究几种沸石的表面组成

本文用XPS研究Y、USY和ZSM-5沸石的表面组成,结果表明:沸石的表面组成(Al/Si)_s与其体相(Al/Si)_b原子比及其骨架Al在晶格中结合强弱有关。Y和载NiY沸石表面层缺Al,USY和ZSM-5沸石表面高度Al富集。在300-600℃加热载NiHY沸石,不伴有Al的移去,结果显示出沸石表面明显缺Al。     

Mesopores in USY Zeolites

Zeolites of type NaY synthesised by use of seed‐solution and zeolite X‐seeds to initialise the crystallisation were compared. A different homogeneity of the internal framework structure related to the Si/Al ratio was expected. Thus, the formation of closed bulk mesopores should be influenced during treatment of NH₄NaY modification for 7 hours at 450 °C and 600 °C, respectively, in the water steam of 1 bar. Occurrence of different mesopores was actually observed in obtained ultra‐stable USY zeolites using nitrogen adsorption. Whereas USY prepared by use of seed‐solution contains only open mesopores at the crystal surface, the X‐seed synthesised material contains open and closed mesopores at the surface and in the nuclei of samples, respectively.