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991.
EPR, UV/Vis and FTIR spectroscopy as well as thermal analysis (TA/MS) were applied to study the influence of sulfate species present in the anatase support on the specific nature of VOx species in supported VOx/TiO2 catalysts. Those sulfate species modify the local structure of the supported vanadyl species and lead to the formation of two types of VO2+ sites instead of only one type being formed on sulfate‐free anatase. EPR and FTIR spectroscopic measurements revealed that a part of the VO2+ species are directly bound to the surface sulfate species. By TA/MS it was found that SO2 is released at lower temperature from VOx/TiO2 in comparison to the vanadium‐free support. The direct bonding between sulfate and VOx species stabilizes the latter on the surface of VOx/TiO2 resulting in three effects: 1) a higher V site dispersion in comparison to sulfate‐free TiO2, 2) a better resistance of surface vanadyls against diffusion into the bulk of the support and 3) a much faster reoxidation of reduced V sites than observed on sulfate‐free TiO2. 相似文献
992.
The chiral compounds (R)‐ and (S)‐1‐benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one ((R)‐ and (S)‐ 1 ), derived from (R)‐ and (S)‐asparagine, respectively, were used as convenient starting materials for the preparation of the enantiomerically pure α‐alkylated (alkyl=Me, Et, Bn) α,β‐diamino acids (R)‐ and (S)‐ 11 – 13 . The chiral lithium enolates of (R)‐ and (S)‐ 1 were first alkylated, and the resulting diasteroisomeric products 5 – 7 were aminated with ‘di(tert‐butyl) azodicarboxylate’ (DBAD), giving rise to the diastereoisomerically pure (≥98%) compounds 8 – 10 . The target compounds (R)‐ and (S)‐ 11 – 13 could then be obtained in good yields and high purities by a hydrolysis/hydrogenolysis/hydrolysis sequence. 相似文献
993.
The resolution of the diastereoisomers of norpristane, pristane, and phytane was studied as a function of the column internal diameter and/or the residence time of the compounds in the column. Increasing the residence time in the column by operating the column at a lower temperature program rate enhances the resolution more than reducing the internal diameter of the column. Practical experience with ultra narrow bore columns is also presented. 相似文献
994.
The
reaction of ilmenite titanium raw material with sulphuric acid was investigated
in ‘hazard’ type calorimetric system. The investigations show
the essential influence of initial temperature, particle size distribution
and concentration of sulphuric acid on rate and heat power of reaction and
determine the limits of safety of the process and also its efficiency. 相似文献
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