Yan-Fei Shen

Manganese Oxide Octahedral Molecular Sieves: Preparation, Characterization, and Applications

A thermally stable 3 x 3 octahedral molecular sieve corresponding to natural todorokite (OMS-1) has been synthesized by autoclaving layer-structure manganese oxides, which are prepared by reactions of MnO4- and Mn2+ under markedly alkaline conditions. The nature and thermal stability of products depend strongly on preparation parameters, such as the MnO4-/Mn2+ ratio, pH, aging, and autoclave conditions. The purest and the most thermally stable todorokite is obtained at a ratio of 0.30 to 0.40. Autoclave treatments at about 150� to 180�C for more than 2 days yield OMS-1, which is as thermally stable (500�C) as natural todorokite minerals. Adsorption data give a tunnel size of 6.9 angstroms and an increase of cyclohexane or carbon tetrachloride uptake with dehydration temperature up to 500�C. At 600�C, the tunnel structure collapses. Both Lewis and Br�nsted acid sites have been observed in OMS-1. Particular applications of these materials include adsorption, electrochemical sensors, and oxidation catalysis.

Oxidative Dehydrogenation Of Propane Over Supported-Vanadium Oxide Catalysts

Abstract Vanadium supported on SiO2, AI2O3, TiO2, MgO, La2O3, Sm2O3 and Bi2O3 as well as La, Sm and Bi orthovanadates have been studied for the oxidative dehydrogenation of propane. It has been found that V-O species in which the V is in octahedral and tetrahedral positions are active, the tetrahedral being less active and more selective. The higher the concentration of species VO2+, and species V2O5 the lower is the selectivity to propene. The acid-base/redox properties of the support and the metal, in the vanadates, controls the proportion of the different vanadium species formed.

Octahedral molecular sieves: preparation, characterization and applications

Synthesis and characterization of a thermally stable analogue of synthetic todorokite, octahedral molecular sieve (OMS-1), is reported.

The structure of new synthetic manganese oxide octahedral molecular sieves

Manganese K-edge X-ray absorption spectra are used to examine the average oxidation state and local structure of new synthetic manganese oxide photocatalysts, including the materials known as octahedral molecular sieves. The structures of these materials are compared to the natural minerals cryptomelane and todorokite.

Immobilization of alkaline phosphatase on protamine-intercalated bentonite

Abstract Two procedures have been attempted to immobilize alkaline phosphatase onto the surface of a bentolite-L clay. In Procedure I the enzyme and protamine are simultaneously added into a clay suspension. In this case alkaline phosphatase and protamine are co-adsorbed on the external surfaces and the edges of the clay sheets, and they can be desorbed by washing with buffer. In Procedure II protamine cations are first intercalated into a bentolite-L clay at pH 10.4 by ion-exchange, giving a protamine-pillared clay with a d spacing of 51 A and producing hydrophobic surfaces. Alkaline phosphatase, which is negatively charged at this pH, is then immobilized on both the interlamellar and external surfaces of the pillared clay via electrostatic and hydrophobic mechanisms, and cannot be removed from clay by washing with buffer. The amount of protamine for pretreating the clay is very important for activity retention of the immobilized enzyme. More protamine can attach more enzyme on the surface of the clay, however, too much protamine causes denaturation of the enzyme due to entrapment and uncoiling. The pH profile for the immobilized enzyme is similar to that of free enzyme, except for a little broader optimum pH region on the acidic side.

Temperature Program Desorption and Reduction Studies of Octahedral Molecular Sieves

Publisher Summary The reactivity of oxygen species in single or mixed transition metal oxides plays an important role in determining the catalytic performance of an oxide as a consequence of the Mars–van Krevelen redox mechanism. Manganese dioxides, such as octahedral molecular sieves (OMSs), are a family of promising compounds for studying relationships between solid and catalytic properties. The incorporation of additional transition metal(s) into OMS materials lends great variability for adjusting oxidative and reductive stoichiometry and, consequently, the valency states and Mn–O binding strengths. Three or more oxygen species can be discriminated in the tunnel structure of both doped OMS 1 and OMS 2 in view of the emerging temperature of peaks during temperature-programmed desorption (TPD) in He. The doping cations do not markedly affect the evolution of TPD peaks. The predominance of oxygen species related to the high-temperature (HT) region peaks in TPD suggests that they are mainly under the influence of Mn ions in the framework because of their relative interatomic distances from Mn and from doping cations.