Chi-Lin O'Young

Studies of oxidative dehydrogenation of ethanol over manganese oxide octahedral molecular sieve catalysts

Abstract A series of manganese oxide octahedral molecular sieve (OMS) materials were prepared and characterized by X-ray diffraction and surface area measurements (Brunauer-Emmett-Teller). Some first row transition metals (Ni 2+ , Cu 2+ , Fe 3+ , Co 2+ , Mg 2+ ) were doped into the framework of these octahedral molecular sieve materials to give [M]-OMS materials. The catalytic activities of these materials were studied in the oxidative dehydrogenation of ethanol in a flow reactor at different temperatures and at various ratios of ethanol to O 2 . The influence of space velocity on the reaction was also tested. The experimental results showed that both the conversions and selectivities of this reaction over each individual OMS material are highly dependent on the nature of OMS materials and the transition metal dopants in their framework structures. The [Co]-OMS-1 materials show the highest conversion and selectivity to acetaldehyde of all materials. Basic sites on both OMS-1 and OMS-2 materials may be responsible for catalytically active sites in this reaction.

Sol–gel synthesis of cryptomelane, an octahedral molecular sieve

The sol–gel synthesis of an octahedral molecular sieve (OMS) having the cryptomelane (2 × 2) MnO6 tunnel structure (OMS-2) is reported.

C02 and NO chemisorptions on Moγ-Al2O3 catalysts

Abstract CO 2 and NO chemisorptions, FT-IR, and TGA techniques were used to study the surface structure of calcined and reduced Mo γ- Al 2 O 3 catalysts. The results clearly show that there are three distinct surface structures whose presence is dependent on the molybdenum loading. At low loadings, molybdenum interacts strongly with the alumina surface hydroxyl groups to form “strong Mo interaction species.” The molybdenum is highly dispersed, difficult to reduce, and has a low coordination number (C.N.). At medium loadings before the monolayer coverage, the MoOMo interaction increases and the Mo-support interaction may decrease to form “Mo interaction species.” Such formed molybdenum is well dispersed, reducible, and has a high C.N. The CO 2 uptake at the monolayer coverage is almost zero. Above the monolayer coverage, excess molybdenum aggregates to form bulk MoO 3 and Al 2 (MoO 4 ) 3 species at the expense of a small amount of well-dispersed molybdenum species to create some exposed alumina surface. The molybdenum formed under this condition is easily reduced, has a large particle size, and has a high C.N. The bulk MoO 3 species interacts with the support to form Al 2 (MoO 4 ) 3 at high calcination temperatures (⩾600 °C). All the molybdenum phases rearrange and agglomerate to create some free alumina and to decrease the molybdenum dispersion after H 2 reduction. The extent of rearrangement and agglomeration depends on the degree of reduction. At low loadings, only a small fraction of free alumina is recovered because of the low reducibility. A significant amount of free alumina is recovered at medium and high loadings due to the high reducibility.

Isomerization reactions of n-butenes over isomorphously substituted B/A1-ZSM-11 zeolites

Abstract Low levels of boron have been isomorphously substituted into pentasil zeolites and are active in butene isomerization reactions. The acidity of B/A1-ZSM-11 zeolites, measured by NH3 adsorption, is significantly lower than the acidity of B3+-free Al/ZSM-11 zeolites. These materials exhibit both Bronsted and Lewis acidities as determined by pyridine adsorption studies. Adsorption/desorption experiments with 1-C4H8 and i-C4H8 were studied to determine reactant and product shape selectivities. Complete isomorphous substitution of framework Al3+ by B3+ in ZSM-11 zeolites results in inactivity. Our data show that the reaction is first order in 1-C4H8 with slow deactivation via coke formation. The effect of flow rates on conversion, yields, selectivities, and product distributions has been studied on B/A1-ZSM-11 materials. Isobutene yields of 22% and selectivities of 47% have been obtained under optimal operating conditions using B/Al-ZSM-11 catalysts. Lower yields of i-C4H8 were obtained using Pt/B/Al-ZSM-11 zeolites with n-C4H10 as a feed gas. A temperature of 523°C was used in isomerization reactions while a temperature of 580°C was required in dehydrogenation/isomerization reactions. Propene is the major byproduct of this reaction, believed to form as a result of cracking of dimerized (and polymerized) olefins. This side reaction is the primary cause for deactivation and coke formation on the catalyst.

Micropore size distribution of octahedral molecular sieves (OMS)

Abstract Argon adsorption isotherms were used to study the micropore size distribution of manganese oxide octahedral molecular sieves, OMS-1 and OMS-2. Using the cylindrical pore model, this characterization tool provides accurate pore size information for OMS-1. However, this method is less accurate when measuring the smaller pore OMS-2. The argon adsorption isotherm measurement can be used to complement other standard characterization techniques to assess the quality of certain OMS products.

Skeletal Isomerization of n-Butenes on Zeolite Catalysts: Effects of Acidity

Abstract ZSM-5 and ZSM-11 zeolites with different contents of aluminum and boron have been synthesized to control their acidity. Results of catalytic studies suggest that there are synergistic effects between framework boron and aluminum to enhance skeletal isomerization activity. In the absence of boron, the competitive reactions like oligomerization, cracking, and H-transfer will dominate, which produce undesired products. In the absence of aluminum, the isomerization activity is low. Incorporation of boron into the framework of aluminum zeolites can reduce the acidity. Consequently, the isomerization activity increases, and the activity of oligomerization, cracking, and H-transfer reaction decrease to some extent. Alumina binder also has effects on boron zeolites because of the migration of aluminum into the framework.

Skeletal isomerization of n-butylenes to isobutylene on zeolites

The conversion of normal olefins such as n-butylenes can be converted to branched olefin species such as isobutylene by skeletal isomerization over zeolite-based catalysts having pore sizes of at least about 4.5 Angstroms and a pore structure characterized by intersecting 10-MR and 8 MR channels. The zeolite-based catalysts have sufficient acidity to catalyze the skeletal isomerization of normal olefins. The catalysts can be used to produce isoolefins for reaction with alcohols in integrated processes to produce alkyl tertiary alkyl ethers such as MTBE.

Synthesis of octahedral molecular sieves

A large number of families of manganese oxide octahedral molecular sieves (OMS) and their precursors, octahedral layered materials (OL), have been synthesized and characterized by various methods. The materials include OMS-1, OMS-2, and OL-1; they all use MnO6 octahedra as the basic structural unit to form (3X3) tunnels, (2X2) tunnels, and layered structures, respectively. Different metal cations can incorporate into the OMS and OL structures through framework, tunnel, and interlayer substitutions. These materials can be synthesized by the reflux, hydrothermal, precipitation, calcination, ion-exchange, isomorphous substitution, and sol-gel methods. The materials have been characterized in detailed by a variety of techniques to study the structure, composition, stability, and morphology. This paper will discuss and review the different methods used to synthesize OMS and OL materials and the resultant changes in physical and chemical properties.

Growth of large buserite crystals: precursors for octahedral molecular sieves

Large buserite crystals that are important in the generation of octahedral molecular sieves are prepared by crystal growth in gels.

CO2 and NO chemisorptions on Mo/γ-Al2O3 catalysts

Etude par spectrometrie infrarouge et par thermogravimetrie de la structure de la surface du catalyseur Mo/Al 2 O 3