Steven G. Thoma

Vapor Phase Transport Synthesis of Zeolites from Sol-Gel Precursors

A study of zeolite crystallization from sol-gel precursors using the vapor phase transport synthesis method has been performed. Zeolites (ZSM-5, ZSM-48, Zeolite P, and Sodalite) were crystallized by contacting vapor phase organic or organic-water mixtures with dried sodium silicate and dried sodium alumino-silicate gels. For each precursor gel, a ternary phase system of vapor phase organic reactant molecules was explored. The vapor phase reactant mixtures ranged from pure ethylene diamene, triethylamine, or water, to an equimolar mixture of each. In addition, a series of gels with varied physical and chemical properties were crystallized using the same vapor phase solvent mixture for each gel. The precursor gels and the crystalline products were analyzed via Scanning Electron Microscopy, Electron Dispersive Spectroscopy, X-ray mapping, X-ray powder diffraction, nitrogen surface area, Fourier Transform Infrared Spectroscopy, and thermal analyses. The product phase and purity as a function of the solvent mixture, precursor gel structure, and precursor gel chemistry is discussed.

Vapor phase transport synthesis of un-supported ZSM-22 catalytic membranes

ZSM-22 has been synthesized from a dry amorphous gel via vapor phase transport crystallization, as bulk crystalline powder as well as an un-supported membrane. Crystalline products were characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, chemical analysis, and thermal analysis. Catalytic testing was performed to demonstrate the membranes ability to perform as an on-line catalyst. The ZSM-22 catalytic membrane showed 1-butene to isobutene conversions in excess of 60% with selectivites close to 40%, which compares well with conventionally synthesized bulk crystals.

Two ammonium templated gallophosphates: synthesis and structure determination from powder diffraction data of 2D and 3D-GAPON

Abstract Two new ammonium templated gallophosphates have been synthesized solvothermally using mixtures of ethylene glycol and water as solvent. The structure of both phases was determined from X-ray powder diffraction data. [Ga(PO 4 )(OH)] − ·[NH 4 ] + (2D-GAPON) crystallizes in monoclinic symmetry, space-group P2 1 / m with cell parameters a =8.564(1) A, b =6.0387(8) A, c =4.4883(6) A, β =98.05(1)° and V =229.84(3) A 3 . Its two-dimensional structure consists of infinite anionic layers separated by ammonium cations. [Ga 2 (PO 4 ) 3 ] 3− ·3[NH 4 ] + (3D-GAPON) has monoclinic symmetry, space-group C2 / c , with unit cell dimensions a =13.462(2) A, b =10.301(1) A, c =8.992(1) A, β =111.28(1)° and V =1161.9(6) A 3 . Its three-dimensional structure contains constricted elliptical channels running along the c axis, which host the ammonium ions.

Oxidation Reactions of Ethane over Ba-Ce-O Based Perovskites

Abstract Ethane oxidation reactions were studied over pure and Ca-, Mg-, Sr-, La-, Nd-, and Y-substituted BaCeO 3 perovskites under oxygen limited conditions. Several of the materials, notably the Ca- and Y-substituted materials, show activity for complete oxidation of the hydrocarbon to CO 2 at temperatures below 650°C. At higher temperatures, the oxidative dehydrogenation (ODH) to ethylene becomes significant. Conversions and ethylene yields are enhanced by the perovskites above the thermal reaction in our system in some cases. The perovskite structure is not retained in the high temperature reaction environment. Rather, a mixture of carbonates and oxides is formed. Loss of the perovskite structure correlates with a loss of activity and selectivity to ethylene.

Development of solid state light sources based on II-VI semiconductor quantum dots

Solid state light sources based on integrating commercial near-UV LED chips with encapsulated CdS quantum dots are demonstrated. Blue, blue-green, and white quantum dot LEDs were fabricated with luminous efficiencies of 9.8, 16.6, and 3.5 lm/W, respectively. These are the highest efficiencies reported for quantum dot LEDs. Quantum dots have advantages over conventional micron-sized phosphors for solid state lighting, such as strong absorption of near-UV to blue wavelengths, smaller Stokes shift, and a range of emission colors based on their size and surface chemistry. Alkylthiol-stabilized CdS quantum dots in tetrahydrofuran solvent with quantum yields (QYs) up to 70% were synthesized using room temperature metathesis reactions. A variety of emission colors and a white spectrum from monodisperse CdS quantum dots (D~2 nm) have been demonstrated. The white emission was obtained from the CdS quantum dots directly, by altering the surface chemistry. When incorporated into an epoxy, the high solution phase QY was preserved. In contrast to other approaches, the white LED contains monodisperse CdS quantum dots, rather than a blend of different-size blue, green, and red-emitting quantum dots. The concentration of CdS quantum dots in epoxy can be increased to absorb nearly all of the incident near-UV light of the LED.

A novel synthesis of zeolite W using organometallic precursors

Abstract Zeolite W has been synthesized hydrothermally using organometallic silicon and aluminum precursors both with and without an organocation. The reaction using the organocation yielded a fully crystalline, relatively uniform crystal size product, with no organic molecules occluded in the pores. In contrast, the product obtained from an identical reaction, except for the absence of the organocation reactant, contained amorphous as well as crystalline material and the crystalline phase showed a large diversity in both crystal size and morphology. The use of organometallic precursors, either with or without an organocation, allows for the crystallization of the MER framework at much lower OH/SiO 2 and (K+Na–Al)/Si ratios than is typical of inorganic systems. The reaction products were characterized by X-ray diffraction, scanning electron microscopy, electron dispersive spectroscopy, Fourier transform infrared, and thermal analyses.

Encapsulation of Nanoparticles for the Manufacture of Solid State Lighting Devices

Solid state lighting devices that utilize semiconducting nanoparticles (quantum dots) as the sole source of visible light emission have recently been fabricated. The quantum dots in these devices have been demonstrated to have quantum efficiencies similar to those of conventional phosphors. The dispersion and concentration of the nanoparticles within a suitable polymeric matrix was found to be critical to device performance. Yet achieving suitable concentrations and adequate dispersion implies chemical compatibility between the nanoparticles and the matrix, which must be achieved without detrimental effect on either the physical/optical properties of the matrix or the stability/surface state of the quantum dots. A number of encapsulation strategies have been identified and are discussed with regard to their effect on nanoparticle dispersion and concentration within silicone and epoxy matrices.

Systems Analysis and Futuristic Designs of Advanced Biofuel Factory Concepts

The U.S. is addicted to petroleum--a dependency that periodically shocks the economy, compromises national security, and adversely affects the environment. If liquid fuels remain the main energy source for U.S. transportation for the foreseeable future, the system solution is the production of new liquid fuels that can directly displace diesel and gasoline. This study focuses on advanced concepts for biofuel factory production, describing three design concepts: biopetroleum, biodiesel, and higher alcohols. A general schematic is illustrated for each concept with technical description and analysis for each factory design. Looking beyond current biofuel pursuits by industry, this study explores unconventional feedstocks (e.g., extremophiles), out-of-favor reaction processes (e.g., radiation-induced catalytic cracking), and production of new fuel sources traditionally deemed undesirable (e.g., fusel oils). These concepts lay the foundation and path for future basic science and applied engineering to displace petroleum as a transportation energy source for good.

Zirconium-Titanium Phosphate Acid Catalysts Synthesized by Sol Gel Techniques

Recently a large effort has been put into identifying solid acid materials, particularly sulfated zirconia and other sulfated metal oxides, that can be used to replace environmentally hazardous liquid acids in industrial processes. The authors are studying a group of mixed metal phosphates, some of which have also been sulfated, for their catalytic and morphological characteristics. Zirconium and titanium are the metals used in this study and the catalysts are synthesized from alkoxide starting materials with H{sub 3}PO{sub 4}, H{sub 2}O, and sometimes H{sub 2}SO{sub 4} as gelling agents. The measurement of acidity was achieved by using the isomerization of 2-methyl-2-pentene as a model reaction. The phosphate stabilized the mixed metal sulfates, preventing them from calcining to oxides boosting their initial catalytic activity. The addition of sulfate prevented the formation of the catalytically inactive mixed metal pyrophosphates when calcined at high temperatures (> 773 K).

SNL-1, a highly selective inorganic crystalline ion exchange material for Sr{sup 2+} in acidic solutions

A new inorganic ion exchange material, called SNL-1, has been prepared at Sandia National Laboratories. Developmental samples of SNL-1 have been determined to have high selectivity for the adsorption of Strontium from highly acidic solutions (1 M HNO{sub 3}). This paper presents results obtained for the material in batch ion exchange tests conducted at various solution pH values and in the presence of a number of competing cations. Results from a continuous flow column ion exchange experiment are also presented.