1,636 Matching Results

Search Results

Advanced search parameters have been applied.

Effect of Palladium Form on Tetraphenylborate Decomposition Rate

Description: Palladium catalyzes the decomposition of tetraphenylborate in alkaline solutions. Researchers postulate several decomposition mechanisms that differ in the form of the palladium catalyst. Potential forms include solid and soluble, different soluble species (such as aqueous or organic soluble), and different oxidation states (i.e., 0, II, and IV). Initial tests measured the reactivity and distribution of four Pd forms in tetraphenylborate slurries.
Date: April 28, 1998
Creator: Walker, D. D.
Partner: UNT Libraries Government Documents Department

Desulfurization of coal: Enhanced selectivity using phase transfer catalysts. Final technical report, September 1, 1995--August 31, 1996

Description: Due to environmental problems related to the combustion of high sulfur Illinois coal, there continues to be interest in the development of viable pre-combustion desulfurization processes. Recent studies by the authors have obtained very good sulfur removals but the reagents that are used are too expensive. Use of cheaper reagents leads to a loss of desired coal properties. This study investigated the application of phase transfer catalysts to the selective oxidation of sulfur in coal using air and oxygen as oxidants. The phase transfer catalyst was expected to function as a selectivity moderator by permitting the use of milder reaction conditions than otherwise necessary. This would enhance the sulfur selectivity and help retain the heating value of the coal. The use of certain coal combustion wastes for desulfurization, and the application of cerium (IV) catalyzed air oxidations for selective sulfur oxidation were also studied. If successful this project would have lead to the rapid development of a commercially viable desulfurization process. This would have significantly improved the marketability of Illinois coal. However, the phase transfer catalysts, the cerium and the scrubber sledge did not catalize the sulfur removal significantly.
Date: May 1, 1997
Creator: Palmer, S.R. & Hippo, E.J.
Partner: UNT Libraries Government Documents Department

Platinum Catalyzed Decomposition of Activated Carbon: 1. Initial Studies

Description: Carbon is an important support for heterogeneous catalysts, such as platinum supported on activated carbon (AC). An important property of these catalysts is that they decompose upon heating in air. Consequently, Pt/AC catalysts can be used in applications requiring rapid decomposition of a material, leaving little residue. This report describes the catalytic effects of platinum on carbon decomposition in an attempt to maximize decomposition rates. Catalysts were prepared by impregnating the AC with two different Pt precursors, Pt(NH{sub 3}){sub 4}(NO{sub 3}){sub 2} and H{sub 2}PtCl{sub 6}. Some catalysts were treated in flowing N{sub 2} or H{sub 2} at elevated temperatures to decompose the Pt precursor. The catalysts were analyzed for weight loss in air at temperatures ranging from 375 to 450 C, using thermogravimetric analysis (TGA). The following results were obtained: (1) Pt/AC decomposes much faster than pure carbon; (2) treatment of the as-prepared 1% Pt/AC samples in N{sub 2} or H{sub 2} enhances decomposition; (3) autocatalytic behavior is observed for 1% Pt/AC samples at temperatures {ge} 425 C; (4) oxygen is needed for decomposition to occur. Overall, the Pt/AC catalyst with the highest activity was impregnated with H{sub 2}PtCl{sub 6} dissolved in acetone, and then treated in H{sub 2}. However, further research and development should produce a more active Pt/AC material.
Date: December 1, 2001
Partner: UNT Libraries Government Documents Department

Evaluation of fine-particle size catalysts using bituminous and subbituminous coals

Description: The objectives of Sandia`s fine-particle size catalyst testing project are to evaluate and compare the activities of fine-particle size catalysts being developed in DOE/PETC`s Advanced Research Coal Liquefaction Program by using Sandia`s standard coal liquefaction test procedures. The first test procedure uses bituminous coal (DECS-17 Blind Canyon coal), phenanthrene as the reaction solvent, and a factorial experimental design that is used to evaluate catalysts over ranges of temperature, time, and catalyst loading. The best catalyst evaluated to date is West Virginia University`s iron catalyst that was impregnated onto the coal. Current work is aimed at developing a standard test procedure using subbituminous Wyodak coal. Ibis test is being developed using Pacific Northwest Laboratories` 6-line ferrihydrite catalyst and coal samples impregnated with either molybdenum or iron at Argonne National Laboratories. Results of testing catalysts with bituminous coal will be summarized and the development of the subbituminous coal test procedure will be presented.
Date: June 1, 1996
Creator: Stohl, F.V.; Diegert, K.V. & Goodnow, D.C.
Partner: UNT Libraries Government Documents Department

Task 4.7 - diesel fuel desulfurization. Semi-annual report, July 1, 1995--December 31, 1995

Description: Reductions in the maximum permissible sulfur content of diesel fuel to less than 0.05 wt% will require deep desulfurization to meet these standards. In some refineries, a new hydrogenation catalyst may be required for diesel fuel production. The work very briefly described in this document is on the use of hydrotalcite-supported molybdenum sulfide in the catalysis of ethanol. The catalyst reaction was highly selective for 1-butanol, providing a very clean reaction. Since the catalysis contains the MoS{sub 2} needed for the dehydrogenation and hydrogenation steps, the reaction can be performed at lower temperatures and higher selectivity. The catalyst was very stable and not destroyed by the water produced in the reaction.
Date: December 31, 1998
Creator: Olson, E.S.
Partner: UNT Libraries Government Documents Department

Technology development for iron fisher-tropsch catalysis

Description: The goal of the proposed work is the development of iron-based Fischer-Tropsch catalysts that combined high activity, selectivity and life with physical robustness for slurry phase reactors that will produce either low-alpha or high-alpha products. the catalyst that is developed will be suitable for testing at the Advanced Fuels Development Facility at LaPorte, Texas or similar sized plant. Previous work by the offeror has produced a catalyst formulation that is 1.5 times as active as the standard-catalyst developed by German workers for slurry phase synthesis, The proposed work will optimize the catalyst composition and pretreatment operation for this low-alpha catalyst. In parallel, work will be conducted to design a high-alpha iron catalyst that is suitable for slurry phase synthesis. Studies will be conducted to define the chemical phases present at various stages of the pretreatment and synthesis stages and to define the course of these changes. the oxidation/reduction cycles that are anticipated to occur in large, commercial reactors will be studies at the laboratory scale. Catalyst performance will be determined for catalysts synthesized in this program for activity, selectivity, and aging characteristics.
Date: July 15, 1997
Creator: Davis, B.H.
Partner: UNT Libraries Government Documents Department

Development of Vanadium Phosphaate Catalysts for Methanol Production by Selective Oxidation of Methane.

Description: This DOE sponsored study of methane partial oxidation was initiated at Amax Research and Development in Golden, CO in October of 1993. Shortly thereafter the management of Amax closed this R&D facility and the PI moved to the Colorado School of Mines. The project was begun again after contract transfer via a novation agreement. Experimental work began with testing of vandyl pyrophosphate (VPO), a well known alkane selective oxidation catalyst. It was found that VPO was not a selective catalyst for methane conversion yielding primarily CO. However, promotion of VPO with Fe, Cr, and other first row transition metals led to measurable yields for formaldehyde, as noted in the summary table. Catalyst characterization studies indicated that the role of promoters was to stabilize some of the vanadium in the V{sup 5+} oxidation state rather than the V{sup 4+} state formally expected for (VO){sub 2}P{sub 2}O{sub 7}.
Date: October 1, 1997
Creator: McCormick, R.L.
Partner: UNT Libraries Government Documents Department

Aerial oxidation of tetraethyl silicate and effect on ammonia catalyzed hydrolysis

Description: Colloidal suspensions of Si0{sub 2} in ethanol prepared by the ammonia catalyzed hydrolysis of tetraethyl silicate (TEOS) in ethanol have been routinely used for over 10 years to prepare antireflective (AR) coatings on the fused silica transmissive optical components of high power fusion lasers. Very high purity coatings are required to avoid laser damage and these are obtained when the TEOS is fractionally distilled under N{sub 2} prior to use. Recently we found that products from aerial oxidation of distilled TEOS, had a significant effect on the particle size of our coating suspensions to the detriment of the optical performance. We require particle sizes less than 20 nm to avoid light loss due to scatter and contaminated TEOS gave suspensions with much higher particle sizes. Oxidation products were identified by GC mass spectroscopy and included acetaldehyde, acetic acid, silicon acetates and reaction products of these compounds with ethanol. Acetic acid and silicon acetates were found to be the major cause of large particle formation. These could be removed by careful redistillation preferably in the presence of a small quantity of magnesium ethoxide. Storage in sealed containers over N{sub 2} avoided further problems.
Date: June 25, 1997
Creator: Thomas, I. M.
Partner: UNT Libraries Government Documents Department

Nano-scale materials

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Highly selective, alumina-supported molybdenum carbonitrides were prepared by solution impregnation using the metal amide Mo{sub 2}(N(CH{sub 3}){sub 2}){sub 6} as a molecular precursor. On the basis of relative weight percents, these materials demonstrate a 5- to 8-fold increase in catalytic activity over similar materials prepared by traditional solid-state approaches. The catalytic activities of these materials are very dependent upon the type of alumina support used. Impregnation of Mo{sub m}C{sub x}N{sub y} into preformed alumina pellets resulted in a material that specifically isomerized n-heptane into equal amounts of 2- and 3-methylhexanes, as well as iso-butane. No evidence of aromatic products was observed at operating temperatures below 420{degrees}C. The product selectivity of the isomers was 56% at a n-heptane conversion efficiency of 57%. Impregnating Mo{sub m}C{sub x}N{sub y} into an alumina powder resulted in an extremely selective aromatized and dehydrogenated material. The products from this material consist only of aromatics and n-heptenes with less than 2% isomerization or cracking products.
Date: December 31, 1998
Creator: Barrera, J.; Smith, D.C. & Devlin, D.J.
Partner: UNT Libraries Government Documents Department

Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

Description: Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, the author synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, they were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of the studies, he synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led them to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides. This report contains the Introduction; ``Chapter 6: Isomerization of Propargylic Alcohols to Enones and Enals Catalyzed by Methylrhenium Trioxide``; and Conclusions.
Date: May 10, 1999
Creator: Jacob, J.
Partner: UNT Libraries Government Documents Department

Cu(II) - Catalyzed Hydrazine Reduction of Ferrous Nitrate

Description: This report discusses the results of a study of catalyzed hydrazine reduction of ferrous nitrate. It is apparent that there is a substantial reaction between hydrazine and nitrate ion (or nitric acid) to produce HN3 during both the reduction of Fe(III) and during storage at room temperature.
Date: October 15, 2001
Creator: Karraker, D.G.
Partner: UNT Libraries Government Documents Department

Adsorption on nanosurfaces: A detailed look at metal clusters using infrared spectroscopy

Description: A technique known as infrared photodissociation spectroscopy is being used at Argonne to probe the intimate details of how molecules and atoms adsorb onto metal clusters. Clusters of transition metal atoms, produced by laser vaporization of a metal target, are allowed to react with small molecules, producing cluster complexes whose properties mimic those of the small metal-containing particles that make up many industrial catalysts. A powerful infrared laser is used to excite the characteristic vibrations of the atoms or molecules adsorbed on the surfaces of the clusters, causing the complexes to fragment. The resulting photodissociation spectrum is capable of revealing whether the adsorbed molecules have undergone a chemical reaction after sticking to the cluster surface. This techniques has been used to show that methyl alcohol molecules readily adsorb to the surfaces of small iron clusters, but do not undergo further reaction once they are there. This behavior is fundamentally different from that observed on macroscopic iron surfaces, where methyl alcohol readily reacts to form smaller fragment species. It is anticipated that these experiments will contribute to the understanding of particle size effects and their influence on reaction mechanisms and pathways in heterogeneous catalysis systems.
Date: August 1, 1997
Creator: Knickelbein, M.B.
Partner: UNT Libraries Government Documents Department

Gallium Zeolites for Light Paraffin Aromatization

Description: The primary original goal of this project was to investigate the active state of gallium-containing MFI catalysts for light paraffin aromatization, in particular the state of gallium in the active material. Our original hypothesis was that the most active and selective materials were those which contained gallium zeolitic cations, and that previously reported conditions for the activation of gallium-containing catalysts served to create these active centers. We believed that in high silica materials such as MFI, ion-exchange is most effectively accomplished with metals in their 1+ oxidation state, both because of the sparsity of the anionic ion-exchange sites associated with the zeolite, and because the large hydration shells associated with aqueous 3+ cations hinder transport. Metals such as Ga which commonly exist in higher oxidation states need to be reduced to promote ion-exchange and this is the reason that reduction of gallium-containing catalysts for light paraffin aromatization often yields a dramatic enhancement in catalytic activity. We have effectively combined reduction with ion-exchange and we term this combined process ''reductive solid-state ion-exchange''. Our hypothesis has largely been proven true, and a number of the papers we have published directly address this hypothesis.
Date: February 10, 1999
Creator: Price, G.L. & Dooley, K.M.
Partner: UNT Libraries Government Documents Department

Attrition Resistant Iron-Based Fischer-Tropsch Catalysts.

Description: The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO and H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. Iron-based (Fe) catalysts are preferred catalysts for F-T when using low CO/H{sub 2} ratio synthesis gases derived from modern coal gasifiers. This is because in addition to reasonable F-T activity, the F-T catalysts also possess high water gas shift (WGS) activity. However, a serious problem with the use of Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment, making the separation of catalyst from the oil/wax product very difficult if not impossible, and results in a steady loss of catalyst from the reactor. The objectives of this research are to develop a better understanding of the parameters affecting attrition resistance of Fe F-T catalysts suitable for use in SBCRs and to incorporate this understanding into the design of novel Fe catalysts having superior attrition resistance. Catalyst preparations will be based on the use of spray drying and will be scalable using commercially available equipment. The research will employ among other measurements, attrition testing and F-T synthesis, including long duration slurry reactor runs in order to ascertain the degree of success of the various preparations. The goal is to develop an Fe catalyst which can be used in a SBCR having only an internal filter for separation of the catalyst from the liquid product, without sacrificing F-T activity and selectivity.
Date: September 22, 1997
Creator: Jothimurugesan, K.; Goodwin, J.S.; Spivey, J.J. & Gangwal, S.K.
Partner: UNT Libraries Government Documents Department

Atomic structure of active sites in O{sub 2} reduction on Au(111)/Tl{sub ad} electrodes in acid and alkaline solutions

Description: Surface x-ray scattering has been used to determine the structure of Tl adlayers on the Au(111) electrode surface during the course of 0{sub 2} reduction. 0. reduction is considerably catalyzed by Ti adlayers on Au(111). The half-wave potential is shifted to more positive values in the presence of the Ti adlayer. In both, acid and alkaline solutions TI causes a change in the reaction mechanism from a 2-ereduction to a 4e-reduction in a limited potential range. The in-plane X-ray diffraction measurements revealed that the close-packed rotated-hexagonal Ti phase, which exists in the potential range between -0.4V and the bulk TI deposition at {approx}{minus} 0.7V, has a lower activity for 0. reduction than the low-coverage phases in both solutions. It supports a 2e-reduction.0{sub 2} reduction does not change the TI coverage in this phase but causes a significant decrease of the in-plane diffracted intensity. The lower coverage phases which exist at more positive potentials, viz., aligned hexagonal in alkaline solution and patches of the (2 {times} 2)TI phase in acid solution, are conducive to a 4e-reduction. The diffraction intensity from these two phases, however, vanishes quickly during O{sub 2} reduction. It appears that the TI coverage remains on the surface unchanged. These observations indicate that the O{sub 2} molecules interact directly with the Tl adatoms prior to the charge transfer. This provides the most direct evidence that the outer sphere charge transfer mechanism in 0{sub 2} reduction is not operative for some surfaces. H{sub 2}0{sub 2} reduction is facile on the surface covered with the low-coverage TI phases, while it is almost completely suppressed by the rotated-hexagonal phase.
Date: December 31, 1995
Creator: Adzic, R.R. & Wang, J.X.
Partner: UNT Libraries Government Documents Department

Surface Modified Coals for Enhanced Catalyst Dispersion and Liquefaction

Description: The aim of this study is to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants and catalysts on to the coal. During this reporting period, liquefaction experiments were conducted with the raw coal and catalyst loaded samples. Pretreatment of the coal and catalyst-loaded samples were done using the surfactants presented in previous reports. Liquefaction samples were tested using 6.6 g of solvent, 3.3 g coal, 6.9 MPa ambient hydrogen pressure, 425 0 C and 30 minutes. The liquid and solid products were removed from the reactor using tetrahydrofuran (THF). Coal conversions were calculated based on THF and heptane solubility. The results showed that in the absence of a catalyst, 33.8% heptane solubles was obtained with the parent coal compared to 27.8% and 27.3% with the SDS and DDAB surfactants. The presence of molybdenum, as expected, resulted in enhanced heptane solubles with or without surfactants. In the absence of surfactants, 50% heptane solubles was obtained compared to 40-47% with surfactants. Thus, it appears that pretreatment, unexpectedly, had a negative effect on liquefaction activity. It is unclear if the observed differences in results are significant. Clearly, additional experiments are needed before any firm deductions and conclusions can be drawn from the results.
Date: December 4, 1998
Creator: Yeboah, Yaw D.
Partner: UNT Libraries Government Documents Department

Novel catalysts for methane activation. Quarterly report No. 12, July 1, 1995--September 30, 1995

Description: Fullerenes are a recently discovered allotrope of carbon that possess unusual properties, some of which may be ideal for methane activation. This project is designed to evaluate these carbon-based materials for conversion of methane into higher hydrocarbons. The project is divided into three technical tasks. Task 1 deals with synthesis and characterization of the fullerenes and fullerene soots, Task 2 with testing of the catalysts, and Task 3 with evaluation of the results and technical reporting. Due to money constraints we have not done any technical work during this period. However, we hope to continue our work and produce a final report including recommendations for future research when funds are available.
Date: December 1, 1995
Creator: Hirschon, A.S.; Du, Y. & Wu, H.J.
Partner: UNT Libraries Government Documents Department

A computational study of ethane cracking in cluster models of zeolite H-ZSM-5.

Description: Protolytic cracking of ethane by zeolites has been studied using quantum-chemical techniques and a cluster model of the zeolite Broensted acid site. Previous computational studies have utilized small cluster models and have not accounted for the long-range effects of the zeolite lattice. These studies have found reaction barriers for cracking which are significantly higher than experimental values. In this work we used a larger zeolite cluster model containing five tetrahedral (Si, Al) atoms (denoted 5T) and searched for stationary points along one possible reaction path for cracking at the HF/6-31 G(d) level of theory. This path involves a multi-step cracking reaction, in which the proton is first transferred from the acid site to the adsorbed ethane molecule to form an ion-pair equilibrium complex. Subsequently the proton attacks the C-C bond to complete the cracking process. The activation barrier for cracking was calculated, including corrections for (i) vibrational energies at the experimental reaction temperature of 773 K; (ii) electron correlation and an extended basis set at the B3LYP/6-311+G(3df,2p) level; and (iii) the influence of the surrounding zeolite lattice in H-ZSM-5. The barrier we obtain, 53 {+-} 5 kcal/mol, is significantly smaller than previous theoretical results and is in good agreement with typical experimental values for small hydrocarbons. Work is currently in progress to extend this study by carrying out geometry optimization of these complexes using the B3LYP method of density functional theory.
Date: August 21, 1998
Creator: Zygmunt, S. A.
Partner: UNT Libraries Government Documents Department