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Theses/Dissertations

Chemical engineering

1988

Articles 1 - 7 of 7

Full-Text Articles in Engineering

Modeling Alloy Catalyst Surfaces And Bimetallic Catalyst Particles , John Kenneth Strohl Jan 1988

Modeling Alloy Catalyst Surfaces And Bimetallic Catalyst Particles , John Kenneth Strohl

Retrospective Theses and Dissertations

Alloy and bimetallic catalyst surfaces have been modelled using two different techniques. Surfaces of a planar, semi-infinite nature have been modelled using a classical thermodynamic approach while surfaces of small (<100 A) bimetallic catalyst particles have been modelled using the Monte Carlo simulation technique;The multilayer surface segregation model which was developed to predict compositions in the surface region of a material is capable of handling more than two components, systems which exhibit non-ideal solution behavior, and systems comprised of elements (or molecules) of differing sizes;This model was applied to the Ag-Au, Cu-Ni, and Au-Ni binary systems as well as the Cu-Ni-Pt ternary system. Silver was found to segregate to the outermost atomic layer in the Ag-Au binary and surface layers were found to be alternately enriched or depleted (relative to the bulk region) in silver. In the Cu-Ni binary, copper was found to segregate to the first atomic layer and decrease in concentration in a monotonic fashion until the bulk region was reached. Both regular solution and Margules solution models were used in this system with the Margules model giving slightly better agreement with experimental data. Gold was found to segregate to the surface in the Au-Ni binary. Greater segregation of gold was predicted when the size difference between the elements was accounted for. In the Cu-Ni-Pt ternary system, copper was found to segregate to the surface causing a relative depletion of both nickel and platinum in the outermost atomic layer;The Monte Carlo simulation technique was used with the surface modified pair potential model in order to study bimetallic catalyst particles with dispersions on the order of 30 to 60%. Systems modelled were the Pt-Ib (Ib = Cu, Ag, Au), Ag-Ru, and Pt-Rh bimetallics. In general, it was found that the Ib metals underwent surface segregation in the group VIII-Ib systems and also tended to occupy the low-coordinated sites on the crystal surface first. With the Pt-Rh bimetallic particles, platinum was found to undergo net surface segregation, although in contrast to the behavior observed in the group VIII-Ib systems, the metal which was segregated was found to be relatively depleted at the low-coordinated corner and edge sites of the crystallite.


The Kinetics Of The Reductive Decomposition Of Calcium Sulfate With Carbon Monoxide , Jae Seung Oh Jan 1988

The Kinetics Of The Reductive Decomposition Of Calcium Sulfate With Carbon Monoxide , Jae Seung Oh

Retrospective Theses and Dissertations

The kinetics for the reductive decomposition of calcium sulfate in the presence of carbon monoxide were investigated using thermogravimetric equipment under various conditions of temperature (1050-1200°C) and gas composition (0-7% carbon monoxide, 0-10% sulfur dioxide, and 10-50% carbon dioxide). Pellets reacted at selected conditions were withdrawn from the reaction system at various stages of the reaction and analyzed by X-ray powder diffraction, scanning electron microscopy with electron microprobe, and BET surface area analysis;In contrast to previous views of the reaction, the reductive decomposition of calcium sulfate was found to involve two separate reactions: (1) the reduction of calcium ...


Mechanistic Studies Of Protein Fractionation By Precipitation With Carboxymethyl Cellulose , Kathleen M. Clark Jan 1988

Mechanistic Studies Of Protein Fractionation By Precipitation With Carboxymethyl Cellulose , Kathleen M. Clark

Retrospective Theses and Dissertations

The effects of pH, ionic strength, and polymer dosage level and manner of addition on the fractionation of egg white proteins by precipitation with carboxymethyl cellulose was examined. Using model solutions of egg white proteins, the behavior was quantified through a mechanistic model that accounted for both solubility and aggregation phenomena;A two stage mechanism for the formation of the protein-polymer floc has been proposed, encompassing both formation of the insoluble complex, and aggregation of these complexes into larger particles. The dual role of the polyelectrolyte in the precipitation process, precipitant and flocculant, has been identified;Only proteins of net ...


Solute Clustering And Crystallization From Solution , Irwan Tjahjadi Rusli Jan 1988

Solute Clustering And Crystallization From Solution , Irwan Tjahjadi Rusli

Retrospective Theses and Dissertations

Three experimental studies, consisting of a laser Raman spectroscopic study, a vertical column experiment, and a microscopic observation, were carried out to evaluate the structures and characteristics of solute clustering in NaNO[subscript]3 solution systems and the relations between solute clustering and crystallization from solution;The results of these experimental studies suggest that solute clustering occurs in NaNO[subscript]3 solution systems. These solute clusters are apparently solvated clusters that have no solid-phase structure, and they may exist in saturated and supersaturated, as well as in undersaturated, solutions. The relative number of the solute clusters and the degree of ...


Characterization Of Substrate Binding And Catalytic Mechanisms Of An Endoxylanase, Amylosucrase, And Porcine Pancreatic Alpha-Amylase , Bernard Yi Tao Jan 1988

Characterization Of Substrate Binding And Catalytic Mechanisms Of An Endoxylanase, Amylosucrase, And Porcine Pancreatic Alpha-Amylase , Bernard Yi Tao

Retrospective Theses and Dissertations

The subsite affinity map of an endo-(1 → 4)-[beta]-xylanase produced by Aspergillus niger has been determined by using linear, [superscript]3H-reducing-end-labeled xylooligosaccharides ranging in length from xylotriose through xylooctaose. No evidence of multiple attack or of condensation and transxylosylation reactions was found. Bond cleavage frequencies were highest near the reducing end of short substrates, with the locus of highest frequencies moving towards the middle of larger substrates. This endoxylanase has five major subsites, with the catalytic site located between the third and fourth subsites, counting from the non-reducing end of the bound substrate. The subsite to the non-reducing ...


Infrared Reflection-Absorption Spectroscopy Of Thin Film Structures , Steven James Finke Jan 1988

Infrared Reflection-Absorption Spectroscopy Of Thin Film Structures , Steven James Finke

Retrospective Theses and Dissertations

Infrared reflection-absorption spectroscopy has been used extensively in the study of adsorbates and thin films on metal surfaces, but little work has been performed on semiconductor and metal oxide surfaces due to the lack of sensitivity of the technique on these surfaces;In this work, IRRAS has been used to investigate the optical properties of thin film structures consisting of an optically thin layer of the nonmetallic component on an optically thick reflecting metal film. The sensitivity of the technique has been investigated by the use of thin polymer films of various thickness spun on thin film structures and compared ...


Mutagenesis Of The Active Site Of Glucoamylase From Aspergillus Awamori , Michael R. Sierks Jan 1988

Mutagenesis Of The Active Site Of Glucoamylase From Aspergillus Awamori , Michael R. Sierks

Retrospective Theses and Dissertations

The Aspergillus awamori glucoamylase gene was modified by cassette mutagenesis, and eleven mutated enzymes were expressed by Saccharomyces cerevisiae;Four mutations were constructed to change the essential Trp 120 residue in subsite 4 to Tyr, Phe, His, and Leu. All the mutations bound maltose (G2) and isomaltose (iG2) more strongly than wild-type glucoamylase. A subsite map of the Tyr 120 mutation showed significantly higher affinities for D-glucosyl residues in subsites 1 and 2, suggesting an interaction of Trp 120 with residues located there;Three carboxylic acid residues in the active site, Asp 176, Glu 179, and Glu 180, were mutated ...