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Dr. Mary Scott Railing
Assistant Professor
Email: mrailing@wju.edu
Phone: 1-304-243-2334

Undergraduate Research Projects

The current projects and faculty mentors are:

  1. Dr. Norman Duffy:  Inorganic Chemistry.
  2. Dr. Michael Baird:  Heterogeneous Catalysis.

    "Deactivation and Regeneration Studies of VOC Oxidation Catalysts"

A recent NSF award of $102,998 to purchase a Thermal Gravimetric Analyzer - FTIR system will fund these studies from Sept. 2003 through August 2006.  Details of each project follows:

Project I: Evaluation of Metal Inorganic Complexes as Precursors for Metal Sulfides for Use in Photovoltaic Cells

The search for more efficient photovoltaic material has led researchers to investigate thin films containing indium sulfides and gallium sulfides prepared via vacuum deposition of the film from precursor compounds. In 1997, Professor Duffy was initially funded by the West Virginia NASA Space Grant Consortium and in 1999 by the NASA Glenn Research Laboratories to examine various dithiocarbamate complexes of indium(III) and gallium(III) as potential precursors for sulfides for photovoltaic applications. Several complexes were prepared. A dibenzyl indium derivative was tested by NASA and found to be a potential candidate for additional testing at NASA. The project continues with modest funding ($3K/year) from NASA for supplies. The recent synthesis in our lab of tris(dibenzyldithiocarbamato)indium(III) and gallium(III) complexes and the subsequent testing using our GC/MS pyrolysis system led to the partial identification of the decomposition products. However, one drawback to the study was the trial and error method that had to be used for determining the decomposition temperature for the programmable chromatoprobe pyrolysis injector on the GC. Studies with the GC/MS indicated that the range of decomposition of the tris(dibenzyldithiocarbamato)indium(III) was 266-300ºC, which is difficult to reconcile with TGA data that showed considerable mass loss at 470ºC. Melting point observations indicated melting at ~203ºC, a color change at 267ºC and a measurable change in mass with darkening in the range 350-400ºC. These results are apparently contradictory and require further investigation. We propose to continue our preparations of In(III) and Ga(III) dithiocarbamates and to investigate their modes of decomposition. The objectives of this project are to:

  1. Prepare In(III) and Ga(III) monoalkyl-dithiocarbamates (derived from primary amines). These novel compounds may well decompose at a lower temperature.
  2. Determine the purity of these samples by H and 13 C NMR using our FT- NMR.
  3. Investigate the thermal decomposition of each of these samples using the TGA/FTIR system. 

The TGA will provide data for determining decomposition rates of the various fragmented species. Preliminary TGA data obtained on the type of instrument requested in this proposal are illustrated in the Supplementary Documentation Section on pages 5-7. The data provides wt% vs. temperature plots for two recently prepared indium dithiocarbamates. The additional 1st derivative data will allow for a more accurate interpretation of the decomposition processes. The organic fragments will be characterized  by the continuous monitoring of the product gases by FTIR. With potential group identification from the FTIR data and the mass spectra from the GC/MS analysis, identification of the decomposition products will be possible. The TGA data will also enable precise programming of the chromatoprobe attachment on the GC/MS. Addition of the TGA/FTIR system will provide more extensive results than ever before possible. Having the availability and use of a TGA/FTIR system will substantially improve our research capabilities on this project.

Project #2 - Deactivation and Regeneration Studies of VOC Oxidation Catalysts

An emerging area in heterogeneous catalysis is environmental cleanup of pollutant streams.  Catalytic processes are being developed to remove SO2 and NOx from stationary sources, for solid-waste reduction, and for VOC conversion. For the cleanup of polluted organic streams, typical catalysts used are platinum and palladium supported on alumina or silica-alumina1. A common problem in all organic catalytic oxidation reactions is catalyst deactivation resulting from carbon laydown. The deposition of carbon decreases the catalyst activity by either adsorbing on active sites or by blocking pores in the support and reducing the effective catalyst surface area.  If this coking process is relatively slow, catalyst regeneration can be used to restore catalyst activity.  Regeneration of coked catalysts is accomplished either by (1) reacting H2 with coke to form CH4 or (2) converting the coke to CO2 using air or air enriched in O2.  In order to optimize the VOC conversion processes, catalyst deactivation and the potential regeneration processes should be examined.

This project will investigate the deactivation and regeneration behavior of common commercial oxidation catalysts. The reaction rates, rate constants and activation energies will be determined for both the deactivation process from coke deposition and for the subsequent catalyst regeneration process based on air oxidation. The experimental data obtained from the TGA and FTIR measurements will be fit to a power rate-law kinetic reaction model.
The following catalysts and organic compounds will be investigated. Platinum and palladium supported on either alumina or silica-alumina will be purchased with similar metal loadings and similar surface areas. It has been shown that platinum is more active for the oxidation of paraffin hydrocarbons, while palladium is the favored metal for oxidation of carbon monoxide and for unsaturated hydrocarbons2. The Al2O3 and Al2O3-SiO2 supports are being utilized to investigate the effect of the support on deactivation and regeneration. To simulate possible organic pollutant streams, model compounds representing common organic pollutants, such as n-hexane, o-xylene and formaldehyde will be used.

Deactivation Studies: The oxidation reaction of each organic compound and each catalyst will be studied in the TGA/FTIR system as a function of reactant concentration and reaction temperature. A gas handling/manifold system will enable different concentrations of the reactant mixture to be fed to the TGA. Cylinders containing He, N2, air, O2 and each organic reactant will be used. Mass flow meters will allow the concentration of each gas in the reactant mixture to be varied. One-gram samples of each catalyst will be added to a perforated sample container in the TGA to insure optimum gas-solid contact. Catalyst deactivation will be indicated from the TGA data of weight gain as a function of time. Reactant and product gases (organic reactant, CO2 and H2O) will be continuously monitored by FTIR.  After the FTIR is calibrated with known concentrations of the organic reactants and CO2, an IR absorption band will be selected and the FTIR software will generate a Beer's Law plot. When monitoring product gases, selected IR bands will be utilized by the software to generate continuous plots of concentration vs. time.

The power-rate law kinetic model describing deactivation for a bimolecular catalytic reaction is:

Rate, -rA {molecules reacted/time, area}  = k CAnCBma

where k = e-E/RT, and k is the rate constant,

E is the activation energy, R the gas constant and T is temperature,

CA is the concentration of reactant A (organic compound),

CB is the concentration of reactant B (oxygen),

n and m are the observed reaction orders,

a is the catalytic activity term defined as the rate at any time/rate at t = 0.

Activity decline is defined as

- da/dt = k, f{CA, CA*}d

where CA* is the concentration of deposited coke and d is the reaction order.

The catalytic rate expression, -rA, can also be expressed based on reaction volume, V, or catalyst weight, W, as

-dCA/dt = 1/V(dNA/dt) = 1/W(dNA/dt)

where NA is moles of A or moles of the organic compound.

The concentration of O2, CB, will be used in excess in order to simplify the kinetics and to lump its term in the rate constant giving: -rA = k' CAna for the oxidation reaction.  Plots of reactant concentration  vs. time will be used to determine the reaction rate constants as a function of temperature. The slope from a plot of  ln k vs 1/T will give activation energies. These kinetic parameters will be determined for each catalyst and reactant compound. It is expected that metal support interactions and active metal will affect the kinetics. The concentration dependency of the organic reactant, n, on rate, will be determined from the slope of plots of ln rate vs. ln CA.

Regeneration Studies:  The regeneration kinetics will then be determined by reacting either air or oxygen-enriched air over the deactivated catalyst. Each catalyst will be deactivated in a stream of the organic reactant and the extent of carbon laydown determined from the TGA data. The deactivated catalysts will be tested for VOC oxidation at a base-line temperature where minimum additional deactivation occurs. The deactivated catalyst will then be regenerated in air. The total weight of carbon in the product CO2 will indicate the extent of regeneration. The activity recovery of each catalyst will be determined.

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