Date of Award

Summer 2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Henry Shaw

Second Advisor

Richard B. Trattner

Third Advisor

Robert Pfeffer

Fourth Advisor

Howard David Perlmutter

Fifth Advisor

Robert J. Farrauto

Abstract

The effects of sulfur poisoning on the oxidation activity of 1.5 % Pt/γ-Al2O3, Pt/TiO2, Pt/ZrO2, and Pt/SiO2, were investigated in this study. Each catalyst was poisoned with an H2S/air or SO2/air mixture at 400°C for 24 hours and a sulfur concentration of 200 ppm. The complete oxidation of mixtures of I % CO, methane, ethane, ethene, ethyne, propane, propene, and n-butane in air were measured over fresh and sulfurpoisoned catalysts.

Non-methane alkane oxidation activity was enhanced significantly after sulfur poisoning on all four catalysts. The temperatures at which 50 % conversion to CO2 was achieved (T50) ranged from 10 to 72°C lower for the sulfur-poisoned catalysts than the corresponding fresh catalyst samples. CO oxidation activity was severely deactivated on all four sulfur-poisoned catalysts and T50 values were 24-75°C higher than, the fresh catalyst T50's. Methane oxidation activity was moderately deactivated on all sulfurpoisoned catalysts with the exception Of Pt/SiO2, for which no effect was found. The effects of sulfur poisoning on alkene and alkyne oxidation activity were small on each catalyst sample.

Catalyst characterization studies, including H2 chemisorption, BET surface area, FTIR spectroscopy, and temperature-programmed reduction and desorption studies were conducted to determine the nature of sulfur interactions on the catalysts' surface and the mechanisms responsible for associated changes in observed catalyst activity. Alkane oxidation enhancement for Pt/γ-Al2O3, Pt/TiO2 , and Pt/ZrO2 was primarily associated with the formation of new active which facilitate the oxidation reaction. New active sites are formed due to the combination of sulfate formation on the catalyst support sulfur-induced Pt crystal growth, Enhanced alkane oxidation activity sulfur poisoned Pt/SiO2 was the result of Pt crystal growth and the formation of a small amount pore blocking Pt sites. Deactivation of CO and methane oxidation reactions was a result of active site inhibition due to sulfate formation.

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