There is economic incentive to operate the ethylbenzene dehydrogenation reaction at low steam/ ethylbenzene ratios. To develop catalysts capable of performing under these conditions, it is necessary to understand the mechanism whereby the concomitant activity loss occurs. A potentially important mechanism is the reduction of the iron oxide. Thermogravimetric analysis in conjunction with X-ray diffraction is used to characterize the reduction properties resulting from potassium addition to iron oxide. The impacts of potassium addition on the temperature required to initiate reduction with hydrogen and on the apparent activation energy of reduction are determined. Reducibility of the potassium/iron oxide system in the presence of other dehydrogenation catalyst promoters is also presented. There is economic incentive to operate the ethylbenzene dehydrogenation reaction at low steam/ ethylbenzene ratios. To develop catalysts capable of performing under these conditions, it is necessary to understand the mechanism whereby the concomitant activity loss occurs. A potentially important mechanism is the reduction of the iron oxide. Thermogravimetric analysis in conjunction with X-ray diffraction is used to characterize the reduction properties resulting from potassium addition to iron oxide. The impacts of potassium addition on the temperature required to initiate reduction with hydrogen and on the apparent activation energy of reduction are determined. Reducibility of the potassium/iron oxide system in the presence of other dehydrogenation catalyst promoters is also presented.

Potassium-promoted iron oxide catalysts are used in large volume for the commercial ethylbenzene dehydrogenation to styrene process. Short-term deactivation of these catalysts, which is addressed by operating in excess steam, is thought to be caused due to reactive site loss through coking and/or reduction. However, the relative importance of the two mechanisms is not known. Presented are results concerning the reduction behavior of potassium-promoted iron oxide materials in the absence of carbon. Thermogravimetric experiments and X-ray diffraction analysis were used to examine the reduction behavior of potassiumpromoted iron oxide materials. The reduction behavior was then compared with results from isothermal ethylbenzene dehydrogenation reactor studies under low steam-to-ethylbenzene operation. Potassium incorporation was found to stabilize the iron oxide against reduction apparently through the formation of KFeO 2. Chromium addition improved the reduction resistance, which gave good qualitative agreement with the dehydrogenation reaction studies. In contrast, vanadium incorporation led to more significant reduction as well as poor stability in the dehydrogenation reaction. Potassium-promoted iron oxide catalysts are used in large volume for the commercial ethylbenzene dehydrogenation to styrene process. Short-term deactivation of these catalysts, which is addressed by operating in excess steam, is thought to be caused due to reactive site loss through coking and/or reduction. However, the relative importance of the two mechanisms is not known. Presented are results concerning the reduction behavior of potassium-promoted iron oxide materials in the absence of carbon. Thermogravimetric experiments and X-ray diffraction analysis were used to examine the reduction behavior of potassium-promoted iron oxide materials. The reduction behavior was then compared with results from isothermal ethylbenzene dehydrogenation reactor studies under low steam-to-ethylbenzene operation. Potassium incorporation was found to stabilize the iron oxide against reduction apparently through the formation of KFeO 2 . Chromium addition improved the reduction resistance, which gave good qualitative agreement with the dehydrogenation reaction studies. In contrast, vanadium incorporation led to more significant reduction as well as poor stability in the dehydrogenation reaction.

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This is to certify that the master's thesis of Sipho Cyril Ndlela Has met the thesis requirements of Iowa State University Signatures have been redacted for privacy iiiTABLE OF CONTENTS ABSTRACT CHAPTER 1. GENERAL INTRODUCTION 1.1. Introduction 1.2. Project objectives 1.3. Literature review on short-term deactivation mechanisms 1.4. Plan for current project CHAPTER2.EXPERIMENTALPROCEDURE 2 .1. Materials 2.2. Characterization 2.3. Experimental MethodCHAPTER 3. RESULTS AND DISCUSSION 3.1. Background 3.2. Reduction of unpromoted iron oxide (Fe 2 0 3 ) 3.3. Reduction of Fe20 3 promoted with Cr, V and K 3.4. Reduction of K-Fe 2 0 3 in the presence of either Cr or V promoter 3.5. Reduction ofKFe0 2 in the presence of either Cr or V promoter 3.6. Development of the kinetic model 3.7. Analysis ofresults CHAPTER 4. GENERAL CONCLUSIONS 4.1. Conclusions 4.2. Recommendations for Future ResearchV