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6023766 
Dissertation 
Partial oxidation reactions on supported silver monolith catalyst 
Wang, Z 
1996 
Ann Arbor 
University of Minnesota 
ProQuest Dissertations and Theses 
198 
English 
Oxidation reactions are usually fast and exothermic. Thus, control of mass and heat transport are crucial for achieving high selectivities to the useful intermediates. In this thesis, $\alpha$-Al$\rm\sb2O\sb3$ foam monolith, an alternative catalyst support which has shown superior transport properties than the traditional pellet support in other catalytic reactions, is tested compared with traditional pellet catalyst in a packed bed reactor in three oxidation reaction systems: (1) methanol oxidative dehydrogenation to formaldehyde; (2) ethylene direct partial oxidation to ethylene oxide; (3) propylene direct partial oxidation to propylene oxide. These reactions are closely related in that they all take place on silver at atmospheric pressure and relatively low temperature, they are all partial oxidations, and they all have a short contact time. The tortuous path in the monolith creates a turbulent and well-mixed flow in the pores which can greatly enhance mass and heat transport. The production of formaldehyde from methanol in the presence of air is examined over a Ag coated monolith and compared with the Ag needle catalyst currently used in industrial processes. The effects of feed composition and catalyst temperature on the product composition are discussed. The optimum selectivity to formaldehyde is about the same, 90% on both Ag catalysts. However methanol conversion observed at optimum selectivity is higher on Ag monolith, 75% in comparison with 60% on the Ag needle catalyst. In addition, these results were observed when the amount of Ag metal coated on Ag monolith is only 6.5 wt.% of silver metal in the Ag needle catalyst. No apparent surface poisoning is observed on either Ag catalysts. A preliminary surface reaction mechanism is developed to explain multiple steady-states and hysteresis in methanol oxidation. The direct oxidations of ethylene and propylene in the presence of air are also studied on both Ag coated monolith and pellet catalysts. Ethylene oxide selectivity is about 40% on both catalysts, and ethylene conversion is higher on pellets than on monolith. The yield of propylene oxide is much lower, $<$1% with a new Ag catalyst on both monolith and pellets. 
Applied sciences; Chemical engineering; 0542:Chemical engineering