Microfibrous Entrapped Catalysts for Low Temperature CO Oxidation in Humid Air
Type of Degreedissertation
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CO oxidation at ambient conditions poses a major challenge due to CO self-poisoning at low temperature as well as passivation of the catalyst in the presence of moisture. A highly active novel catalyst has been developed for CO oxidation at ambient conditions. The use of ceria as a promoter for supported noble metal catalysts was investigated. A ceria promoted catalyst was found to be highly active, yielding more than 99% conversion at low (<500 ppm) as well as high (>2500 ppm) CO concentrations. Further, the impact of the ceria deposition method and the type of catalyst support on catalytic activity was also studied. Activity measurements as well as O2 – H2 titration studies revealed that ceria deposition by incipient wetness impregnation resulted in close association of ceria and Pt which resulted in better activity of the catalyst. Pt – CeO2/SiO2 catalysts with Pt > 2.5% (w/w) and CeO2 > 15% (w/w) were found to be highly active (conversion ≥99%) and stable at 10-90% relative humidity (RH) at ambient temperature. The catalyst was further optimized experimentally by varying the catalyst preparation variables such as the type of silica support, the type of Pt precursor, and the drying and calcination conditions of Pt and ceria precursors. Further, the catalytic activity was correlated with surface characteristics using characterization techniques such as TPR, TEM, H2 and CO chemisorption and BET surface area, pore volume and pore size measurements. The Pt precursor with neutral metal ion species in solution resulted in a catalyst (TOF: 0.12 s-1) that was more than 10 times better active compared to a catalyst prepared with acidic Pt precursor (TOF: 0.01 s-1). Also, the drying and calcination conditions for both Pt and ceria precursors had a major impact on the dispersion and/or the distribution profile of metal (oxide) on the support. With the composition and preparation procedure for the preparation of the Pt-CeO2/SiO2 catalyst established, the catalysts entrapment in the nickel microfibrers was carried out. The microfibrous entrapped catalysts (MFEC) were highly active and outperformed the packed bed as well as diluted packed bed. MFEC’s unique structure with uniform voidage: (a) minimized axial dispersion; (b) reduced flow maldistributions and improved radial dispersion. Further, MFECs made of metal fibers (MF) showed many advantages: (a) improved heat conduction in the catalyst bed, due to micron sized MF matrix; (b) uniform temperature profile, minimized cold spots in the reactor bed. MFECs were highly active and more stable in comparison with packed bed. This experimental observation was also confirmed with a one dimensional pseudo-homogeneous reactor model that was solved by commercial software COMSOL®. The MFECs with their high activity and great stability could be used in various CO removal applications such as fire escape emergency face masks, advanced filtration units, and the like.