Metal oxide catalysts for green applications

Cobalt oxide compounds are effective in decomposing N2O. A series of supported cobalt oxide catalysts with different amounts of cobalt oxide were synthesized by incipient wetness impregnation of gamma-alumina and by coprecipitation with precursors of cerium oxide. Each of the series of alkali metals (lithium, sodium, potassium, rubidium, and cesium) were added to each of the catalysts of varying cobalt oxide content to examine the promotion effect of these metals. The catalysts were characterized by surface area analysis, temperature programmed reduction, X-ray Diffraction, and UV-visible spectroscopy. Catalytic activity was investigated for the decomposition of both NO and N 2O.;The ceria-supported catalysts were significantly more active than the alumina-supported ones. With the same amount of cobalt, the ceria-supported catalysts produced equal reaction rates at around 200 K lower temperatures than the alumina-supported catalysts. All catalysts showed good activity for direct N2O decomposition over a temperature range of 573 K to 973 K. At 873 K, the reaction rate for alumina supported catalysts had values depending on cobalt loading between 1.4 and 1.7 x 10-7 mol/(s gcatalyst), while at the same temperature for ceria supported catalysts the values are 3.3 x 10-7 mol/(s gcatalyst). None of the catalysts maintained activity with NO as reactant, presumably forming surface nitrates or nitrites stoichiometrically without any catalytic turnover. The best alumina supported catalysts contained no alkali. Small amounts (0.01-0.05 atom %) of potassium or rubidium decreased the rate of N2O decomposition.;The Water Gas Shift (WGS) project has as a goal to develop an integrated system to produce high purity hydrogen and generating CO2 at the purity required by its use in industry or needed for sequestration. As part of the present work, the production of an improved monolithic WGS catalyst that provides efficient conversion of CO and structural support for a stacked assembly of membranes was studied. This can be subdivided in two major parts: (1) The synthesis of more active catalysts having good compatibility with the monolithic support. The catalysts were prepared by adding alumina or ceria in the iron oxide based WGS catalyst; (2) The production and use of ceramic supports for the water gas shift catalysts; Alumina (Al2O 3) was added as a component of conventional High Temperature.;Addition of between 10 and 20 wt% alumina increased the catalyst activity and thermal stability, with approximately 15 wt% alumina addition being optimum as its reaction rate (normalized per mass) was 74% higher than the reference catalyst. The effect of alumina addition was greater than the surface area increase alone, which suggests that alumina increases the activity of the iron oxide domains, likely through an increase in reducibility, as shown by the TPR results.;A series of high temperature water gas shift catalysts containing iron, chromia, and copper oxides were prepared with small amounts of added ceria in the system Fe-Cr-Cu-Ce-O. The catalysts were prepared by coprecipitation and compared with a reference catalyst containing 88 wt% FeOx, 8 wt% Cr2O3, and 4 wt% CuO. Unlike the other catalysts studied, the catalysts containing more than 85 wt% ceria do not exhibit the typical logarithmic decay curve in rate with time under reaction conditions, but instead show a minimum followed by an increased rate. This behavior, in addition to observations of the catalyst morphology from the SEM images, suggests that iron oxide-chromia is deposited on the surface of ceria and the magnetite-ceria interface is important for catalyst performance.;Mullite porous ceramic disks were prepared by impregnation of foam rubber (to provide porosity) with a suspension containing kaolin and alumina and calcined at temperatures ranging between 1300 and 1400°C. The catalyst deposited on ceramic showed stability to oxygen and atmospheric humidity when exposed to air during handling between tests, losing only 17% of the activity it displayed at the end of the first test. A cordierite honeycomb type ceramic monolith was also impregnated. The monoliths are commercially available and provide better flow hydrodynamics for the reaction. (Abstract shortened by UMI.).