Kwang-Sup Song

Catalytic combustion of CH4 and CO on La1-xMxMnO3 perovskites

The activities of perovskites depend on compositions and preparation methods. Various perovskites, La1-xMxMnO3 (M=Ag, Sr, Ce, La), have been prepared by two different methods (co-precipitation and spray decomposition). The new preparation method, spray decomposition, produced perovskites of a high surface area of over 10 m(2)/g. The catalytic activities for CH4 and CO oxidation have been studied on a series of catalysts, La1-xMxMnO3. The perovskite-type oxide, La0.7Ag0.3MnO3, shows the highest catalytic activity: the complete conversion of CO and CH4 at 370 and 825 K, respectively

Preparation and characterization of Ag/MnOx/perovskite catalysts for CO oxidation

The spray decomposition method with lanthanum nitrate, manganese nitrate, silver nitrate and citric acid was used to synthesize Ag- and Mn-incorporated perovskites. The resulting samples were characterized by X-ray diffraction, BET adsorption measurement, X-ray photoelectron spectroscopy, and temperature-programmed oxygen desorption (O2-TPD) measurement. The obtained composite Ag/MnOx/perovskites catalysts exhibit higher activity by a few orders of magnitude at 338 K than that of LaMnO3. From the O2-TPD measurement, the high activity of the Ag/MnOx/perovskites may result from the increase of weak oxygen adsorption below 373 K.

The catalytic heat exchanger using catalytic fin tubes

Abstract The characteristics of a catalytic heat exchanger which integrates heat generation and heat exchange into one equipment have been investigated by the experiment and numerical simulation. The surface of the fin tubes was catalyzed by the formation of the oxide layer and the subsequent washcoating of ZrO2, followed by the impregnation of Pd catalyst. The experimental results showed that the performance of catalytic combustion in the catalytic heat exchanger was more significantly affected by the inlet velocity of the mixture than by its inlet temperature and equivalence ratio. It was also found that the catalytic surface area was a critical parameter to obtain the complete conversion of the mixture. Numerical simulation has been performed with a commercial software FLUENT. The calculated results indicated that the performance of the catalytic combustion was influenced by the catalytic fin configuration as well as the flow pattern of the mixture over the catalytic fins. The results recommend that the number and thickness of catalytic fins should be designed above 6 pieces/inch and less than 1.0 mm to achieve the best performance in the catalytic heat exchanger.

Studies of surface and gas reactions in a catalytically stabilized combustor

A numerical investigation of a catalytically stabilized thermal (CST) combustor was conducted for a multichannel catalyst bed, and both the catalyst bed and thermal combustor were simultaneously modeled. The numerical model handled the coupling of the surface and gas reaction in the catalyst bed as well as the gas reaction in the thermal combustor. The behavior of the catalyst bed was investigated at a variety of operating conditions, and location of the flame in the CST combustor was investigated via an analysis of the distribution of CO concentration. Through parametric analyses of the flame position, it was possible to derive a criterion to determine whether the flame is present in the catalyst bed or the thermal combustor for a given inlet condition. The results showed that the maximum inlet temperature at which the flame is located in the thermal combustor increased with increasing inlet velocity.

Characteristics of surface reaction and heat transfer in a catalytic heat exchanger

The characteristics of a catalytic heat exchanger which can integrate heat generation and heat exchange were numerically investigated. The catalytic heat exchanger was modeled in a three-dimensional, steady state and laminar flow system, including the surface reaction on catalytic fins. The surface reaction was modeled with one-step reaction incorporating the diffusion effect on the catalysts. The surface reaction on catalytic fins was significantly influenced by the heat transfer rate in fin tubes. In order to achieve both the complete conversion of the mixture and the efficient recovery of heat generated, the results suggest that the surface reaction should be completed in the first stage of the catalytic heat exchanger and the second stage should function only as a heat recovery. The effects of the catalytic fin configuration on the catalytic combustion performance were also investigated at a variety of operating conditions.

Development of a catalytic combustor with heat exchanger

Catalytic combustion is thought to be a considerable improvement on the traditional one under specific conditions. Due to its special features, catalytic combustion has two strong points compared to flame: no NOx emission and high reaction efficiency. However, the preheating process of catalytic combustion is an obstacle that deteriorates profitability in operation. So the HTHE (High Temperature Heat Exchanger) is adapted to the system to reinforce the preheating process, and we show that the catalytic combustion is maintained steadily without exceptional heat injection. As a result, the stability on the catalytic surface is the most important operational factor. To achieve it, both mixture gas property and temperature distribution should be controlled.

Catalytic Microchannels Stacked by Brazing Method

Abstract Each stack of microstructured stainless steel and aluminum plates was coated and brazed in vacuum. As a supporter of the catalyst, the coating layer was formed by the sol-gel method and anodizing, respectively. Though the number of brazed plates extended to one hundred, the thickness of the coating layer on the coated plate was relatively uniform, and the leakage of assembly was effectively minimized. The critical variables for brazing were both the thickness and shape of filler metal. Consequently, the brazing method had a good resolution for 200μ m, three-dimensional, multilayer structures. Through these results, coating to support catalysts in highly stacked layers by brazing can be applied to microcatalytic heat exchangers where the reaction and heat transfer occur simultaneously.

Micro Heat Exchanger for Gas Phase Reaction

Each microstructured stainless steel foil was brazed in vacuum for stacking. Inner surface of micro channels was coated with Al2 O3 layer to support Pt catalyst by sol-gel method. The stack was designed like a cross-flow type heat exchanger to perform the combination of exothermic and endothermic reactions simultaneously. It is expected to apply to the micro reformer which produces hydrogen for micro PEMFC (Proton Exchange Membrane Fuel Cell). As the first step in our study, we measured experimentally the heat transfer rate and the spatial temperature distribution of the stack. An then, the reaction of C3 H8 -air with heat transfer to cold air flow was performed in the stack. As a consequence, quantitative and qualitative thermal characteristics of the stack for reaction were investigated.Copyright

Catalytic Micro Channels Stacked by Brazing Method

Each stack of microstructured stainless steel and aluminum plates was coated and brazed in vacuum. As a supporter of catalyst, the coating layer was formed by solgel method and anodizing respectively. Though the number of brazed plates extended to a hundred, the thickness of coating layer on the respectively coated plate was relatively uniform and the leakage of assembly was effectively minimized. The critical variables for brazing were both thickness and shape of filler metal. Consequently, brazing method had good resolution for 200μm three dimensional multi layer structures. Through these results, coating to support catalysts in highly stacked layers by brazing can be applied to micro catalytic heat exchanger where the reaction and heat transfer occur simultaneously.Copyright