Catalytic Incineration of CO and VOC Emissions over Supported Metal Oxide Catalysts
Abstract: Catalytic incineration is one of the methods to reduce the emissions of CO and VOCs. Low operation temperature and low catalyst cost are essential parameters for catalytic incinerators. Pt/Al2O3 catalysts are frequently used today, but the cheaper metal oxide catalysts can be very competitive if comparable overall activity is obtained. This thesis concerns how it is possible to decrease the operation temperature for supported metal oxide catalysts by using different supports, active metal oxides and additives. In the thesis it is demonstrated that different copper oxide based catalysts have the best activity and durability for complete oxidation among several tested metal oxide catalysts. CuOx supported on TiO2 and Al2O3 showed increased activity with the CuOx loading up to the threshold coverage for formation of crystalline CuO particles, which is 12 micromol/m2 on TiO2 and 6 micromol/m2 on Al2O3. Up to the threshold coverage for CuO formation, well dispersed copper oxide species were formed on TiO2, and a dispersed copper aluminate surface phase was formed on Al2O3. Durability tests showed accelerated sintering of TiO2 by copper, but stabilisation was possible by modification of the TiO2 with CeOx before the deposition of CuOx. The stabilisation was obtained by formation of a Ce-O-Ti surface phase. Addition of CeOx also enhanced the activity of the copper oxide species thanks to favourable interaction between the active copper oxide species and the CeOx on the support, which could be seen as increased reducibility in TPR experiments. The increased activity and reducibility was also observed for CuOx supported on ceria modified Al2O3. In this regard it was shown that CuOx deposited on CeO2(001) surfaces was substantially more active for CO oxidation than copper oxide deposited on CeO2(111) surfaces. This can be due to an epitaxial relationship during reaction conditions, or that the CeO2(001) surface has a greater ability, compared with the CeO2(111) surface, to assist the copper oxide in changing valences and supplying oxygen to the CO. A CuOx-CeO2/Al2O3 catalyst was more active than a CuMn2O4/Al2O3 catalyst for CO oxidation, but the CuMn2O4/Al2O3 catalyst was more active for combustion of ethyl acetate and ethanol. This shows that the activity order for complete oxidation over different metal oxide catalysts depends on the combustible component. In addition, these metal oxide catalysts were found to be more active than a Pt/Al2O3 catalyst for the combustion of ethyl acetate and ethanol. However, for methanol and formaldehyde combustion the Pt/Al2O3 catalyst was the best alternative. Consequently, catalytic waste gas incineration can be more efficient by using the right type of catalyst in each application. By-products as acetaldehyde and acetic acid were observed during catalytic combustion of an ethyl acetate/ethanol mixture. However, in stationary catalytic incineration it is easy to secure complete oxidation to CO2 and H2O.
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