Ceramic Foam-Supported Perovskites as Catalysts for Combustion of Methane

Abstract

Methane combustion in the presence of various types of perovskites supported on ceramic foams has been studied with respect to the CO and NOx formation. The effect of the catalyst composition and of the air-to-methane ratio on the CO and NOx concentration has been evaluated for different burner capacities.

Structured Perovskite-Based Catalysts and Their Application as Three-Way Catalytic Converters—A Review

“…ZrO 2 [128] and MgO [129] supports are chemically inert with respect to most of active phases. On the contrary, extensive interaction exists on γ-Al 2 O 3 supported systems, which results, as earlier mentioned, in the formation of less active spinel structures, simple oxides and aluminate phases [66,130]. LaAl 11 O 18 and LaCr 1−x Al x O 3 form upon solid-state reaction between LaCrO 3 and γ-Al 2 O 3 at high temperature [131] while Mn from LaMnO 3 is incorporated in the alumina lattice even at low temperature [129].…”

“…Washcoated supported perovskite-type catalysts can be prepared by impregnation or deposition-precipitation of the active phase on an oxide support powder (e.g., γ-Al 2 O 3 , ZrO 2 , MgO) either before [39] or after [127][128][129][130][131][132] that the latter is washcoated on the structured carrier. This produces a homogeneously distributed active phase [127] on a porous support firmly anchored to the walls of the substrate [66,128].…”

“…A three times higher specific rate of methane combustion per gram of catalyst (corresponding to a 14-fold increase in the specific rate per gram of active phase) was obtained on the supported system [128]. Activity enhancement is however not always so spectacular [119] and has a limit: large perovskite crystals form upon increase of the perovskite-type oxide loading and exposure to high temperatures, which leads to pore blocking and loss of dispersion [39,[128][129][130][131]. The decrease of activity was reported to be proportional to the loss of specific surface area: a reduction of both these parameters by a factor four was observed after treating a monolithic γ-Al 2 O 3 supported LaMnO 3 catalyst for 9 h at 1100 °C [127].…”

“…Such features improve mass and heat transfers, which are crucial parameters in exhaust after-treatment applications. There are very few studies on perovskite-type oxides based foam catalysts [119,130] and none of them evaluates the performance of the foams in relation to the conventional honeycomb monoliths.…”

Fundamentals and Applications of Structured Ceramic Foam Catalysts

“…An early use for ceramic foams was gas-burner enhancement, where the turbulent mixing of air and fuel and improved radiation within the structure gives very uniform combustion characteristics for flames. ,, By adding catalytic components to the foam, combustion occurs at lower temperature, thereby decreasing NO x emissions. Catalytic combustion using a wide range of ceramic foams and catalytic agents have reinforced these concepts. − Two applications are apparent: (1) for process heating up to ∼1000 °C, high radial heat-transfer rates with foams decrease the size of the catalyst beds, and (2) for gas-turbine applications, the adiabatic bed has better mixing than its honeycomb counterpart and there is less possibility of the development of hot spots . Thermal shock and size issues should be the same, because identical materials are used for both foams and monoliths.…”