Preparation of monolithic catalysts for space propulsion applications

Cellular ceramics (honeycomb monoliths and foams) are attractive alternatives to conventional catalyst carriers for propulsion applications. Conventional procedures to prepare the corresponding catalysts, however, cannot be simply transferred to monolithic catalysts. The procedure is discussed focusing on the quality of the wash-coat layer deposited on the internal surface of the monolith. The deposition of active phases like noble metals on a wash-coated monolith is carried out in a similar manner as with catalyst pellets using impregnation with an excess of solvent. The concentration of active phase precursor in the impregnation solution is linked to the porous volume of the wash-coat layer and the desired final metal loading. The phase compositions of monolithic catalysts were investigated using powder X-ray diffraction. The morphology and active phase distribution in the wash-coat materials are studied by scanning electron microscopy (SEM) equipped with an energy X-ray dispersive spectrometer (EDS) and the particle size is determined from transmission electron microscopy (TEM).