This invention relates to the process of coating substrates with one or more components to form a catalyst; specifically, the process of layering one or more catalytic components onto a honeycomb monolith to form a carbon monoxide oxidation that combines CO and O2 to form CO2, or alternatively, a volatile organic compound oxidation catalyst that combines the compound and O2 to form CO2 and H2O.

First, the substrate is infused with an excess of solution having a starting material comprising a catalytic component precursor, where the thermal decomposition product of the precursor is a catalytic component. Second, the excess of the solution is removed from the substrate, thereby leaving a coating of the catalytic component precursor on the surface of the substrate. Third, the coating of the catalytic component precursor is converted to the catalytic component by thermal decomposition. This is achieved by heating the coated substance to approximately 300 °C, where the rate of heating is controlled to prevent high-temperature calcination of the catalytic component precursor and where any remaining starting material is thermally decomposed, oxidized, and/or volatilized without high-temperature calcining, thereby leaving only the catalytic component and no residues on the substrate surface. Finally, the coated substance is etched to increase the surface area. This can be achieved by submerging and refluxing the coated substance in a dilute solution of nitric acid.

The first three steps of the above process are repeated in order to successively layer more than one catalytic component on the substrate. In addition, the first step may be improved by infusing the substrate with an excess of solution by vacuum deaeration, and the second step may be improved by removing the excess of the solution by draining away and/or evaporating off the excess of the solution. If the catalyst is “cured” by heating in an atmosphere of a reducing gas prior to its use, its activity may be substantially improved even further. The potential reducing gases include, but are not limited to, carbon monoxide and hydrogen.

This work was done by Eric J. Kielin, Billy T. Upchurch, and David R. Schryer of Langley Research Center. LAR-15851-1

NASA Tech Briefs Magazine

This article first appeared in the December, 2014 issue of NASA Tech Briefs Magazine.

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