Hopcalite nanoparticle catalysts with high water vapour stability for catalytic oxidation of carbon monoxide
Hopcalite catalysts (copper manganese oxides) with high catalytic activity in CO oxidation catalysis under humid conditions were obtained via flame spray pyrolysis. While commercial hopcalites, for example produced by precipitation methods, immediately deactivate under humid conditions, the new catalysts show significantly reduced deactivation at humidity levels up to 75% and are thus promising materials for personal respiratory protection in respiratory filters for fire fighters and miners. The hopcalite catalysts were obtained by a scalable production route using flame spray pyrolysis (FSP) of mixtures of oleates, 2-ethylhexanoates as well as nitrates dispersed by a surfactant. The textural compositional and also catalytic properties of the FSP-hopcalites were found to be highly tuneable by the type of precursor and the spraying parameters. Adjusting the spraying conditions lead to catalysts with specific surface areas as high as 180m2g-1 being mainly composed of Cu1.5Mn1.5O4 by applying 2-ethylhexanoates as precursors. Microemulsions and 2-ethylhexanoates were found to yield hopcalite nanoparticles with very high activity for the catalytic oxidation of carbon monoxide at ambient temperature. The humidity tolerance is attributed to carbon deposits exhibiting a hydrophobic characteristic as indicated by physisorption measurements using water vapour and nitrogen as adsorbates.