Molecular Precursors for Tailoring Humidity Tolerance of Nanoscale Hopcalite Catalysts Via Flame Spray Pyrolysis

Abstract

AbstractA systematic investigation of copper‐ and manganese‐carboxylate precursors derived from various organic acids (arylcarboxylate, alkylcarboxyate) and their transformation into copper manganese nanoparticles via flame spray pyrolysis (FSP) reveals significant impact on their physical and catalytic properties. A sodium‐free protocol is essential to achieve high purity copper(II) and manganese(II) 2‐ethylhexanoates, benzoates, 1‐naphthenates and 9‐ anthracenates as revealed by infrared spectroscopy (IR) and thermogravimetry (TG). In order to exclude the influence of other parameters, the FSP syntheses were carried out using fixed air/feed ratio. Especially aromatic precursors lead to smaller nanoparticles with high surface areas up to 180 m2g−1 and that these also have a higher carbon content. TPR investigations have shown that the copper and manganese atoms are in close contact with each other, which significantly reduces their reduction temperature. In catalytic CO oxidation, all samples synthesized from organometallic precursors have shown higher CO conversions at room temperature under dry conditions and improved long‐term stability under wet conditions compared to a commercial reference. The activity depends mainly on the Cu : Mn ratio and the specific surface area. At room temperature under dry conditions, catalytic CO conversion exceeding 80 % could be achieved. A decreased deactivation rate under humid conditions could be related to an increased carbon content of the nanocatalysts. By optimization of the synthesis parameters and the use of pure precursors, it was possible to show that flame spray pyrolysis is an efficient, scalable and single‐stage synthesis method for Hopcalite nanoparticles, which additionally provides more active catalysts than those from alternative synthesis methods.