Flame Aerosol Synthesis of Metal Oxide Catalysts with Unprecedented Structural and Catalytic Properties

Abstract

In the past two decades flame aerosol synthesis of novel materials has experienced significant growth in both industry and academia. Recent research is focused on the development of new materials in the nanosized range to be used in various applications, such as catalysts, gas sensors, pigments, and batteries. Several studies indicate that this scalable synthesis method can result in novel and metastable phases of mixed metal oxides of high purity, which may not be easy accessible by conventional wet‐ or solid‐state processes. Especially for catalytic applications this synthesis method is emerging as an attractive fast and single‐step production route for high surface area materials, often with unprecedented structural and catalytic properties. The large variety of possible organometallic precursors especially for the liquid‐fed aerosol flame synthesis makes this technique very versatile for catalyst synthesis. Using the example of the widely used vanadia‐based mixed oxide catalysts, we analyze the structural and catalytic properties of flame‐derived catalysts and compare them to corresponding catalysts prepared by classical wet‐chemistry methods. The often unique structural properties along with their control at proper synthesis conditions and their influence on catalyst performance in selected reactions are discussed. Subsequently, we give an overview of other recent flame‐made mixed metal oxide based catalysts and make an attempt to assess the potential and limitations of flame synthesis for the preparation of catalytic mixed metal oxide materials, and finally we identify future challenges in research.

VOx/SiO2 Catalyst Prepared by Grafting VOCl3 on Silica for Oxidative Dehydrogenation of Propane

“…The VO x /SiO 2‐(1000) catalyst was further investigated at 580 °C with time‐on‐stream of 72 h. As shown in Figure , the initial propane conversion (≈31 %) is quite stable in the long‐term test, and does not change with time on stream. The calculated TOF propane value at this reaction condition is 2.59 min −1 , which is close to the results in the previous reports . More importantly, the selectivities to all the products including propylene, ethylene, CO, CO 2 , acetaldehyde, and acrolein are substantially maintained in 72 h catalytic reaction.…”

“…The calculated TOF propane value at this reaction condition is 2.59 min À1 ,w hich is close to the results in the previous reports. [4][5][6][7][8][9] More importantly,t he selectivities to all the products including propylene, ethylene, CO, CO 2 ,acetaldehyde, and acrolein are substantially maintained in 72 hc atalytic reaction. The propylenes electivity of 60 %i sw ell kept, which corresponds to the propyleney ield of 18 %.…”

“…It has been demonstrated that the preparation method has a significant influence on the nature of VO x species at the surface of the support. To develop effective vanadia catalyst for propane ODH, a variety of synthetic methods, such as impregnation, grafting, thermolytic molecular precursor, atomic layer deposition, and flame spray pyrolysis, have been applied. Herein, we use a grafting method to anchor VOCl 3 at the surface of SiO 2 .…”

“…[4a] It has been demonstrated that the preparation method has as ignificant influence on the nature of VO x species at the surface of the support. To develop effective vanadia catalyst for propaneO DH, av ariety of synthetic methods, such as impregnation, [5] grafting, [6] thermolytic molecular precursor, [7] atomic layer deposition, [8] and flame spray pyrolysis, [9] have been applied. Herein, we use ag rafting methodt oa nchorV OCl 3 at the surfaceo fS iO 2 .T he density of grafting sites (OH groups)a tt he silica surface is strongly dependentonits dehydroxylationtemperature, and thus the final VO x loading and dispersion at SiO 2 surfacec an be controlleds ystematicallyb yt he variation of SiO 2 pretreatment temperature.…”

Flame-Sprayed Pure and Ce-Doped TiO2 Photocatalysts

“…This technique enables the production of unique oxide nanoparticles in one step, and it has been used to produce oxides for sensors [6,7] and industrial catalysts [8]. In this technique, liquid or solid precursor compounds are rapidly evaporated by high temperature flame exposure, resulting in vapors that transform into clusters by quickly growing into nanometer-sized particles by coagulation [9].…”