Combining flame spray pyrolysis and high throughput experimentation for preparation and testing of multi-component noble metal catalysts
Multi-scale and/or multi-disciplinary approach to process-product innovation
Nanotechnology & Nanomanufacturing (T3-1)
Keywords: flame spray pyrolysis, high throughput experimentation, noble metal catalysts, alloys, partial oxidation of methane
S. Hannemann, J.-D. Grunwaldt, S.E. Pratsinis, A. Baiker
High-throughput experimentation (HTE) techniques have received great attention in the past years and are applied in various fields, ranging from nanoparticle research to heterogeneous catalysis. Particularly, high-throughput preparation of solids, automated catalyst testing, and high-throughput characterization have been in the focus of recent studies [1, 2]. High-throughput preparation comprises robot-controlled deposition-precipitation, impregnation, chemical vapor deposition, and sol–gel preparation methods [2]. The preparation routines become more complex and the task more demanding if several components are present, e.g., in multicomponent nanomaterials or supported multimetallic catalysts.
Flame spray pyrolysis (FSP) gives the opportunity to prepare conveniently such multi-component nanomaterials in a single step [3]. The rapid quenching after the FSP process typically affords materials with high surface area and tunable structural and chemical properties. Furthermore, the noble metal particle size can be kept relatively small [4].
In this contribution, mono and multi-noble metal particles on Al2O3 were prepared by flame spray pyrolysis (FSP) of the corresponding noble metal precursors dissolved in methanol and acetic acid (v/v 1:1) or xylene [5]. The noble metal loading of the catalysts was close to the theoretical composition as determined by WD-XRF and LA-ICP-MS. The nanomaterials were further analysed using XPS, BET, STEM-EDXS and XANES/EXAFS. The catalysts exhibited always a specific surface area of more than 100 m2/g, and were made up of ca. 10 nm alumina particles on which the smaller noble metal particles (1–2 nm, partially oxidized state) were discernible. The question of alloy formation was addressed by STEM-EDXS and EXAFS analysis. In some cases, particularly for Pt–Pd and Pt–Rh, alloying close to the bulk alloys was found, in contrast to Pt–Ru being only partially alloyed.
The nanoparticles are interesting for partial oxidation of methane to CO and hydrogen, total combustion of hydrocarbons, and (selective) CO-oxidation. Therefore the preparation method was combined with high-throughput catalyst testing. Samples containing 0.1–5 wt% noble metals (Ru, Rh, Pt, Pd) on Al2O3 were investigated in the catalytic partial oxidation of methane. The ignition of the reaction towards carbon monoxide and hydrogen depended on the loading and the noble metal constituents. The selectivity of these noble metal catalysts towards CO and H2 was similar under the conditions used (methane: oxygen ratio 2:1, temperature from 300 to 500 °C) and exceeded significantly those of nickel, gold or silver containing catalysts. In situ X-ray absorption spectroscopy on selected samples was used to gain insight into the structure of the catalysts under reaction conditions. [5]
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[2] D.K. Kim and W.F. Maier, J. Catal. 238 (2006), 142.
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[4] S. Hannemann, J.-D. Grunwaldt, F. Krumeich, P. Kappen, A. Baiker, Appl. Surf. Sci. 252, (2006), 7862; R. Strobel, J.-D. Grunwaldt, A. Camenzind, S.E. Pratsinis, A. Baiker, Catal. Lett. 104, (2005) 9.
[5] S. Hannemann, J.-D. Grunwaldt, D. Günther, F. Krumeich, P. Lienemann, S. E. Pratsinis, A. Baiker, Appl. Catal. A: General (2006), doi:10.1016/j.apcata.2006.09.034
Presented Monday 17, 15:20 to 15:40, in session Nanotechnology & Nanomanufacturing (T3-1).
