Klaeden, K.

Timpe, O.

Trunschke, A.

English

MPG.PuRe

  XXXIX Jahrestreffen Deutscher Katalytiker Weimar, 15. – 17. März 2006   HPA as freighter to introduce RuOx into MOX host catalysts further work based on this concept  Timpe, O. Trunschke, A.; Klaeden, K.   Introduction In a previous contribution [1], we proposed the concept how to manage the doping of MOX catalyst host systems with small amounts of RuOx and presented first results. The basis idea underlying this concept is the linking of cationic Ru to large heteropoly (HPA) anions. These metastable adducts tend do decompose under thermal treatment to generate RuOx species  dispersed in a MOX matrix. As discussed earlier, the degree of dispersion might be decisive for the catalytic behavior of the RuOx-species, first of all the selectivity to partial oxidized products of hydrocarbon educts. The beneficial effect of the HPA system is the large separation of the Ru-cations in the the lattice due to the dimensions of the cage anions. This is likely to prevent the agglomeration of the Ru during thermal decomposition of the precursor adducts. The precursor adduct (Ru-HPA) is mechanically mixed with the MOX catalyst to be doped. Tempering of this mixture will finally lead to a catalyst loaded with highly dispersed RuOx.   The suitability of this concept, however, should be negotiated under reserve in respect to some major uncertainties. The effect of the added Ru-HPA adduct on the hosting MOX catalyst may not be simply additive in nature. A most welcome intimate guest host interaction suitable for preservation of high Ru dispersion on the one hand, is not excluded to derogate the catalytic potential of the host in the whole on the other hand. This becomes even more valid regarding the fact that with every Ru atom a more than10 fold multiple of other transition metal atoms and the heteroatom constitutional for the HPA are added as well.     To elucidate this point of general importance, the composition of the parent HPA compound is systematically varied. In addition to the qualitative variation, Ru-HPA adducts are mixed up with the MOX host in different ratios. The impact of this modifications on the catalytic properties is tested in the oxidation of propane. Structural (XRD) and morphological (SEM) dependencies are analyzed.   Results It turned out that a higher mixing ratio of the Ru-HPA adduct to the MOX-host, referred to as the “loading”, tends to reduce the activity of the resulting catalyst and, moreover, to worsen the selectivity to the products of partial oxidation, namely acrolein and acrylic acid. A loading in the lower percentage range, however, in some cases brings about distinct enhancement of propane conversion rates without a substantial dump in selectivity. Analysis of the structure revealed that the high loading of HPA material changes the phase composition in the final catalyst. In parallel, the typical spherical morphology of the (spray-dried) MOX-host partly disappears.  Secondly, the composition of the parent HPA,  that is the composition of the KEGGIN cage in the present case, is of major impact both for activity and selectivity. Interestingly, the same compositions have been found to be preferable if the pure Ru-HPA adduct precursors are subjected to the catalytic test reaction after thermal decomposition in inert atmosphere.     Preprint of the Department of Inorganic Chemistry, Fritz-Haber-Institute of the MPG (for personal use only) (www.fhi-berlin.mpg.de/ac)   XXXIX Jahrestreffen Deutscher Katalytiker Weimar, 15. – 17. März 2006   # 1738# 1736# 1762# 1751# 1764# 1756# 1755# 1752# 1975# 1263# 1763# 1750# 1754# 1082# 1737# 19770510Ru[SiVMo]Ru[SiMo]Ru[SiW]Ru[PVW]MovteRu[PW]Ru[SiVW]Ru[PW]Ru[PNbMo]Ru[PMo]Ru[SiVMo]Ru[PVW]Ru[SiW]Ru[PMo]Ru[SiMo]Ru[PNbMo]0.00.51.01.52.02.53.0rel. yield water.norm co2.norm prp.norm acro.norm a.a.norm load [%]   References [1] Poster Contribution XXXVIII annual meeting in 2005: Access to highly dispersed Ru-oxide in Mo-oxide based catalyst matrices, Timpe et al.          Preprint of the Department of Inorganic Chemistry, Fritz-Haber-Institute of the MPG (for personal use only) (www.fhi-berlin.mpg.de/ac) 

HPA as freighter to introduce RuO<sub>x</sub> into MOX host catalysts further work based on this concept

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MPG.PuRe