MS-1-P-1432 Morphological changes induced by reaction in a RuFe bimetallic catalyst: a BF-TEM and XED-Spectrum Imaging investigation

Catalyst deactivation is a major challenge for the catalysis community. The proposed mechanisms of catalyst deactivation include sintering, re-oxidation of metal components and surface reconstruction and mechanical deactivation through attrition. The bimetallic RuFe system has been investigated and employed as an interesting alternative catalyst in many applications. [1]
In this work we show results on the determination of morphological changes of an alloyed (1:1) RuFe/TiO2 (6% m/m) catalyst. This material was prepared by impregnating the TiO2 support with a solution of Ru3+ and Fe3+ and subsequently drying the suspension in a rotatory evaporator. The material was oxidized in ambient atmosphere at 600C for 2 h and then thermally processed in a H2-rich atmosphere at 400C for 1 h. The as prepared catalyst was used in the hydrogenation of dimethyl adipate in a Parr reactor at 250C and 50 atm of H2 for 15h. After the reaction, the catalyst was recovered and analyzed by TEM and XED-SI. The images and spectroscopic information shown here are representative of a detailed investigation of this system.
Figure 1 shows bright field (BF-TEM) images of RuFe particles deposited on the surface of TiO2 support. The as prepared bimetallic nanoparticles appear as dispersed dark hemispheres. A marked morphological change is observed in the catalyst after the reaction: in Fig. 1-A, small dark particles are seen embedded in an irregular shaped gray matrix. The inset in B show fragmented particles in detail.
In Figure 2, BF-TEM images and XED-SI chemical maps of the as prepared catalyst show correlated distributions of Fe and Ru, which is evidence of the formation of a RuFe solid solution. After the reaction, the Fe content is distributed throughout the gray matrix observed in Fig. 1 and Ru is concentrated at positions associated with the small dark gray particles seen in BF.
The decrease in the catalytic performance observed during the reaction can be attributed to the change in the distribution of metallic domains within individual particles. The initial morphology of the hemispherical RuFe solid solution particles changes to Ru-rich particles embedded into a matrix of iron oxide. This morphological description will provide new arguments to the understanding of the observed catalytic performance.

1. Nikolaos E. Tsakoumis, Magnus Rønning, Øyvind Borg, Erling Rytter, Anders Holmen, Catalysis Today 154 (2010) 162-182.