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Rh-Induced Support Transformation and Rh Incorporation in Titanate Structures and Their Influence on Catalytic Activity

1
Department of Applied and Environmental Chemistry, University of Szeged, Interdisciplinary Excellence Centre, Rerrich Béla tér 1, H-6720 Szeged, Hungary
2
MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, Rerrich Béla tér 1, H-6720 Szeged, Hungary
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Author to whom correspondence should be addressed.
Catalysts 2020, 10(2), 212; https://doi.org/10.3390/catal10020212
Received: 23 December 2019 / Revised: 28 January 2020 / Accepted: 7 February 2020 / Published: 10 February 2020
(This article belongs to the Special Issue Recent Developments in Rh Catalysts)
Rh is one of the most effective metals in several technologically important heterogeneous catalytic reactions, like the hydrogenation of CO2, and CO, the CO+H2O reaction, and methane and ethanol transformations. Titania and titanates are among the most frequently studied supports for Rh nanoparticles. The present study demonstrates that the nature of the support has a marked influence on the specific activity. For comparison, the catalytic activity of TiO2 P25 is also presented. It is pointed out that a certain amount of Rh can be stabilized as cation (Rh+) in ion-exchange positions (i.e., in atomic scale distribution) of the titanate framework. This ionic form does not exists on TiO2. We pay distinguished attention not only to the electronic interaction between Rh metal and the titania/titanate support, but also to the Rh-induced phase transitions of one-dimensional titanate nanowires (TiONW) and nanotubes (TiONT). Support transformation phenomena can be observed in Rh-loaded titanates. Rh decorated nanowires transform into the TiO2(B) phase, whereas their pristine counterparts recrystallize into anatase. The formation of anatase is dominant during the thermal annealing process in both acid-treated and Rh-decorated nanotubes; Rh catalysis this transformation. We demonstrate that the phase transformations and the formation of Rh nanoclusters and incorporated Rh ions affect the conversion and the selectivity of the reactions. The following initial activity order was found in the CO2 + H2, CO + H2O and C2H5OH decomposition reactions: Rh/TiO2 (Degussa P25) ≥ Rh/TiONW > Rh/TiONT. On the other hand it is remarkable that the hydrogen selectivity in ethanol decomposition was two times higher on Rh/TiONW and Rh/TiO(NT) catalysts than on Rh/TiO2 due to the presence of Rh+ cations incorporated into the framework of the titanate structures.
Keywords: Rh catalyst; titanate nanowires; titanate nanotubes; ion-exchange; phase transformation; CO2 hydrogenation; methanation; water-gas-shift reaction; ethanol decomposition Rh catalyst; titanate nanowires; titanate nanotubes; ion-exchange; phase transformation; CO2 hydrogenation; methanation; water-gas-shift reaction; ethanol decomposition
MDPI and ACS Style

Kiss, J.; Sápi, A.; Tóth, M.; Kukovecz, Á.; Kónya, Z. Rh-Induced Support Transformation and Rh Incorporation in Titanate Structures and Their Influence on Catalytic Activity. Catalysts 2020, 10, 212.

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