L. Schlicker, M. Bekheet, A. Gili, A. Doran, A. Gurlo, K. Ploner, T. Schachinger, S. Penner:
"Hydrogen reduction and metal-support interaction in a metastable metaloxide system: Pd on rhombohedral In2O3";
Journal of Solid State Chemistry, 266 (2018), S. 93 - 99.

Kurzfassung englisch:
Structural and chemical consequences of reactive metal-support interaction (RMSI) effects occurring under
hydrogen reduction in a metastable metal-oxide system have been exemplified for small PdO particles loaded
onto rhombohedral In2O3 (PdO/rh-In2O3) using synchrotron-based in situ X-ray diffraction experiments at
temperatures up to 500 °C. rh-In2O3 is a meta-stable In2O3 polymorph that is prone to gas-phase dependent
phase transformation to cubic In2O3 (c-In2O3). Cross-influence of metal-support interaction and phase
transformation can therefore be expected in similar temperature regimes. To separate both effects, comparable
experiments have also been conducted on pure rh-In2O3. Phase transformation of pure rh-In2O3 to cubic In2O3
in hydrogen occurs between 415 °C and 450 °C. On Pd/rh-In2O3, a sequence of PdO reduction to Pd metal,
followed by PdH0.706 hydride formation and subsequently, InPd and In3Pd2 intermetallic compound formation
have been observed between 30 °C and 500 °C. After the intermetallic compound formation is finished at around
400 °C, the phase transformation to c-In2O3 sets in at exactly the same temperature as on pure rh-In2O3 and
extends over the same temperature range. This proves that the phase transformation of rh-In2O3 to c-In2O3 is
not influenced by the reduction and the intermetallic compound formation. In contrast to Pd on c-In2O3, In-Pd
compound formation from rh-In2O3 occurs at much lower temperatures (230 °C vs. 300 °C), despite finally
approaching the same compound stoichiometries (InPd and In3Pd2). This points to a high structural stability of
reduced rh-In2O3/stability of oxygen vacancies (compared to c-In2O3) as well as to facilitated diffusion of
reduced In(-O) species at low temperatures.

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