Walace Peterle Soares Kierulf-Vieira

• Jensen, Martin Myhre; Verne, Mathilde Ingeborg Nilsen; Kierulf-Vieira, Walace Peterle Soares; Skau, Karl Isak; Dhak, Prasanta & Sjåstad, Anja Olafsen (2025). Pt–Rh Model Nanoparticle Catalysts for Selective Oxidation of Ammonia to Nitrogen─A Systematic Screening Study. ACS Applied Nano Materials. 8(28), s. 14029–14040. doi: 10.1021/acsanm.5c01442. Fulltekst i vitenarkiv Vis sammendrag

  Abatement processes for ammonia (NH3) slip have gained renewed attention due to growing interest in using liquid NH3 as a marine fuel. A promising approach is selective catalytic oxidation (SCO) of NH3 to nitrogen (N2). This study presents the catalytic performance of five well-defined Al2O3-supported mono- and bimetallic Pt–Rh model catalysts for this reaction. Key findings show that the larger Pt nanoparticles (17 nm) exhibit a higher NH3 turnover frequency (TOF) than the smaller ones (8 nm) while maintaining similar product selectivity. Additionally, the NH3 TOF decreases in the order Pt > Pt1–xRhx solid solution > Rh. Despite this trend, the catalysts Pt, Pt1–xRhx solid solution, and Rh exhibit narrow and distinct temperature windows where the N2 selectivity exceeds 80% at 195–225, 240–250, and 300–315 °C, respectively. Thermal stability tests conducted in air for 8 h and 1 week reveal that both the Rh(core)–Pt(shell) and the Pt1–xRhx solid solution nanoparticles undergo Rh surface enrichment. These results indicate that neither elemental configuration remains stable under the SCO-NH3 conditions.

• Jensen, Martin Myhre; Kierulf-Vieira, Walace Peterle Soares; Kooyman, Patricia J. & Sjåstad, Anja Olafsen (2023). Variable temperature in situ TEM mapping of the thermodynamically stable element distribution in bimetallic Pt-Rh nanoparticles. Nanoscale Advances. 5(19), s. 5286–5294. doi: 10.1039/d3na00448a. Fulltekst i vitenarkiv Vis sammendrag

  We report here the first variable temperature in situ transmission electron microscopy (TEM) study on smaller Pt–Rh nanoparticles (≤24 nm) under vacuum conditions. Well-defined 50 at% Pt/50 at% Rh Pt–Rh solid solution and Rh(core)–Pt(shell) nanoparticles, obtained via colloidal synthesis routes, were investigated between room temperature and 650 °C to elucidate the tendency of elemental mixing/segregation. Key findings are that Pt–Rh nanoparticles <13 nm are stable in a solid solution configuration over the entire studied temperature range, whereas nanoparticles >13 nm tend to segregate upon cooling. Such a cross-over in element distribution with nanoparticle size has not been reported for the Pt–Rh system previously. The results demonstrate the technique's ability to extract valuable information concerning the intricate dynamic processes that take place in the bimetallic Pt–Rh system at the nanoscale, which may be indispensable when optimizing, e.g., the metal composition in catalytically active materials.

• Jensen, Martin; Gonano, Bruno Raymond Gino; Kierulf-Vieira, Walace Peterle Soares; Kooyman, Patricia J. & Sjåstad, Anja Olafsen (2022). Innovative approach to controlled Pt-Rh bimetallic nanoparticle synthesis. RSC Advances. 12(31), s. 19717–19725. doi: 10.1039/d2ra03373a. Fulltekst i vitenarkiv Vis sammendrag

  Precise control of the elemental composition and distribution in bimetallic nanoparticles is of great interest for both fundamental studies and applications, e.g. in catalysis. We present a new innovative and facile synthesis strategy for the production of true solid solution Pt1−xRhx nanoparticles. This constitutes a development of the established heat-up method, where undesired shell formation is fully suppressed, despite utilizing metal precursors with different reaction rates. The concept is demonstrated through synthesis of selected Pt1−xRhx solid solution compositions via the polyalcohol reduction approach. In addition, we provide modified procedures, using the same surface stabilizing agent/metal precursors reaction matrix yielding controlled model Rh(core)–Pt(shell) and Pt(core)–Rh(shell) nanoparticles. Tunable bimetallic solid solution and core–shell nanoparticles with the same capping agent are of key importance in systematic fundamental studies, as functional materials properties may be altered by modifying the surface termination.

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• Kierulf-Vieira, Walace Peterle Soares; Sjåstad, Anja Olafsen & Jensen, Martin (2022). Solid Solution PtxRh1–x Nanoparticles Synthesis, Characterization, Catalyst Preparation and Thermal Stability Evaluations. Universitetet i Oslo. Fulltekst i vitenarkiv

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