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Combined in situ XAFS/DRIFTS Studies of the Evolution of Nanoparticle Structures from Molecular Precursors

DOI: 10.1021/acs.chemmater.7b02552 DOI Help

Authors: Ellie K. Dann (University College London; UK Catalysis Hub) , Emma K. Gibson (University College London; UK Catalysis Hub) , Richard A. Catlow (University College London; UK Catalysis Hub) , Paul Collier (Johnson Matthey Technology Centre) , Tugce Eralp Erden (University of Reading) , Diego Gianolio (Diamond Light Source) , Christopher Hardacre (The University of Manchester; UK Catalysis Hub) , Anna Kroner (Diamond Light Source) , Agnes Raj (Johnson Matthey Technology Centre) , Alexandre Goguet (Queen's University of Belfast) , Peter Wells (UK Catalysis Hub; Diamond Light Source; University of Southampton)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: July 2017
Diamond Proposal Number(s): 10306

Abstract: The rational design of catalysts is of great industrial significance, yet there is a fundamental lack of knowledge in some of the most well-established processes e.g. formation of supported nanoparticle structures through impregnation. Here, the choice of precursor has a significant influence on the resulting catalytic properties of the end material, yet the chemistry that governs the transformation from defined molecular systems to dispersed nanoparticles is often over-looked. A spectroscopic method for advanced in situ characterization is employed to capture the formation of PdO nanoparticles supported on γ-Al2O3 from two alternative molecular precursors; Pd(NO3)2 and Pd(NH3)4(OH)2. Time resolved DRIFTS is able to identify the temperature assisted pathway for ligand decomposition, showing that NH3 lig-ands are oxidised to N2O and NO- species, whereas, NO3- ligands assist in joining Pd centres via bidentate bridging co-ordination. Combining with simultaneous XAFS, the resulting nucleation and growth mechanism of the precious metal oxide nanoparticles are resolved. The bridging ability of palladium nitrate aids formation and growth of larger PdO nanoparticles at lower onset temperature (<250°C). Conversely, impregnation from [Pd(NH3)4]2+ results in well isolated Pd centres, anchored to the support, which require higher temperature (>360°C) for migration to form observ-able Pd-Pd distances of PdO nanoparticles. These smaller nanoparticles have improved dispersion and an increased number of step and edge sites compared to those formed from the conventional Pd(NO3)2 salt, favouring a lower light off temperature for complete methane oxidation.

Subject Areas: Chemistry, Materials

Instruments: B18-Core EXAFS