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Quantitative Distinction between Noble Metals Located in Mesopores from Those on the External Surface |
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| Authors: | Carolin Rieg Daniel Dittmann Zheng Li Dr Robert Lawitzki Katrin Gugeler Sarah Maier Prof Guido Schmitz Prof Johannes Kästner Prof Deven P Estes Dr Michael Dyballa |
| Institution: | 1. Institute of Technical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany;2. Institute of Materials Science, University of Stuttgart, Heisenbergstraße 3, 70569 Stuttgart, Germany;3. Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany |
| Abstract: | We compare three methods for quantitatively distinguishing the location of noble metal (NM) particles in mesopores from those found on the external support surface. MCM-41 and SBA-15 with NM located in mesopores or on the external surface were prepared and characterized by TEM. 31P MAS NMR spectroscopy was used to quantify arylphosphines in complexes with NM. Phosphine/NM ratios drop from 2.0 to 0.2 when increasing the probe diameter from 1.08 to 1.54 nm. The reaction between NM and triphenylphosphine (TPP) within 3.0 nm MCM-41 pores takes due to confinement effects multiple weeks. In contrast, external NM react with TPP instantly. A promising method is filling the pores by using the pore volume impregnation technique with tetraethylorthosilicate (TEOS). TPP loading revealed that 66 % of NMs are located on the external surface of MCM-41. The pore filling method can be used in association with any probe molecule, also for the quantification of acid sites. |
| Keywords: | external surfaces mesoporous materials platinum solid-state NMR spectroscopy surface chemistry |