Polyhedral Organic Silsesquioxane Cage Structures Formed via Reaction of Methylchlorosilanes with Re/CeO2 in Catalytic Oxygen Depletion–Regeneration Cycle

• Published in: Industrial & engineering chemistry research Vol. 61; no. 26; pp. 9206 - 9217
• Main Authors: Larsen, Robert T., McLaughlin, Matthew, Katsoulis, Dimitris E.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.06.2022
• Subjects: air; catalysts; chlorine; gas chromatography-mass spectrometry; Kinetics, Catalysis, and Reaction Engineering; ligands; oxygen; process design; silica; silsesquioxanes
• ISSN: 0888-5885; 1520-5045; 1520-5045
• DOI: 10.1021/acs.iecr.2c00920

Polyhedral oligomeric silsesquioxane (POSS) cage structures were exclusively generated as the reaction products of methyltrichlorosilane, CH3SiCl3 (or MeSiCl3 where Me denotes a CH3-group), with a supported Re/CeO2 catalyst at 500 °C. The cage structures are generated by the exchange of oxygen for chlorine in the ceria support under a H2 reducing atmosphere. Regeneration of the support can occur by passing air over the catalyst at 500 °C, and then the reaction can be repeated. This presents a novel way of generating cage structures exclusively via a gas-phase reaction. Gas chromatography-mass spectrometry (GC-MS) of the reaction products indicates that the cage structures that are formed are Me6-T6, Me8-T8, and Me10-T10. The reaction proceeds at high conversion and high yield toward these POSS cages. When dimethyldichlorosilane ((CH3)2SiCl2 or Me2SiCl2) is used as the reactant, mostly cyclic siloxanes D4–D6 are produced. Hydrido-chlorosilane, methyldichlorosilane (CH3SiHCl2 or MeHSiCl2), generates cage structures through an additional Si–H–O ligand exchange reaction that is facilitated by the oxygen vacancies on the ceria support. When Si–H ligands are present, rearrangement reactions are also observed under these conditions and constitute a supplementary process for the formation of the POSS cage structures. Trichlorosilane (HSiCl3) does not form cage structures, but it does undergo rearrangement. It also undergoes Si–H–O ligand exchange with oxygen vacancies on the ceria support to form cristobalite (crystalline SiO2) on the support.