Synthesis of high-silica ZSM-5 in microgravity

• Published in: Microporous and mesoporous materials Vol. 38; no. 2; pp. 423 - 432
• Main Authors: Warzywoda, Juliusz, Baç, Nurcan, Rossetti, George A., van der Puil, Nelleke, Jansen, Jacobus C., Bekkum, Hermann van, Sacco, Albert
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.08.2000; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Crystal growth; Exact sciences and technology; General and physical chemistry; Hydrothermal synthesis; Ion-exchange; Isomerization; Microgravity; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties; ZSM-5; Crystal growth; Hydrothermal synthesis; Microgravity; Isomerization; ZSM-5; Scanning electron microscopy; Catalytic reaction; Hydrocarbon; Zeolite; X ray diffraction; Molecular sieve; Heterogeneous catalysis; Preparation; Ethylenic compound; Hydrothermal condition
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/S1387-1811(00)00163-3

High-silica ZSM-5 crystals were grown in the microgravity environment (10 −3–10 −6 g) of the space shuttle from precursor solutions held unmixed until activation on orbit. The flight crystals grown from untreated (not heat-treated) silica gel grade 12 had the intergrown disk morphology and were larger than the spherulitic aggregates of small elementary crystals observed for the terrestrial/control samples. The flight and the terrestrial/control crystals grown from silica gel grade 12 heat-treated at 973 K prior to synthesis had similar intergrown disk morphologies. The similar morphologies of the flight crystals grown from untreated silica gel and the terrestrial/control crystals grown from heat-treated silica gel imply that the nucleation rate of ZSM-5 was reduced in microgravity. The results of isomerization of 2,4,4-trimethyl-1-pentene (2,4,4-TMP-1) to 2,4,4-trimethyl-2-pentene on crystals grown from untreated silica gel showed that the flight crystals exhibited a lower external surface activity than the terrestrial/control crystals with an identical total external surface area (∼0.6% conversion of 2,4,4-TMP-1 after 3 h on flight versus ∼1.3% conversion on the terrestrial crystals). This indicated that the flight crystals had a lower surface roughness than their terrestrial controls. An atomic force microscopy examination of the crystal surfaces confirmed these results. In contrast, both the flight and the terrestrial/control crystals grown from heat-treated silica gel had similar surface topographies and roughness.