Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Solvent-free synthesis of MFI-type zeolites and their degradation properties of gas-phase styrene

In this study, a series of MFI-type zeolites with various compositions were synthesized by a solvent-free synthesis method at a comparatively mild condition. The results of investigations showed that the as-synthesized samples displayed a good crystallinity grade and regular morphology of layered structure. The crystallization process of TS-1 was systematic investigated. It was revealed that the transition stage of crystallization process was the formation of nucleation intermediates (Na₂SiF₆), which was the key factor for dropping Ti atoms into MFI framework. Meanwhile, it showed a high apparent nucleation activation energy (64.8 kJ mol^-1), and low growth activation energy (25.3 kJ mol^-1) in a spontaneous nucleation system, and the nucleation activation energy could be reduced to 17.2 kJ mol^-1 in non-spontaneous nucleation system. The as-synthesized zeolites were evaluated for their catalytic activity for the degradation of gas-phase styrene. The titanium silicalite-1 sample doped with iron exhibited excellent catalytic activity with 100% degradation of styrene. The method employed in this work not only decreases the production cost and energy-consumption of MFI-type zeolites, but also significantly enhances their production yield. Moreover, it is an efficient pathway to solve the pollution of volatile organic compounds using solid waste.

The comparison of two classes of bifunctional SBA-15 supported platinum–heteropolyacid catalysts for the isomerization of n-hexane

SBA-15 supported bifunctional acidic HSiW–Pt catalysts proved to be active, stable and highly selective in the isomerization of n-hexane.

Mechanism Studies of the Conversion of13C-Labeledn-Butane on Zeolite H-ZSM-5 by Using13C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

By using 13C MAS NMR spectroscopy (MAS = magic angle spinning), the conversion of selectively 13C-labeled n-butane on zeolite H-ZSM-5 at 430-470 K has been demonstrated to proceed through two pathways: 1) scrambling of the selective 13C-label in the n-butane molecule, and 2) oligomerization-cracking and conjunct polymerization. The latter processes (2) produce isobutane and propane simultaneously with alkyl-substituted cyclopentenyl cations and condensed aromatic compounds. In situ 13C MAS NMR and complementary ex situ GC-MS data provided evidence for a monomolecular mechanism of the 13C-label scrambling, whereas both isobutane and propane are formed through intermolecular pathways. According to 13C MAS NMR kinetic measurements, both pathways proceed with nearly the same activation energies (E(a) = 75 kJ mol(-1) for the scrambling and 71 kJ mol(-1) for isobutane and propane formation). This can be rationalized by considering the intermolecular hydride transfer between a primarily initiated carbenium ion and n-butane as being the rate-determining stage of the n-butane conversion on zeolite H-ZSM-5.

Imaging Reflection IR Spectroscopy as a Tool to Achieve Higher Integration for High-Throughput Experimentation in Catalysis Research

FTIR spectroscopy in reflection mode combined with a focal plane array (FPA) detector was employed for high-throughput screening of activity of catalysts in n-pentane hydroisomerization. The reactor system was evaluated using reference catalysts Pt-MOR and gamma-alumina of known catalytic activity. By using the reflection setup, a higher degree of parallelization was possible, as compared to previous reports, in which transmission cells had been used. The 49-channel parallel reactor in combination with the FPA-IR optical setup was able to provide reliable information about the activity of different catalysts with relative data error of less than +/-20%.