Chemistry is the experimental and theoretical study of materials on their properties at both the macroscopic and microscopic levels.In a patent£¬ Quality Control of: Tetrapropylammonium bromide, Which mentioned a new discovery about 1941-30-6
ZSM-5 zeolites modified with Zn and their effect on the crystal size in the conversion of methanol to light aromatics (MTA)
ZSM-5 zeolite catalysts modified with zinc were prepared by two forms of Zn incorporation the synthesis gel, and ion exchange techniques. The physico-chemical properties of zeolites were studied by XRD, N2-adsorption, NH3 temperature-programmed desorption, 27Al and 29Si MAS NMR, SEM, TEM and TGA. ZSM-5 zeolite in its acid form was exchanged using an aqueous zinc salt solution and demonstrated a significantly higher selectivity for the aromatic products in comparison with the purely acidic catalysts. The samples with distribution of ZnOH+ species are more active than the samples with ZnO sites in the zeolites. The synthesis of zeolite ZSM-5 of nanometric size resulted to present high stability and selectivity towards light aromatics. The influence of the form of zinc incorporation, the acidity and the reaction temperature had a great influence on the catalytic activity. The MTA catalyst lifetime is increased by several times due to the enhanced mesoporosity and decreased acidity. In the present work the zeolite HZSM-5 exchanged with Zn with Si/Al 25 ratio presented conversions close to 100% methanol with 32% selectivity to the BTX fraction, however, this catalyst was deactivated after 8?h of reaction with a weight hourly space velocity of 4.74?h?1 at 450?C. On the other hand, a HZSM-5 zeolite with nanoscale crystals was found to be more stable in the MTA reaction. The nanometric catalyst showed conversions around 100% methanol after 8?h of reaction and 32.5% selectivity to the BTX fraction to 450?C. These results clearly indicate that crystal size significantly influence the ZSM-5 lifetime and product distribution.
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Reference£º
Metal catalyst and ligand design,
Ligand Template Strategies for Catalyst Encapsulation – NCBI