The zeolite mcm-22 is used as an alternative to alumina in the preparation of many catalysts for petroleum and chemical production.zeolite mcm-22 The mcm-22 zeolite has a unique structure that is characterized by its large size, high specific surface area and low porosity. The mcm-22 zeolite also has high catalytic activity. It is used as a coke synthesis catalyst, alkane-alkylation catalysts (benzene and hexane), methane aromatization, cracking reaction catalyst, 1-butene skeletal isomerization and Fischer-Tropsch reactions. The mcm-22 zeolite is a very active catalytic material that requires little maintenance and has a long lifetime.
Zeolite mcm-22 is synthesized from an alumina precursor by hydrothermal treatment.zeolite mcm-22 The alumina is pre-dissolved in NaOH solution and silica is added to the system in the form of a dry powder (Carlo Erba). Then hexamethylene imine (HMI) is introduced into the system as a structure-directing agent. The resulting MCM-22 system is calcined at 540 degC for 20 h to obtain MCM-22 zeolite.
A series of characterization techniques was performed to evaluate the catalytic performance of zeolite mcm-22 samples.zeolite mcm-22 XRD was recorded on a Siemens D5000 Cu Ka XRD analyzer to determine the 2D zeolite structure. N2 adsorption was used to determine the BET surface area and pore volume of the zeolite samples. Thermogravimetric analysis was performed to measure the thermal stability of the zeolite samples. The morphological characteristics of the zeolite were examined by scanning electron microscopy (SEM). N2 adsorption was also used to determine the acidity of the zeolite samples.
The mcm-22 zeolite can be pillarized to yield MCM-36 (layers separated by pillars, face-to-face orientation) or exfoliated to form ITQ-2 (random orientation of layers, edge-to-edge). The ITQ-2 structure has the advantage of easy access to 12 MR super cage acid sites, which are not available in the calcined 3D MCM-22 material.
Dealumination of MCM-22 results in the formation of MCT-2 (Micro-cluster quaternary ammonium) and FTQ-1 (Fischer-Tropsch zeolite). The MCT-2 structure has superior catalytic properties to MCM-22 and the dealuminated H-MCM-22 structures. It has the lowest disproportionation energy and higher conversion of paraffinic fractions to light olefins at 650 degC. It is also able to retain acid sites, which is important in the control of secondary reactions in Fischer-Tropsch reactions.
In addition, the ITQ-2 zeolite shows a significant improvement in glycerol dehydration to acrolein. The improvement in catalytic activity is attributed to the improved textural properties of the delaminated zeolite. The control of acidity and the ability to reposition the layer distribution are likely responsible for these improvements. In general, delaminated zeolites have superior catalytic activity to their unmodified counterparts. This is mainly due to the removal of aluminum atoms from the MWW framework, which leads to better textural properties and improved acidity.
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