The development of materials and methods efficient for carbon capturing, methane storage, and selective separation of CO 2 and CH 4 from gas mixtures is a crucial approach to addressing the problems of these two greenhouse gases. In this regard, metal organic framework (MOF)-based composite materials are recognized as a promising class of materials, which could combine the advantages of MOFs and the other constituents to reduce their current drawbacks in the adsorption/separation systems. In this context, a series of MOF composites recently developed for CO 2 and CH 4 adsorption and their selective separation from gas mixtures are presented and discussed: MOF/carbon-based materials, MOF/Si-based composites, MOF mixed-matrix membranes, MOF/MOF, and MOF/metal oxide structures. Here, with an emphasis on the most recent signs of progress, we hope to shed a light on the MOF composites and assist future research to promote the performance of current composites and develop new MOF hybrid structures considering the proposed challenges.
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SAPO-34/AlMCM-41, as a hierarchical nanocomposite molecular sieve was prepared by sequential
hydrothermal and dry-gel methods studied for catalytic conversion of methanol to light olefins. Pure
AlMCM-41, SAPO-34, and their physical mixture were also produced and catalytically compared.
Physicochemical properties of materials were mainly investigated using XRD, N2 isothermal adsorptiondesorption, FESEM, FT-IR, NH3-TPD, and TG/DTG/DTA techniques. Micro-meso hierarchy of prepared
composite could be demonstrated by XRD and BET analyses. Catalytic performance of materials illustrated
that the methanol conversion on the prepared composite was about 98% for 120 min which showed a higher
activity than the other catalysts. The initial reaction selectivity to light olefins for the composite was also
comparable with those for the other catalysts. Furthermore, the results revealed that SAPO-34/AlMCM-41
preparation decreased the concentration and strength of active acid sites of the catalyst which could
beneficially affect the deposition of heavy molecular products on the catalyst. However, as observed, the
prepared composite was deactivated in olefins production faster than pure SAPO-34. The small mean pore
diameter of composite could be mainly responsible for its pore blockage and higher deactivation rate.
Meanwhile, since the SAPO-34 prepared by dry-gel method had inherently high mesoporosity, the
AlMCM-41 introduction didn't promote the molecular diffusion in the composite structure. The coke
content was found 15.5% for deactivated composite smaller than that for the SAPO-34 catalyst which could
be due to the pore blockage and deactivation of the composite in a shorter period.
In an experimental and statistical study, the effects of five synthesis parameters on the degree of order of nano‐sized Al‐MCM‐41 were basically investigated. In a series of designed experiments, hydrothermal conditions (temperature and time), Si/Al, NaOH/Si, and cetyltrimethylammonium bromide/Si molar ratios were studied each at three levels. Degree of order of mesoporous channels was evaluated using small angle XRD. Nitrogen adsorption‐desorption technique, scanning and transmission electron microscopy (SEM‐TEM), and field‐emission SEM were also applied to detect the textural properties and the morphology of prepared nanoparticles. Energy‐dispersive X‐ray spectroscopy and mapping (EDS‐Map), inductively coupled plasma‐optical emission spectroscopy, and small angle X‐ray scattering were provided as complementary analyses. An accurate reduced quadratic equation was proposed as a function of effective terms in good agreement with the experimental results. Based on the analysis of variance, the amount of aluminum incorporated, sodium hydroxide, and the hydrothermal treatment duration was found to possess more dramatic effects on the degree of order than the other factors. The optimum conditions for the synthesis of a well‐ordered Al‐MCM‐41 were also obtained with the lowest template and the minimum hydrothermal duration verified by two validation tests.
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