Busting the efficiency of SAPO-34 catalysts for the methanol-to-olefin conversion by post-synthesis methods

As an effective non-petroleum based process for producing light olefins, the methanol-to-olefin(MTO) route has become an indispensable alternative to the industrial production of light olefins. The silicoaluminophosphate SAPO-34 zeolite(CHA-type structure) has proven to be an efficient industrial catalyst for the production of ethylene and propylene by the MTO reaction. However, the inherent structure and related diffusion limitations of SAPO-34 limit the mass transport and thus cause rapid deactivation of the catalyst. Fabrication of hierarchical SAPO-34 zeolite is one of the most effective strategies to address the intrinsic diffusion limitation. As simple, inexpensive, and efficient approach, the post-synthetic route has attracted considerable attention and widely used to introduce secondary meso-/macropores into the microporous SAPO-34 material. Significant effort has been dedicated to the development of post-synthesis strategies to prepare hierarchical SAPO-34 zeolite, thereby enhancing its catalytic performance in the MTO process. This mini-review addresses the post-synthesis preparation of hierarchical SAPO-34 catalysts and their MTO performance. Furthermore, some current problems and prospects of the post-synthesis route to hierarchical SAPO-34 catalysts are also revised. We expect this minireview to inspire the more efficient preparation of hierarchical SAPO-34 catalysts for the MTO process.

Using ultrasound to improve the sequential post-synthesis modification method for making mesoporous Y zeolites

Mesoporous Y zeolites were prepared by the sequential chemical dealumination(using chelating agents such as ethylenediaminetetraacetic acid,H EDTA,and citric acid aqueous solutions)and alkaline desilication(using sodium hydroxide,NaOH,aqueous solutions)treatments.Specifically,the ultrasound-assisted alkaline treatment(i.e.,ultrasonic treatment)was proposed as the alternative to conventional alkaline treatments which are performed under hydrothermal conditions.In comparison with the hydrothermal alkaline treatment,the ultrasonic treatment showed the comparatively enhanced efficiency(with the reduced treatment time,i.e.,5 min vs.30 min,all with 0.2 mol·L NaOH at 65°C)in treating the dealuminated Y zeolites for creating mesoporosity.For example,after the treatment of a dealuminated zeolite Y(using 0.1 mol·L H EDTA at 100°C for 6 h),the ultrasonic treatment produced the mesoporous zeolite Y with the specific external surface area()of 160 m·g and mesopore volume()of 0.22 cm·g,being slightly higher than that by the conventional method(i.e.,=128 m·g and=0.19 cm·g).The acidic property and catalytic activity(in catalytic cracking of-octane)of mesoporous Y zeolites obtained by the two methods were comparable.The ultrasonic desilication treatment was found to be generic,also being effective to treat the dealuminated Y zeolites by citric acid.Additionally,the first step of chemical dealumination treatment was crucial to enable the effective creation of mesopores in the parent Y zeolite(with a silicon-to-aluminium ratio,Si/Al=2.6)regardless of the subsequent alkaline desilication treatment(i.e.,ultrasonic or hydrothermal).Therefore,appropriate selection of the condition of the chemical dealumination treatment based on the property of parent zeolites,such as Si/Al ratio and crystallinity,is important for making mesoporous zeolites effectively.

Crystalline framework nanosheets as platforms for functional materials

The integration of organic and inorganic materials has been widely used in various applications to generate novel functional nanomaterials characterized by unique properties.Functional crystalline framework nanosheets and their synergistic effects have been studied recently for possessing the advantages of functional species as well as crystalline framework nanosheets.Hence,we have focused on the preparation methods and applications of functional crystalline framework nanosheets in this review.We introduced crystalline framework nanosheets and discussed the importance of integrating functional species with nanosheets to form functional crystalline framework nanosheets.Then,two aspects of the preparation methods of functional crystalline framework nanosheets were reviewed:in situ synthesis and post-synthesis modification.Subsequently,we discussed the properties of the crystalline framework nanosheets combined with various functional species and summarized their applications in catalysis,sensing,separation,and energy storage.Finally,we have shared our insights on the challenges of functional crystalline framework nanosheets,hoping to contribute to the knowledge base for optimizing the preparation methods,expanding categories,improving stability,and exploring potential applications.

Different Routes to the Pore Engineering of Spherical MCM-41

Different routes,including the replacements of the template,addition of pore expander and hydrothermal post-synthesis treatment have been used for the pore engineering of spherical MCM-41.A comparison among the pore engineering effects of these methods has been made.The results show that the hydrothermal post-synthesis treatment affords the synthesized material with a larger pore size and narrow pore size distribution without changing the spherical morphology.As far as the pore-size expansion is concerned,the addition of DMTA is the most effective one,but this might be limited by the spherical morphology.Combining the replacement of C 16TMABr with the Gemini surfactant GEM 16-8-16 with an addition of DMTA gives rise to the largest pore volume and surface area.

Diamine-modified porous indium frameworks with crystalline porous materials(CPM)-5 structure for carbon dioxide fixation under co-catalyst and solvent free conditions

In the presentwork,functional diamine groups into indium frameworks to synthesize cyclic carbonates from CO_(2)and epoxides with efficient catalytic activity in the absence of cocatalyst and solvent are reported for the first time.Crystalline porous materials(CPM)-5 modified with 1,2-phenylene diamine and ethylene diamine(CPM-5-PhDA and CPM-5-EDA),were prepared using a post-synthetic modification(PSM)method.The properties of the modified CPM-5 were characterized by powder X-ray diffraction(PXRD),Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),N2-adsorption,scanning electron microscopy(SEM),CO_(2)adsorption,and temperature programmed desorption TPD methods.The presence of diamine groups as basic sites and indium Lewis acid sites in the framework structure were desirable for high catalytic activity.For a given catalyst weight,CPM-5-PhDA was the best candidate to appear with great catalytic activity and selectivity for the cycloaddition reaction at 100°C and1MPa CO_(2)under co-catalyst and solvent free conditions.CPM-5-PhDA alsowas found to afford large and bulky epoxides.The catalyst can be easily separated and reused five times without any decline in activity.

Visible-light-induced photocatalytic CO_(2)reduction over zirconium metal organic frameworks modified with different functional groups

The reduction of CO_(2)into high value-added chemicals and fuels by a photocatalytic technology can relieve energy shortages and the environmental problems caused by greenhouse effects.In the current work,an amino-functionalized zirconium metal organic framework(Zr-MOF)was covalently modified with different functional groups via the condensation of Zr-MOF with 2-pyridinecarboxaldehyde(PA),salicylaldehyde(SA),benzaldehyde(BA),and trifluoroacetic acid(TA),named Zr-MOF-X(X=PA,SA,BA,and TA),respectively,through the post-synthesis modification.Compared with Zr-MOF and Zr-MOF-TA,the introduction of PA,SA,or BA into the framework of Zr-MOF can not only enhance the visible-light harvesting and CO_(2)capture,but also accelerate the photogenerated charge separation and transfer,thereby improving the photocatalytic ability of Zr-MOF for CO_(2)reduction.These results indicate that the modification of Zr-MOF with electron-donating groups can promote the photocatalytic CO_(2)reduction.Therefore,the current work provides an instructive approach to improve the photocatalytic efficiency of CO_(2)reduction through the covalent modification of MOFs.

Bifunctional metal–organic frameworks toward photocatalytic CO2reduction by post-synthetic ligand exchange

Photocatalytic reduction of CO2 to useful fuel has been identified as a promising strategy to address the energy and environmental issues.Development of welldefined photocatalysts toward CO2 reduction has attracted increasing interest to gain insight into the reactive mechanism.Herein,by post-synthetic ligand exchange,a bifunctional Re-based metal–organic framework(MOF)was successfully prepared.It not only serves as a photosensitizer but also acts as a catalyst for photochemical reduction of CO2.Furthermore,it is found that a Re-based MOF containing 30%Re-based ligands displays improved activity compared to MOF with 100%Re-based ligands.This work provides clues to the design and synthesis of bifunctional MOFs toward photocatalytic CO2 reduction.

Engineering porous organic polymers for carbon dioxide capture

As atmospheric CO_2 levels rise, the development of physical or chemical adsorbents for CO_2 capture and separation is of great importance on the way towards a sustainable low-carbon future. Porous organic polymers are promising candidates for CO_2 capture materials owing to their structural flexibility, high surface area, and high stability. In this review, we highlight high-performance porous organic polymers for CO_2 capture and summarize the strategies to enhance CO_2 uptake and selectivity, such as increasing surface area, increasing interaction between porous organic polymers and CO_2, and pore surface functionalization.

A mini review on two-dimensional nanomaterial assembly

Two-dimensional(2D)nanomaterials have attracted a great deal of attention since the discovery of graphene in 2004,due to their intriguing physicochemical properties and wide-ranging applications in catalysis,energy-related devices,electronics and optoelectronics.To maximize the potential of 2D nanomaterials for their technological applications,controlled assembly of 2D nanobulding blocks into integrated systems is critically needed.This mini review summarizes the reported strategies of 2D materials-based assembly into integrated functional nanostructures,from in-situ assembly method to post-synthesis assembly.The applications of 2D assembled integrated structures are also covered,especially in the areas of energy,electronics and sensing,and we conclude with discussion on the remaining challenges and potential directions in this emerging field.

Phenol-triggered supramolecular transformation of titanium-oxo cluster based coordination capsules

Supramolecular transformations of coordination cage or capsule have received much attention recently,which help elucidate this natural self-assembly behavior in biological systems.The current study describes the first supramolecular transformation of titanium-o rganic coordination capsule triggered by phenol(and H_(3) PO_(3)).The structural alterations are accompanied by the reconstruction of 5-coordinated Ti centers to 6-coordinated ones.Meanwhile,different amounts of encapsulated phenol guest molecules can be identified,dependent on the sizes of the obtained cavities.In addition,they display much better visible light absorption and air stability than the isopropanol stabilized ones.