CO_(2)utilization in syngas conversion to dimethyl ether and aromatics:Roles and challenges of zeolites-based catalysts

Several studies have proven a strong correlation between global warming and CO_(2)emissions.Annually,38 billion tons of CO_(2)are approximately emitted into the atmosphere.Utilizing CO_(2)via chemical conversion to clean fuels and value-added aromatics can substantially contribute to controlling the problem.Considering the thermodynamic and environmental limitations of hydrogenation of CO_(2)alone to value-added aromatics and fuels,CO_(2)utilization has currently emerged as a promising and practical approach for the production of fuels and aromatics with simultaneous utilization of both CO and CO_(2)wastes.As such,the approach is economically preferable.CO_(2)could be converted directly to fuels by the hydrogenation process or as a part of a syngas mixture.Dimethyl ether(DME)is a clean fuel with a higher energy density,which could be used as a substituent for several fuels such as diesel.In the same vein,value-added aromatics such as benzene,toluene,and xylene(BTX)can be produced from a similar process.Herein,we report a review that collects the most recent studies for the conversion of CO_(2)to DME and aromatics via zeolite-based bifunctional catalysts.We highlighted the main routes for producing DME and aromatics,as well as thoroughly discussed the conducted studies on CO_(2)hydrogenation and CO_(2)-rich syngas utilized as feedstock for conversion to DME and aromatics.The CO_(2)hydrogenation mostly occurs through the methanol-mediated reaction route but is most often limited by low selectivity and catalyst deactivation,particularly in the utilization of CO_(2)alone for the reduction reaction.The review takes an overview of the progress made so far and concluded by identifying the roles and challenges of zeolite-based catalysts for CO_(2)utilization and conversion to DME and aromatics.Accordingly,despite the incredible growth the field received in the last couple of years,however,many research challenges and opportunities associated with this process are still abounded and required to be addressed.Special attention is required for the development of approaches to block diffusion of H2O through zeolite to suppress the excess formation of CO_(2)in CO_(2)-rich syngas hydrogenation to DME and aromatics,exceed the product distribution limits,and suppress catalysts deactivation.

Microwave-assisted solvothermal synthesis of ZSM-22 zeolite with controllable crystal lengths

ZSM-22 （TON） zeolite crystal morphology was successfully controlled using a microwave-assisted solvothermal fabrication method. Different co-solvents, including ethanol, 2-propanol, glycerol, and ethylene glycol, were also applied in the synthesis mixture. The effects of various parameters such as the aging time, the type and amount of co-solvent on the ZSM-22 crystal aspect ratio were investigated. When employing this microwave irradiation synthesis, a long aging time was crucial to obtain smaller and more uniform crystal sizes. The addition of co-solvent resulted in elongated ZSM-22 crystals, regard- less of the actual co-solvent used, although ZSM-22 zeolite crystallinity was sensitive to the co-solvent type. In general, the use of a co-solvent stimulated the appearance of ZSM-5 zeolite as an impurity and the amount of this impurity was proportional to the concentration of co-solvent in the synthesis mixture.

Synthesis of zeolite-magadiite composites＂ Effects of co-solvent and aluminum source

The one-pot synthesis of ZSM-5-magadiite, ZSM-23-magadiite, and ZSM-5-ZSM-23-magadiite using isopropylamine and 2-propanol as an organic structure-directing agent and co-solvent, respectively, was studied. Zeolite mixtures were prepared by adding 2-propanol （0 to 10wt%） to the reaction solu- tion. The intergrowth of composites was observed when 2-propanol was introduced as a co-solvent into the reaction mixture. Synthesized samples were characterized by X-ray diffraction, field-emission scan- ning electron microscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. The results revealed that the amount of 2-propanol and source of aluminum influenced the nature of the zeolite-magadiite composites formed.