Role of Catalyst Domain Size in the Hydrogenation of CO2 to Aromatics over ZnZrOx/ZSM-5 Catalysts

The direct conversion of carbon dioxide into aromatic compounds may provide an environmentally friendly resource for a family of chemical building blocks wit h high global demand-aromatic chemicals. An array of bifunctional catalysts composed of ZnZrOx for the conversion of CO2 to methanol and ZSM-5 for methanol aromatization is evaluated considering multiple operational and catalytic parameters, with a focus on the particle size of each catalyst functionality. Aromatic yields generally increase as the ZSM-5 domain size decreases for different configurations of catalyst domains-mixed powders, mixed pellets, and separate beds. However, for a physical mixture of the catalyst components prior to pelletization (mixed powder case), varying the ZSM-5 crystal size inversely impacts the particle size of ZnZrOx, leading to enlarged metal oxide domains and enhanced intermediate diffusion barriers for very small crystals of ZSM-5. Larger crystals of ZSM-5 can be employed to obtain a higher concentration of benzene, toluene, and xylene (BTX) among aromatics. Upon employing a physical mixture of the ZnZrOx/ZSM-5 catalyst with a Si/Al ratio of 300 and a ZSM-5 crystal size of 300 nm, a total aromatics selectivity of 44% at CO2 conversion of 6% was obtained at 320 degrees C, WHSV of 7200 mL gcatalyst-1 h-1, and H2/CO2 ratio of 3.

Automated summary

The direct conversion of carbon dioxide into aromatic compounds provides an environmentally friendly resource for aromatic chemicals with high global demand. Bifunctional catalysts composed of ZnZrOx and ZSM-5 showed improved aromatics yields by decreasing the ZSM-5 domain size. However, for a physical mixture of catalyst components, the particle size of ZnZrOx increased due to the inverse impact of ZSM-5 crystal size, resulting in enhanced diffusion barriers for small crystals of ZSM-5. Larger crystals of ZSM-5 can be used to obtain a higher concentration of benzene, toluene, and xylene.