Role of Catalyst Domain Size in the Hydrogenation of CO<sub>2</sub> to Aromatics over ZnZrO<sub><i>x</i></sub>/ZSM-5 Catalysts
Iman Nezam, Wei Zhou, Dhrumil R. Shah, Maxim P. Bukhovko, Madelyn R. Ball, Gabriel S. Gusmão, Andrew J. Medford, Christopher W. Jones
Abstract
High Resolution Image Download MS PowerPoint Slide The direct conversion of carbon dioxide into aromatic compounds may provide an environmentally friendly resource for a family of chemical building blocks with high global demand─aromatic chemicals. An array of bifunctional catalysts composed of ZnZrO x for the conversion of CO 2 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 ZnZrO x, 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 ZnZrO x /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 CO 2 conversion of 6% was obtained at 320 °C, WHSV of 7200 mL g catalyst –1 h –1, and H 2 /CO 2 ratio of 3.