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 demandaromatic chemicals.
An array of bifunctional catalysts composed of ZnZrO
x
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
domainsmixed 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 CO2 conversion of 6% was obtained
at 320 °C, WHSV of 7200 mL gcatalyst
–1 h–1, and H2/CO2 ratio of
3.