Integration of Nano-Sized HZSM-5 with ZnZrO x as a Bifunctional Catalyst to Boost Benzene Alkylation with Carbon Dioxide and Hydrogen

Benzene alkylation with CO2/H-2 isa doublybeneficial option to upgrade benzene toward valuable products, inwhich benzene can be converted into valuable toluene and xylene, whileCO(2) can be utilized as an alkylation reagent to mitigatethe greenhouse effect. It is quite challenging to ascertain the criticalrule of zeolite regulation for the synergistic effect in oxide-zeolitecomposite (OXZEO) catalysts, a series of bifunctional catalysts wereinvestigated in this work, consisting of ZnZrO x solid solution and nano-sized HZSM-5 with uniform size distributionand distinct acid properties. Key parameters affecting the catalystperformance were analyzed and optimized in this tandem reaction, namely,the mass ratio of two components, the SiO2/Al2O3 ratio of HZSM-5, and the proximity between ZnZrO x and HZSM-5. Due to the increased activesite accessibility originating from nano-sized HZSM-5, the combinedselectivity of toluene and xylene reaches 94.6% at 31.3% benzene conversion,respectively. Moreover, low ethylbenzene selectivity (<1%) hasbeen achieved. It is worth noting that the long-term stability testindicates a faster deactivation in the nano-sized HZSM-5 system ascompared with the micro-sized counterpart. Based on EDS mappings,it is found that nano-sized HZSM-5 experiences a more severe metalmigration issue, resulting in lower catalyst stability. The reactionmechanism with formate-methoxy intermediates and the synergistic effectof CO2 hydrogenation-alkylation were further confirmedby in situ diffuse reflectance infrared Fourier transformationsspectroscopy and gas chromatography-mass spectrometry. By correlatingzeolite size and acidity with catalytic performances, these findingscould facilitate the further rational design of OXZEO catalysts towardCO(2) catalytic conversions. Thiswork reports the integration of nano-sized HZSM-5 withZnZrOx as bifunctional catalyst to boost benzene alkylation with CO2/H-2.