Highly Active ZnO-ZrO₂ Aerogels Integrated with H-ZSM-5 for Aromatics Synthesis from Carbon Dioxide

Abstract

Bifunctional catalysis coupling CO 2 to methanol and methanol to hydrocarbons is a promising strategy for the direct hydrogenation of CO 2 into high-value chemicals. However, bifunctional catalysts suffer from low productivity due to the inertness of CO 2 and high activation energy of C−C coupling. Herein, we report a highly active bifunctional catalyst consisting of a ZnO-ZrO 2 aerogel and zeolite H-ZSM-5 for the hydrogenation of CO 2 into aromatics with 76% selectivity at a singlepass CO 2 conversion of 16%. The selectivity of CH 4 is lower than 1% at the same time. The space−time yield of aromatic hydrocarbons is as high as 0.24 g g oxide −1 h −1 under the reaction conditions of 340 °C and 40 bar over ae-ZnO-ZrO 2 /H-ZSM-5 catalyst, which outperforms the previously reported catalysts, including modified Fischer−Tropsch catalysts. We demonstrate that the ZnO-ZrO 2 aerogel catalyst, which is prepared by a combined sol−gel and subsequent supercritical drying method, not only possesses high surface area but also provides large amounts of oxygen vacancies. The formation rate of the methanol intermediate over ZnO-ZrO 2 is dominated by the total amount of oxygen vacancies. Moreover, the stable performance of the bifunctional catalyst under industrially relevant conditions suggests promising prospects for industrial applications.

Single-pass transformation of syngas into ethanol with high selectivity by triple tandem catalysis

“…Our electron paramagnetic resonance (EPR) spectroscopy measurements showed a signal at g value of 2.003 ( Supplementary Fig. 3), which could be attributed to oxygen vacancies over ZrO 2 -based metal oxides 46 . The incorporation of ZnO into ZrO 2 to form solid solution enhanced the signal at g value of 2.003 and thus the generation of oxygen vacancies over both ZnO-ZrO 2 and K + -ZnO-ZrO 2 samples.…”

Novel Heterogeneous Catalysts for CO2 Hydrogenation to Liquid Fuels

“…Additionally, many studies have demonstrated that the C 5 –C 11 isoparaffin/aromatic ratio depends on the nature of oxides and zeolites and the proximity of the two components. 113 , 115 For the oxide/zeolite catalyst system, the CO 2 conversion is still low (<20%), and the selectivity of byproduct CO is usually >30%. As mentioned above, the introduction of highly dispersed metals can improve the CO 2 -to-methanl performance of In 2 O 3 .…”

“… CO 2 hydrogenation hydrocarbon product distribution over (A) In 2 O 3 /HZSM-5 under reaction conditions of 340 °C, 3.0 MPa, H 2 /CO 2 = 3, and 9000 mL g –1 h –1 , 111 (B) composite catalyst containing ZnCrO x and various HZSM-5 zeolites (with and without Zn-exchange) at 330 °C, 5.0 MPa, H 2 /CO 2 = 3, and 2000 mL g –1 h –1 , 114 and (C) ZnO-ZrO 2 /HZSM-5 (reaction conditions: 340 °C, 4.0 MPa, H 2 /CO 2 = 3, and 7200 mL g –1 h –1 ). 115 Reprinted with permission from refs ( 111 ), ( 114 ), and ( 115 ). Copyright 2017 Springer-Nature, Copyright 2019 Royal Society of Chemistry, and Copyright 2020 American Chemical Society.…”

Selective Conversion of CO2 into para‐Xylene over a ZnCr2O4‐ZSM‐5 Catalyst

“…To further understand the reaction mechanism of CO 2 conversion on the oxide‐zeolite catalyst, in situ DRIFTS was performed to investigate the surface species on the process of CO 2 to aromatics (Figure 3). For blank ZnCr 2 O 4 , the peaks at 2962, 2865, 2730, and 1598 cm −1 were attributed to the HCOO* species, and the peak at 1365 cm −1 was ascribed to the CO 3 2− * species, which have been widely recognized as the precursors for methanol synthesis [6b,7,17] . For ZnCr 2 O 4 ‐ZSM‐5 catalyst, the new peaks of C−O stretching at 1168 cm −1 and H 3 CO* at 1101 cm −1 appeared, indicating formation of ethers on ZSM‐5 zeolite [7,17,18] .…”