M_xO_y–ZrO₂ (M = Zn, Co, Cu) Solid Solutions Derived from Schiff Base-Bridged UiO-66 Composites as High-Performance Catalysts for CO₂ Hydrogenation

Abstract

Metal–organic frameworks have been exploited as excellent solid precursors and templates for the preparation integrated nanocatalysts with multicomponent and hierarchical structures. Herein, a novel synthetic protocol has been developed to fabricate versatile Zr-based solid solutions (such as ZnO–ZrO2, Co3O4–ZrO2, and CuO–ZrO2) via pyrolysis of Schiff base-modified UiO-66 octahedrons (size <100 nm), which were then utilized as efficient catalysts for CO2 hydrogenation. The Schiff base serves as an effective bridge to dope secondary metal ions into UiO-66 frameworks with controlled amounts of 0.13–8.8 wt %, which are initially hard to achieve. Interestingly, by simply changing the loading metal ions, the selectivity of C1 hydrogenation products can be facilely tuned. For instance, the maximum CO2 conversion of ZnO–ZrO2, Co3O4–ZrO2, and CuO–ZrO2 solid solutions were 5.8, 11.4, and 22.5%, with the main product selectivity of 70% CH3OH, 92.5% CH4, and 86.7% CO, respectively. Moreover, in situ diffuse reflectance infrared Fourier transform spectra characterization reveals that the significant difference in C1 product selectivity is mainly determined by the balance of *HCOO, *CH3O, and *CO intermediate species over the Zr-based solid solutions.

Selective methylation of toluene using CO 2 and H 2 to para -xylene

“…When ZZO-4SZ5 is exposed to CO 2 + H 2 , the species of HCOO* (1584 cm −1 ) and slight CO 3 * (1694 and 1525 cm −1 ) are detected ( fig. S7A) (31)(32)(33)(34). When the catalyst is exposed to C 7 H 8 + CO 2 + H 2 , no any peak of CO 3 * is observed (Fig.…”

CO2hydrogenation to methanol and hydrocarbons over bifunctional Zn-doped ZrO2/zeolite catalysts

“…21 ZrO 2 has been investigated as a support material in many binary and ternary systems for CO/CO 2 hydrogenation to methanol. [23][24][25][26][27][28][29] IR and TPD studies over pristine zirconia conducted by Pokrovski et al 30 showed that CO and CO 2 are mainly adsorbed as HCO − , CO 3 2− and HCO 3…”

“…These findings highlight that operation at high temperature thermodynamically favors side reactions, such as RWGS. 16 In another recent contribution, Li et al 29 used a metalorganic approach to prepare the catalysts by means of a Schiff base, yielding a Zn-doped ZrO 2 solid solution (with a 1 : 1 ratio). This catalyst showed a methanol selectivity of 70% with 5.7% CO 2 conversion at 320°C, V(CO 2 )/V(H 2 )/V(N 2 ) = 24/ 72/4% and GHSV = 18 000 mL g −1 h −1 .…”

Enhanced active site extraction from perovskite LaCoO3 using encapsulated PdO for efficient CO2 methanation

“…7(B), observable peaks at 3600-3800 cm À1 are attributed to overtones of the gaseous CO 2 species for spent PdO@LaCoO 3 [35]. The intense bands at 2360-2450 cm À1 can be ascribed to stretching vibrations of the adsorbed gaseous CO 2 [50]. Meanwhile, the chemisorption of CO 2 results in the formation of peaks located at 1474, 1512, 1541, 1560 and 1627 cm À1 , which are assigned to the formation of carbonate and bicarbonate species, respectively [50].…”