CO₂ Hydrogenation to Methanol over Ce and Zr Containing UiO-66 and Cu/UiO-66

• Main Authors: Michalina Stawowy, Radosław Ciesielski, Tomasz Maniecki, Krzysztof Matus, Rafał Łużny, Janusz Trawczynski, Joaquin Silvestre-Albero, Agata Łamacz
• Format: Article
• Language: English
• Published: MDPI AG 2019-12-01
• Series: Catalysts
• Subjects: uio-66; cerium; copper; co₂ hydrogenation; methanol
• Online Access: https://www.mdpi.com/2073-4344/10/1/39

Direct hydrogenation of CO₂ to methanol is an interesting method to recycle CO₂ emitted e.g., during combustion of fossil fuels. However, it is a challenging process because both the selectivity to methanol and its production are low. The metal-organic frameworks are relatively new class of materials with a potential to be used as catalysts or catalysts supports, also in the reaction of MeOH production. Among many interesting structures, the UiO-66 draws significant attention owing to its chemical and thermal stability, developed surface area, and the possibility of tuning its properties e.g., by exchanging the zirconium in the nodes to other metal cations. In this work we discuss—for the first time—the performance of Cu supported on UiO-66(Ce/Zr) in CO₂ hydrogenation to MeOH. We show the impact of the composition of UiO-66-based catalysts, and the character of Cu-Zr and Cu-Ce interactions on MeOH production and MeOH selectivity during test carried out for 25 h at T = 200 °C and p = 1.8 MPa. Significant increase of selectivity to MeOH was noticed after exchanging half of Zr⁴⁺ cations with Ce⁴⁺; however, no change in MeOH production occurred. It was found that the Cu-Ce coexistence in the UiO-66-based catalytic system reduced the selectivity to MeOH when compared to Cu/UiO-66(Zr), which was ascribed to lower concentration of Cu⁰ active sites in Cu/UiO-66(Ce/Zr), and this was caused by oxygen spill-over between Cu⁰ and Ce⁴⁺, and thus, the oxidation of the former. The impact of reaction conditions on the structure stability of tested catalyst was also determined.