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

Abstract

Direct hydrogenation of CO 2 to methanol is an interesting method to recycle CO 2 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 CO 2 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 Zr 4+ cations with Ce 4+ ; 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 Cu 0 active sites in Cu/UiO-66(Ce/Zr), and this was caused by oxygen spill-over between Cu 0 and Ce 4+ , and thus, the oxidation of the former. The impact of reaction conditions on the structure stability of tested catalyst was also determined.Catalysts 2020, 10, 39 2 of 17Synthesis of MeOH is an exothermic reaction that leads to the reduction of the number of molecules; therefore, according to the Le Chatelier's principle, the increase of the pressure and decrease of temperature will favor product formation. However, CO 2 is a chemically inert molecule and its activation requires some increase in reaction temperature. The process is usually carried out over Cu/ZnO/Al 2 O 3 catalyst at temperatures between 230 and 280 • C and at elevated pressure of 50-120 bar [1][2][3][4][5]. The active site for MeOH production from CO 2 consists of Cu steps decorated with Zn atoms. Copper, when alone, interacts with CO 2 poorly; hence, the presence of Zn is necessary to enhance its adsorption and speed up its conversion to methanol [6].MeOH production via CO 2 hydrogenation is a challenging process since the selectivity of the reaction is low and a number of unnecessary and undesired by-products is formed. At higher temperatures the CO formation is favored, so the RWGS reaction (Equation (3)) can occur during MeOH synthesis. That reaction consumes hydrogen and lowers alcohol production. Besides, both the MeOH synthesis (Equation (2)) and RWGS reaction (Equation (3)) produce H 2 O that leads to catalyst deactivation by inhibiting the active metal [7].Direct hydrogenation of CO 2 to obtain methanol is an interesting method to recycle the CO 2 produced, e.g., during combustion of fossil fuels; therefore,...

Modular assembly of electron transfer pathways in bimetallic MOFs for photocatalytic ammonia synthesis

“…23,28 Therefore, the vibration modes at 679, 580 and 473 cm −1 are attributed to the stretching vibrations of M-O, μ 3 -O and μ 3 -OH, respectively. 20,28 The FTIR spectra of other NU6(Ce-Hf) samples were similar to those of NU6(1Ce-1Hf), indicating that these materials had a similar organic framework composition. Fig.…”

“…Synthesis of NU6(Ce-Hf) samples NU6(Ce-Hf) samples were in situ synthesized according to the previous literature with modification (Scheme 1). 20,21 First, 1 mmol (NH 4 ) 2 Ce(NO 3 ) 6 and HfCl 4 with different molar ratios (1Ce : 0Hf, 3Ce : 1Hf, 1Ce : 1Hf, 1Ce : 3Hf, 0Ce : 1Hf) were placed in a 100 mL quartz glass bottle. Then, 1 mmol (181 mg) 2-aminoterephthalic acid (TPA-NH 2 ) was added into the bottle.…”

Enhanced Mitigation of Fire and Explosion Risks due to Hydrogen Leakage Using Targeted Nitrogen Nozzle Spray Approach

“…The hydrogen mass flow inlet was based on the choked flow calculations for flange opening and crack opening, which are 0.3857 and 0.8248 kg/s, respectively. The gauge pressure and temperature were set as 12 MPa and 553.15 K, respectively, because these values are mostly used in hydrogenation reactions. − The inlet nitrogen mass flow was set as 10 kg/s. The exhaust fan pressure jump was set as 270 Pa in accordance with industrial standards, based on the size of the pilot plant.…”

Inner transition metal-modulated metal organic frameworks (IT-MOFs) and their derived nanomaterials: a strategic approach towards stupendous photocatalysis

“…83 Additionally, Stawowy et al reported high selectivity for CH 3 OH as the CO 2 photo-reduced product using Cu-doped (Ce/Zr)-MOF. 102 All these reports represent the specific tendencies of IT-MOFs towards product-selective CO 2 reduction.…”