Role of Graphene Oxide Aerogel Support on the CuZnO Catalytic Activity: Enhancing Methanol Selectivity in the Hydrogenation Reaction of CO₂

Abstract

A novel CuZnO multicomponent catalyst, involving reduced graphene oxide (rGO) as a support, was synthesized to be applied in the catalytic hydrogenation of CO 2 to methanol. The CuZnO@rGO composite was prepared as a 3D aerogel by a twostep process involving supercritical CO 2 for macrostructuration and H 2 treatment for reduction. Electron microscopy was applied to visualize the meso/macroporous morphology formed by the supercritical drying. The elemental mapping depicted a homogenous distribution of CuZnO nanoparticles deposited on the rGO flakes. It was demonstrated that methanol production increases for the CuZnO@rGO composite in comparison to unsupported similar CuZnO nanoparticles. This behavior was ascribed to a different interaction established between the Cu 0 and ZnO nanoparticles used as synthetized or deposited on rGO. It is shown that the highly reduced rGO component stimulates H 2 O desorption produced during the hydrogenation reaction, thus it serves as a support hindering the sintering of Cu 0 nanoparticles. The formation of a diluted surface alloy of Zn into Cu 0 was determined for the unsupported CuZnO NPs, while for the CuZnO@rGO aerogel composite, the absence of any additional phase, e. g., a surface alloy or reduced ZnO, was confirmed. The composite aerogels show excellent MeOH selectivity at high temperature (up to 260 °C) and low pressure (10 bar).

Hydrogenation of Carbon Dioxide to Methanol over Non-Noble Catalysts: A State-of-the-Art Review

“…It is well known that the preparation methods of catalysts have significant influences on the catalytic performances, which mainly include coprecipitation [22,23,49], impregnation [47,70,71], and sol-gel [65,70,72]. However, to further enhance the activity, selectivity, water tolerance, and stability of Cu-based catalysts, some emerging methods have appeared in recent reports [25,46,50,73,74]. For example, metal nanoparticles (NPs) attracted growing interest due to their outstanding applications in numerous fields, but so far, no large-scale synthesis of CuNPs has been reported using the disproportionation route and the reductive pathway.…”

“…Overall, the study offers many prospects for the rapidly developing field of copper plasmonic catalysis. Kubovics et al [46] prepared its precursor CuOZnO NPs via conventional chemistry and designed rGO aerogels-supported CuZnO NPs with water repulsion as efficient 3D catalysts. Then, the supercritical CO 2 was applied for the nano-structuration and the fabrication of 3D devices with macro-and mesoporosity, and the targeted sample was obtained through H 2 reduction.…”

“…[44] aCZZ-LDH 3 (G) 2000 3 4.9 78.3 0.037 [45] CuZnO@rGO 1 20,000 b 3 N.A. ~100 0.007 [46] 15Cu/6.4ZnO/AlFum MOF 5 (G) 10,000 3 45.6 3.48 0.057 [47] CuZn10Zr 3 (W) 6000 3 14.0 54.4 0.65 [48] 30Cu-ZZ 66…”

“…Some emerging supports have been gradually successfully developed, such as mesoporous aluminosilicate support, Mg-Al layered double hydroxide (LDH) [43,45]. For example, Kubovics et al [46] synthesized a novel Cu-ZnO multicomponent catalyst as a 3D aerogel, using reduced graphene oxide (rGO) as a support. It was found that the addition of rGO to the catalytic system significantly increased the methanol production rate by fourfold compared to pristine Cu-ZnO NPs at 220 • C. This was mainly because the intrinsic activity of Cu was enhanced due to the strain imposed at the ZnO interphase, causing a misfit at the contact surface.…”

Green Supercritical CO2 Synthesis of [Copper Clusters@FeBTC]@rGO Catalyst for Highly Efficient Hydrogenation of CO2 to Methanol

“…Porous oxides (alumina, silica, or zirconia), carbides, zeolites, carbon-based compounds (activated carbon, graphene, carbon nanotubes, etc.) and polymers are frequently used supports. − …”