Influence of ZrO₂ Structure and Copper Electronic State on Activity of Cu/ZrO₂ Catalysts in Methanol Synthesis from CO₂

Abstract

Cu/ZrO2 catalysts obtained by impregnation of ZrO2 and complexation with citric acid were studied for CO2 hydrogenation to methanol. The catalyst structure, texture, and active copper surface were determined using XRD, BET, and reactive adsorption of N2O, respectively. The XPS and Auger spectroscopies were used to determine the surface structure and copper electronic state. FT-IR pyridine adsorption was studied to determine acidity of the catalysts. The results of quantum-chemical calculations concerning the formation of oxygen vacancies in monoclinic and tetragonal ZrO2 have been also presented. It was found that selection of the appropriate conditions of the catalyst preparation influences the degree of copper dispersion, its electronic state, and contents of the zirconia polymorphic phases (tetragonal and monoclinic). The presence of oxygen vacancies stabilizes both the thermodynamically unstable t-ZrO2 phase and Cu1+ cations, which are present in the vicinity of oxygen vacancies. Complexes formed preferentially on tetragonal ZrO2 built from Cu cations and oxygen vacancies are the acid centers active in methanol synthesis reaction; therefore the catalytic activity toward methanol increases with increasing t-ZrO2 content. The implications of the obtained results for the mechanism of the catalytic hydrogenation of CO2 are discussed.

Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts

“…These S-shaped logistic curves indicate an acceleration of the conversion rate that decelerates after a t0 turn point and finally reaches an equilibrium value. The logistic functions of total and partial CO2 conversion percentages to methanol and DME are given as Equation (10), (11), and (12). The time evolutions of methanol and DME conversion are observed to be different.…”

“…Methanol is one of the main CO2 hydrogenation products 2,6 which can be directly dehydrated to DME in a single batch reaction. Both these molecules are valuable alternative fuels 2,[7][8][9] and they are also used as feedstocks and intermediates for producing various chemicals and as energy carriers for fuel cells 7,[10][11][12] . Methanol can typically be produced from synthesis gas at a pressure between 50-100 bar and at a temperature between 200-300 °C 6,[12][13][14] .…”

One step microwave-assisted synthesis of nanocrystalline WOx–ZrO2 acid catalysts

“…By plotting the yield of acetophenone versus the tetragonal phase percentage (Figure 9), one can observe that the catalytic activity increases with increasing content of tetragonal ZrO 2 , thus confirming the primary role of this polymorph. Several authors have studied the influence of the zirconia polymorphs in supported Cu, [63][64][65] Au, 66 Ag, 67 Rh, 68 and Mo…”

“…The reason for this trend lies in the presence of anion vacancies in the metastable tetragonal polymorph originating from the introduction of trivalent or divalent ions. 69 As a consequence, the more ionic character of the tetragonal polymorph induces higher Lewis and Brønsted acidity 63 (see Figure S8 and Table S3) than in the more covalent monoclinic structure. Thus the more acid species stabilized over the tetragonal zirconia could explain the higher activity in the hydration of alkynes.…”

Catalytic Performance of Cu/ZnO/A12O3/ZrO2 for Slurry Methanol Synthesis from CO2 Hydrogenation: Effect of Cu/Zn Molar Ratio

“…At present the conventional CZA catalysts exhibit poor activity for CO 2 hydrogenation, because of water formation and strong hydrophilic character of alumina (Arena et al 2007). Several authors have established that copper based catalysts containing zirconia are active in the synthesis of methanol from CO 2 and H 2 (Samson et al 2014;Ud Din et al 2016;Witoon et al 2016;Zhang et al 2006). Arena (2008) investigated the reaction of CO 2 hydrogenation in a fixed bed reactor on Cu-ZnO/ZrO 2 , (ZrO 2 loading, 43 wt.…”