17 research outputs found
Influence of ZrO<sub>2</sub> Structure and Copper Electronic State on Activity of Cu/ZrO<sub>2</sub> Catalysts in Methanol Synthesis from CO<sub>2</sub>
Cu/ZrO<sub>2</sub> catalysts obtained by impregnation of ZrO<sub>2</sub> and
complexation with citric acid were studied for CO<sub>2</sub> hydrogenation
to methanol. The catalyst structure, texture,
and active copper surface were determined using XRD, BET, and reactive
adsorption of N<sub>2</sub>O, 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 ZrO<sub>2</sub> 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-ZrO<sub>2</sub> phase and Cu<sup>1+</sup> cations, which
are present in the vicinity of oxygen vacancies. Complexes formed
preferentially on tetragonal ZrO<sub>2</sub> 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-ZrO<sub>2</sub> content. The implications of the
obtained results for the mechanism of the catalytic hydrogenation
of CO<sub>2</sub> are discussed