Hydrogenation of CO₂ on MoO₃/Al₂O₃ and γ-Al₂O₃

Abstract

The physicochemical and catalytic (CO₂ hydrogenation) characteristics of Mo-containing catalysts were studied. The catalysts containing 8 and 15 wt % Mo oxide were prepared by impregnation of γ‑Al₂O₃ with ammonium paramolybdate, followed by drying and calcination at 500°C. The introduction of Mo oxide reduced the pore volume of the support and increased the average pore size, indicating that molybdenum oxide was distributed in the support pores. According to the X-ray diffraction analysis, the calcinated catalyst did not contain the crystalline MoO₃ phase. According to the Raman spectra, oxygen-containing formations were present on the catalyst surface, with Mo atoms tetrahedrally and octahedrally coordinated to the oxygen atoms. The impregnated MoO₃ was partially reduced with hydrogen during linear heating, starting from 320°C. The hydrogenation of CO₂ (gas composition, vol %: 30.7 CO₂, 68 H₂, the rest was N₂; 0.5 g sample) was studied under conditions of linear heating to 400°C. The main reaction was the reverse reaction of CO steam reforming. The contribution of methanation to CO₂ hydrogenation was small. An increase in the temperature and pressure had a positive effect on CO₂ conversion. When the pressure increased from 1 to 5 MPa, the CO content was approximately doubled. In the CO₂ hydrogenation, appreciable activity (although significantly lower compared to that of Mo-containing catalysts) was also exhibited by γ-Al₂O₃, preliminarily heated to 400°C in an H₂ flow. The activity of alumina also increased with pressure.