Hydrogenation of CO2 on MoO3/Al2O3 and γ-Al2O3

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 gamma-Al2O3 with ammonium paramolybdate, followed by drying and calcination at 500 degrees 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 degrees C. The hydrogenation of CO2 (gas composition, vol %: 30.7 CO2, 68 H-2, the rest was N-2; 0.5 g sample) was studied under conditions of linear heating to 400 degrees 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 gamma-Al2O3, preliminarily heated to 400 degrees C in an H-2 flow. The activity of alumina also increased with pressure.