Gengshen Hu

CO2 Adsorption and Desorption on MgO/Al2O3: An In Situ Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) Study

The adsorption and desorption of CO2 on MgO/Al2O3 were investigated by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with the method of curve-fitting analysis. The spectroscopic results indicate that there are three chemisorbed surface species formed on the MgO/Al2O3, i.e., free carbonate ion, bridged carbonate, and bidentate carbonate species, which correspond to the peaks at 1675, 1403, and two peaks at 1610 and 1340 cm−1, respectively, when the sample was exposed in CO2 flow at 130 °C. The quantification analysis of the spectra during CO2 adsorption and desorption shows that the formation and desorption rates of all surface species are coverage dependent. Among the three species, the bridged carbonate shows the highest speed of formation and desorption, indicating that this type of species may be beneficial to CO2 capture and release. It should also be noted that the contribution of support Al2O3 to CO2 capture is negligible. This study may help us to understand the interaction between CO2 and metal oxides and thus to give more insights into CO2 capture using solid sorbents.

Great improvement on the selective hydrogenation of crotonaldehyde over CrOx- and FeOx-promoted Ir/SiO2 catalysts

Catalytic selective hydrogenation of α,β-unsaturated aldehydes to α,β-unsaturated alcohols is very important in the synthesis of various fine chemicals. However, the development of highly efficient catalyst systems is challenging because of the low selectivity and severe deactivation of the currently employed catalysts such as Pt and Au. In this work, a series of CrOx- and FeOx-promoted Ir/SiO2 catalysts were prepared by a sequential impregnation method and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that the addition of promoters could greatly enhance the catalytic performance. The Ir/SiO2 catalyst promoted with combined CrOx–FeOx with a (Cr + Fe)/Ir ratio of 0.05 showed the highest steady state crotyl alcohol yield of 64.5% at a selectivity of 86%, which is 4-fold higher than that of the unpromoted Ir/SiO2 (15.5%) catalyst. Such an enhancement was due to the formation of new active sites generated at the Ir–CrOx and/or Ir–FeOx interfaces. Also, catalysts with low loadings of promoters showed excellent stability due to their appropriate electronic properties, while the catalyst with a high loading of promoters deactivated quickly due to the strong adsorption of products on the surface.

In situ real-time diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) study of hydrogen adsorption and desorption on Ir/SiO2 catalyst.

The adsorption and desorption of hydrogen on Ir/SiO2 catalyst were studied by using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with curve-fitting analysis. The results indicate that there are three different surface species formed on the catalyst that correspond to the peaks at 1950, 2010, and 2035 cm−1, respectively, when exposed in H2 flow at 130 °C. These surface species display different adsorption and desorption trends. Surface hydride forms after the catalyst is cooled to 80 °C and it disappears after the catalyst is heated to 130 °C again. This study may help us understand the interaction between hydrogen and noble metals and thus give more insights to heterogeneous catalytic mechanism involving hydrogen and hydrogen storage using metal materials.