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

Abstract

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 CrO_x- and FeO_x-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 CrO_x–FeO_x 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–CrO_x and/or Ir–FeO_x 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.