High performance of Ir-promoted Ni/TiO2 catalyst toward the selective hydrogenation of cinnamaldehyde

The catalytic performance of Ni/TiO2 and Ni–Ir/TiO2 catalysts in the selective hydrogenation of cinnamaldehyde (CAL) has been investigated. The Ni–Ir/TiO2 presented higher activity than the Ni/TiO2. Here, we studied and gave some insights into the interaction between Ni and Ir species and the role of Ir using X-ray diffraction (XRD), transmission electron microscope (TEM), hydrogen temperature-programmed reduction (H2 TPR), hydrogen temperature-programmed desorption (H2 TPD), and X-ray photoelectron spectroscopy (XPS). The size of Ni particles on the Ni–Ir/TiO2 was 10.1 nm, smaller than that (12.7 nm) on the Ni/TiO2. The reducibility of Ni was improved by addition of a small amount of Ir, as confirmed with the H2 TPR analysis. The Ni–Ir/TiO2 could be reduced at a temperature of 352 °C, which is lower than the temperature for Ni/TiO2 (385 °C); moreover, a new reduction peak appeared at 240 °C due to the stronger interaction of Ni–Ir species, which was certified by XPS analysis. The H2 TPD results indicate that the hydrogen spillover effect may occur in Ni–Ir/TiO2. The electronic structure of the surface Ni atoms was modified upon addition of Ir, resulting in an enhanced activity of the Ni–Ir/TiO2 catalyst, about four times as high as that of the Ni/TiO2 catalyst.