Studying the Stability of Supported Heteropoly Compounds Using Data from Diffuse Reflectance Infrared Spectroscopy

The effect redox treatment has on the stability of supported heteropoly compounds with Keggin structure in the KxH6 – х [SiW11NiO39] + PtCl4/ZrO2–Al2O3, KxH6 – х[SiW11NiO39] + PtCl4/Al2O3, and KxH6 – х[SiW11CoO39] + H2PtCl6/ZrO2–Al2O3 hybrid catalysts is studied via DRIFTS using CO as a probe molecule. It is found that the electronic state of nickel and cobalt remains unchanged during the redox treatment under the static conditions at 300°C. The Ni-HPC and Co-HPC complexes are stable during redox treatment. Platinum is in three electronic states in the calcined Ni-HPC + PtCl4/ZrO2–Al2O3 sample: Pt4+, Pt2+, and Pt+. Redox treatment reduces platinum to Pt+ cations. Platinum is in two electronic states in the calcined Ni-HPC+PtCl4/Al2O3 sample: Pt2+ and Pt+. Redox treatment reduces platinum to Pt+ cations and small metal particles. A comparison of two Ni-HPC + PtCl4 samples supported on different carriers indicates that ZrO2 in the carriers prevents the reduction of platinum to metal. Platinum is in two electronic states in the Co-HPC + H2PtCl6/ZrO2–Al2O3 calcined sample: Pt4+ and Pt+. Redox treatment reduced platinum to form Pt+.