Low temperature CO oxidation and water gas shift reaction over Pt/Pd substituted in Fe/TiO2 catalysts

We demonstrate the activity of Ti_0.84Pt_0.01Fe_0.15O_2−δ and Ti_0.73Pd_0.02Fe_0.25O_2−δ catalysts towards the CO oxidation and water gas shift (WGS) reaction. Both the catalysts were synthesized in the nano crystalline form by a low temperature sonochemical method and characterized by different techniques such as XRD, FT-Raman, TEM, FT-IR, XPS and BET surface analyzer. H₂-TPR results corroborate the intimate contact between noble metal and Fe ions in the both catalysts that facilitates the reducibility of the support. In the absence of feed CO₂ and H₂, nearly 100% conversion of CO to CO₂ with 100% H₂ selectivity was observed at 300 °C and 260 °C respectively, for Ti_0.84Pt_0.01Fe_0.15O_2−δ and Ti_0.73Pd_0.02Fe_0.25O_2−δ catalyst. However, the catalytic performance of Ti_0.73Pd_0.02Fe_0.25O_2−δ deteriorates in the presence of feed CO₂ and H₂. The change in the support reducibility is the primary reason for the significant increase in the activity for CO oxidation and WGS reaction. The effect of Fe addition was more significant in Ti_0.73Pd_0.02Fe_0.25O_2−δ than Ti_0.84Pt_0.01Fe_0.15O_2−δ. Based on the spectroscopic evidences and surface phenomena, a hybrid reaction scheme utilizing both surface hydroxyl groups and the lattice oxygen was hypothesized over these catalysts for WGS reaction. The mechanisms based on the formate and redox pathway were used to fit the kinetic data. The analysis of experimental data shows the redox mechanism is the dominant pathway over these catalysts.