Synthesis of ordered mesoporous La2O3-ZrO2 composites with encapsulated Pt NPs and the effect of La-dopping on catalytic activity

In this work, we report a feasible approach to synthesize a ternary nanocomposites , Pt/lanthanum doped mesoporous zirconium oxide (Pt/La 2 O 3 -ZrO 2 ), via an effective two-step method. Ordered mesoporous La 2 O 3 -ZrO 2 composites were firstly fabricated with mesoporous silica KIT-6 as a hard template. Subsequently, uniform Pt nanoparticles encapsulated by 4 hydroxyl-terminated poly (amidoamine) (G4-OH PAMAM) dendrimers were deposited on the La 2 O 3 -ZrO 2 composites. The as-prepared samples were characterized by transmission electron microscope (TEM), N 2 adsorption–desorption isotherm analysis, energy dispersion X-ray analysis (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (H 2 -TPR). The average size of PtDENs was found to be 1.48   nm in diameter. Furthermore, the introduction of La could improve the structure of the supports which was confirmed by XRD and H 2 -TPR analysis. The reduction of p-nitrophenol to p-aminophenol by NaBH 4 was utilized to evaluate the catalytic performances of catalysts. Results indicated that the Pt/La 2 O 3 -ZrO 2 catalyst calcined in nitrogen at 550   °C exhibited the highest catalytic performance and still kept the high catalytic activity even after six cycles. This phenomenon suggests that synergistic effect among Pt-Zr-La could enhance the catalytic efficiency. Finally, reaction mechanism was proposed for the reduction of p-nitrophenol.