Combined promoting effect of molybdenum on the bimetallic Al2O3-La2O3 catalysts for NOx reduction by CO

Abstract

Promotional effect of molybdenum on bimetallic Al2O3-La2O3-based catalysts was investigated in the selective catalytic reduction (CO-SCR) reaction. The physicochemical properties of the solids were evaluated through X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), nitrogen physisorption analyses, Temperature programmed reduction (TPR), NH3-temperature programmed desorption (NH3-TPD) and Transmission electron microscopy (TEM). Structural characterizations confirmed the formation of porous nanostructured solids with molybdenum helping the dispersion of the Ni or Pt active sites close to the molybdenum particles. The catalysts have acid sites of medium to low strengths effectively enhancing the catalytic activity of the solids. Investigation of the various active sites revealed PtMo supported on Al2O3-La2O3 as the best catalyst using distinct temperatures and poisoning conditions in the CO-SCR reaction, rather than NiMo and CoMo counterparts. The oxidation of the species and phase transformation were more significant on the CoMo than NiMo catalyst, with the latter having a modest performance. The low interaction of the PtMo with the support provided the formation of a Pto and Mo6+ redox pair, which resulted in high CO and NOx adsorption to form CO2 and N2. This was due to the synergistic effect of valence-rich Mo transition oxides with Pt species, resulting in the inhibition of irreversible sulfatation and coking over PtMo/Al2O3-La2O3 catalyst.