SnO2 nano-rods promoted by In, Cr and Al cations for toluene total oxidation: The impact of oxygen property and surface acidity on the catalytic activity

Abstract

SnO2 nano-rods doped by In, Cr and Al cations have been fabricated by using hydrothermal method and evaluated for toluene total oxidation. SEM results demonstrate that the initial nano-rods aggregated into three-dimensional microspheres for all the samples. XRD testifies that all the SnO2 nano-rod catalysts are well crystallized with low surface areas and big crystallite sizes. It is revealed by HRTEM images that the pure SnO2 and Sn99Al1 nano-rods preferentially exposed (101) facets, while the Sn99In1 and Sn99Cr1 nano-rods exposed (110) facets, which demonstrated that the doping with a small amount of the secondary cations into the crystal matrix can significantly influence the crystallization process and change the preferentially exposed facets of SnO2 nano-rods. As testified by XPS and O2-TPD, the introduction of Al3+ cations into the crystal matrix of SnO2 nano-rods leads to the formation of more mobile oxygen species. In addition, NH3-TPD results substantiate that the surface acidity of catalysts modified by Al and Cr cations can also be significantly enhanced, which is favorable for the adsorption and activation of the toluene molecules. In conclusion, the oxygen mobility and surface acidity are regarded as the two predominant factors accounting for the improved activity of the doped SnO2 nano-rod catalysts for toluene total oxidation. Due to the optimized concerted action of the two factors, Sn99Al1-rod, a catalyst doped by Al cations shows the highest activity among all the catalysts.