Demonstration of low-temperature toluene degradation mechanism on hydrotalcite-derived oxides with ultrasonic intervention

A series of transition binary metal oxides were derived from Mg-Al, Ni-Al and Co-Al hydrotalcite-like compounds (HTLCs) with the intervention of ultrasound during the crystallization process, and the toluene removal rate of the hydrotalcite-derived oxides (HTOs) was investigated. The results of the toluene oxidation test showed that the conversion efficiency of ultrasonic intervened samples was higher than those of untreated samples. Focus solely on the elements difference, the conversion efficiency of CoAl-HTO is the highest among all samples, followed by NiAl-HTO, and MgAl-HTO is the lowest for both ultrasonic-treated and untreated samples. However, the conversion efficiency of ultrasonic treated NiAl-HTO (T90 = 275 °C) is higher than that of untreated CoAl-HTO (T90 = 300 °C) but still lower than that of treated CoAl-HTO (T90 = 270 °C), inferred the positive influence of the ultrasonic intervention to the HTOs on toluene degradation. The properties of those samples were characterized by XRD, XPS, SEM, H2-TPR and physisorption equipment. The characterization results showed that the better toluene degradation ability might be attributed to the more reactive Co2+ and abundant oxygen vacancies exposed on the sample’s surface which revealed by the ultrasonic intervention, as well as the large surface area and the high Oads/Olatt. This work provided novel evidence for the influence of ultrasonic intervention on the material surface modification and toluene degradation which corresponding to the Mars-van Krevelen mechanism.