Abstract
A series of Co3O4 catalysts were synthesized by an ammonia precipitation method at various precipitating pH values (8.0, 8.5, 9.0, 9.5, and 10.0) and with different numbers of washings. Their performance in the total oxidation of two selected hydrocarbons, toluene and propane, was evaluated at a reactant/oxygen molar ratio of 1/210 and a Weight Hourly Space Velocity (WHSV) of 40,000 mL g−1 h−1. The physicochemical properties of the catalysts were characterized by thermogravimetric and differential thermal analysis (TG/DTA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and N2 absorption–desorption. The results show that the catalysts are in the cubic spinel phase (Fd-3m (227), a = 8.0840 Å) with average crystalline sizes of 29−40 nm and specific surface areas of 12–20 m2 g−1. All catalysts allowed 100% conversion of both toluene and propane at temperatures below 350 °C. The precipitating pH and the number of washings were observed to significantly affect the catalytic performance. The optimal synthesis condition was established to be pH 8.5 with two washings. The best catalyst gave 100% conversion of toluene and propane at 306 °C and 268 °C, respectively.
Highlights
Volatile organic compounds (VOCs) represent one of the major issues of this century because of their participation in atmospheric photochemical reactions, since they cause an increase of ozone (O3 ) concentration in the troposphere, produce photochemical smog, and sometimes form tiny health-damaging particulate matter (PM) [1]
The second stage between 150 and 300 ◦ C exhibited a total weight loss ranging from 34 to 37 wt.%, which was much larger than that expected for the decomposition of cobalt hydroxide into cobalt oxide (13.6 wt.%)
Co3 O4 -based catalysts prepared via ammonia-precipitation were synthesized, characterized, and tested for the total oxidation of toluene and propane
Summary
Volatile organic compounds (VOCs) represent one of the major issues of this century because of their participation in atmospheric photochemical reactions, since they cause an increase of ozone (O3 ) concentration in the troposphere, produce photochemical smog, and sometimes form tiny health-damaging particulate matter (PM) [1]. One effective way is to use porous material by the hard or soft template method since high porosity favours mass transfer and adsorption [10,11] Another way to improve catalytic performance is to dope catalysts with metal or mixed oxides [12,13]. Tang et al found that alkali-metal (Li, Na, K) had a poisoning effect on the oxidation of both CO and propane over Co3 O4 catalysts [21] Given this fact, the ammonia route was preferable because the NH4 NO3 species would completely decompose after calcination, ruling out the effect of impurities issues on catalytic activity. A series of Co3 O4 -based catalysts were prepared via the ammonia-precipitation method at different pH values and with different number of washings, characterized by thermogravimetric and differential thermal analysis (TG/DTA), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), and evaluated for the total oxidation of toluene and propane
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