Alkaline carbon nanotubes as effective catalysts for H2S oxidation

Carbon nanotubes (CNTs) were made alkaline by impregnation with Na2CO3 and used for the direct oxidation of H2S into sulfur at 30 °C. The alkaline CNTs before and after H2S oxidation were characterized by N2 adsorption, scanning and transmission electron microscopy, X-ray diffraction, and thermogravimetry analysis. The effects of Na2CO3 loading and the structure of the CNTs on the catalytic activity of alkaline CNTs were investigated. Results indicated that the saturation sulfur capacity of alkaline CNTs was up to 1.86 g H2S/g catalyst, which was about 3.9 times higher than that of a common commercial H2S oxidation catalyst. The introduction of Na2CO3, which provided alkalinity needed for H2S dissociation, significantly enhanced the catalytic performance. The optimum content of Na2CO3 loading was determined to be 20 wt.% in the CNTs. The catalytic performance was also dependent on the structure of the CNTs, and the single-walled CNTs with the smallest tube diameter exhibited the highest sulfur capacity. Tangled CNTs provided their external voids to store the sulfur produced, which was a key feature of this high-performance CNT catalyst.