N-doped CNT nanocatalyst prepared from camphor and urea for gas phase desulfurization: Experimental and DFT study

Abstract

In the present work, mesoporous nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by using a low-cost and unique set of precursors (camphor and urea). The CVD method at 1000°C was used with different camphor/urea ratios, and Co-Mo/MgO nanocatalyst was utilized as growth catalyst. Application of mesoporous N-CNTs in selective oxidation of H2S was studied experimentally and N-CNTs interactions with H2S was also investigated using DFT calculations. The as-synthesized N-CNTs were characterized using FTIR, FE-SEM, elemental analysis, X-ray diffraction (XRD), XPS and nitrogen adsorption/desorption. The N-CNT2 sample with urea to camphor ratio (U/C) of 1 showed the highest sulfur yield at the three temperatures studied for which selectivity and conversion of 89% and 97% were obtained at 190°C. Considering experimental results, the relatively higher amount of pyridinic nitrogen (i.e. pyridinic and pyridinic oxide) was suggested as the reason for such high catalytic activity which was proved by quantum mechanical calculations. Further, DFT calculations were performed for elucidating the reaction and finding the most active nitrogen atoms in which the pyridinic oxide was found to be the most active followed by pyridinic. According to experiment and DFT results, the pyridinic species were determined as the most active phases of N-CNT toward H2S oxidation.