Methane aromatization study on M-Mo2C/HZSM-5 (M = Ce or Pd or Nb) nano materials

Abstract

The aim of this work is to understand the influence of second metals (M = Ce or Pd or Nb) on Mo2C active phase reduction into metallic molybdenum and on surface MoOx species of M-Mo2C/HZSM-5 catalysts studied for methane dehydroaromatization at 700 °C with GHSV 1800 mL. gcat−1. h−1. The fresh and spent catalysts were characterized by using ATR-FTIR, HRTEM/STEM, BET surface area, XRD, TPO, NH3-TPD-mass, XPS and H2-TPR techniques. Essentially, the highest benzene yield of 8.4% on Pd–Mo2C/HZSM-5 catalyst for 10 h of continuous operation was associated with limited Mo2C active phase reduction into metallic molybdenum at Pd–Mo proximity via Pd2+ to Pd0 step and promoted coke burning through reduced carbon deposits formation. Further, the surface reduction of CeO2 to Ce2O3 decreased the methane conversion due to sluggish MoOx species transformation to Mo2C active phase. On the other side, Nb2O5 primarily reduced into NbO2/NbO resulted in surface MoOx species and external surface Mo2C particles eventually produced superior coke via CH4 decomposition on Nb–Mo2C/HZSM-5 catalyst. The decreasing order of benzene yield after 10 h of reaction at 700 °C as follows: Pd–Mo2C/HZSM-5 (8.4%) > Mo2C/HZSM-5 (7.4%) > Nb–Mo2C/HZSM-5 (5.8%) > Ce–Mo2C/HZSM-5 (5.2%).

Keywords

• Methane
• Aromatization
• Molybdenum carbide
• Benzene
• HZSM-5
• Bronsted acidity