Enhanced catalytic performance for methane dehydro-aromatization on Mo/HMCM-49 prepared with citric acid

A simple citric acid (CA)-ammonium molybdate co-impregnation method was applied to prepare the Mo-based MCM-49 catalyst to ameliorate the dispersion of metallic Mo for methane dehydro-aromatization reaction (MDA). The newly prepared catalyst has higher crystallinity and maintains the original morphology of zeolite, which proves that the addition of citric acid will not destroy the basic structure of the catalyst. Based on H2-TPR, UV-vis, NH3-TPD and XPS characterization results, it can be corroborated that the introduction of citric acid changes the coordination state of Mo element. Bronsted acid sites can stabilize the monomeric Mo oxide species by increasing MoOx migration into the MCM-49 zeolite pores channel after calcination, which may affect the distribution of active sites MoCx and thus improve MDA catalytic activity. The experimental results show that the Mo-based MCM-49 catalyst with nCA : nMo ratios of 1.0 has higher methane conversion (14.5 %) and aromatics yield (9.8 %). The combination of XPS, TG and Raman tests of the spent catalyst confirms that the newly synthesized catalysts produce less carbon deposition, thus improving the catalytic durability during the MDA reaction. Catalytic test indicated that 4MoM-CA(1.0) prepared with citric acid-ammonium molybdate co-impregnation method performs 14.5 % of CH4 conversion and 9.8 % of aromatics yield. Meanwhile, the catalytic stability of 4MoM-CA(1.0) was better than the catalyst 4MoM prepared with conventional ammonium molybdate impregnation method.image

Automated summary

In this study, a Mo-based MCM-49 catalyst was successfully prepared using a citric acid-ammonium molybdate co-impregnation method to improve the dispersion of metallic Mo. Through a series of characterization results, it was found that the introduction of citric acid changed the coordination state of Mo and improved the catalytic activity by affecting the distribution of active sites. The experimental results showed that the catalyst prepared under specific conditions exhibited high methane conversion and aromatics yield, and demonstrated good catalytic stability.