Tailoring acidity of HZSM-5 nanoparticles for methyl bromide dehydrobromination by Al and Mg incorporation.

Zhen Liu,Zifeng Yan,Xiaoping Zhou,Zhongdong Zhang,Sridhar Komarneni,Xionghou Gao,Wei Xing

doi:10.1186/1556-276x-9-550

Abstract

Three kinds of HZSM-5 nanoparticles with different acidity were tailored by impregnating MgO or varying Si/Al ratios. Both the textural and acidic properties of the as-prepared nanoparticles were characterized by nitrogen adsorption-desorption measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy (FTIR or Py-FTIR). It was found that the intensity of Lewis acid sites with weak strength was enhanced by impregnating MgO or reducing Al concentration, and such an enhancement could be explained by the formation of Mg(OH)+ or charge unbalance of the MgO framework on the surface of HZSM-5 support. The effect of HZSM-5 nanoparticles' acidity on methyl bromide dehydrobromination as catalyst was evaluated. As the results, MgHZ-360 catalyst with the highest concentration of Lewis acid sites showed excellent stability, which maintained methyl bromide conversion of up 97% in a period of 400 h on stream. Coke characterization by BET measurements and TGA/DTA and GC/MS analysis revealed that polymethylated naphthalenes species were formed outside the channels of the catalyst with higher acid intensity and higher Brønsted acid concentration during the initial period of reaction, while graphitic carbon formed in the channels of catalyst with lower acid intensity and higher Lewis acid concentration during the stable stage.

Highlights

Natural gas is industrially converted to syngas by steam reforming reaction, which can be converted either to liquid fuel by Fisher-Tropsch (F-T) process directly [1] or to methanol using Cu/ZnO/Al2O3 catalyst [2]
Three kinds of catalysts were prepared by loading 2.0 wt. % MgO on HZSM-5 zeolites with different Si/Al ratios to investigate the effect of acid strength and intensity on methyl bromide dehydrobromination
The structure and crystallinity of HZSM-5 were retained after impregnation with Mg salt, but no Mg phases could be detected by X-ray diffraction (XRD)

Summary

Introduction

Natural gas is industrially converted to syngas by steam reforming reaction, which can be converted either to liquid fuel by Fisher-Tropsch (F-T) process directly [1] or to methanol using Cu/ZnO/Al2O3 catalyst [2]. F-T or MTH process could convert natural gas into liquid fuel as alternative to crude oil, an unavoidable reality is that syngas should be firstly synthesized. The location of such unconventional gas is usually far away from abundant water sources and inconveniently transported. All those reality of the condition limits cost-effective utilization of natural gas via syngas process on a world-wide scale [7]

Methods

Results

Conclusion