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

Liu Z, Zhang Z, Xing W, Komarneni S, Yan Z, Gao X, Zhou X - Nanoscale Res Lett (2014)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Heavy Oil Processing; Key Laboratory of Catalysis, CNPC, China University of Petroleum, Qingdao 266580, People's Republic of China ; Department of Chemical Engineering, Hunan University, Changsha 410082, People's Republic of China.

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.

No MeSH data available.


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FTIR spectra after pyridine adsorption on HZs and MgHZs with Si/Al ratios. Parent HZs (above) and as-prepared MgHZs (bottom) with Si/Al ratios 50 (A), 100 (B), and 360 (C).
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Figure 6: FTIR spectra after pyridine adsorption on HZs and MgHZs with Si/Al ratios. Parent HZs (above) and as-prepared MgHZs (bottom) with Si/Al ratios 50 (A), 100 (B), and 360 (C).

Mentions: The adsorption of pyridine on solid catalyst materials and its analysis by FTIR have been widely used to distinguish the presence of Lewis or Brønsted acid sites. Herein, the acid type was identified by collecting IR spectra from pyridine adsorption on HZs or MgHZs (Figure 6). The spectra of pyridine adsorbed on parent HZs exhibit characteristic bands at 1548 and 1448 cm-1, which are attributed to Brønsted acid sites and Lewis acid sites, respectively. The band at 1490 cm-1 is assigned to pyridine on both Brønsted and Lewis acid sites. The spectrum from HZ with low Si/Al ratio of 50 only exhibits an intense band at 1548 cm-1, which indicates that most of the acid sites are Brønsted acid type. In contrast, HZ with highest Si/Al ratio of 360 only exhibits an intense band at 1448 cm-1, which suggests that most of the acid sites are Lewis acid type.


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

Liu Z, Zhang Z, Xing W, Komarneni S, Yan Z, Gao X, Zhou X - Nanoscale Res Lett (2014)

FTIR spectra after pyridine adsorption on HZs and MgHZs with Si/Al ratios. Parent HZs (above) and as-prepared MgHZs (bottom) with Si/Al ratios 50 (A), 100 (B), and 360 (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4199779&req=5

Figure 6: FTIR spectra after pyridine adsorption on HZs and MgHZs with Si/Al ratios. Parent HZs (above) and as-prepared MgHZs (bottom) with Si/Al ratios 50 (A), 100 (B), and 360 (C).
Mentions: The adsorption of pyridine on solid catalyst materials and its analysis by FTIR have been widely used to distinguish the presence of Lewis or Brønsted acid sites. Herein, the acid type was identified by collecting IR spectra from pyridine adsorption on HZs or MgHZs (Figure 6). The spectra of pyridine adsorbed on parent HZs exhibit characteristic bands at 1548 and 1448 cm-1, which are attributed to Brønsted acid sites and Lewis acid sites, respectively. The band at 1490 cm-1 is assigned to pyridine on both Brønsted and Lewis acid sites. The spectrum from HZ with low Si/Al ratio of 50 only exhibits an intense band at 1548 cm-1, which indicates that most of the acid sites are Brønsted acid type. In contrast, HZ with highest Si/Al ratio of 360 only exhibits an intense band at 1448 cm-1, which suggests that most of the acid sites are Lewis acid type.

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Heavy Oil Processing; Key Laboratory of Catalysis, CNPC, China University of Petroleum, Qingdao 266580, People's Republic of China ; Department of Chemical Engineering, Hunan University, Changsha 410082, People's Republic of China.

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.

No MeSH data available.


Related in: MedlinePlus