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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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GC/MS analysis of trapped organic compounds in different catalysts. Spent catalysts of MgHZ-50 (A), MgHZ-100 (B), and MgHZ-360 (C).
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Figure 11: GC/MS analysis of trapped organic compounds in different catalysts. Spent catalysts of MgHZ-50 (A), MgHZ-100 (B), and MgHZ-360 (C).

Mentions: Figure 11 presents the GC/MS result of the organic compounds trapped in the spent catalyst. Compared to the reaction of methanol to hydrocarbon (MTH) process, aromatics were detected in extracted organic phase but with some differences. Methylated naphthalene compounds were observed in the spent catalysts with lower Si/Al ratio, which is in contrast to the results of Bjørgen et al. [35]. They found that no methylated naphthalene was trapped in the HZSM-5 when using methanol as the reactant. Organics formed in the MgHZs depended on the acid intensity and type to a certain extent (Figure 11), which means that the catalyst with higher acid site intensity and more Brønsted acid type tended to generate naphthalene species while only methyl substituted benzene species were observed in the retained catalyst with higher acid site intensity and more 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)

GC/MS analysis of trapped organic compounds in different catalysts. Spent catalysts of MgHZ-50 (A), MgHZ-100 (B), and MgHZ-360 (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 11: GC/MS analysis of trapped organic compounds in different catalysts. Spent catalysts of MgHZ-50 (A), MgHZ-100 (B), and MgHZ-360 (C).
Mentions: Figure 11 presents the GC/MS result of the organic compounds trapped in the spent catalyst. Compared to the reaction of methanol to hydrocarbon (MTH) process, aromatics were detected in extracted organic phase but with some differences. Methylated naphthalene compounds were observed in the spent catalysts with lower Si/Al ratio, which is in contrast to the results of Bjørgen et al. [35]. They found that no methylated naphthalene was trapped in the HZSM-5 when using methanol as the reactant. Organics formed in the MgHZs depended on the acid intensity and type to a certain extent (Figure 11), which means that the catalyst with higher acid site intensity and more Brønsted acid type tended to generate naphthalene species while only methyl substituted benzene species were observed in the retained catalyst with higher acid site intensity and more 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