کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10243806 | 47177 | 2005 | 16 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
The roles of gallium hydride and Brønsted acidity in light alkane dehydrogenation mechanisms using Ga-exchanged HZSM-5 catalysts: A DFT pathway analysis
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی شیمی
کاتالیزور
پیش نمایش صفحه اول مقاله
![عکس صفحه اول مقاله: The roles of gallium hydride and Brønsted acidity in light alkane dehydrogenation mechanisms using Ga-exchanged HZSM-5 catalysts: A DFT pathway analysis The roles of gallium hydride and Brønsted acidity in light alkane dehydrogenation mechanisms using Ga-exchanged HZSM-5 catalysts: A DFT pathway analysis](/preview/png/10243806.png)
چکیده انگلیسی
We have used density functional theory (DFT) to study light alkane dehydrogenation by Ga-exchanged HZSM-5 by considering two types of catalytic sites: a mono-Al site of the form Zâ[HGaX]+ (XÂ =Â H, CH3, OH, Cl) and a di-Al site of the form Z2â[GaH]2+. For the mono-Al site, we report a new, direct one-step dehydrogenation mechanism; however, we conclude in general that mono-Al sites in ZSM-5 are not likely responsible for alkane dehydrogentation, as calculated activation energies are too high compared to experimental values (â¼60Â kcal/mol versus 39Â kcal/mol). Instead, we propose [GaH]2+ residing near di-Al sites (Z2â[GaH]2+) are more active sites for dehydrogenation. We report a three-step mechanism for di-Al sites consisting of (1) C-H activation, followed by (2) alkene desorption and (3) H2 removal. We find that as Al-Al distance increases, the activation barrier for C-H activation decreases (ranging from 85.72 to 38.38 to 19.69Â kcal/mol), while the barrier for H2 removal increases (ranging from 15.49 to 36.71 to 47.38Â kcal/mol)-resulting in an optimal Al-Al separation distance of 4.53Â Ã
arising from these competing trends. As a result, we propose a simple 'structure-to-activity' correlation based on the Sabatier principle, which could be used to model and design the catalyst with required dehydrogenation activity.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Catalysis Today - Volume 105, Issue 1, 15 July 2005, Pages 106-121
Journal: Catalysis Today - Volume 105, Issue 1, 15 July 2005, Pages 106-121
نویسندگان
Yogesh V. Joshi, Kendall T. Thomson,