Acidic Strengths of Br酶nsted and Lewis Acid Sites in Solid Acids Scaled by 31P NMR Chemical Shifts of Adsorbed Trimethylphosphine

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• 作者：Yueying Chu ; Zhiwu Yu ; Anmin Zheng ; Hanjun Fang ; Hailu Zhang ; Shing-Jong Huang ; Shang-Bin Liu ; Feng Deng
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：April 21, 2011
• 年：2011
• 卷：115
• 期：15
• 页码：7660-7667
• 全文大小：895K
• 年卷期：v.115,no.15(April 21, 2011)
• ISSN：1932-7455

文摘

The validity of using ³¹P NMR of adsorbed trimethylphosphine (TMP) as a probe molecule for discerning the types (Br酶nsted vs Lewis) and strengths of acid sites in solid acid catalysts have been studied by density functional theory (DFT) calculations. Br酶nsted acid sites with varied acidic strengths covering from weak, strong, to superacid, mimicked by 8T zeolite cluster models having different Si鈭扝 bond lengths and hence proton affinities, were examined together with Lewis acid systems having different metallic centers, e.g., BCl_nF_3鈭?i>n (n = 0鈭?), AlCl_nF_3鈭?i>n (n = 0鈭?), and TiCl_nF_4鈭?i>n (n = 0鈭?) and their mixed halides. The theoretical ³¹P chemical shifts predicted for the hydrogen-bonded TMP路路路H complex and the TMPH⁺ adducts were 鈭?1 卤 1 and 鈭? 卤 1 ppm, respectively, in good agreement with the experimental data. For the TMP鈭扡ewis acid complex, a linear correlation between the calculated ³¹P chemical shifts and corresponding binding energies was observed for the B-, Al-, and Ti-containing Lewis acids, respectively, indicating the feasibility of using the ³¹P chemical shift of adsorbed TMP as a scale for Lewis acidic strength.