A Solid Acid Catalyst at the Threshold of Superacid Strength: NMR, Calorimetry, and Density Functional Theory Studies of Silica-Supported Aluminum Chloride
A Solid Acid Catalyst at the Threshold of Superacid Strength: NMR, Calorimetry, and Density Functional Theory Studies of Silica-Supported Aluminum Chloride
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DOI：
10.1021/ja970850n
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发表时间：
1997-12
影响因子：
15
通讯作者：
Teng Xu;Nicholas Kob;R. Drago;‡. A. John B. Nicholas;J. F. Haw
中科院分区：
文献类型：
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作者：
Teng Xu;Nicholas Kob;R. Drago;‡. A. John B. Nicholas;J. F. Haw
固态核磁共振、量热法和密度泛函理论 (DFT) 都对固体酸催化剂 (SG)nAlCl2 的酸性提供了一致的解释，该催化剂是通过氯化铝与调节硅胶反应制备的。这些研究证实，酸性位点本质上是布朗斯台德性质，并且它们的强度明显大于沸石中的酸性位点。质子 NMR 结果（包括利用 1H−27Al 偶极耦合的实验）表明，布朗斯台德酸位点的各向同性 1H 化学位移为 5.7 ppm，浓度为 0.58 mmol/g。该固体酸上最强的位点为 0.03 mmol/g，与吡啶反应的 -ΔHav 值为 52 kcal/mol。吡啶增量添加至 0.1 mmol/g 时，维持 44 kcal/mol 的值。相比之下，HZSM-5沸石中最强位点的-ΔHav仅为42 kcal/mol。吸附吡啶的 15N 魔角旋转 (MAS) NMR 研究和三甲基膦的 31P MAS NMR 研究证实了...
Solid state NMR, calorimetry, and density functional theory (DFT) all provide a consistent interpretation of the acidity of the solid acid catalyst (SG)nAlCl2, which is prepared by reacting aluminum chloride with conditioned silica gel. These studies firmly establish that the acid sites are Bronsted in nature and that their strength is significantly greater than those in zeolites. Proton NMR results, including experiments exploiting 1H−27Al dipolar couplings, demonstrate that the Bronsted acid sites have an isotropic 1H chemical shift of 5.7 ppm and a concentration of 0.58 mmol/g. The strongest sites on this solid acid, present at 0.03 mmol/g, have −ΔHav values of 52 kcal/mol for reaction with pyridine. A value of 44 kcal/mol is maintained for incremental addition of pyridine up to 0.1 mmol/g. In comparison, −ΔHav for the strongest sites in zeolite HZSM-5 is only 42 kcal/mol. 15N magic angle spinning (MAS) NMR studies of adsorbed pyridine and 31P MAS NMR of trimethylphosphine confirm the Bronsted nature o...