沸石(Zeolite)一直被廣泛的應用於許多工業應用及異相觸媒催化反應中，但是對於沸石結構中的路易士酸(Lewis acid site)及布忍司特酸(Brønsted acid site)，仍然存在著許多問題。所以要了解沸石的結構及組成在催化反應中的影響，首先必須先確定酸性位置分佈及其大小。 因此我們利用多核的固態核磁共振來探討有相似矽鋁比率(Si/Al ratios)H-mordenite(H-MOR)和H-Beta布忍司特酸(Brønsted acid)的性質。在1H/27Al TRAPDOR NMR檢定到H-Beta有兩個不同的布忍司特酸(Brønsted acid site)，反之H-MOR只得到一個布忍司特酸(Brønsted acid site)。固態31P MAS NMR來研究H-MOR和H-Beta吸附trimethylphosehine oxide(TMPO)後展現出多共振特徵峰的31P NMR光譜圖，這些共振特徵峰代表不同的布忍司特酸(Brønsted acid)與TMPO反應後的位置，這結果表明了H-MOR和H-Beta布忍司特酸(Brønsted acid)強度的分布。當使用TMP探測分子時，在H-MOR和H-Beta兩著都只得到單一的31P NMR共振特徵峰，不過H-MOR吸附TMP相對於H-Beta吸附TMP顯示出31P有一較低磁場的化學位移和一較大的JP-H值。因此提議H-MOR和H-Beta的31P NMR光譜的化學位移和JP-H值可能跟沸石中的平均布忍司特酸和它的催化活性有相當的關聯。 Despite the widespread use of zeolites in many industrial processes, there still remain many unanswered questions as tot he nature of the Lewis and Brønsted acid sites. A full characterization of the structure and acidity of these acid sites is essential if an understanding of the effect of composition and structure on the catalytic properties of the material is to be obtained. The Brønsted acidity of H-mordenite (H-MOR) and H-Beta with similar Si/Al ratios has been characterized by conventional multinuclear solid-state NMR. 1H/27Al TRAPDOR NMR detected two different types of Brønsted acid sites in H-Beta whereas only a single 1H resonance due to Brønsted acid sites in H-MOR was observed. Solid-state 31P MAS NMR investigation of H-MOR and H-Beta zeolites loaded with trimethyl -phosphine oxide (TMPO) reveals multiple 31P resonances, which arise from the reaction of TMPO with different types of Brønsted acid sites. The results demonstrate that there is a wide distribution in the strength of the Brønsted acidity in H-MOR and H-Beta zeolites. When trimethyl -phosphine (TMP) was used as a probe molecule, however, only a single 31P resonance was observed for both samples. Nevertheless, H-MOR loaded with TMP exhibits a larger 31P downfield shift and a larger JP-H value as compared to H-Beta. This suggests that both 31P chemical shift and JP-H value might be used to correlate with the average Brønsted acidity in zeolites, and thus their catalytic activity.
