Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia, Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos s/n, 46022 Valencia, Spain.
Phys Chem Chem Phys. 2010 Jun 28;12(24):6396-403. doi: 10.1039/c002427a. Epub 2010 May 7.
Theoretical calculations and in situ solid state NMR spectroscopy have been combined to get insight on the nature of the active sites for the Beckmann rearrangement reaction in borosilicate zeolites. The interaction of a B site in zeolite Beta with a series of probe molecules (ammonia, pyridine, acetone and water) has been modelled and the (15)N and (11)B NMR isotropic chemical shift of the resulting complexes calculated and compared with experimental in situ NMR results. This approach has allowed validation of the methodology to model the adsorption on a zeolite boron site of molecules of varying basicity which are either protonated or non-protonated. The limitation is that theoretical calculations overestimate the effect of molecular adsorption through hydrogen bonds on the calculated isotropic (11)B NMR chemical shift.Theoretical and experimental results on the adsorption of acetophenone and cyclohexanone oximes on zeolite B-Beta indicate that Brønsted acid sites protonate the oximes, changing the boron coordination from trigonal to tetrahedral. Comparison of theoretical and experimental (15)N NMR chemical shifts of the adsorbed amides (acetanilide and epsilon-caprolactam) indicates that they are non-protonated, and the (11)B NMR spectra show that, as expected, boron remains in trigonal coordination with an isotropic delta(11)B(exp) which differs from the calculated value delta(11)B(calc).
理论计算和原位固态 NMR 光谱学已结合使用，以深入了解硼硅酸盐沸石中 Beckmann 重排反应活性位的性质。模拟了沸石 Beta 中 B 位与一系列探针分子（氨、吡啶、丙酮和水）的相互作用，并计算了所得配合物的（15）N 和（11）B NMR 各向同性化学位移，并与原位 NMR 实验结果进行了比较。这种方法验证了模拟不同碱性探针分子（质子化或非质子化）在沸石硼位吸附的方法的有效性。其局限性在于理论计算通过氢键高估了分子吸附对计算各向同性（11）B NMR 化学位移的影响。关于苯乙酮和环己酮肟在沸石 B-Beta 上吸附的理论和实验结果表明，Brønsted 酸位质子化肟，将硼配位从三角转变为四面体。吸附酰胺（乙酰苯胺和ε-己内酰胺）的（15）N NMR 化学位移的理论和实验比较表明，它们是非质子化的，（11）B NMR 谱表明，如预期的那样，硼仍然以三角配位形式存在，各向同性δ（11）B（exp）与计算值δ（11）B（calc）不同。
