Boron vs. aluminum in ZSM-5 zeolites: Solid-state NMR, acidity, and C1/C2 reactant conversion

IF 4.8 3区材料科学 Q1 CHEMISTRY, APPLIED

Microporous and Mesoporous Materials Pub Date : 2024-09-28 DOI:10.1016/j.micromeso.2024.113353

Michael Dyballa, Zheng Li , Daniel Dittmann

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Abstract

Three zeolite catalysts with comparable amounts of aluminum and/or boron ([Al]ZSM-5, [B,Al]ZSM-5, and [B]ZSM-5) are herein synthesized. Water (H₂O), ammonia (NH₃), acetonitrile-d₃ (ACN), and trimethylphosphine oxide (TMPO) are applied as probe molecules to investigate the acidity of the respective materials in combination with ¹¹B, ²⁷Al, and ²⁹Si MAS NMR spectroscopy. Ammonia is not protonated to ammonium on Si(OH)B groups and only LAS-bound ammonia persists desorption. Thus, ammonia gives a realistic, quantitative picture of the present acid sites. ACN interacts only with Si(OH)Al as desired. The strong base TMPO results in a misleading, not quantifiable picture. Subsequent hydration is unsuited to distinguish BAS and LAS densities. The samples were catalytically tested in the conversion of methanol, ethanol, and ethylene. [B]ZSM-5 is unreactive in hydrocarbon formation due to absence of BAS, instead LAS are present. The mixed [B,Al]ZSM-5 shows a decreased lifetime in MTO conversion compared to the [Al]ZSM-5, due to LAS presence. A sometimes reported superior reactivity of [B,Al]ZSM-5 catalysts is thus explained primarily by an optimized BAS density.

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ZSM-5 沸石中的硼与铝：固态核磁共振、酸度和 C1/C2 反应物转换

本文合成了三种铝和/或硼含量相当的沸石催化剂（[Al]ZSM-5、[B,Al]ZSM-5 和 [B]ZSM-5）。水 (H2O)、氨 (NH3)、乙腈-d3 (ACN) 和三甲基氧化膦 (TMPO) 被用作探针分子，结合 11B、27Al 和 29Si MAS NMR 光谱来研究各自材料的酸性。氨不会在 Si(OH)B 基团上质子化为铵，只有与 LAS 结合的氨才会持续解吸。因此，氨能真实、定量地反映目前的酸性位点。ACN 只与 Si(OH)Al 起作用。而强碱 TMPO 则会产生误导，无法量化。随后的水合作用无法区分 BAS 和 LAS 密度。这些样品在甲醇、乙醇和乙烯的转化过程中进行了催化测试。由于缺乏 BAS，[B]ZSM-5 在碳氢化合物的形成过程中没有反应，反而存在 LAS。与[Al]ZSM-5 相比，混合[B,Al]ZSM-5 在 MTO 转化过程中的寿命缩短，原因是存在 LAS。因此，[B,Al]ZSM-5 催化剂有时被报道具有更高的反应活性，其主要原因是优化了 BAS 密度。

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来源期刊

Microporous and Mesoporous Materials 化学-材料科学：综合

CiteScore

10.70

自引率

5.80%

发文量

649

审稿时长

26 days

期刊介绍： Microporous and Mesoporous Materials covers novel and significant aspects of porous solids classified as either microporous (pore size up to 2 nm) or mesoporous (pore size 2 to 50 nm). The porosity should have a specific impact on the material properties or application. Typical examples are zeolites and zeolite-like materials, pillared materials, clathrasils and clathrates, carbon molecular sieves, ordered mesoporous materials, organic/inorganic porous hybrid materials, or porous metal oxides. Both natural and synthetic porous materials are within the scope of the journal. Topics which are particularly of interest include: All aspects of natural microporous and mesoporous solids The synthesis of crystalline or amorphous porous materials The physico-chemical characterization of microporous and mesoporous solids, especially spectroscopic and microscopic The modification of microporous and mesoporous solids, for example by ion exchange or solid-state reactions All topics related to diffusion of mobile species in the pores of microporous and mesoporous materials Adsorption (and other separation techniques) using microporous or mesoporous adsorbents Catalysis by microporous and mesoporous materials Host/guest interactions Theoretical chemistry and modelling of host/guest interactions All topics related to the application of microporous and mesoporous materials in industrial catalysis, separation technology, environmental protection, electrochemistry, membranes, sensors, optical devices, etc.