High-loading Ga-exchanged MFI zeolites as selective and coke-resistant catalysts for nonoxidative ethane dehydrogenation
High-loading Ga-exchanged MFI zeolites as selective and coke-resistant catalysts for nonoxidative ethane dehydrogenation
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高负载 Ga 交换 MFI 沸石作为非氧化乙烷脱氢的选择性抗焦催化剂
DOI：
10.1039/d1cy01799c
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发表时间：
2022
影响因子：
5
通讯作者：
Shimizu Ken-ichi
中科院分区：
文献类型：
--
作者：
Huang Mengwen;Yasumura Shunsaku;Li Lingcong;Toyao Takashi;Maeno Zen;Shimizu Ken-ichi
在本文中，我们研究了还原固态离子交换反应中Ga负载量和H2处理温度对Ga交换MFI沸石（Ga-MFI）中生成的Ga物种的影响及其对乙烷脱氢（EDH）的催化作用。为了在沸石中形成孤立的Ga氢化物，在550℃下用H2处理的低负载量Ga-MFI（Ga/Al=0.3）中优先形成[GaH]2+离子，对应于常规制备条件（Ga-MFI-0.3（550）），而在高Ga负载量（Ga/Al=1.0）和高温H2处理（800℃）中优先形成[GaH]2+离子。原位傅立叶变换红外光谱（包括使用 D2 的同位素实验）表明，(Ga-MFI-1.0(800)) 诱导形成了主要 Ga 氢化物的 [GaH2]+ 离子。吡啶吸附实验表明，在其他 Ga 物种（例如 Ga+ 阳离子和部分还原的 Ga 氧化物 (GaOX)）的情况下，Ga+ 阳离子和 GaOX 在 Ga-MFI-0.3(550) 中共存。另一方面，在Ga-MFI-1.0(800)中几乎观察不到GaOX，并且形成大量的Ga+阳离子。剩余的 Brønsted 酸位 (BAS) 也通过 NH3 吸附实验进行了表征。在 EDH 反应中，Ga-MFI-1.0(800) 由于焦炭形成量低而表现出高选择性，从而在测试的 Ga-MFI 系列中具有最高的耐久性。在优化条件下，Ga-MFI-1.0(800)在之前报道的无Pt催化剂中表现出最高的C2H4形成率。根据表征、催化剂测试和动力学研究的综合结果，Ga-MFI-1.0(800) 的高选择性和耐久性可归因于孤立的 Ga 物种（[GaH]2+、[GaH2]+ 离子和 Ga+ 阳离子）剩余 BAS 的量较低以及孤立的 Ga 氢化物中主要形成 [GaH2]+ 离子。
In this paper, we investigated the effects of the Ga loading amount and H2 treatment temperature for the reductive solid-state ion-exchange reaction on the generated Ga species in Ga-exchanged MFI zeolites (Ga-MFIs) as well as their catalysis for ethane dehydrogenation (EDH). For the formation of isolated Ga hydrides in the zeolites, [GaH]2+ ions were preferentially formed in the low-loading Ga-MFI (Ga/Al = 0.3) treated with H2 at 550 °C, corresponding to the conventional preparation conditions, (Ga-MFI-0.3(550)), while the high Ga loading (Ga/Al = 1.0) and high-temperature H2 treatment (800 °C) (Ga-MFI-1.0(800)) induced the formation of [GaH2]+ ions as the major Ga hydrides, as revealed by in situ Fourier transform infrared spectroscopy including the isotope experiment using D2. In the context of other Ga species, such as Ga+ cations and partially reduced Ga oxides (GaOX), Ga+ cations and GaOX coexist in Ga-MFI-0.3(550), as indicated by pyridine adsorption experiments. On the other hand, GaOX was hardly observed and a larger amount of Ga+ cations was formed in Ga-MFI-1.0(800). The remaining Brønsted acid sites (BASs) were also characterized by the NH3 adsorption experiment. In the EDH reaction, Ga-MFI-1.0(800) exhibited high selectivity owing to low coke formation, resulting in the highest durability among the series of Ga-MFIs tested. Under the optimized conditions, Ga-MFI-1.0(800) exhibited the highest C2H4 formation rate among previously reported Pt-free catalysts. Based on the combined results of characterization, catalyst tests, and kinetic studies, the high selectivity and durability of Ga-MFI-1.0(800) can be ascribed to the low amount of the remaining BASs by isolated Ga species ([GaH]2+, [GaH2]+ ions and Ga+ cations) as well as the major formation of [GaH2]+ ions among isolated Ga hydrides.