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首页> 外文期刊>Catalysis science & technology >Isobutane aromatization over a complete Lewis acid Zn/HZSM-5 zeolite catalyst: performance and mechanism
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Isobutane aromatization over a complete Lewis acid Zn/HZSM-5 zeolite catalyst: performance and mechanism

机译：在一个完整的路易斯酸异丁烷芳构化锌/ HZSM-5沸石催化剂:性能和机制

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In short-chain alkane aromatization catalyzed by metal-modified HZSM-5, the metal cations acting as Lewis acid sites are considered to be the active centres for the dehydrogenation. However, other possible effects of the metal cations during the reaction have been neglected. In this study, a combination of experiments and DFT calculations has been carried out to investigate the complete effects of the Zn on ZSM-5 in isobutane aromatization. Zn-8.47/HZSM-5 (Zn/Al 1) with weak acidic properties was prepared as a Lewis acid sites-dominated catalyst. It was found that the (Zn-O-Zn)(2+) Lewis acid sites acted as the main active sites and no bridged hydroxyl groups (BrOnsted acid sites) were present. In isobutane conversion, it was surprisingly found that Zn-8.47/HZSM-5 showed better catalytic performance at low temperature than HZSM-5 (BrOnsted acid sites-dominated catalyst) and Zn-2.34/HZSM-5 (BrOnsted and Zn-Lewis acid sites co-existing catalyst). DFT calculations and operando dual-beam Fourier transform infrared spectrometry (DB-FTIR) characterization were employed to understand how the isobutane aromatization could be catalyzed on the Lewis acid site (Zn-O-Zn)(2+) exclusively without the participation of bridged hydroxyl groups. It was directly observed over DB-FTIR that the Lewis acid-type Zn/HZSM-5 enjoyed a faster aromatization rate and higher stability than HZSM-5 under real aromatization conditions. This firstly testified that the complete reaction of isobutane aromatization could be exclusively catalyzed by (Zn-O-Zn)(2+) Lewis acid sites without the participation of bridged hydroxyl groups. The [Zn-(OH)(-)](+) species could be produced in situ and acted as the BrOnsted acid sites. Owing to the weak acidity of [Zn-(OH)(-)](+), the Lewis acid sites played a key role during the aromatization reactions via the carbanionic mechanism.
机译：在短链烷烃芳构化催化metal-modified HZSM-5,金属阳离子表演路易斯酸网站被认为是脱氢活性中心。其他可能的金属阳离子的影响反应过程中一直被忽视。研究中,实验和DFT的组合计算进行了探讨完整的ZSM-5的锌的影响异丁烷芳构化。比;作为路易斯酸sites-dominated催化剂。发现(Zn-O-Zn)(2 +)路易斯酸的网站作为主要的活跃的网站,没有桥接羟基(布仑斯惕酸网站)礼物。惊讶地发现,锌- 8.47 / HZSM-5显示低温更好的催化性能比HZSM-5(布仑斯惕酸sites-dominated催化剂)和锌- 2.34 / HZSM-5(布仑斯惕Zn-Lewis酸网站共存催化剂)。计算和operando双光束傅里叶变换红外光谱法(DB-FTIR)描述了了解异丁烷的芳构化可以催化路易斯酸站点(Zn-O-Zn) (2 +)没有桥接羟基的参与组。路易斯酸性锌/ HZSM-5享受更快的芳构化率和更高的稳定性真正的芳构化条件下比HZSM-5。这首先作证说,完整的反应异丁烷的芳构化完全催化(Zn-O-Zn)(2 +)路易斯酸的网站没有桥接羟基的参与组。原位产生并作为布仑斯惕酸网站。(锌(哦 )(-)](+), 路易斯酸的网站了通过关键作用在芳构化反应carbanionic机制。

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