Understanding the Correlation between Ga Speciation and Propane Dehydrogenation Activity on Ga/H-ZSM-5 Catalysts
Understanding the Correlation between Ga Speciation and Propane Dehydrogenation Activity on Ga/H-ZSM-5 Catalysts
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DOI：
10.1021/acscatal.1c01497
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发表时间：
2021-08
期刊：
影响因子：
12.9
通讯作者：
Yong Yuan;Casper Brady;R. Lobo;Bingjun Xu
中科院分区：
文献类型：
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作者：
Yong Yuan;Casper Brady;R. Lobo;Bingjun Xu
H-ZSM-5分子筛负载Ga（Ga/H-ZSM-5）作为丙烷非氧化脱氢（PDH）的选择性催化剂已有几十年的历史，但其反应机理仍是一个值得探讨的话题。特别地，在反应条件下存在于催化剂上的各种Ga物质与PDH活性之间的相关性尚未建立。在本工作中，本征PDH速率和活化能的Ga/H-ZSM-5样品上的Ga+-H+对网站和孤立的Ga+网站具有较宽的Si/Al和Ga/Al比的测定。在PDH中的Ga+-H+对位点上的周转频率比孤立的Ga+位点的周转频率高1.5倍。结合双位模型的实验测量表明，PDH中Ga+-H+对位和孤立Ga+位的激活能分别为90.8 ± 1.5和117 ± 4.7kJ·mol-1.这些结果表明，Ga+-H+对网站是更活跃的PDH比孤立的Ga+网站。GaHx分解生成H2的活化能比PDH在Ga物种上分解生成H2的活化能高40-60 kJ·mol-1，表明GaHx分解不可能是PDH机理的一部分.虽然布朗斯特酸和Ga位都与丙烷相互作用，但傅里叶变换红外光谱结果提供了强有力的证据，表明Ga/H-ZSM-5催化剂上的PDH更可能是烷基机理。
H-ZSM-5 zeolite-supported Ga (Ga/H-ZSM-5) has been considered as a selective catalyst for nonoxidative propane dehydrogenation (PDH) for decades; however, the reaction mechanism remains a topic of considerable discussion. In particular, the correlation between various Ga species present on the catalyst at the reaction conditions and the PDH activity has yet to be established. In this work, intrinsic PDH rates and activation energies were determined on Ga+–H+pair sites and isolated Ga+sites on Ga/H-ZSM-5 samples with a wide range of Si/Al and Ga/Al ratios. The turnover frequency on Ga+–H+pair sites in the PDH is higher than that of isolated Ga+sites by a factor of ∼15. Experimental measurements combined with a dual-site model show the activation energy in the PDH on the Ga+–H+pair sites and isolated Ga+sites to be 90.8 ± 1.5 and 117 ± 4.7 kJ·mol–1, respectively. These results demonstrate that Ga+–H+pair sites are much more active in the PDH than isolated Ga+sites. The activation energy of GaHxdecomposition to form H2was determined to be 40–60 kJ·mol–1higher than that of the PDH on Ga species, suggesting that the GaHxdecomposition is unlikely to be part of the PDH mechanism. Although both Brønsted acid and Ga sites interact with propane, Fourier transform infrared spectroscopy results provide strong evidence suggesting that the alkyl mechanism is more likely in the PDH on Ga/H-ZSM-5 catalysts.