Understanding the catalytic structure–activity relationship over active sites is of fundamental importance in heterogeneous catalysis field. Herein, a series of H-ZSM-5 zeolites with Al pairs contents in the range of 31% to 82% are used to explore the structure sensitivity of olefin aromatization reaction. Compared with high reaction temperatures (385 ℃ and above), prominently different initial aromatic yields are observed over the samples at 150 ℃. In addition, the 1-octene temperature-programmed surface reaction (TPSR) and theoretical calculation results give a thorough understanding on active site dependent activation temperature (100 vs 150 ℃ over Al pairs and single Al). However, the catalytic cycle of olefin aromatization is not sustainable at low reaction temperature, which is due to the formation and blocking of big molecules in the micropores (e.g., trimethylbenzene etc.). In conclusion, the desorption of big molecules is the rate-determining step for olefin aromatization reaction over H-ZSM-5, which masks the structure sensitivity over Al pairs and single Al.
Polymer monolith microextraction (PMME) based on capillary monolithic column is an effective and useful technique to preconcentrate trace analytes from environmental and biological samples. Here, we report the fabrication of a novel aluminum terephthalate metal-organic framework (MIL-53(Al)) incorporated capillary monolithic column via in situ polymerization for the PMME of non-steroidal anti-inflammatory drugs (NSAIDs) (ketoprofen, fenbufen and ibuprofen) in water and urine samples. The fabricated MIL-53(Al) incorporated monolith was characterized by X-ray powder diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, and nitrogen adsorption experiment. The MIL-53(Al) incorporated monolith gave larger surface area than the neat polymer monolith. A 2-cm long MIL-53(Al) incorporated capillary monolith was applied for PMME coupled with high-performance liquid chromatography for the determination of the NSAIDs. Potential factors affecting the PMME were studied in detail. Under the optimized conditions, the developed method gave the enhancement factors of 46–51, the linear range of 0.40–200 μg L −1 , the detection limits (S/N = 3) of 0.12–0.24 μg L −1 , and the quantification limits (S/N = 10) of 0.40–0.85 μg L −1 . The recoveries for spiked NSAIDs (20 μg L −1 ) in water and urine samples were in the range of 77.3–104%. Besides, the MIL-53(Al) incorporated monolith was stable enough for 120 extraction cycles without significant loss of extraction efficiency. The developed method was successfully applied to the determination of NSAIDs in water and urine samples.
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