Catalysis Science & Technology
·
2022
·Vol. 12
·期 20
·6268-6284
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IF 6.177
Tingyu Liang,Jialing Chen,Sen Wang,Pengfei Wang,Zhangfeng Qin,Fang Jin,Mei Dong,Jianguo Wang,Weibin Fan
A series of H-MCM-22 zeolites with different Si/Al ratios (H-M22-x, x = 15–90) were hydrothermally synthesized by boron incorporation to investigate the influences of acid density on the methanol-to-hydrocarbon (MTH) performances and deactivation behaviors. The acid density of H-M22-x zeolites is nearly proportional to their aluminum contents; the residual boron barely affects the overall acidity of H-M22-x zeolites. 27Al and 29Si MAS NMR experiments support the existence of competitive occupancy of various framework T sites among boron, aluminum and silicon during zeolite synthesis, which leads to different distribution of Brønsted acid sites/framework aluminum among three types of pores in H-MCM-22 zeolites. Increasing the Si/Al ratio of H-M22-x zeolites leads to a gradual increase in the proportion of Brønsted acid sites in supercages while those in sinusoidal channels decrease. However, the acid density has a significantly larger impact than acid distribution on the MTH performances of H-M22-x zeolites. Increasing the acid density can accelerate the hydrogen transfer reactions in the MTH conversion and promote the formation of aromatics, ethene, and alkanes. The deactivation of H-M22-x zeolites with low acid density (x = 50–90) is mainly ascribed to coke covering the acid sites inside the micropores and partly blocking the pore mouths. Nevertheless, the deactivation of H-M22-x zeolites with high acid density (x = 15–30) is mainly caused by massive coke deposition on the external surface which blocks the pore mouths of inner micropores. The coke on the external surface exhibits a lower decomposition temperature than that inside the micropores. The deactivation behaviors of H-M22-x zeolites for the MTH reaction can be divided into three stages. Firstly, rapid deactivation of supercages occurred for all the H-M22-x zeolites in spite of their different acid densities, suggesting a much stronger influence of pore structure than acidity on the initial deactivation behaviors of H-M22-x zeolites. Secondly, the acid sites in sinusoidal channels of H-M22-x zeolites are highly resistant to coke formation, which dominates the MTH reaction in the second stage. Finally, with the continuous formation of coke in the surface pockets, which gradually covers the acid sites and pore mouths of sinusoidal channels, complete deactivation of H-M22-x zeolites can be observed. GC-MS and UV-vis analysis of partly or completely deactivated H-M22-x zeolites reveals that the retained species in H-M22-x zeolites gradually condense into bulky hydrocarbon species through successive hydrogen transfer reactions and form methylbenzenes, naphthalene, polymethylnaphthalenes, phenalenone, pyrenes and eventually graphite-like carbonaceous species.
研究领域:
催化化学
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材料科学
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能源化学
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产品关联
DOI
高影响因子
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY
·
2024
·
IF 4.3
Rui Cao,Mengyu Zhang,Wen Tang,Jing Wu,Yang Luo,Yi Chen,Zhaodi Liu,Fuying Hao,Liangquan Sheng,Huajie Xu
In this work, a stable ratiometric nanofluorescent probe for the detection of 2,6-dipicolinic acid (DPA), a Bacillus anthracis biomarker, was developed based on confinement-induced emission enhancement of cationic styrylpyridine salt derivative L in MCM-22 molecular sieve pores. The cationic L and the lanthanide Tb 3+ were loaded into the pores of the molecular sieve by electrostatic interaction with the negatively charged AlO 4 tetrahedron unit, and L exhibited enhanced red fluorescence emission as a stable fluorescence reference mark in the nanoprobe platform due to the restricted molecular torsion of L in the pores of MCM-22. At the same time, the characteristic green fluorescence emission of Tb 3+ can be excited by energy transfer due to the “antenna effect” of DPA. The prepared Tb-L@MCM-22 nanoprobe showed specific selectivity and stable fluorescence ratiometric detection of DPA in tap water, lake water, bovine serum and actual bacterial spores. Benefiting from the confinement-induced fluorescence enhancement effect of L in the MCM-22 molecular sieve pores, the obtained Tb-L@MCM-22 can provide a stable reference signal for the fluorescence ratiometric detection of DPA with a limit of detection (LOD) of 78.6 nM and 1.310 × 10 4 spores per mL. More importantly, combining of the Tb-L@MCM-22 based DPA detection test strips with a smartphone app demonstrated a stable, convenient and rapid method for detecting of anthrax biomarkers.
研究领域:
分析化学
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生物医学工程
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材料科学
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产品关联
DOI
PubMed
高影响因子
Catalysis Science & Technology
·
2020
·Vol. 10
·期 19
·6583-6598
·
IF 5.721
Jialing Chen,Gang Peng,Wei Zheng,Wenbo Zhang,Li Guo,Xiaoqing Wu
A superior Fe-containing MCM-22 zeolite prepared by a one-pot synthesis method (OP-Fe/M22) showed excellent NH3 selective catalytic reduction (NH3-SCR) activity and almost 100% N2 selectivity in a wide temperature window (200–500 °C). To investigate the effects of preparation strategies on the NH3-SCR reaction, other three Fe/MCM-22 zeolites with similar iron content (4.4–4.8 wt%) were prepared by solid-state ion exchange (SSIE-Fe/M22), incipient wetness impregnation (IM-Fe/M22) and mechanical mixing (MM-Fe/M22) methods, respectively. Catalytic results in NH3-SCR demonstrate that OP-Fe/M22 gives significantly higher activity in the whole temperature range (100–550 °C) than the other three post-synthesized catalysts. As revealed by XRD, UV-vis, H2-TPR, NH3-TPD, and Py-IR experiments, OP-Fe/M22 has the highest concentrations of isolated Fe3+ species and acid sites, and the lowest concentration of Fe2O3 nanoparticles among the four catalysts, which ensures its highest activity in the NH3-SCR reaction. Besides, OP-Fe/M22 exhibits the higher activity both in NH3 oxidation and NO oxidation reactions than IM-Fe/M22, indicating the better NO oxidation ability and NH3 storage capacity of OP-Fe/M22 which also facilitates the NH3-SCR process. In contrast with Cu-based MCM-22 zeolite obtained from the incipient wetness impregnation method at similar metal content (5% Cu/M22), OP-Fe/M22 shows comparable activity with 5% Cu/M22 in the low-temperature range (100–300 °C) while obviously higher activity at high temperatures (300–550 °C). Moreover, by removing part of undesired iron oxides in OP-Fe/M22 through mild acid post-treatments, the NH3-SCR activity of OP-Fe/M22 in the medium and high temperature ranges (200–550 °C) can be further improved, suggesting that OP-Fe/M22 is a potential catalyst with highly-efficient NH3-SCR activity in a wide temperature window.
研究领域:
环境科学
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催化化学
✓ 已验证
产品关联
DOI
高影响因子
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