K ions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging.The changes in structure and copper-species contents of these ...K ions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging.The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction(SCR)activity.For the fresh Cu/SAPO-34 catalysts,K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites.After hydrothermal aging,the structural integrity and amount of active sites decreased on pure Cu/SAPO-34.While the K-loaded catalysts showed improved chabazite structure,acidity,and active site conservation with increasing K loading.However,although the 0.7 wt%K catalyst maintained the same crystallinity,active site abundance,and low-temperature SCR activity as the fresh catalyst upon aging,an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Brönsted acid sites.To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature,Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34,and a wide active temperature window of SCR activity was obtained.Thus,our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NOx in real-world applications.展开更多
Hierarchical Fe-Beta obtained by hydrothermal synthesis exhibited higher low-temperature NH_3-SCR activity than conventional Fe-Beta. In order to identify the main factors leading to the difference in catalytic activi...Hierarchical Fe-Beta obtained by hydrothermal synthesis exhibited higher low-temperature NH_3-SCR activity than conventional Fe-Beta. In order to identify the main factors leading to the difference in catalytic activity, we investigated the pore structure, acidity and Fe sites of the hierarchical Fe-Beta and conventional Fe-Beta. The enhanced activity of hierarchical Fe-Beta was mainly due to the increase of the quantity of active Fe species. NH_3-TPD and DRIFTS results of NH_3 adsorption clearly verified that hierarchical Fe-Beta had more Lewis acid sites, which is beneficial to the adsorption and activation of NH_3. The H_2-TPR, UV–vis DRS, and EPR results confirmed that the hierarchical Fe-Beta had more isolated active Fe species, which may be associated with that the hierarchical structure introduced more structural defects as ion-exchange sites. Based on the analysis of kinetics experiments and the abovementioned characterizations, it can be concluded that the improvement of NH_3-SCR activity was not due to an intrinsic effect of the specific structural characteristics, but was related to more Fe active sites and better dispersion of Fe species in the hierarchical Fe-Beta.展开更多
Two practical methods for highly stereoselective synthesis of (Z)-2-acylamido-4-phenylcrotonates 2a similar to b have been developed. The key step in the first route was how to control the acid-catalyzed isomerization...Two practical methods for highly stereoselective synthesis of (Z)-2-acylamido-4-phenylcrotonates 2a similar to b have been developed. The key step in the first route was how to control the acid-catalyzed isomerization of condensation mixtures of alpha-keto ester 5 with carbomite. In the second route the key step was reduction of oxime 8, derived from alpha-keto ester 5, with iron powder in the presence of acetic anhydride.展开更多
基金the funding from National Key Research and Development Program of China(No.2017YFC0211302)National Natural Science Foundation for Youth of China(Grant No.21908207)+1 种基金China Postdoctoral Science Foundation(No.2020M670659)Shanxi Province Science Foundation for Youths(Nos.201901D211224 and 201801D221351).
文摘K ions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging.The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction(SCR)activity.For the fresh Cu/SAPO-34 catalysts,K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites.After hydrothermal aging,the structural integrity and amount of active sites decreased on pure Cu/SAPO-34.While the K-loaded catalysts showed improved chabazite structure,acidity,and active site conservation with increasing K loading.However,although the 0.7 wt%K catalyst maintained the same crystallinity,active site abundance,and low-temperature SCR activity as the fresh catalyst upon aging,an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Brönsted acid sites.To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature,Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34,and a wide active temperature window of SCR activity was obtained.Thus,our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NOx in real-world applications.
基金financial supports from the National Natural Science Foundation of China (Nos. 51822811, 21637005)the National Key R&D Program of China (Nos. 2017YFC0212502, 2017YFC0211101)the Young Talent Project of the Center for Excellence in Regional Atmospheric Environment, CAS (No. CERAE201806)
文摘Hierarchical Fe-Beta obtained by hydrothermal synthesis exhibited higher low-temperature NH_3-SCR activity than conventional Fe-Beta. In order to identify the main factors leading to the difference in catalytic activity, we investigated the pore structure, acidity and Fe sites of the hierarchical Fe-Beta and conventional Fe-Beta. The enhanced activity of hierarchical Fe-Beta was mainly due to the increase of the quantity of active Fe species. NH_3-TPD and DRIFTS results of NH_3 adsorption clearly verified that hierarchical Fe-Beta had more Lewis acid sites, which is beneficial to the adsorption and activation of NH_3. The H_2-TPR, UV–vis DRS, and EPR results confirmed that the hierarchical Fe-Beta had more isolated active Fe species, which may be associated with that the hierarchical structure introduced more structural defects as ion-exchange sites. Based on the analysis of kinetics experiments and the abovementioned characterizations, it can be concluded that the improvement of NH_3-SCR activity was not due to an intrinsic effect of the specific structural characteristics, but was related to more Fe active sites and better dispersion of Fe species in the hierarchical Fe-Beta.
文摘Two practical methods for highly stereoselective synthesis of (Z)-2-acylamido-4-phenylcrotonates 2a similar to b have been developed. The key step in the first route was how to control the acid-catalyzed isomerization of condensation mixtures of alpha-keto ester 5 with carbomite. In the second route the key step was reduction of oxime 8, derived from alpha-keto ester 5, with iron powder in the presence of acetic anhydride.
