Iron-containing zeolites play an important role in the selective oxidation of methane to oxygenates by nitrous oxide.A solid-state ion exchange method is adopted to prepare Fe-MOR zeolite catalysts with different amou...Iron-containing zeolites play an important role in the selective oxidation of methane to oxygenates by nitrous oxide.A solid-state ion exchange method is adopted to prepare Fe-MOR zeolite catalysts with different amounts of extra-framework Al.EPR spectra and UV-vis spectra show that the percentage of iron ions in tetrahedral or octahedral coordination increases while those of clustered Fe species decrease by the addition of extra-framework Al species.Nitrous oxide titration reveals that more active Fe centers are formed,which promote the nitrous oxide consumption.The number of active centers in the catalyst with the introduction of extra-framework Al is about four times that of the catalyst without the addition of extra-framework Al.Due to this,there is an increase in the methane conversion,total selectivity and yield of oxygenates.展开更多
The location of aluminum within the framework or extra-framework of zeolites is a critical factor in determining its catalytic performance.Despite extensive research on the identification and formation mechanism of ex...The location of aluminum within the framework or extra-framework of zeolites is a critical factor in determining its catalytic performance.Despite extensive research on the identification and formation mechanism of extra-framework aluminum(EFAl),its impact on catalytic performance requires further investigation.Herein,mordenite(MOR)zeolites with comparable acid density within the 8MR and 12MR channels but different EFAl contents were prepared,and their catalytic roles were examined in syngas conversion.Intelligent gravimetric analysis,model experiment of ethylene conversion and thermogravimetric analysis demonstrate that the existence of EFAl species can inhibit the secondary conversion of ethylene to long chain hydrocarbons(i.e.,C_(5+))as well as the over-accumulation of carbonaceous species.However,excessive EFAl species lead to rapid deactivation due to restricted space and thus severe diffusion limitation.MOR zeolite with a moderate amount of EFAl species achieves a superior ethylene selectivity and exhibits an enhanced stability in syngas conversion when combined with ZnAlOx oxide.The insights gained in this work provide important guidance for the design of more efficient zeolite-based catalysts.展开更多
1 Introduction Recently, catalytic cracking catalysts have been developed from using USY zeolites as octane enhancement catalysts (mainly to improve the research-method octane number) to employing REUSY zeolites as hi...1 Introduction Recently, catalytic cracking catalysts have been developed from using USY zeolites as octane enhancement catalysts (mainly to improve the research-method octane number) to employing REUSY zeolites as high octane number-high gasoline yield catalysts (octanebarreled catalyst). The peculiarities of REUSY zeolites are the increase of the researchmethod octane number, the motor-method octane number and the gasoline yield. At pres-展开更多
High-temperature treatment is key to the preparation of zeolite catalysts.Herein,the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work.X-Ray diffraction,...High-temperature treatment is key to the preparation of zeolite catalysts.Herein,the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work.X-Ray diffraction,N2physisorption,27Al magic angle spinning nuclear magnetic resonance(MAS NMR),and temperature-programmed desorption of ammonia results indicated that the hightemperature treatment at 650℃ hardly affected the inherent crystal and texture of HZSM-5zeolites but facilitated the conversion of framework Al to extra-framework Al,reducing the acid site and enhancing the acid strength.Moreover,the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking,promoting the conversion and light olefins yield while inhibiting coke formation.Based on the kinetic and mechanism analysis,the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al,which enhanced the acid strength,facilitated the bimolecular reaction,and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.展开更多
Titanium silicalite-1 （TS-1） has been hydrothermally synthesized with tetrapropylammonium hydroxide （TPAOH） as the template in the presence of various amounts of Na＋, characterized by inductively coupled plasma, ...Titanium silicalite-1 （TS-1） has been hydrothermally synthesized with tetrapropylammonium hydroxide （TPAOH） as the template in the presence of various amounts of Na＋, characterized by inductively coupled plasma, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and ultro-violet-visible spectroscopy and studied in cyclohexanone ammoximation. The characterization results show that with the increase of Na＋ concentration in the synthesis, both the crystal sizes of TS- land extra framework Ti increase but framework Ti decreases. The addition of Na＋ below 3 mol-% of TPAOH in the synthesis does not influence the catalytic properties with above 98% conversion of cyclohexanone and 99.5% selectivity to cyclohexanone oxime. However, at the concentrations of Na＋≥3mol-% of TPAOH in the synthesis, the catalysts are deactivated faster with the increase of Na＋ addition, which can be attributed to more high molecular weight byproducts deposited in the large TS-1 particles and the loss of the frame-work titanium. The results of this work are of great importance for the industry.展开更多
基金This research was supported by the Zhejiang Provincial Natural Science Foundation of China(LR18B060001)Basic Research Project of Sinopec Group(415025)the Fundamental Research Funds for the Central Universities.
文摘Iron-containing zeolites play an important role in the selective oxidation of methane to oxygenates by nitrous oxide.A solid-state ion exchange method is adopted to prepare Fe-MOR zeolite catalysts with different amounts of extra-framework Al.EPR spectra and UV-vis spectra show that the percentage of iron ions in tetrahedral or octahedral coordination increases while those of clustered Fe species decrease by the addition of extra-framework Al species.Nitrous oxide titration reveals that more active Fe centers are formed,which promote the nitrous oxide consumption.The number of active centers in the catalyst with the introduction of extra-framework Al is about four times that of the catalyst without the addition of extra-framework Al.Due to this,there is an increase in the methane conversion,total selectivity and yield of oxygenates.
文摘The location of aluminum within the framework or extra-framework of zeolites is a critical factor in determining its catalytic performance.Despite extensive research on the identification and formation mechanism of extra-framework aluminum(EFAl),its impact on catalytic performance requires further investigation.Herein,mordenite(MOR)zeolites with comparable acid density within the 8MR and 12MR channels but different EFAl contents were prepared,and their catalytic roles were examined in syngas conversion.Intelligent gravimetric analysis,model experiment of ethylene conversion and thermogravimetric analysis demonstrate that the existence of EFAl species can inhibit the secondary conversion of ethylene to long chain hydrocarbons(i.e.,C_(5+))as well as the over-accumulation of carbonaceous species.However,excessive EFAl species lead to rapid deactivation due to restricted space and thus severe diffusion limitation.MOR zeolite with a moderate amount of EFAl species achieves a superior ethylene selectivity and exhibits an enhanced stability in syngas conversion when combined with ZnAlOx oxide.The insights gained in this work provide important guidance for the design of more efficient zeolite-based catalysts.
基金Project supported by the National Natural Science Foundation of China
文摘1 Introduction Recently, catalytic cracking catalysts have been developed from using USY zeolites as octane enhancement catalysts (mainly to improve the research-method octane number) to employing REUSY zeolites as high octane number-high gasoline yield catalysts (octanebarreled catalyst). The peculiarities of REUSY zeolites are the increase of the researchmethod octane number, the motor-method octane number and the gasoline yield. At pres-
基金the financial support from the National Natural Science Foundation of China(21908010)Jilin Provincial Department of Science and Technology(20220101089JC)the Education Department of Jilin Province(JJKH20220694KJ)。
文摘High-temperature treatment is key to the preparation of zeolite catalysts.Herein,the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work.X-Ray diffraction,N2physisorption,27Al magic angle spinning nuclear magnetic resonance(MAS NMR),and temperature-programmed desorption of ammonia results indicated that the hightemperature treatment at 650℃ hardly affected the inherent crystal and texture of HZSM-5zeolites but facilitated the conversion of framework Al to extra-framework Al,reducing the acid site and enhancing the acid strength.Moreover,the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking,promoting the conversion and light olefins yield while inhibiting coke formation.Based on the kinetic and mechanism analysis,the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al,which enhanced the acid strength,facilitated the bimolecular reaction,and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.
基金Acknowledgements This work has been supported by the National Natural Science Foundation of China （Grant No. 21276183） and Program of Introducing Talents of Discipline to Universities （No. B06006）.
文摘Titanium silicalite-1 （TS-1） has been hydrothermally synthesized with tetrapropylammonium hydroxide （TPAOH） as the template in the presence of various amounts of Na＋, characterized by inductively coupled plasma, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and ultro-violet-visible spectroscopy and studied in cyclohexanone ammoximation. The characterization results show that with the increase of Na＋ concentration in the synthesis, both the crystal sizes of TS- land extra framework Ti increase but framework Ti decreases. The addition of Na＋ below 3 mol-% of TPAOH in the synthesis does not influence the catalytic properties with above 98% conversion of cyclohexanone and 99.5% selectivity to cyclohexanone oxime. However, at the concentrations of Na＋≥3mol-% of TPAOH in the synthesis, the catalysts are deactivated faster with the increase of Na＋ addition, which can be attributed to more high molecular weight byproducts deposited in the large TS-1 particles and the loss of the frame-work titanium. The results of this work are of great importance for the industry.
