Although metal oxide-zeolite hybrid materials have long been known to achieve enhanced catalytic activity and selectivity in NO_(x)removal reactions through the inter-particle diffusion of intermediate species,their s...Although metal oxide-zeolite hybrid materials have long been known to achieve enhanced catalytic activity and selectivity in NO_(x)removal reactions through the inter-particle diffusion of intermediate species,their subsequent reaction mechanism on acid sites is still unclear and requires investigation.In this study,the distribution of Brønsted/Lewis acid sites in the hybrid materials was precisely adjusted by introducing potassium ions,which not only selectively bind to Brønsted acid sites but also potentially affect the formation and diffusion of activated NO species.Systematic in situ diffuse reflectance infrared Fourier transform spectroscopy analyses coupled with selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR)reaction demonstrate that the Lewis acid sites over MnO_(x)are more active for NO reduction but have lower selectivity to N_(2)than Brønsted acids sites.Brønsted acid sites primarily produce N_(2),whereas Lewis acid sites primarily produce N_(2)O,contributing to unfavorable N_(2)selectivity.The Brønsted acid sites present in Y zeolite,which are stronger than those on MnO_(x),accelerate the NH_(3)-SCR reaction in which the nitrite/nitrate species diffused from the MnO_(x)particles rapidly convert into the N_(2).Therefore,it is important to design the catalyst so that the activated NO species formed in MnO_(x)diffuse to and are selectively decomposed on the Brønsted acid sites of H-Y zeolite rather than that of MnO_(x)particle.For the physically mixed H-MnO_(x)+H-Y sample,the abundant Brønsted/Lewis acid sites in H-MnO_(x)give rise to significant consumption of activated NO species before their inter-particle diffusion,thereby hindering the enhancement of the synergistic effects.Furthermore,we found that the intercalated K+in K-MnO_(x)has an unexpected favorable role in the NO reduction rate,probably owing to faster diffusion of the activated NO species on K-MnO_(x)than H-MnO_(x).This study will help to design promising metal oxide-zeolite hybrid catalysts by identifying the role of the acid sites in two different constituents.展开更多
The performances of heterogeneous catalysts can be effectively tuned by changing the catalyst structures.Here we report a controllable nitrile synthesis from alcohol ammoxidation,where the nitrile hydration side react...The performances of heterogeneous catalysts can be effectively tuned by changing the catalyst structures.Here we report a controllable nitrile synthesis from alcohol ammoxidation,where the nitrile hydration side reaction could be efficiently prevented by changing the manganese oxide catalysts.α-Mn_(2)O_(3)based catalysts are highly selective for nitrile synthesis,but MnO_(2)-based catalysts includingα,β,γ,andδphases favour the amide production from tandem ammoxidation and hydration steps.Multiple structural,kinetic,and spectroscopic investigations reveal that water decomposition is hindered onα-Mn2O3,thus to switch off the nitrile hydration.In addition,the selectivity-control feature of manganese oxide catalysts is mainly related to their crystalline nature rather than oxide morphology,although the morphological issue is usually regarded as a crucial factor in many reactions.展开更多
Superoxide dismutase （SOD） is one of the most important antioxidant defense enzymes, and is considered as the first line against oxidative stress. In this study, we cloned a mitochondrial manganese （Mn） SOD （mMn...Superoxide dismutase （SOD） is one of the most important antioxidant defense enzymes, and is considered as the first line against oxidative stress. In this study, we cloned a mitochondrial manganese （Mn） SOD （mMnSOD） cDNA from the ridgetail white prawn Exopalaemon carinicauda by using rapid amplification of cDNA ends （RACE） methods. The fulMength cDNA for mMnSOD was 1 014-bp long, containing a 5＇-untranslated region （UTR） of 37-bp, a 3＇-UTR of 321-bp with a poly （A） tail, and included a 657-bp open reading frame encoding a protein of 218 amino acids with a 16-amino-acid signal peptide. The protein had a calculated molecular weight of 23.87 kDa and a theoretical isoelectric point of 6.75. The mMnSOD sequence included two putative N-glycosylation sites （NHT and NLS）, the MnSOD signature sequence 18~DVWEHAYY^87, and four putative Mn binding sites （H48, H96, D180, and H184）. Sequence comparison showed that the mMnSOD deduced amino acid sequence of E. carinicauda shared 97%, 95%, 89%, 84%, 82%, 72%, and 69% identity with that ofMacrobrachium rosenbergii, Macrobrachium nipponense, Fenneropeneaus chinensis, Callinectes sapidus, Perisesarma bidens, Danio rerio, and Homo sapiens, resectively. Quantitative real-time RT-PCR analysis showed that mMnSOD transcripts were present in all E. carinicauda tissues examined, with the highest levels in the hepatopancreas. During an ammonia stress treatment, the transcript levels of mMnSOD and cMnSOD were up-regulated at 12 h in hemocytes and at 24 h in the hepatopancreas. As the duration of the ammonia stress treatment extended to 72 h, the transcript levels of mMnSOD and cMnSOD significantly decreased both in hemocytes and hepatopancreas. These findings indicate that the SOD system is induced to respond to acute ammonia stress, and may be involved in environmental stress responses in E. carinicauda.展开更多
The amino acid Schiff base complex (Sal-AMBA-Mn) was prepared with p-amino-methylbenzoic acid, salicylaldehyde and Mn(OAc)2·4H2O. Its structures was characterized with IR and UV spectra. Oxygenation mechanism of ...The amino acid Schiff base complex (Sal-AMBA-Mn) was prepared with p-amino-methylbenzoic acid, salicylaldehyde and Mn(OAc)2·4H2O. Its structures was characterized with IR and UV spectra. Oxygenation mechanism of the complex in N, N-dimethylformamide solution was investigated. The results show that lower temperature is in favor of the oxygenation, and energy, enthalpy and entropy are -3.8 kJ/mol, -4.2 J/mol and -161.44 J/(mol·K), respectively. In the presence of the manganese complex, dehydroepiandrosterone acetate is effectively oxidized by molecular oxygen and the corresponding enone 7-ketodehydroepiandrosterone acetate is obtained. The yield is 62.1% when the oxidation is carried out under the reaction conditions of 60 ℃, 2 MPa of O2 pressure, C5H5N as a solvent and molar ratio of the substrate to the complex of 1:10.展开更多
文摘Although metal oxide-zeolite hybrid materials have long been known to achieve enhanced catalytic activity and selectivity in NO_(x)removal reactions through the inter-particle diffusion of intermediate species,their subsequent reaction mechanism on acid sites is still unclear and requires investigation.In this study,the distribution of Brønsted/Lewis acid sites in the hybrid materials was precisely adjusted by introducing potassium ions,which not only selectively bind to Brønsted acid sites but also potentially affect the formation and diffusion of activated NO species.Systematic in situ diffuse reflectance infrared Fourier transform spectroscopy analyses coupled with selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR)reaction demonstrate that the Lewis acid sites over MnO_(x)are more active for NO reduction but have lower selectivity to N_(2)than Brønsted acids sites.Brønsted acid sites primarily produce N_(2),whereas Lewis acid sites primarily produce N_(2)O,contributing to unfavorable N_(2)selectivity.The Brønsted acid sites present in Y zeolite,which are stronger than those on MnO_(x),accelerate the NH_(3)-SCR reaction in which the nitrite/nitrate species diffused from the MnO_(x)particles rapidly convert into the N_(2).Therefore,it is important to design the catalyst so that the activated NO species formed in MnO_(x)diffuse to and are selectively decomposed on the Brønsted acid sites of H-Y zeolite rather than that of MnO_(x)particle.For the physically mixed H-MnO_(x)+H-Y sample,the abundant Brønsted/Lewis acid sites in H-MnO_(x)give rise to significant consumption of activated NO species before their inter-particle diffusion,thereby hindering the enhancement of the synergistic effects.Furthermore,we found that the intercalated K+in K-MnO_(x)has an unexpected favorable role in the NO reduction rate,probably owing to faster diffusion of the activated NO species on K-MnO_(x)than H-MnO_(x).This study will help to design promising metal oxide-zeolite hybrid catalysts by identifying the role of the acid sites in two different constituents.
文摘The performances of heterogeneous catalysts can be effectively tuned by changing the catalyst structures.Here we report a controllable nitrile synthesis from alcohol ammoxidation,where the nitrile hydration side reaction could be efficiently prevented by changing the manganese oxide catalysts.α-Mn_(2)O_(3)based catalysts are highly selective for nitrile synthesis,but MnO_(2)-based catalysts includingα,β,γ,andδphases favour the amide production from tandem ammoxidation and hydration steps.Multiple structural,kinetic,and spectroscopic investigations reveal that water decomposition is hindered onα-Mn2O3,thus to switch off the nitrile hydration.In addition,the selectivity-control feature of manganese oxide catalysts is mainly related to their crystalline nature rather than oxide morphology,although the morphological issue is usually regarded as a crucial factor in many reactions.
基金Supported by the National High Technology Research and Development Program of China(863 Program)(No.2012AA10A409)the Modern AgroIndustry Technology Research System(No.CARS-47)+1 种基金the Special Fund for Independent Innovation of Shandong Province(No.2013CX80202)the Special Fund for Agro-Scientific Research in the Public Interest(No.201103034)
文摘Superoxide dismutase （SOD） is one of the most important antioxidant defense enzymes, and is considered as the first line against oxidative stress. In this study, we cloned a mitochondrial manganese （Mn） SOD （mMnSOD） cDNA from the ridgetail white prawn Exopalaemon carinicauda by using rapid amplification of cDNA ends （RACE） methods. The fulMength cDNA for mMnSOD was 1 014-bp long, containing a 5＇-untranslated region （UTR） of 37-bp, a 3＇-UTR of 321-bp with a poly （A） tail, and included a 657-bp open reading frame encoding a protein of 218 amino acids with a 16-amino-acid signal peptide. The protein had a calculated molecular weight of 23.87 kDa and a theoretical isoelectric point of 6.75. The mMnSOD sequence included two putative N-glycosylation sites （NHT and NLS）, the MnSOD signature sequence 18~DVWEHAYY^87, and four putative Mn binding sites （H48, H96, D180, and H184）. Sequence comparison showed that the mMnSOD deduced amino acid sequence of E. carinicauda shared 97%, 95%, 89%, 84%, 82%, 72%, and 69% identity with that ofMacrobrachium rosenbergii, Macrobrachium nipponense, Fenneropeneaus chinensis, Callinectes sapidus, Perisesarma bidens, Danio rerio, and Homo sapiens, resectively. Quantitative real-time RT-PCR analysis showed that mMnSOD transcripts were present in all E. carinicauda tissues examined, with the highest levels in the hepatopancreas. During an ammonia stress treatment, the transcript levels of mMnSOD and cMnSOD were up-regulated at 12 h in hemocytes and at 24 h in the hepatopancreas. As the duration of the ammonia stress treatment extended to 72 h, the transcript levels of mMnSOD and cMnSOD significantly decreased both in hemocytes and hepatopancreas. These findings indicate that the SOD system is induced to respond to acute ammonia stress, and may be involved in environmental stress responses in E. carinicauda.
基金Project(76132020) supported by the Post-Doctoral Science Fund of Central South University
文摘The amino acid Schiff base complex (Sal-AMBA-Mn) was prepared with p-amino-methylbenzoic acid, salicylaldehyde and Mn(OAc)2·4H2O. Its structures was characterized with IR and UV spectra. Oxygenation mechanism of the complex in N, N-dimethylformamide solution was investigated. The results show that lower temperature is in favor of the oxygenation, and energy, enthalpy and entropy are -3.8 kJ/mol, -4.2 J/mol and -161.44 J/(mol·K), respectively. In the presence of the manganese complex, dehydroepiandrosterone acetate is effectively oxidized by molecular oxygen and the corresponding enone 7-ketodehydroepiandrosterone acetate is obtained. The yield is 62.1% when the oxidation is carried out under the reaction conditions of 60 ℃, 2 MPa of O2 pressure, C5H5N as a solvent and molar ratio of the substrate to the complex of 1:10.
