It is urgent to develop catalysts with application potential for oxidative coupling of methane(OCM)at relatively lower temperature.Herein,three-dimensional ordered macro porous(3 DOM)La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)(...It is urgent to develop catalysts with application potential for oxidative coupling of methane(OCM)at relatively lower temperature.Herein,three-dimensional ordered macro porous(3 DOM)La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)(A_(2)B_(2)O_(7)-type)catalysts with disordered defective cubic fluorite phased structure were successfully prepared by a colloidal crystal template method.3DOM structure promotes the accessibility of the gaseous reactants(O2and CH4)to the active sites.The co-doping of Ca and Sr ions in La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)catalysts improved the formation of oxygen vacancies,thereby leading to increased density of surface-active oxygen species(O_(2)^(-))for the activation of CH4and the formation of C2products(C2H6and C2H4).3DOM La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)catalysts exhibit high catalytic activity for OCM at low temperature.3DOM La1.7Sr0.3Ce1.7Ca0.3O7-δcatalyst with the highest density of O_(2)^(-)species exhibited the highest catalytic activity for low-temperature OCM,i.e.,its CH4conversion,selectivity and yield of C2products at 650℃are 32.2%,66.1%and 21.3%,respectively.The mechanism was proposed that the increase in surface oxygen vacancies induced by the co-doping of Ca and Sr ions boosts the key step of C-H bond breaking and C-C bond coupling in catalyzing low-temperature OCM.It is meaningful for the development of the low-temperature and high-efficient catalysts for OCM reaction in practical application.展开更多
The sand fly Lutzomyia longipalpis is the main vector of Leishmania infantum in the Americas.Female sand flies ingest sugar-rich solutions and blood,which are digested in the midgut.Digestion of nutrients is an essent...The sand fly Lutzomyia longipalpis is the main vector of Leishmania infantum in the Americas.Female sand flies ingest sugar-rich solutions and blood,which are digested in the midgut.Digestion of nutrients is an essential function performed by digestive enzymes,which require appropriate physiological conditions.One of the main aspects that influence enzymatic activity is the gut pH,which must be tightly controlled.Considering second messengers are frequently involved in the coordination of tightly regulated physiological events,we investigated if the second messenger cAMP would participate in the process of alkalinization in the abdominal midgut of female L.longipalpis.In midguts containing the indicator dye bromothymol-blue,cAMP stimulated the alkalinization of the midgut lumen.Through another technique based on the use of fluorescein as a pH indicator,we propose that cAMP is involved in the alkalinization of the midgut by activating HCO3-transport from the enterocyte's cytoplasm to the lumen.The results strongly suggested that the carrier responsible for this process would be a HCO3−/Cl−antiporter located in the enterocytes’apical membrane.Hematophagy promotes the release of alkalinizing hormones in the hemolymph;however,when the enzyme adenylyl cyclase,responsible for cAMP production,was inhibited,we observed that the hemolymph from blood-fed L.longipalpis’females did not stimulate midgut alkalinization.This result indicated that hormone-stimulated alkalinization is mediated by cAMP.In the present study,we provide evidences that cAMP has a key role in the control of intestinal pH.展开更多
基金supported by the National Key Research and Development Program of China(Nos.2022YFB3504100,2022YFB3506200)the National Natural Science Foundation of China(Nos.22208373,22376217)+1 种基金the Beijing Nova Program(No.20220484215)the Science Foundation of China University of Petroleum,Beijing(No.2462023YJRC030)。
文摘It is urgent to develop catalysts with application potential for oxidative coupling of methane(OCM)at relatively lower temperature.Herein,three-dimensional ordered macro porous(3 DOM)La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)(A_(2)B_(2)O_(7)-type)catalysts with disordered defective cubic fluorite phased structure were successfully prepared by a colloidal crystal template method.3DOM structure promotes the accessibility of the gaseous reactants(O2and CH4)to the active sites.The co-doping of Ca and Sr ions in La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)catalysts improved the formation of oxygen vacancies,thereby leading to increased density of surface-active oxygen species(O_(2)^(-))for the activation of CH4and the formation of C2products(C2H6and C2H4).3DOM La_(2-x)Sr_(x)Ce_(2-y)CayO_(7-δ)catalysts exhibit high catalytic activity for OCM at low temperature.3DOM La1.7Sr0.3Ce1.7Ca0.3O7-δcatalyst with the highest density of O_(2)^(-)species exhibited the highest catalytic activity for low-temperature OCM,i.e.,its CH4conversion,selectivity and yield of C2products at 650℃are 32.2%,66.1%and 21.3%,respectively.The mechanism was proposed that the increase in surface oxygen vacancies induced by the co-doping of Ca and Sr ions boosts the key step of C-H bond breaking and C-C bond coupling in catalyzing low-temperature OCM.It is meaningful for the development of the low-temperature and high-efficient catalysts for OCM reaction in practical application.
基金This work was supported by Fundacao de Amparo a Pesquisa do Estado de Minas Gerais(FAPEMIG),Conselho Nacional de Desenvolvimento Cientifico e Teenologico(CNPq),Instituto Nacional de Ciencia e Teenologia-Entomologia Molecular(INCT-EM),and Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior(CAPES).
文摘The sand fly Lutzomyia longipalpis is the main vector of Leishmania infantum in the Americas.Female sand flies ingest sugar-rich solutions and blood,which are digested in the midgut.Digestion of nutrients is an essential function performed by digestive enzymes,which require appropriate physiological conditions.One of the main aspects that influence enzymatic activity is the gut pH,which must be tightly controlled.Considering second messengers are frequently involved in the coordination of tightly regulated physiological events,we investigated if the second messenger cAMP would participate in the process of alkalinization in the abdominal midgut of female L.longipalpis.In midguts containing the indicator dye bromothymol-blue,cAMP stimulated the alkalinization of the midgut lumen.Through another technique based on the use of fluorescein as a pH indicator,we propose that cAMP is involved in the alkalinization of the midgut by activating HCO3-transport from the enterocyte's cytoplasm to the lumen.The results strongly suggested that the carrier responsible for this process would be a HCO3−/Cl−antiporter located in the enterocytes’apical membrane.Hematophagy promotes the release of alkalinizing hormones in the hemolymph;however,when the enzyme adenylyl cyclase,responsible for cAMP production,was inhibited,we observed that the hemolymph from blood-fed L.longipalpis’females did not stimulate midgut alkalinization.This result indicated that hormone-stimulated alkalinization is mediated by cAMP.In the present study,we provide evidences that cAMP has a key role in the control of intestinal pH.
