查看更多>>摘要：To develop robust and cost-effective catalysts for propene total oxidation,LaFe_(1-x)CoxO3(x = 0,0.1,0.2,0.3,1)perovskites were prepared via a citrate sol-gel method.XRD,FTIR and Raman analyses suggested that after cobalt substitution,the LaFeO3 structure was well maintained,whereas abundant lattice distortions were generated accompanied by weaker Fe-O bond.H2-TPR and O2-TPD results demonstrated that cobalt incorporation led to better reducibility and higher oxygen mobility of the oxides.The propene oxidation activity of the catalysts was found to increase with the cobalt content,which correlated well with the amount of surface-active oxygen species.The optimal catalyst LaFe_(0.8)Co_(0.2)O3 presented comparable activity to LaCoO3 at much lower cost.Moreover,it showed excellent cyclability(6 cycles)and stability(35 h),decent performance at high space velocity(24,0000 mL g~(-1)h~(-1))or in the presence of 5 vol% water,thereby being a promising candidate for industrial application.
Agustin de ArribaBenjamin SolsonaEster Garcia-Gonzalez
13页
查看更多>>摘要：Undoped and Te-doped MoV-Oxide(Ml phase)catalysts have been prepared hydrothermally(Te/Mo ratio in the synthesis gel from 0 to 0.17; and heat-treated at 400 or 600° C in N2 atmosphere),characterized by several physicochemical techniques and tested in the oxidative dehydrogenation(ODH)of ethane.The morphology and microporosity of the catalysts,the nature of V-species on the catalyst surface and the catalytic performance strongly depend on the composition and the heat-treatment temperature.When calcined at 400° C,the selectivity to ethylene decreases when the amount of tellurium increases,whereas when heat treated at 600° C,the selectivity to ethylene increases when the Te-loading increases.These trends have been explained on the basis of the good correlation between selectivity to ethylene and the concentration of V~(4+)species on the surface of catalysts,in which the most selective catalyst is that prepared with a Te/Mo ratio of 0.17 and heat-treated at 600℃.
查看更多>>摘要：p-Hydroxy p-methylbutyric acid(HMB)is expected as a promising therapeutic agent or a supplement.For industrial production of HMB,Pt-catalyzed aerobic oxidation of isoprene glycol is a potent synthetic method.However,the previous report using Pt-Bi catalyst supported on active carbon suffered from low tolerance to high substrate concentration conditions,which leads to low volumetric productivity.Herein,we report aerobic oxidation of isoprene glycol using Pt-Bi catalysts supported on ZrO2 or TiO2,showing high tolerance to the high substrate concentration conditions.In addition,these catalysts exhibited high recyclability.Scanning transmission electron microscopy analyses suggested the Pt-Bi species supported on ZrO2 or TiO2 are less likely to aggregate than those supported on activated carbon.Additionally,these metal oxides supported catalysts showed lower metal leaching than the carbon supported catalysts.Besides,the results of the various control experiments indicated the prevention of dehydration of an aldehyde intermediate is important for further improvement.
查看更多>>摘要：H2O2 production over carbon nitride photocatalyst is an emerging alternative and ecological solar-driven application.However,bulk carbon nitride(BCN)has stubbornly weak visible light absorption and easy recombination of carriers.Here,a sodium/potassium co-doped N vacancy(Nv)rich carbon nitride was synthesized by a one-step melamine and cyanuric acid self-assembly coupled with alkali metal molten salts.The hybridization of sodium is found to locate on edge site of CN layers,which introduces Nv structure and cyano structure on CN layers,hence modulates the migration of in-plane electrons.The potassium is found to intercalate between CN layers,which promotes carrier transportation between the interlayers.Both effects induce higher carrier transfer efficiency of catalysts and the co-doping of Na and K bring us the optimal sample(CNNK)with an ultra-high production rate(6289.6 |imol/g/h)and apparent quantum yield(44.70 %,380 nm),which is 124.5 and 10.4 times higher than BCN during the hydrogen peroxide process,respectively.Mechanistic analysis confirms the two-step single-electron oxygen reduction reaction pathway of H2O2 production.This strategy provides an achievable coupling strategy idea to design photocatalysts with elaborate structures for energy conservation.
查看更多>>摘要：The production of higher alcohols(C4+)via ethanol liquid-phase condensation is studied in this work,screening catalysts with different acid/base properties,observing similarities but also relevant differences with respect to gas-phase reactions in the gas phase.The mechanistic analysis demonstrates the relevance of acidity,mainly to promote the dehydrogenation steps.In the same way,side reactions and hydrogenations have less relevance than in gas-phase,promoting the condensations and,subsequently,obtaining heavy compounds.The highest alcohol selectivity is reached with MgAl(2/1),with more than 79% of C4+ selectivity,but the activity of this material is conditioned by the low conversion obtained.The presence of water reduces the activity because of a competitive adsorption on the catalytic sites whereas the activity increases significantly when using bifunctional catalysts.The best results,obtained with 1% Cu/MgAl(2/1),allow rising the conversion up to more than 460% respect to the parent mixed oxide,with almost 44% of the alcohol mixture enriched in heavy compounds,mainly C6 and C8.
查看更多>>摘要：Direct conversion of CO2 to hydrocarbons by hydrogenation was used in the production of light olefins.Hy-drothermal coating and physical blending procedures were used to synthesize Y2O3/Fe-Co-SAPO-34 in this study.Based on the results from characterization,a unique micro-mesoporous structural composite with co-existing basic and acidic sites was obtained without any excessive close-fitting between the active sites in the physically blended composite.The catalyst's overall selectivity for the light olefins was 82.6% with CO2 conversion of 19.9% for H2/CO2 of 3.0,with space velocity of 10 L.g.cat~(-1)h~(-1)at 400 ℃ and 20 bars.Furthermore,an increase in the number of acidic-basic sites,meso-microporous structures,alongside the synergetic effects of the com-positephases over the catalyst without any support,improved the catalyst's activity for CO2 conversion which in turn yielded higher C_2~=-C_4~= selectivity.The hybrid catalyst had a commendable stability within 80-hours of operation without losing its activity
查看更多>>摘要：Alkylation of benzene with carbon dioxide(CO2)is significant for converting greenhouse gas and surplus benzene into value-added toluene and xylene.Herein,a bifunctional catalyst comprising Zn/Ga oxides and HZSM-5 zeolite was developed to efficiently promote the methylation of benzene with CO2 and H2.This catalytic system exhibited excellent performance at 425 ℃ and 3.0 MPa,through which benzene conversion of 39.1% and total xylene/toluene selectivity of 92.7% have been achieved.Furthermore,the catalysts are carefully characterized; compositions of Zn/Ga oxides and Si/Al ratios of HZSM-5 zeolite are recognized as decisive factors for reaction activity and selectivity respectively.Additionally,primary reaction pathways are explored and testified to provide detailed understanding for the establishment of reaction networks,especially for mechanisms of eth-ylbenzene evolution.These findings are able to provide more deep insights into the process of benzene alkylation,which further facilitates the emergence of effective catalysts with potential industrial applications.
查看更多>>摘要：Rational design of efficient,earth-abundant,and durable electrocatalysts to accelerate the oxygen evolution reaction(OER)is critical for hydrogen ion by water electrolysis.In the present work,nanostructured Ni_(12-x)FexP5(x = 1.2,2.4,3.6)OER electrocatalysts synthesized by a colloidal method is reported.For x = 1.2,an alloy of Ni,Fe,and P is formed.For x = 2.4 or x = 3.6,a core-shell NiFeP@Fe3O4 structure is formed.The nanoparticles are encapsulated in a self-generated carbon layer.The carbon layer is formed during synthesis from synthesis residues.The carbon-encapsulated Ni_(9.6)Fe_(2.4)P5 catalyst offers the outstanding mass activity of 0.1 A mg~(-1)and overpotential of 220 mV at 10 mA cm~(-2),assigned to a combination of enhanced electrical conductivity provided by the carbon shell,a large surface area,and a high specific catalytic activity.Post-mortem characterization indicates that the carbon encapsulation remains intact under conditions of the OER.
查看更多>>摘要：Series of Co(OH)2/Cr2O3 catalysts before and after calcination(denoted as CoCrOx)were prepared and used for the selective oxidation of toluene using oxygen in the absence of solvent.Co(OH)2/Cr2O3 catalyst before calcination has exhibited excellent catalytic activity for the oxidation of toluene,conversion of toluene reaches 37.8% and selectivity of benzoic acid is up to 94.4%.Interestingly,calcined catalyst CoCrOx mainly produces benzaldehyde,and the selectivity for benzaldehyde can be as high as 63.6%(conversion of toluene remains high at 14.5%).A series of characterizations including XRD,TEM,FT-IR,XPS,H2-TPR and CO2-TPD illustrate that calcination makes phase transformation occur and leads to the change of acid-basic sites and reactive oxygen species,which affect the activity and selectivity of toluene oxidation.After calcination,Co~(2+)migrates to vacant sub-surface position of surface oxygen(O_(sur))and remains on the surface.The formation of Co-Co bond widens defect area so that activated O_(sur)induces oxidation of toluene,leading to an increase in the amount of adsorbed oxygen,which becomes the decisive factor for high selectivity of benzaldehyde.
查看更多>>摘要：By encapsulating metal nanoparticles(NPs),the synergistic effect between the metalloporphyrins and the metal nanoparticles in metalloporphyrin organic frameworks(P-MOFs)can boost its catalytic performance.The self-coupling reaction of terminal alkynes is a kind of important organic reaction and can take place with the aid of the catalyst.A nanorod-like metal-organic skeleton PCN-222(Cu)with carboxy porphyrins as ligands was synthesized as the precursor.By a double-solvent approach,the composite catalysts with varying copper nano-loadings in PCN-222(Cu)pores were obtained.Among them,1.9 wt% of Cu NPs in Cu@PCN-222(Cu)has excellent catalytic activity and stability for the self-coupling reaction of terminal alkynes.PCN-222(Cu)can stabilize the Cu NPs,control the size selectivity and crystal form.The copper porphyrins and Cu NPs in Cu@PCN-222(Cu)both serve as the catalytic active sites.This strategy,which using porphyrin-structured MOFs to construct dual active sites with the same element,has promising applications in MOFs catalysis.
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