Selective synthesis of ethanol from syngas under the Co-based catalysts is still challenging due to the hard of regulating the active site Co^(0) and Co^(2+)ratio.In this work,a series of CaTi_(0.9-x)Co_(x)Mo_(0.1)O_(...Selective synthesis of ethanol from syngas under the Co-based catalysts is still challenging due to the hard of regulating the active site Co^(0) and Co^(2+)ratio.In this work,a series of CaTi_(0.9-x)Co_(x)Mo_(0.1)O_(3)(x=0,0.1-0.4)and CaTi_(0.7)Co_(0.3)O_(3) catalysts were prepared by using citric acid complexation method to promote the synthesis of ethanol.It was found that Mo species in the perovskite lattice can regulate the Co^(0) and Co^(2+)ratio through the domain-limiting effect of perovskite and the degree of Co reduction could be adjusted by changing the Co/Mo molar ratio.Among these investigated catalysts,the total selectivity of alcohols over the catalyst with the optimal Co/Mo ratio CaTi_(0.6)Co_(0.3)Mo_(0.1)O_(3) reached 39.1%,with ethanol accounting for 74.7%,which was ascribed to the moderate and tightly bound ratio of dissociative to non-dissociative adsorption sites on the surface and the balance of CH_(x)-CH_(y) coupling and C^(O) insertion.展开更多
The adsorption behavior and description behavior of benzene , ethylene and ethylbenzene over HZSM-5 and Co/HZSM-5 catalysts were studied by means of TPSR (Temperature programmed surface reaction) technique. TPSR resul...The adsorption behavior and description behavior of benzene , ethylene and ethylbenzene over HZSM-5 and Co/HZSM-5 catalysts were studied by means of TPSR (Temperature programmed surface reaction) technique. TPSR results of ben- zene and ethylene co-adsorption show that the maian products are styrene , ethylben- zene, toluene, propane, and butane. In a separate experiment of ethylbenzene ad- sorption, styrene . toluene and benzene are formed due to cracking and dehydro- genation. The mechanism of styrene formation was proposed , i. e. , the reaction was carried out via. the dehydrogenation of mediate species ethylbenzene according to the results of TPSR-MS , activity testing and thermodynamic analysis.展开更多
TiO2‐supported Pd‐Sb bimetallic catalysts were prepared and evaluated for the direct synthesis of H2O2 at ambient pressure.The addition of Sb to Pd significantly enhanced catalytic performance,and a Pd50Sb catalyst ...TiO2‐supported Pd‐Sb bimetallic catalysts were prepared and evaluated for the direct synthesis of H2O2 at ambient pressure.The addition of Sb to Pd significantly enhanced catalytic performance,and a Pd50Sb catalyst showed the greatest selectivity of up to 73%.Sb promoted the dispersion of Pd on TiO2,as evidenced by transmission electron microscopy and X‐ray diffraction.X‐ray photoelectron spectroscopy indicated that the oxidation of Pd was suppressed by Sb.In addition,Sb2O3 layers were formed and partially wrapped the surfaces of Pd catalysts,thus suppressing the activation of H2 and subsequent hydrogenation of H2O2.In situ diffuse reflection infrared Fourier transform spectroscopy for CO adsorption suggested that Sb homogenously located on the surface of Pd‐Sb catalysts and isolated contiguous Pd sites,resulting in the rise of the ratio of Pd monomer sites that are favorable for H2O2 formation.As a result,the Sb modified Pd surfaces significantly enhanced the non‐dissociative activation of O2 and H2O2 selectivity.展开更多
Focused exploration of earth-abundant and cost-efficient non-noble metal electrocatalysts with superior hydrogen evolution reaction(HER)performance is very important for large-scale and efficient electrolysis of water...Focused exploration of earth-abundant and cost-efficient non-noble metal electrocatalysts with superior hydrogen evolution reaction(HER)performance is very important for large-scale and efficient electrolysis of water.Herein,a sandwich composite structure(designed as MS-Mo2C@NCNS)ofβ-Mo2C hollow nanotubes(HNT)and N-doped carbon nanosheets(NCNS)is designed and prepared using a binary NaCl–KCl molten salt(MS)strategy for HER.The temperature-dominant Kirkendall formation mechanism is tentatively proposed for such a three-dimensional hierarchical framework.Due to its attractive structure and componential synergism,MS-Mo2C@NCNS exposes more effective active sites,confers robust structural stability,and shows significant electrocatalytic activity/stability in HER,with a current density of 10 mA cm-2 and an overpotential of only 98 mV in 1 M KOH.Density functional theory calculations point to the synergistic effect of Mo2C HNT and NCNS,leading to enhanced electronic transport and suitable adsorption free energies of H*(ΔGH*)on the surface of electroactive Mo2C.More significantly,the MS-assisted synthetic methodology here provides an enormous perspective for the commercial development of highly active non-noble metal electrocatalysts toward efficient hydrogen evolution.展开更多
Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to ...Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to develop an eco‐friendly and nuisanceless OSDA for zeolite synthesis.Herein,choline is employed as a non‐toxic and green OSDA to synthesize high silica Y zeolite with SiO2/Al2O3 ratios of 6.5–6.8.The prepared Y zeolite samples exhibited outstanding(hydro)thermal stability at ultrahigh temperature owing to the higher SiO2/Al2O3 ratio.The XRF,SEM,29Si‐NMR and 13Na+results suggested that choline plays a structure‐directing role in the synthesis of Y zeolite,while the feed molar fraction of Na+is a crucial determinant for the framework SiO2/Al2O3 ratio and the crystal morphology.展开更多
A bi-component catalyst comprising CuC1 and metallic copper was used in the direct synthesis of me- thylchlorosilane to study the catalytic synergy between the different copper sources. The catalyst exhibited high ac-...A bi-component catalyst comprising CuC1 and metallic copper was used in the direct synthesis of me- thylchlorosilane to study the catalytic synergy between the different copper sources. The catalyst exhibited high ac- tivity and high selectivity of dimethyldichlorosilane （M2） in the stirred bed reactor. The effect of the proportion of CuC1 used was studied and 10%-30% CuC1 gave the best yield of M2. The use of CuC1 decreased the induction pe- riod of reaction, improved the selectivity in the induction stage, and gave a longer stable stage. These results sug- gest that bi-comoonent catalyst has advantazes in the direct synthesis reaction.展开更多
Series of heterogeneous interfacial engineered TiO2(C-TiO2) with controllable carbon content were facilely synthesized by incipient-wet impregnation using glucose and subsequent thermal carbonization. The obtained C-T...Series of heterogeneous interfacial engineered TiO2(C-TiO2) with controllable carbon content were facilely synthesized by incipient-wet impregnation using glucose and subsequent thermal carbonization. The obtained C-TiO2 were used as catalytic supports to load Pd nanoparticles for H2 O2 direct synthesis from H2 and O2. The as-prepared samples were systematically studied by transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS), air isothermal microcalorimeter, temperature-programmed reduction of H2(H2-TPR), and so on. The catalytic results showed that H2 O2 productivity and H2O2 selectivity of Pd/C-TiO2 firstly rose with increasing carbon content and then declined. Pd/C-TiO2 catalyst with 1.89 wt% of carbon content showed the best catalytic performance that had 61.2% of selectivity and 2192 mmol H2O2/g Pd/h of productivity, which were significantly better than those of pristine Pd/TiO2(45.2% and 1827 mmol H2O2/g Pd/h). Various characterization results displayed that the carbon species were heterogeneously dispersed on TiO2 surface. Moreover, no obvious geometric transformation in supports and Pd nanoparticles were observed among different catalysts. The superficial hydrophobicity of Pd/C-TiO2 was gradually promoted with increasing carbon content, which led to the corresponding decrease in adsorption energy of H2O2 with catalysts. According to structure-performance relationship analyses, the heterogeneous interfacial engineering of carbon could maintain the interaction of Pd nanoparticles with TiO2 and simultaneously accelerate the H2O2 desorption. Both factors further determined the excellent H2O2 direct synthesis performance of Pd/C-TiO2.展开更多
The direct electrocatalytic synthesis of ammonia from N2 and H2O by using renewable energy sources and ambient pressure/temperature operations is a breakthrough technology,which can reduce by over 90%the greenhouse ga...The direct electrocatalytic synthesis of ammonia from N2 and H2O by using renewable energy sources and ambient pressure/temperature operations is a breakthrough technology,which can reduce by over 90%the greenhouse gas emissions of this chemical and energy storage process.We report here an in-situ electrochemical activation method to prepare Fe2O3-CNT(iron oxide on carbon nanotubes)electrocatalysts for the direct ammonia synthesis from N2 and H2O.The in-situ electrochemical activation leads to a large increase of the ammonia formation rate and Faradaic efficiency which reach the surprising high values of 41.6μg mgcat^−1 h^−1 and 17%,respectively,for an in-situ activation of 3 h,among the highest values reported so far for non-precious metal catalysts that use a continuous-flow polymer-electrolytemembrane cell and gas-phase operations for the ammonia synthesis hemicell.The electrocatalyst was stable at least 12 h at the working conditions.Tests by switching N2 to Ar evidence that ammonia was formed from the gas-phase nitrogen.The analysis of the changes of reactivity and of the electrocatalyst characteristics as a function of the time of activation indicates a linear relationship between the ammonia formation rate and a specific XPS(X-ray-photoelectron spectroscopy)oxygen signal related to O2−in iron-oxide species.This results together with characterization data by TEM and XRD suggest that the iron species active in the direct and selective synthesis of ammonia is a maghemite-type iron oxide,and this transformation from the initial hematite is responsible for the in-situ enhancement of 3-4 times of the TOF(turnover frequency)and NH3 Faradaic efficiency.This transformation is likely related to the stabilization of the maghemite species at CNT defect sites,although for longer times of preactivation a sintering occurs with a loss of performances.展开更多
Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The ...Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The industrial synthesis of DMM is mainly involved two-step process:methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor.Due to huge energy consumption,this typical synthesis route of DMM needs to be upgraded and more green routes should be determined.In this review,four state-of-the-art one-step direct synthetic routes,including two upgrading routes(methanol direct oxidation and direct dehydrogenation)and two green routes(methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation),have been summarized and compared.Combination with the reaction mechanism and catalytic performance on the different catalysts,the challenges and opportu nities for every synthetic route are proposed.The relationships between catalyst structu re and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in.Hopefully,this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future.展开更多
Copper supported over silica exhibited very high activity and selectivity for the direct synthesis of indole at atmospheric pressure. Under the reaction temperature of 325C,the yield of indole could obtain 88%.
Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 ...Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 nm)by impregnation method.Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H2O2 among the prepared catalysts,together with highest formation rate of H2O2(38.0 mmol·(g cat)^-1·h^-1),1.9 times than that of Pd supported on conventional HZSM-5 zeolite(Pd/CZ-50).Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H2 dissociation,more BrΦnsted acid sites and stronger metal-support interaction which inhibited the dissociation of O-O bond in H2O2.The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching,leading to a better catalytic stability with 90%activity retained after 3 cycles,which was almost 3 times than that of Pd/CZ-50(30.4%activity retained).展开更多
Two families of catalysts, based on Pd nanoparticles supported on ceramic asymmetric tubular alumina membranes, are studies in the direct synthesis of H2O2. They are prepared by depositing Pd in two ways：（i） reduct...Two families of catalysts, based on Pd nanoparticles supported on ceramic asymmetric tubular alumina membranes, are studies in the direct synthesis of H2O2. They are prepared by depositing Pd in two ways：（i） reduction with N2H4 in an ultrasonic bath and（ii） by impregnation-deposition. The first preparation leads to larger particles, with average size of around 11 nm, while the second preparation leads to smaller particles, with average size around 4 nm. The catalytic membranes were tested as prepared, after thermal treatment in air and after further pre-reduction with H2 in mild（100 ℃） conditions. Samples were characterized by TEM, CO-chemisorption monitored by DRIFTS method and TPR, while catalytic tests have been performed in a semi-batch recirculation membrane reactor. Experimental catalytic results were analysed using two kinetics models to derive the reaction constants for the parallel and consecutive reactions of the kinetic network. Smaller particles of Pd show lower selectivity due to the higher rate of parallel combustion, even if the better dispersion of Pd and thus higher metal surface area in the sample lead to a productivity in H2O2 similar or even higher than the sample with the larger Pd particles. Independently on the presence of smaller or larger Pd nanoparticles, an oxidation treatment leads to a significant enhancement in the productivity, although the catalyst progressively reduces during the catalytic process. The inhibition of the parallel combustion reaction（to water） induced from the calcination treatment remains after the in-situ reduction of the oxidized Pd species formed during the pre-treatment.This is likely due to the elimination of defect sites which dissociatively activate oxygen, and tentatively attributed to Pd sites able to give three- and four-fold coordination of CO.展开更多
Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix(TM) of a scattering medium. We report a simple but powerful method, ...Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix(TM) of a scattering medium. We report a simple but powerful method, direct digital frequency synthesis(DDS) technology to modulate the phase front of the laser and measure the TM. By judiciously modulating the phase front of a He–Ne laser beam, we experimentally generate a high quality focus at any targeted location through a 2 mm thick 120 grit ground glass diffuser, which is commercially used in laser display and laser holographic display for improving brightness uniformity and reducing speckle. The signal to noise ratio(SNR) of the clear round focus is 50 and the size is about 44 μm. Our study will open up new avenues for enhancing light energy delivery to the optical engine in laser TV to lower the power consumption, phase compensation to reduce the speckle noise, and controlling the lasing threshold in random lasers.展开更多
A two steps direct copolymerisation process was developed. The first step is to produce oligomer and then the oligomer of lactic acid/glycolic acid (90/10) is polymerized with binary catalyst tin chloride dihydrate/p-...A two steps direct copolymerisation process was developed. The first step is to produce oligomer and then the oligomer of lactic acid/glycolic acid (90/10) is polymerized with binary catalyst tin chloride dihydrate/p-toluenesulfonic acid. In this way, the direct synthesis of copoly (lactic acid/glycolic acid) without any organic solvent was investigated. The properties and structures of products were characterized by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), X-ray diffraction and so on. The results show that comparatively high molecular weight copolymer of lactic acid and glycolic acid can be prepared by direct processing under appropriate technological conditions.展开更多
The choice of support is one of the most significant components in the direct synthesis of H_(2)O_(2).Aiming to improvement of activity and selectivity of H_(2)O_(2) on Pd/TiO_(2) surface,we systematically investigate...The choice of support is one of the most significant components in the direct synthesis of H_(2)O_(2).Aiming to improvement of activity and selectivity of H_(2)O_(2) on Pd/TiO_(2) surface,we systematically investigated the important elementary steps on Pd/TiO_(2)-Vo@C,Pd/TiO_(2)-Vo,Pd/TiO_(2)-2 Vo,Pd/TiO_(2),and Pd/C using the first-principles calculations.The Bader charge analysis and charge density difference of O_(2) adsorption elucidate the relationship between the electronic distribution and chemisorption energy.The effective barrier analysis further enables to quantitatively estimate the reactivity of H_(2)O_(2) and H2O.We demonstrate unambiguously that the selectivity of H2O formation is boosted as the oxygen vacancy concentration raised.Moreover,the introduction of C into a TiO_(2) with appropriate oxygen vacancies can slightly reduce the effective barrier for H_(2)O_(2) formation and increase the effective barrier for H2O formation leading to a higher activity and selectivity of H_(2)O_(2) formation.Our finding suggests that carbon-doped oxygen vacancy TiO_(2) supported Pd is potential alternative catalyst compared with the Pd/TiO_(2).展开更多
Single-phaseα-CaSO4·0.5H2O whiskers were directly synthesized from waste Ca(NO3)2 solution using a hydrothermal method,and HNO3 was synchronously regenerated.The effects of reaction temperature and Ca^2+concentr...Single-phaseα-CaSO4·0.5H2O whiskers were directly synthesized from waste Ca(NO3)2 solution using a hydrothermal method,and HNO3 was synchronously regenerated.The effects of reaction temperature and Ca^2+concentration on the phase composition and morphology of products were determined by X-ray diffraction and optical microscopy.On the basis of the experimental results,the formation diagram ofα-CaSO4·0.5H2O was plotted within the range of 5–35 g·L^-1 Ca^2+and 115°C–150°C.In addition,the conditions of the direct synthesis ofα-CaSO4·0.5H2O were determined.Well-crystallized,single-phaseα-CaSO4·0.5H2O whiskers with high aspect ratios(length,1785μm;diameter,10.63μm;aspect ratio,168)and HNO3(70.25 g·L^-1)were obtained at the optimal conditions of 25 g·L^-1 Ca^2+and 125°C.展开更多
We investigate the XY control and manipulation of the superconducting qubit state using direct digital synthesis(DDS)for the microwave pulse signal generation.The decoherence time, gate fidelity, and other qubit prope...We investigate the XY control and manipulation of the superconducting qubit state using direct digital synthesis(DDS)for the microwave pulse signal generation.The decoherence time, gate fidelity, and other qubit properties are measured and carefully characterized, and compared with the results obtained by using the traditional mixing technique for the microwave pulse generation.In particular, the qubit performance in the state manipulation with respect to the sampling rate of DDS is studied.Our results demonstrate that the present technique provides a simple and effective method for the XY control and manipulation of the superconducting qubit state.Realistic applications of the technique for the possible future scalable superconducting quantum computation are discussed.展开更多
Low temperature direct synthesis (LTDS) involves the preparation of a base solution of Sr^(2+),and the mixing of base solution with tetrabutyl titanate solution.LTDS is an advantageous method because it does not requi...Low temperature direct synthesis (LTDS) involves the preparation of a base solution of Sr^(2+),and the mixing of base solution with tetrabutyl titanate solution.LTDS is an advantageous method because it does not require the complex hydrothermal facilities and it can prevent the agglomeration in calcinations of other liquid methods.In our work,we adopted LTDS method to prepare the nano strontium titanate powders,and characterize them by XRD,FT-IR and TGA.The influences of preparation temperature and solvents on grain size and lattice parameters were investigated.The results show that preparation temperature can slightly change the lattice parameters of grain,while solvents also play important roles in the preparation.展开更多
Pure titanate nanotubes and titanate nanotubes doped with Fe^3＋/Ni^2＋/Mn^2＋ ions were synthesized by the hydrothermal method. In this process,titanate nanotubes were first prepared synchronously with doping Fe^3＋/...Pure titanate nanotubes and titanate nanotubes doped with Fe^3＋/Ni^2＋/Mn^2＋ ions were synthesized by the hydrothermal method. In this process,titanate nanotubes were first prepared synchronously with doping Fe^3＋/Ni^2＋/Mn^2＋ ions. The morphology,structure,thermal stability and magnetic property of titanate nanotubes were characterized by X-ray diffraction （XRD）,transmission electron microscope （TEM）,and magnetic measurement. The titanate nanotubes transformed into the anatase titania nanocrystals,and further the mixture of anatase and rutile titania along with increasing temperature. The results indicate that the titanate nanotubes doped with Fe^3＋/Ni^2＋/Mn^2＋ ions are paramagnetic behaviors.展开更多
基金National Natural Science Foundation of China(21872101,21962014)Science and Technology Program of Zungeer County,Inner Mongolia(2020YY-12)。
文摘Selective synthesis of ethanol from syngas under the Co-based catalysts is still challenging due to the hard of regulating the active site Co^(0) and Co^(2+)ratio.In this work,a series of CaTi_(0.9-x)Co_(x)Mo_(0.1)O_(3)(x=0,0.1-0.4)and CaTi_(0.7)Co_(0.3)O_(3) catalysts were prepared by using citric acid complexation method to promote the synthesis of ethanol.It was found that Mo species in the perovskite lattice can regulate the Co^(0) and Co^(2+)ratio through the domain-limiting effect of perovskite and the degree of Co reduction could be adjusted by changing the Co/Mo molar ratio.Among these investigated catalysts,the total selectivity of alcohols over the catalyst with the optimal Co/Mo ratio CaTi_(0.6)Co_(0.3)Mo_(0.1)O_(3) reached 39.1%,with ethanol accounting for 74.7%,which was ascribed to the moderate and tightly bound ratio of dissociative to non-dissociative adsorption sites on the surface and the balance of CH_(x)-CH_(y) coupling and C^(O) insertion.
文摘The adsorption behavior and description behavior of benzene , ethylene and ethylbenzene over HZSM-5 and Co/HZSM-5 catalysts were studied by means of TPSR (Temperature programmed surface reaction) technique. TPSR results of ben- zene and ethylene co-adsorption show that the maian products are styrene , ethylben- zene, toluene, propane, and butane. In a separate experiment of ethylbenzene ad- sorption, styrene . toluene and benzene are formed due to cracking and dehydro- genation. The mechanism of styrene formation was proposed , i. e. , the reaction was carried out via. the dehydrogenation of mediate species ethylbenzene according to the results of TPSR-MS , activity testing and thermodynamic analysis.
基金supported by the National Natural Science Foundation of China(91534127,U1463205)the Innovation Scientists and Technicians Troop Construction Projects of Henan Provincethe Chinese Education Ministry 111 Project(B08021)~~
文摘TiO2‐supported Pd‐Sb bimetallic catalysts were prepared and evaluated for the direct synthesis of H2O2 at ambient pressure.The addition of Sb to Pd significantly enhanced catalytic performance,and a Pd50Sb catalyst showed the greatest selectivity of up to 73%.Sb promoted the dispersion of Pd on TiO2,as evidenced by transmission electron microscopy and X‐ray diffraction.X‐ray photoelectron spectroscopy indicated that the oxidation of Pd was suppressed by Sb.In addition,Sb2O3 layers were formed and partially wrapped the surfaces of Pd catalysts,thus suppressing the activation of H2 and subsequent hydrogenation of H2O2.In situ diffuse reflection infrared Fourier transform spectroscopy for CO adsorption suggested that Sb homogenously located on the surface of Pd‐Sb catalysts and isolated contiguous Pd sites,resulting in the rise of the ratio of Pd monomer sites that are favorable for H2O2 formation.As a result,the Sb modified Pd surfaces significantly enhanced the non‐dissociative activation of O2 and H2O2 selectivity.
基金the National Natural Science Foundation of China(Nos.52072151,52171211,52102253,52271218,U22A20145)the Jinan Independent Innovative Team(2020GXRC015)+1 种基金the Major Program of Shandong Province Natural Science Foundation(ZR2021ZD05)the Science and Technology Program of University of Jinan(XKY2119).
文摘Focused exploration of earth-abundant and cost-efficient non-noble metal electrocatalysts with superior hydrogen evolution reaction(HER)performance is very important for large-scale and efficient electrolysis of water.Herein,a sandwich composite structure(designed as MS-Mo2C@NCNS)ofβ-Mo2C hollow nanotubes(HNT)and N-doped carbon nanosheets(NCNS)is designed and prepared using a binary NaCl–KCl molten salt(MS)strategy for HER.The temperature-dominant Kirkendall formation mechanism is tentatively proposed for such a three-dimensional hierarchical framework.Due to its attractive structure and componential synergism,MS-Mo2C@NCNS exposes more effective active sites,confers robust structural stability,and shows significant electrocatalytic activity/stability in HER,with a current density of 10 mA cm-2 and an overpotential of only 98 mV in 1 M KOH.Density functional theory calculations point to the synergistic effect of Mo2C HNT and NCNS,leading to enhanced electronic transport and suitable adsorption free energies of H*(ΔGH*)on the surface of electroactive Mo2C.More significantly,the MS-assisted synthetic methodology here provides an enormous perspective for the commercial development of highly active non-noble metal electrocatalysts toward efficient hydrogen evolution.
基金supported by the National Natural Science Foundation of China(Grant No.21802136)~~
文摘Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to develop an eco‐friendly and nuisanceless OSDA for zeolite synthesis.Herein,choline is employed as a non‐toxic and green OSDA to synthesize high silica Y zeolite with SiO2/Al2O3 ratios of 6.5–6.8.The prepared Y zeolite samples exhibited outstanding(hydro)thermal stability at ultrahigh temperature owing to the higher SiO2/Al2O3 ratio.The XRF,SEM,29Si‐NMR and 13Na+results suggested that choline plays a structure‐directing role in the synthesis of Y zeolite,while the feed molar fraction of Na+is a crucial determinant for the framework SiO2/Al2O3 ratio and the crystal morphology.
文摘A bi-component catalyst comprising CuC1 and metallic copper was used in the direct synthesis of me- thylchlorosilane to study the catalytic synergy between the different copper sources. The catalyst exhibited high ac- tivity and high selectivity of dimethyldichlorosilane （M2） in the stirred bed reactor. The effect of the proportion of CuC1 used was studied and 10%-30% CuC1 gave the best yield of M2. The use of CuC1 decreased the induction pe- riod of reaction, improved the selectivity in the induction stage, and gave a longer stable stage. These results sug- gest that bi-comoonent catalyst has advantazes in the direct synthesis reaction.
基金supported by the National Natural Science Foundation of China(21878143,21476106,21838004)Joint Re-search Fund for Overseas Chinese Scholars and Scholars in Hong Kong and Macao Young Scholars(21729601)+1 种基金the fund of State Key Laboratory of Materials-Oriented Chemical Engineering(ZK201702)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)~~
文摘Series of heterogeneous interfacial engineered TiO2(C-TiO2) with controllable carbon content were facilely synthesized by incipient-wet impregnation using glucose and subsequent thermal carbonization. The obtained C-TiO2 were used as catalytic supports to load Pd nanoparticles for H2 O2 direct synthesis from H2 and O2. The as-prepared samples were systematically studied by transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS), air isothermal microcalorimeter, temperature-programmed reduction of H2(H2-TPR), and so on. The catalytic results showed that H2 O2 productivity and H2O2 selectivity of Pd/C-TiO2 firstly rose with increasing carbon content and then declined. Pd/C-TiO2 catalyst with 1.89 wt% of carbon content showed the best catalytic performance that had 61.2% of selectivity and 2192 mmol H2O2/g Pd/h of productivity, which were significantly better than those of pristine Pd/TiO2(45.2% and 1827 mmol H2O2/g Pd/h). Various characterization results displayed that the carbon species were heterogeneously dispersed on TiO2 surface. Moreover, no obvious geometric transformation in supports and Pd nanoparticles were observed among different catalysts. The superficial hydrophobicity of Pd/C-TiO2 was gradually promoted with increasing carbon content, which led to the corresponding decrease in adsorption energy of H2O2 with catalysts. According to structure-performance relationship analyses, the heterogeneous interfacial engineering of carbon could maintain the interaction of Pd nanoparticles with TiO2 and simultaneously accelerate the H2O2 desorption. Both factors further determined the excellent H2O2 direct synthesis performance of Pd/C-TiO2.
基金the frame of ERC Synergy SCOPE(project 810182)PRIN 2015 SMARTNESS project nr.2015K7FZLH projects which are gratefully acknowledgeda SINCHEM Grant.SINCHEM is a Joint Doctorate program selected under the Erasmus Mundus Action 1 Programme(FPA 2013-0037)。
文摘The direct electrocatalytic synthesis of ammonia from N2 and H2O by using renewable energy sources and ambient pressure/temperature operations is a breakthrough technology,which can reduce by over 90%the greenhouse gas emissions of this chemical and energy storage process.We report here an in-situ electrochemical activation method to prepare Fe2O3-CNT(iron oxide on carbon nanotubes)electrocatalysts for the direct ammonia synthesis from N2 and H2O.The in-situ electrochemical activation leads to a large increase of the ammonia formation rate and Faradaic efficiency which reach the surprising high values of 41.6μg mgcat^−1 h^−1 and 17%,respectively,for an in-situ activation of 3 h,among the highest values reported so far for non-precious metal catalysts that use a continuous-flow polymer-electrolytemembrane cell and gas-phase operations for the ammonia synthesis hemicell.The electrocatalyst was stable at least 12 h at the working conditions.Tests by switching N2 to Ar evidence that ammonia was formed from the gas-phase nitrogen.The analysis of the changes of reactivity and of the electrocatalyst characteristics as a function of the time of activation indicates a linear relationship between the ammonia formation rate and a specific XPS(X-ray-photoelectron spectroscopy)oxygen signal related to O2−in iron-oxide species.This results together with characterization data by TEM and XRD suggest that the iron species active in the direct and selective synthesis of ammonia is a maghemite-type iron oxide,and this transformation from the initial hematite is responsible for the in-situ enhancement of 3-4 times of the TOF(turnover frequency)and NH3 Faradaic efficiency.This transformation is likely related to the stabilization of the maghemite species at CNT defect sites,although for longer times of preactivation a sintering occurs with a loss of performances.
文摘Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The industrial synthesis of DMM is mainly involved two-step process:methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor.Due to huge energy consumption,this typical synthesis route of DMM needs to be upgraded and more green routes should be determined.In this review,four state-of-the-art one-step direct synthetic routes,including two upgrading routes(methanol direct oxidation and direct dehydrogenation)and two green routes(methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation),have been summarized and compared.Combination with the reaction mechanism and catalytic performance on the different catalysts,the challenges and opportu nities for every synthetic route are proposed.The relationships between catalyst structu re and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in.Hopefully,this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future.
文摘Copper supported over silica exhibited very high activity and selectivity for the direct synthesis of indole at atmospheric pressure. Under the reaction temperature of 325C,the yield of indole could obtain 88%.
基金Financial supports by the National Natural Science Foundation of China(21776210)Science and Technology Research Project of Henan Province(No.202102210048)。
文摘Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 nm)by impregnation method.Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H2O2 among the prepared catalysts,together with highest formation rate of H2O2(38.0 mmol·(g cat)^-1·h^-1),1.9 times than that of Pd supported on conventional HZSM-5 zeolite(Pd/CZ-50).Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H2 dissociation,more BrΦnsted acid sites and stronger metal-support interaction which inhibited the dissociation of O-O bond in H2O2.The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching,leading to a better catalytic stability with 90%activity retained after 3 cycles,which was almost 3 times than that of Pd/CZ-50(30.4%activity retained).
文摘Two families of catalysts, based on Pd nanoparticles supported on ceramic asymmetric tubular alumina membranes, are studies in the direct synthesis of H2O2. They are prepared by depositing Pd in two ways：（i） reduction with N2H4 in an ultrasonic bath and（ii） by impregnation-deposition. The first preparation leads to larger particles, with average size of around 11 nm, while the second preparation leads to smaller particles, with average size around 4 nm. The catalytic membranes were tested as prepared, after thermal treatment in air and after further pre-reduction with H2 in mild（100 ℃） conditions. Samples were characterized by TEM, CO-chemisorption monitored by DRIFTS method and TPR, while catalytic tests have been performed in a semi-batch recirculation membrane reactor. Experimental catalytic results were analysed using two kinetics models to derive the reaction constants for the parallel and consecutive reactions of the kinetic network. Smaller particles of Pd show lower selectivity due to the higher rate of parallel combustion, even if the better dispersion of Pd and thus higher metal surface area in the sample lead to a productivity in H2O2 similar or even higher than the sample with the larger Pd particles. Independently on the presence of smaller or larger Pd nanoparticles, an oxidation treatment leads to a significant enhancement in the productivity, although the catalyst progressively reduces during the catalytic process. The inhibition of the parallel combustion reaction（to water） induced from the calcination treatment remains after the in-situ reduction of the oxidized Pd species formed during the pre-treatment.This is likely due to the elimination of defect sites which dissociatively activate oxygen, and tentatively attributed to Pd sites able to give three- and four-fold coordination of CO.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFB0401902 and 2016YFB0402001)Key-Area Research and Development Program of Guang Dong Province,China(Grant No.2019B010926001)。
文摘Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix(TM) of a scattering medium. We report a simple but powerful method, direct digital frequency synthesis(DDS) technology to modulate the phase front of the laser and measure the TM. By judiciously modulating the phase front of a He–Ne laser beam, we experimentally generate a high quality focus at any targeted location through a 2 mm thick 120 grit ground glass diffuser, which is commercially used in laser display and laser holographic display for improving brightness uniformity and reducing speckle. The signal to noise ratio(SNR) of the clear round focus is 50 and the size is about 44 μm. Our study will open up new avenues for enhancing light energy delivery to the optical engine in laser TV to lower the power consumption, phase compensation to reduce the speckle noise, and controlling the lasing threshold in random lasers.
文摘A two steps direct copolymerisation process was developed. The first step is to produce oligomer and then the oligomer of lactic acid/glycolic acid (90/10) is polymerized with binary catalyst tin chloride dihydrate/p-toluenesulfonic acid. In this way, the direct synthesis of copoly (lactic acid/glycolic acid) without any organic solvent was investigated. The properties and structures of products were characterized by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), X-ray diffraction and so on. The results show that comparatively high molecular weight copolymer of lactic acid and glycolic acid can be prepared by direct processing under appropriate technological conditions.
基金financial support from the National Natural Science Foundation of China(NSFC-21625604,91934302,and 22008211)Zhejiang Innovation Team(2017R5203)。
文摘The choice of support is one of the most significant components in the direct synthesis of H_(2)O_(2).Aiming to improvement of activity and selectivity of H_(2)O_(2) on Pd/TiO_(2) surface,we systematically investigated the important elementary steps on Pd/TiO_(2)-Vo@C,Pd/TiO_(2)-Vo,Pd/TiO_(2)-2 Vo,Pd/TiO_(2),and Pd/C using the first-principles calculations.The Bader charge analysis and charge density difference of O_(2) adsorption elucidate the relationship between the electronic distribution and chemisorption energy.The effective barrier analysis further enables to quantitatively estimate the reactivity of H_(2)O_(2) and H2O.We demonstrate unambiguously that the selectivity of H2O formation is boosted as the oxygen vacancy concentration raised.Moreover,the introduction of C into a TiO_(2) with appropriate oxygen vacancies can slightly reduce the effective barrier for H_(2)O_(2) formation and increase the effective barrier for H2O formation leading to a higher activity and selectivity of H_(2)O_(2) formation.Our finding suggests that carbon-doped oxygen vacancy TiO_(2) supported Pd is potential alternative catalyst compared with the Pd/TiO_(2).
基金supported by the Beijing Natural Science Foundation of China(2182040)the National Natural Science Foundation of China(51674026,U1802253)+1 种基金the Fundamental Research Funds for the Central Universities(FRF-TT-19-001)the China Scholarship Council(201906465004)。
文摘Single-phaseα-CaSO4·0.5H2O whiskers were directly synthesized from waste Ca(NO3)2 solution using a hydrothermal method,and HNO3 was synchronously regenerated.The effects of reaction temperature and Ca^2+concentration on the phase composition and morphology of products were determined by X-ray diffraction and optical microscopy.On the basis of the experimental results,the formation diagram ofα-CaSO4·0.5H2O was plotted within the range of 5–35 g·L^-1 Ca^2+and 115°C–150°C.In addition,the conditions of the direct synthesis ofα-CaSO4·0.5H2O were determined.Well-crystallized,single-phaseα-CaSO4·0.5H2O whiskers with high aspect ratios(length,1785μm;diameter,10.63μm;aspect ratio,168)and HNO3(70.25 g·L^-1)were obtained at the optimal conditions of 25 g·L^-1 Ca^2+and 125°C.
基金Project was supported by the National Natural Science Foundation of China(Grant No.11890704)the National Key Research and Development Program of China(Grant No.2016YFA0301802)+1 种基金the National Basic Research Program of China(Grant Nos.2015CB921104 and 2016YFA0300601)the Key R&D Program of Guangdong Province,China(Grant No.2018B0303326001)
文摘We investigate the XY control and manipulation of the superconducting qubit state using direct digital synthesis(DDS)for the microwave pulse signal generation.The decoherence time, gate fidelity, and other qubit properties are measured and carefully characterized, and compared with the results obtained by using the traditional mixing technique for the microwave pulse generation.In particular, the qubit performance in the state manipulation with respect to the sampling rate of DDS is studied.Our results demonstrate that the present technique provides a simple and effective method for the XY control and manipulation of the superconducting qubit state.Realistic applications of the technique for the possible future scalable superconducting quantum computation are discussed.
基金support from Jiangxi Education Science FoundationNanchang University Science Foundation.
文摘Low temperature direct synthesis (LTDS) involves the preparation of a base solution of Sr^(2+),and the mixing of base solution with tetrabutyl titanate solution.LTDS is an advantageous method because it does not require the complex hydrothermal facilities and it can prevent the agglomeration in calcinations of other liquid methods.In our work,we adopted LTDS method to prepare the nano strontium titanate powders,and characterize them by XRD,FT-IR and TGA.The influences of preparation temperature and solvents on grain size and lattice parameters were investigated.The results show that preparation temperature can slightly change the lattice parameters of grain,while solvents also play important roles in the preparation.
文摘Pure titanate nanotubes and titanate nanotubes doped with Fe^3＋/Ni^2＋/Mn^2＋ ions were synthesized by the hydrothermal method. In this process,titanate nanotubes were first prepared synchronously with doping Fe^3＋/Ni^2＋/Mn^2＋ ions. The morphology,structure,thermal stability and magnetic property of titanate nanotubes were characterized by X-ray diffraction （XRD）,transmission electron microscope （TEM）,and magnetic measurement. The titanate nanotubes transformed into the anatase titania nanocrystals,and further the mixture of anatase and rutile titania along with increasing temperature. The results indicate that the titanate nanotubes doped with Fe^3＋/Ni^2＋/Mn^2＋ ions are paramagnetic behaviors.
