In-situ construction of abundant active centers on hierarchically porous carbon electrode toward high-performance phosphate electrosorption: Synergistic effect of electric field and capture sites

Phosphate removal is crucial for eutrophication control and water quality improvement.Electro-assisted adsorption,an eco-friendly elec-trosorption process,exhibited a promising potential for wastewater treatment.However,there are few works focused on phosphate electro-sorption,and reported electrodes cannot attach satisfactory removal capacities and rates.Herein,electro-assisted adsorption of phosphate via in-situ construction of La active centers on hierarchically porous carbon(LaPC)has been originally demonstrated.The resulted LaPC composite not only possessed a hierarchically porous structure with uniformly dispersed La active sites,but also provided good conductivity for interfacial electron transfer.The LaPC electrode achieved an ultrahigh phosphate electrosorption capability of 462.01 mg g^(-1) at 1 V,outperforming most existing electrodes.The superior phosphate removal performance originates from abundant active centers formed by the coupling of electricfield and capture sites.Besides,the stability and selectivity toward phosphate capture were maintained well even under comprehensive conditions.Moreover,a series of kinetics and isotherms models were employed to validate the electrosorption process.This work demonstrates a deep understanding and promotes a new level of phosphate electrosorption.

Investigation of the characteristics and deactivation of catalytic active center of Cr-Al_2O_3 catalysts for isobutane dehydrogenation

Deactivation mechanism of Cr-Al2O3catalyst and the interaction of Cr-A1 in the dehydrogenation of isobutane, as well as the nature of the catalytic active center, were studied using XRD, SEM, XPS, H2-TPR, isobutane-TPR and TPO techniques. The results revealed that the deactivation of Cr-Al2O3 catalyst was mainly caused by carbon deposition on its surface. The Cr3＋ ion could not be reduced by hydrogen but could be reduced to Cr2＋ by hydrocarbons and monoxide carbon. The active center for isobutane dehydrogenation could be Cr2＋/Cr3＋ produced from Cr6＋ by the on line reduction of hydrocarbon and carbon monoxide. The binding energy of Al3＋ was strongly affected by the state of chromium cations in the catalysts.

EFFECTS OF EXTERNAL DONOR ON ACTIVE CENTER DISTRIBUTION OF SUPPORTED ZIEGLER-NATTA CATALYST

The composition distribution (CD) and microisotacticity distribution (ID) of propene/1-hexene copolymer synthesized by MgCl2/DIBP/TiCl4 (DIBP: diisobutyl phthalate) were determined by fractionating the copolymers according to crystallinity and characterizing the fractions by (CNMR)-C-13. The effects of two alkoxysilane donors, triethoxyphenylsilane (PTES) and dimethoxydi-tert-butylsilane (TBMS), on CD and ID of the copolymers were compared. Three main parts in the CD diagram of each copolymer were distinguished, which were correlated to active center distribution (ACD) based on three groups of different active centers. By studying the changes in l-hexene content, microisotacticity and reactivity ratio product of three typical fractions, the effects of external donor on ACD were better elucidated. It was found that TBMS shows much stronger effects on ACD than PTES. In the former system, most fractions were produced on active centers with relatively lower r(1)r(2), higher reactivity to I-hexene, and higher stereospecificity as compared to the system without external donor. It is concluded that the observed very extensive changes in ACD are mainly resulted by the formation of new types of active centers, possibly by coordination of external donor to certain positions on the catalyst.

Study on the distribution of active centers in novel low Ti-loading MgCl2-supported Ziegler-Natta catalyst

Novel MgCl2-supported Ziegler-Natta (Z-N) catalysts prepared using a new one-pot ball milling method can effectively control the amounts of Ti-loading in the catalysts. Complex GPC data on polypropylene synthesized by these novel catalysts were analyzed using the method of fitting the molecular weight distribution (MWD) curves with a multiple Flory-Schulz function. It was found that multiple active centers exist in these novel catalysts. Detailed study of the effects of the Ti-loadings in the catalysts on the distribution of the active centers showed that the Ti-loadings in the novel MgCl2-supported Z-N catalysts might affect the proportion of each type of active centers; and might be the main factor responsible for the effect of the Ti-loadings on the microstructure, the molecular weight and molecular weight distribution width of the resultant polymer, the catalytic activity and polymerization kinetics.

STUDY ON THE MECHANISM OF 1-OCTENE ZIEGLER-NATTA POLYMERIZATION BASED ON THE NUMBER OF ACTIVE CENTERS

The number of active centers (C_p)-t and k_p-t profiles of Solvay type TiCl_3 - AlR_3 (R=C_2H_5, i-C_4H_9) or Stauffer AA TiCl_3-Al (C_2H_5)_3 catalyzed 1-octene polymerization were determined by using an acetyl chloride quenching method as well as kinetic data. The results show that in the studied systems k_p decreases when C_p increases, indicating the presence of two or more types of different active centers. The C_(p^(-t)) plots of the Solvay TiCl_3-AlR_3 systems show the presence of both stable active centers and unstable centers which decay in the polymerization process. The phenomena are explained based on a model of active center plurality. The increases of C_p in the induction periods are also discussed.

FUNCTIONALIZED CYCLODEXSTRINS BEARING AM INOALKYLIMINO GROUPS AS ACTIVE CENTERS TO CATALYZE ALDOL CONDENSATIONS

Efficient catalysis of functinnatized β-cyctodextrins bearing aninoatkytimino groups for atdot condensations of nitrobenzatdehydes and acetone has been effected and substantiated by preparative experiments

DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Distribution of active centers(ACD)of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl_2/TiCl_4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components.Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducingα-olefin on ethyle...

Research on the Comprehensive Development Trend of National Fitness Activity Centers

With the further advancement of the“National Fitness”strategy and the continuous development of the information age,the National Fitness Activity Centers have become more comprehensive.The comprehensiveness is reflected in the design of diversified sports functions and spaces.The article serves to explore the comprehensive development trend of National Fitness Activity Centers.Through summarizing and sorting out domestic and foreign cases,the trend of the comprehensive development of National Fitness Activity Centers is predicted at three levels:industry,city,and individual functions.

Highly efficient overall urea electrolysis via single-atomically active centers on layered double hydroxide

Anodic urea oxidation reaction(UOR)is an intriguing half reaction that can replace oxygen evolution reaction(OER)and work together with hydrogen evolution reaction(HER)toward simultaneous hydrogen fuel generation and urea-rich wastewater purification;however,it remains a challenge to achieve overall urea electrolysis with high efficiency.Herein,we report a multifunctional electrocatalyst termed as Rh/Ni V-LDH,through integration of nickel-vanadium layered double hydroxide(LDH)with rhodium single-atom catalyst(SAC),to achieve this goal.The electrocatalyst delivers high HER mass activity of0.262 A mg^(-1) and exceptionally high turnover frequency(TOF)of 2.125 s^(-1) at an overpotential of100 m V.Moreover,exceptional activity toward urea oxidation is addressed,which requires a potential of 1.33 V to yield 10 mA cm^(-2),endorsing the potential to surmount the sluggish OER.The splendid catalytic activity is enabled by the synergy of the Ni V-LDH support and the atomically dispersed Rh sites(located on the Ni-V hollow sites)as evidenced both experimentally and theoretically.The selfsupported Rh/Ni V-LDH catalyst serving as the anode and cathode for overall urea electrolysis(1 mol L^(-1) KOH with 0.33 mol L^(-1) urea as electrolyte)only requires a small voltage of 1.47 V to deliver 100 mA cm^(-2) with excellent stability.This work provides important insights into multifunctional SAC design from the perspective of support sites toward overall electrolysis applications.

Polymerization Kinetics of Propylene with the MgCl_(2)-Supported Ziegler-Natta Catalysts——Active Centers with Different Tacticity and Fragmentation of the Catalyst

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_(4)/MgCl_(2) Ziegler-Natta(Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant kp, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature(60 ℃) resulted higher activity, kp and lower [C*], and the isotactic active centers Ci* as the majority ones producing the highest isotactic polypropylene(iPP) components showed much higher kp when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.

Rich B active centers in Penta-B_(2)C as high-performance photocatalyst for nitrogen reduction

The photocatalytic nitrogen reduction reaction(NRR) has mild reaction conditions and only requires sunlight energy as a driving force to replace the traditional ammonia synthesis method. We herein investigate the catalytic activity and selectivity on Penta-B_(2)C for NRR by using density functional theory calculations. Penta-B_(2)C is a semiconductor with an indirect bandgap(2.328 e V) and is kinetically stable based on molecular dynamic simulations. The optical absorption spectrum of Penta-B;C is achieved in the ultraviolet and visible range. Effective light absorption is more conducive to generate photo-excited electrons and improving photocatalytic performances. Rich B atoms as activation sites in Penta-B_(2)C facilitate capturing N_(2). The activated N_(2)molecule prefers the side-on adsorption configuration on Penta-B_(2)C, which facilitates the subsequent reduction reaction. Among considered NRR mechanisms on Penta-B_(2)C, the best pathway prefers the enzymatic mechanism, only required a low onset potential of 0.23 V. The hydrogen evolution reaction is inhibited when the hydrogen adsorption concentration is increased or N_(2)molecules first occupy the adsorption sites. Our results indicate Penta-B_(2)C is a highly reactive and selective photocatalyst for NRR. Our work provides theoretical insights into the experiments and has guiding significance to synthesize efficient NRR photocatalysts.

Active oxygen center in oxidative coupling of methane on La_(2)O_(3) catalyst

La_(2)O_(3) catalyzed oxidative coupling of methane(OCM) is a promising process that converts methane directly to valuable C_(2)(ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C_(2) products, and a lower light-off temperature as well. Further study is focused on carbonate-free La_(2)O_(3) catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 e V correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results,DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexacoordinate lattice oxygen sites, with energy 2.18 e V lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C_(2) products selectivity in OCM over La_(2)O_(3) catalyst.

Insights into ionic association boosting water oxidation activity and dynamic stability

There have been reports about Fe ions boosting oxygen evolution reaction(OER)activity of Ni-based catalysts in alkaline conditions,while the origin and reason for the enhancement remains elusive.Herein,we attempt to identify the activity improvement and discover that Ni sites act as a host to attract Fe(Ⅲ)to form Fe(Ni)(Ⅲ)binary centres,which serve as the dynamic sites to promote OER activity and stability by cyclical formation of intermediates(Fe(Ⅲ)→Fe(Ni)(Ⅲ)→Fe(Ni)-OH→Fe(Ni)-O→Fe(Ni)OOH→Fe(Ⅲ))at the electrode/electrolyte interface to emit O_(2).Additionally,some ions(Co(Ⅱ),Ni(Ⅱ),and Cr(Ⅲ))can also be the active sites to catalyze the OER process on a variety of electrodes.The Fe(Ⅲ)-catalyzed overall water-splitting electrolyzer comprising bare Ni foam as the anode and Pt/Ni-Mo as the cathode demonstrates robust stability for 1600 h at 1000 mA cm^(-2)@~1.75 V.The results provide insights into the ioncatalyzed effects boosting OER performance.

Valence State of Active Copper in CuO_x/CeO_2 Catalysts for CO Oxidation

CuOx/CeO2 catalysts were prepared by adsorption-impregnation method, CO conversion was tested over the catalysts pretreated under different conditions for preferential CO oxidation in H2, and the catalysts were characterized with X-ray photoelectron spectroscopy and temperature programmed reduction. Experimental results show that there are two kinds of copper, which are Cu^＋ and Cu^2＋ in calcined CuOx/CeO2, Among them, the Cu^＋ is the key active component for CO oxidation. The main reason is as follows： CO is activated by copper for CO oxidation over CuOx/CeO2, while CO can not be activated by Cu^2＋. Only when Cu^2＋ is reduced to Cu ^＋ or Cu^0, the copper may be active for CO oxidation, moreover, the experimental results show that the reduction of Cu^2＋ does not lead to an increase of catalytic activity. So the active species is Cu^＋ in CuOx/CeO2 catalysts.

Boost oxygen reduction reaction performance by tuning the active sites in Fe-N-P-C catalysts

Cost-effective atomically dispersed Fe-N-P-C complex catalysts are promising to catalyze the oxygen reduction reaction(ORR)and replace Pt catalysts in fuel cells and metal-air batteries.However,it remains a challenge to increase the number of atomically dispersed active sites on these catalysts.Here we report a highly efficient impregnation-pyrolysis method to prepare effective ORR electrocatalysts with large amount of atomically dispersed Fe active sites from biomass.Two types of active catalyst centers were identified,namely atomically dispersed Fe sites and Fe_(x)P particles.The ORR rate of the atomically dispersed Fe sites is three orders of magnitude higher than it of Fe_(x)P particles.A linear correlation between the amount of the atomically dispersed Fe and the ORR activity was obtained,revealing the major contribution of the atomically dispersed Fe to the ORR activity.The number of atomically dispersed Fe increases as the Fe loading increased and reaching the maximum at 1.86 wt%Fe,resulting in the maximum ORR rate.Optimized Fe-N-P-C complex catalyst was used as the cathode catalyst in a homemade Zn-air battery and good performance of an energy density of 771 Wh kgZn^(-1),a power density of 92.9 m W cm^(-2) at 137 m A cm^(-2) and an excellent durability were exhibited.

Theoretical studies of CO oxidation with lattice oxygen on Co_3O_4 surfaces

Low-temperature CO oxidation has attracted extensive interest in heterogeneous catalysis because of the potential applications in fuel cells,air cleaning,and automotive emission reduction.In the present study,theoretical investigations have been performed using density functional theory to elucidate the crystal plane effect and structure sensitivity of Co3O4 nano-catalysts toward catalyzing CO oxidation.It is shown that the surface Co–O ion pairs are the active site for CO oxidation on the Co3O4 surface.Because of stronger CO adsorption and easier removal of lattice oxygen ions,the Co3O4（011）surface is shown to be more reactive for CO oxidation than the Co3O4（001）surface,which is consistent with previous experimental results.By comparing the reaction pathways at different sites on each surface,we have further elucidated the nature of the crystal plane effect on Co3O4 surfaces and attributed the reactivity to the surface reducibility.Our results suggest that CO oxidation catalyzed by Co3O4 nanocrystals has a strong crystal plane effect and structure sensitivity.Lowering the vacancy formation energy of the oxide surface is key for high CO oxidation reactivity.

Efficient production of biodiesel from both esterification and transesterification over supported SO^(2-)_4–MoO_3–ZrO_2–Nd_2O_3/SiO_2 catalysts

SO2-4–Mo O3–Zr O2–Nd2O3/Si O2（SMZN/Si O2） catalysts for the production of biodiesel via both esterification and transesterification were prepared and characterized by N2adsorption-desorption isotherms,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,thermogravimetry analysis（TGA）,ammonia adsorption Fourier transform infrared spectra（NH3-FTIR）,and ammonia adsorption temperature programmed desorption（NH3-TPD） to reveal the dependence of the stable catalytic activity on calcination time. The reason for catalyst deactivation was also studied. The calcination time remarkably affected the types of active centers on SMZN/Si O2-2,and 4 h was found to be the optimal calcination time. SO4 species bonded with small size Zr O2 were found to be the stable active centers,where the leaching of SO2-4and the deposition of coke were inhibited. The deposition of coke was easier on large size Zr O2 than on small size ones. Calcination in air flow could eliminate the deposited coke to recover the deactivated catalysts.

Surface density of synthetically tuned spinel oxides of Co^(3+) and Ni^(3+) with enhanced catalytic activity for methane oxidation

Spinel oxides containing Co and Ni are a promising substitute as a noble metal catalyst for methane combustion.Achieving a complete oxidation of methane under 400°C remains challenging,andhydrothermal 60 h NiClittle impact on activity,especially at high space velocities due to the long hydrothermal time with less absorbed oxygen species and crystal defects.Overall,these results help clarify methane activa-tion mechanisms and aid the development of more efficient low-cost catalysts.

Fe, V-co-doped C_(2)N for electrocatalytic N_(2)-to-NH_(3) conversion

Designing providential catalyst is the key to drive the electrochemical nitrogen reduction reactions(NRR),which is referring to multiple intermediates and products. By means of density functional theory(DFT)calculations, we studied heteronuclear bi-atom electrocatalyst(HBEC) for NRR. Our results revealed that compared to homonuclear bi-atom electrocatalyst(Fe_2@C_2N, V_2@C_2N), Fe, V-co-doped C_2N(Fe V@C_2N)had a smaller limiting potential of-0.17 V and could accelerate N_2-to-NH_3 conversion through the enzymatic pathway of NRR. Importantly, N–N bond length monotonically increases with increasing the Bader charges of adsorbed N_2 molecule but decreases with increasing the Bader charge difference of two adsorbed N atoms. Additionally, the Fe V@C_2N could suppress the production of H_2 by the preferential adsorption and reduction of N_2 molecule. Thus, the as-designed HBEC may have the outstanding electrochemical NRR performance. This work opens a new perspective for NRR by HBECs under mild conditions.

COMPLETE STREETS&LIVABLE CENTERSWhy Location Matters

INTRODUCTION In recent years,Houston has made great strides in green building,moving into the top ten nationally on both LEED certified and Energy Star rated structures.At the same time,fewer steps have been taken to address transportation,which accounts for one third of U.S.greenhouse gas emissions.3 To achieve greater sustainability,architects,planners,and developers must take the space between buildings into greater account.