Understanding the Pt-like Catalytic Activity of Transition Metal Carbide Ta4C_(3) for I_(3)^(-) Reduction

This paper attempts to understand the Pt-like catalytic activity of transition metal carbide Ta4C_(3) for IRR(I_(3)^(-)reduction reaction)based on the correlation of adsorption energy to d-band center(εd).Ta4C_(3) was prepared by carbothermal reduction method with a template.Its photoelectrochemical properties were investigated as a CE(counter electrode)in DSSC(dye-sensitized solar cell).Its surface electronic structures,including DOS(density of state)andεd,and adsorption energy were computed by first-principle DFT(density functional theory).In TMC(transition metal carbide)Ta4C_(3),the interaction between Ta and C atoms makes the d-band of Ta broaden and results in the downward shift of itsεd.A moderate absorption energy corresponding to theεd is achieved,which is the nature of the Pt-like catalytic activity of Ta4C_(3).Appropriate change of adsorption energy by adjustingεd is a promising strategy to improve catalytic activity.This work is of great significance to the fundamental and application researches.

Highly Sensitive Ammonia Gas Sensors at Room Temperature Based on the Catalytic Mechanism of N,C Coordinated Ni Single-Atom Active Center

Significant challenges are posed by the limitations of gas sensing mechanisms for trace-level detection of ammonia(NH3).In this study,we propose to exploit single-atom catalytic activation and targeted adsorption properties to achieve highly sensitive and selective NH3 gas detection.Specifically,Ni singleatom active sites based on N,C coordination(Ni-N-C)were interfacially confined on the surface of two-dimensional(2D)MXene nanosheets(Ni-N-C/Ti_(3)C_(2)Tx),and a fully flexible gas sensor(MNPE-Ni-N-C/Ti_(3)C_(2)Tx)was integrated.The sensor demonstrates a remarkable response value to 5 ppm NH3(27.3%),excellent selectivity for NH3,and a low theoretical detection limit of 12.1 ppb.Simulation analysis by density functional calculation reveals that the Ni single-atom center with N,C coordination exhibits specific targeted adsorption properties for NH3.Additionally,its catalytic activation effect effectively reduces the Gibbs free energy of the sensing elemental reaction,while its electronic structure promotes the spill-over effect of reactive oxygen species at the gas-solid interface.The sensor has a dual-channel sensing mechanism of both chemical and electronic sensitization,which facilitates efficient electron transfer to the 2D MXene conductive network,resulting in the formation of the NH3 gas molecule sensing signal.Furthermore,the passivation of MXene edge defects by a conjugated hydrogen bond network enhances the long-term stability of MXene-based electrodes under high humidity conditions.This work achieves highly sensitive room-temperature NH3 gas detection based on the catalytic mechanism of Ni single-atom active center with N,C coordination,which provides a novel gas sensing mechanism for room-temperature trace gas detection research.

Biocatalytic enhancement of laccase immobilized on ZnFe_(2)O_(4) nanoparticles and its application for degradation of textile dyes

Efficient and convenient treatment of industrial dyeing wastewater is of great significance to guarantee human and animal health.This work presented the enhanced catalytic activity at pH 3.0 of laccase immobilized on amino-functionalized ZnFe_(2)O_(4) nanoparticles(ZnFe_(2)O_(4)-laccase)and its application for the degradation of textile dyes.Due to the existence of a large number of oxygen vacancies on the surface of the ZnFe_(2)O_(4) nanoparticles,negative ions accumulated on the magnetic carriers,which resulted in a harsh optimal pH value of the ZnFe_(2)O_(4)-laccase.Laccase activity assays revealed that the ZnFe_(2)O_(4)-laccase possessed superior pH and thermal stabilities,excellent reusability,and noticeable organic solvent tolerance.Meanwhile,the ZnFe_(2)O_(4) laccase presented efficient and sustainable degradation of high concentrations of textile dyes.The initial decoloration efficiencies of malachite green(MG),brilliant green(BG),azophloxine,crystal violet(CV),reactive blue 19(RB19),and procion red MX-5B were approximately 99.1%,95.0%,93.3%,87.4%,86.1%,and 85.3%,respectively.After 10 consecutive reuses,the degradation rates of the textile dyes still maintained about 98.2%,92.5%,83.2%,81.5%,79.8%and 65.9%,respectively.The excellent dye degradation properties indicate that the ZnFe_(2)O_(4)-laccase has a technical application in high concentrations of dyestuff treatment.

Effects of Co_3O_4 nanocatalyst morphology on CO oxidation:Synthesis process map and catalytic activity

This study focuses on drawing a hydrothermal synthesis process map for Co3O4 nanoparticles with various morphologies and investigating the effects of Co3O4 nanocatalyst morphology on CO oxidation.A series of cobalt-hydroxide-carbonate nanoparticles with various morphologies（i.e.,nanorods,nanosheets,and nanocubes） were successfully synthesized,and Co3O4 nanoparticles were obtained by thermal decomposition of the cobalt-hydroxide-carbonate precursors.The results suggest that the cobalt source is a key factor for controlling the morphology of cobalt-hydroxide-carbonate at relatively low hydrothermal temperatures（≤ 140℃）.Nanorods can be synthesized in CoCl2 solution,while Co（NO3）2 solution promotes the formation of nanosheets.Further increasing the synthesis temperature（higher than 140 ℃） results in the formation of nanocubes in either Co（NO3）2 or CoCl2 solution.The reaction time only affects the size of the obtained nanoparticles.The presence of CTAB could improve the uniformity and dispersion of particles.Co3O4 nanosheets showed much higher catalytic activity for CO oxidation than nanorods and nanocubes because it has more abundant Co^（3＋） on the surface,much higher reducibility,and better oxygen desorption capacity.

Effect of Precipitation Method and Ce Doping on the Catalytic Activity of Copper Manganese Oxide Catalysts for CO Oxidation

The influence of Ce doping and the precipitation method on structural properties and the catalytic activity of copper manganese oxides for CO oxidation at ambient temperature have been investigated. The catalysts were characterized by means of the powder X-ray diffraction and N2 adsorption-desorption, the inductively coupled plasma atomic emission spectrometry, the temperature programmed reduction, diffuse reflectance UV-Vis spectra, and the X-ray photoelectron spectroscopy. It was found that after doping little amount of Ce in copper manganese oxide, CeO2 phase was highly dispersed and could prevent sintering and aggregating of the catalyst, the size of the catalytic material was decreased, the reducibility was enhanced, the specific surface area was increased and the formation of the active sites for the oxidation of CO was improved significantly. Therefore, the activity of the rare earth promoted catalyst was enhanced remarkably.

Size-dependent peroxidase-like catalytic activity of Fe_3O_4 nanoparticles

Peroxidase-like catalytic properties of Fe3O4 nanoparficles （NPs） with three different sizes, synthesized by chemical coprecipitation and sol-gel methods, were investigated by UV-vis spectrum analysis. By comparing Fe3O4 NPs with average diameters of 11, 20, and 150 nm, we found that the catalytic activity increases with the reduced nanoparticle size. The electrochemical method to characterize the catalytic activity of Fe3O4 NPs using the response currents of the reaction product and substrate was also developed.

Synthesis of Hierarchically Porous CaFe204/Carbon Fiber Hybrids and Microwave Induced Catalytic Activity

Hierarchically porous CaFe204/carbon fiber hybrids with enhanced microwave induced cat- alytic activity for the degradation of methyl violet （MV） from water were synthesized from kapok by a novel two-step process coupling pore-fabricating and nanoparticles assembling. The as-prepared samples exhibited characteristic hollow fiber morphology, CaFe204 nanopar- ticles dispersed uniformly on the surface of hollow carbon fibers （HCF）. The effects of various factors such as CaFe204 loading, microwave power, catalyst doses, initial concen- tration of MV solution and pH value on the microwave induced degradation of MV over CaFe204/HCF were evaluated. It was found that the microwave induced degradation of MV over CaFe204/HCF had high reaction rate and short process time. The kinetic study indicated that the degradation of MV over CaFe204/HCF followed pseudo-first-order kinet- ics model. The high catalytic activity of CaFe204/HCF was facilitated by the synergistic relationship between microwave induced catalytic reaction and adsorption characteristics.

Preparation of SO_4^(2-)/TiO_2-WO_3 solid superacid and its catalytic activity in acetalation and ketaltion

SO_4^(2-)/TiO_2-WO_3 was prepared and its catalytic activity under differentsynthetic conditions was discussed with esterification of n-butanoic acid and n-butyl alcohol asprobing reaction. The optimum conditions are found that the mass fraction of H_2WO_4 used in thecompound is 12.5 percent, the calcination temperature is 580 deg C, the calcination time is 3 h, andthe soaked consistency of H_2SO_4 is 1.0 mol centre dot L^(-1). Then SO_4^(2-)/TiO_2-WO_3 wasapplied as the catalyst in the catalytic synthesis of eight similar important ketals and acetalsunder the optimum conditions and revealed high catalytic activity. On condition that the molar ratioof aldehyde/ketone to glycol is 1:1.5, the mass fraction of the catalyst used in the reactants is0.5 percent, and the reaction time is 1.0 h, the yields of ketals and acetals can reach 64.2percent-95.1 percent. Moreover, it can be easily recovered and reused.

Study on Hydrothermal Stability and Catalytic Activity of Al-SBA-15 Mesoporous Materials Prepared by Impregnation Method

The mesoporous Al-SBA-15 zeolite was obtained via impregnation of pure silica-based SBA-15 zeolite with aluminum nitrate.The Al-SBA-15 sample was calcined in air at 800 ℃ for 6 h and hydrothermally treated at near 100 ℃ for 120 h,respectively,and then the thermal and hydrothermal stability of Al-SBA-15 sample was investigated by X-ray diffractometry (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM) and nitrogen adsorption and desorption techniques.The Al-SBA-15 sample was also studied by 27 Al nuclear magnetic resonance (27 Al NMR) and ammonia temperature programmed desorption (NH 3-TPD) techniques.In addition,the catalytic activity of Al-SBA-15 zeolite was investigated by the Friedel-Crafts reactions of 2,4-di-tert-butylphenol with cinnamyl alcohol.The test results showed that the thermal and hydrothermal stability of Al-SBA-15 zeolite was better than that of SBA-15 zeo-lite.The Al-SBA-15 zeolite sample prepared by impregnation method exhibits more framework aluminum species and Al-O-Si units.Therefore,the number of the surface hydroxyl groups was reduced,resulting in the stabilization of framework structure ofAl-SBA-15 zeolite.The aluminum species can form weak and medium-strong acid sites with catalytic activity.

Metal-organic interface engineering for boosting the electroactivity of Pt nanodendrites for hydrogen production

Recently, the surface chemical functionalization and morphology control of precious metal nanostructures have been recognized as two efficient strategies for improving their electroactivity and/or selectivity. In this work, 1, 10-phenanthroline monohydrate(PM) functionalized Pt nanodendrites(Pt-NDs) on carbon cloth(CC)(denoted as PM@Pt-NDs/CC) and polyethylenimine(PEI) functionalized Pt-NDs on CC(denoted as PEI@Pt-NDs/CC) are successfully achieved by immersing Pt-NDs/CC into PM and PEI aqueous solutions, respectively. PEI functionalization of Pt-NDs/CC improves its electroactivity for hydrogen evolution reaction(HER) due to local proton enrichment whereas PM functionalization of Pt-NDs/CC improves its electroactivity for formic acid oxidation reaction(FAOR) by facilitating dehydrogenation pathway. With such high activity, a two-electrode electrolyzer is assembled using PM@Pt-NDs/CC as the anodic electrocatalyst and PEI@Pt-NDs/CC as the cathodic electrocatalyst for electrochemical reforming of formic acid, which only requires 0.45 V voltage to achieve the current density of 10 mA cm^(-1) for highpurity hydrogen production, much lower than conventional water electrolysis(1.59 V). The work presents an example of interfacial engineering enhancing electrocatalytic activity and indicates that electrochemical reforming of formic acid is an energy-saving electrochemical method for high-purity hydrogen production.

Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Surface properties （viz. surface area, basicity/base strength distribution, and crystal phases） of alkali metal doped CaO （alkali metal/Ca= 0.1 and 0.4） catalysts and their catalytic activity/selectivity in oxidative coupling of methane （OCM） to higher hydrocarbons at different reaction conditions （viz. temperature, 700 and 750 ℃; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140-20550 cm^3 ·g^-1·h^-1） have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties （viz. surface area, basicity/base strength distribution） and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity （strong basic sites） and the C2＋ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO （Na/Ca = 0.1, before calcination） catalyst （calcined at 750 ℃）, showed best performance （C2＋ selectivity of 68.8% with 24.7% methane conversion）, whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.

One-step fabrication of TiO2/graphene hybrid mesoporous film with enhanced photocatalytic activity and photovoltaic performance

We synthesized a mesoporous film based on TiO2-reduced graphene oxide(RGO)hybrids using a one-step vapor-thermal method without the need for an additional annealing process.The vapor-thermally prepared TiO2-graphene hybrid(VTH)features unique structures with an ultra-large specific surface area of^260 m^2 g^-1 and low aggregation,giving rise to enhanced light harvesting and increased charge generation and separation efficiency.It was observed that a mesoporous film with uniform pore distribution is simultaneously obtained during the VTH growth process.When a 5.0 wt%RGO VTH film was used as the active layer in photocatalysis,the highest photocatalytic activity for degradation of methyl orange was achieved.For another,when a 0.75 wt%RGO VTH film was used as the photoanode in a dye-sensitized solar cell,the power conversion efficiency reached 7.58%,which represents an increase of 73.1%compared to a solar cell using an a photoanode of pure TiO2 synthesized by a traditional solvothermal method.It is expected that this facile method for the synthesis of TiO2/graphene hybrid mesoporous films will be useful in practical applications for preparing other metal oxide/graphene hybrids with ultra-high photocatalytic activity and photovoltaic performance.

Effects of Colloidal Silica Binder on Catalytic Activity and Adhesion of HZSM-5 Coatings for Structured Reactors

HZSM-5 coating using three colloidal silica binders, acidic colloidal silica （ACS）, neutral colloidal silica （NCS） and basic colloidal silica （BCS）, was prepared to study the effect of hinders on their adhesion and catalytic activity. Scanning electron microscopy characterization indicated that the zeolite coating using BCS shows the smoothest surface with higher homogeneity and adherence strength. The specific surface area, relative crystallization and acid site strength of zeolites are also dependent on the binder used. Catalytic cracking of supercritical n- dodecane over the series of zeolite coating with various binders indicated that HZSM-5 coating with BCS exhibits the highest and the most stable catalytic activity compared with other kinds of binders, and also exhibits a stable catalytic activity ascribed to its proper acid property and microstructure.

Theoretical Study on the Catalytic Activity and Sulfur Resistibility of Amorphous Alloy Ni-B-P

In the present paper, one hundred cluster models NinBP （n = 1-6） have been designed and studied by density functional theory （DFT） to get an insight into the local structure, catalytic properties and sulfur resistibility of amorphous alloy Ni-B-P. The configurations in triplet state are found more stable than those in the singlet state. It is found： that as the content of Ni in the clusters increases, the value of Fermi level in clusters fluctuated, which shows that the content of Ni can influence the Fermi level to a certain extent. Based on the Fermi level and DOS, we consider the activity of catalyst in hydrogenation reaction is the best in cluster Ni3BP. On the basis of the charge of clusters NinBP （n = 1 -6）, we conclude the amorphous alloy Ni-B-P with high Ni content has better sulfur resistibility and the best hydrogenation activity, strong sulfur resistibility appears in clusters Ni3BP, and the amorphous alloy Ni60B20P20 with similar proportion is expected to prepare in the future.

A new method to improve surface morphology of Ni-Fe-Mo-Co alloy electrode and its catalytic activity for HER

A new pretreatment method has been developed to improve the catalytic activity of the Ni-Fe-Mo-Co alloy electrode for hydrogen evolution reaction （HER）. The procedure involves pre-electrolyzing the Ni-Fe-Mo-Co alloy electrode in 30% KOH solution containing 10% potassium sodium tartrate at 70℃ for 2 h, until some of the Mo and Fe elements are leached out. The surface morphology of the Ni-Fe-Mo-Co alloy demonstrates a unique hive-like structure after the pre- treatment, which has the pore size in a nanometer range （about 50 nm）, a very large real surface area, and good stability. The results of the electrochemical studies show that compared to other similar electrode materials and the treated Ni-Fe-Mo-Co electrode by leaching method, the pre-treated Ni-Fe-Mo-Co electrode has a much lower overpotential and much higher exchange current density for HER. In addition, a long-term continuous electrolysis test with a current interruption shows that the Ni-Fe-Mo-Co alloy has excellent catalytic stability.

Kinetics of catalytically activated duplication in aggregation growth

We propose a catalytically activated duplication model to mimic the coagulation and duplication of the DNA polymer system under the catalysis of the primer RNA. In the model, two aggregates of the same species can coagulate themselves and a DNA aggregate of any size can yield a new monomer or double itself with the help of RNA aggregates. By employing the mean-field rate equation approach we analytically investigate the evolution behaviour of the system. For the system with catalysis-driven monomer duplications, the aggregate size distribution of DNA polymers αk（t） always follows a power law in size in the long-time limit, and it decreases with time or approaches a time-independent steady-state form in the case of the duplication rate independent of the size of the mother aggregates, while it increases with time increasing in the case of the duplication rate proportional to the size of the mother aggregates. For the system with complete catalysis-driven duplications, the aggregate size distribution αk（t） approaches a generalized or modified scaling form.

Unraveling the catalytically active phase of carbon dioxide hydrogenation to methanol on Zn/Cu alloy: Single atom versus small cluster

Methanol synthesis from CO_(2)hydrogenation catalyzed by Zn/Cu alloy has been widely studied,but there is still debate on its catalytic active phase and whether the Zn can be oxidized during the reaction process.What is more,as Zn atoms could locate on Zn/Cu alloy surface in forms of both single atom and cluster,how Zn surface distribution affects catalytic activity is still not clear.In this work,we performed a systematic theoretical study to compare the mechanistic natures and catalytic pathways between Zn single atom and small cluster on catalyst surface,where the surface oxidation was shown to play the critical role.Before surface oxidation,the Zn single atom/Cu is more active than the Zn small cluster/Cu,but its surface oxidation is difficult to take place.Instead,after the easy surface oxidation by CO_(2)decomposition,the oxidized Zn small cluster/Cu becomes much more active,which even exceeds the hardlyoxidized Zn single atom/Cu to become the active phase.Further analyses show this dramatic promotion of surface oxidation can be ascribed to the following factors:i)The O from surface oxidation could preferably occupy the strongest binding sites on the center of Zn cluster.That makes the O intermediates bind at the Zn/Cu interface,preventing their too tight binding for further hydrogenation;ii)The higher positive charge and work function on the oxidized surface could also promote the hydrogenation of O intermediates.This work provided one more example that under certain condition,the metal cluster can be more active than the single atom in heterogeneous catalysis.

Evolution of catalytic activity driven by structural fusion of icosahedral gold cluster cores

Atomically precise gold cluster catalysts have emerged as a new frontier in catalysis science,owing to their unexpected catalytic properties.In this work,we explore the evolution of the catalytic activity of clusters formed by the structural fusion of icosahedral Au13 units,namely Au25(SR)18,Au38(SR)24,and Au25(PPh3)10(SC2H4Ph)5Cl2,in the oxidation of pyrrolidine toγ-butyrolactam.We demonstrate that the structural fusion of icosahedral Au13 units,forming vertex-fused(vf),face-fused(ff),and body-fused(bf)clusters,can induce a decrease in the catalytic activity in the following order:Aubf>Auff>Auvf.The structural fusion of icosahedral Au13 units in the clusters does not distinguish the adsorption modes of pyrrolidine over the three clusters from each other,but modulates the chemical adsorption capacity and electronic properties of the three clusters,which is likely to be the key reason for the observed changes in catalytic reactivity.Our results are expected to be extendable to study and design atomically defined catalysts with elaborate structural patterns,in order to produce desired products.

Evolution behavior of catalytically activated replication-decline in a coagulation process

We propose a catalytically activated replication-decline model of three species, in which two aggregates of the same species can coagulate themselves, an A aggregate of any size can replicate itself with the help of B aggregates, and the decline of A aggregate occurs under the catalysis of C aggregates. By means of mean-field rate equations, we derive the asymptotic solutions of the aggregate size distribution ak（t） of species A, which is found to depend strongly on the competition among three mechanisms： the self-coagulation of species A, the replication of species A catalyzed by species B, and the decline of species A catalyzed by species C. When the self-coagulation of species A dominates the system, the aggregate size distribution a^（t） satisfies the conventional scaling form. When the catalyzed replication process dominates the system, ak（t） takes the generalized scaling form. When the catalyzed decline process dominates the system, ak（t） approaches the modified scaling form.

Kinetics of catalytically activated aggregation-fragmentation process

We propose a catalytically activated aggregation-fragmentation model of three species, in which two clusters of species A can coagulate into a larger one under the catalysis of B clusters; otherwise, one cluster of species A will fragment into two smaller clusters under the catalysis of C clusters. By means of mean-field rate equations, we derive the asymptotic solutions of the cluster-mass distributions ak（t） of species A, which is found to depend strongly on the competition between the catalyzed aggregation process and the catalyzed fragmentation process. When the catalyzed aggregation process dominates the system, the cluster-mass distribution ak（t） satisfies the conventional scaling form. When the catalyzed fragmentation process dominates the system, the scaling description of ak （t） breaks down completely and the monodisperse initial condition of species A would not be changed in the long-time limit. In the marginal case when the effects of catalyzed aggregation and catalyzed fragmentation counteract each other, ak（t） takes the modified scaling form and the system can eventually evolve to a steady state.