Ni-Zn/活性炭催化剂的程序升温还原研究

采用ＴＰＲ技术对甲醇、乙醇羰基化反应的Ｎｉ／Ｃ和Ｎｉ－Ｚｎ／Ｃ催化剂进行了研究．实验发现，负载于活性炭上的ＮｉＯ比非负载的ＮｉＯ容易还原；Ｎｉ与Ｚｎ之间有相互作用，Ｎｉ－Ｚｎ／Ｃ的还原峰温介于Ｎｉ／Ｃ与Ｚｎ／Ｃ之间；还原后的Ｎｉ／Ｃ和Ｎｉ－Ｚｎ／Ｃ催化剂比非负载ＮｉＯ还原后的Ｎｉ更易氧化；氧化后的Ｎｉ／Ｃ和Ｎｉ－Ｚｎ／Ｃ在相同的升温速率下再一次还原，其峰温θｍ比第一次还原时低３０～５０℃，而对Ｚｎ／Ｃ的θｍ无影响．经反复氧化－还原操作，得到不同升温速率下的ＴＰＲ谱，提出一种用ＴＰＲ谱直接计算［Ｈ２］ｍ的方法。

Electrodeposition of Ir on platinum in NaCl-KCl molten salt

The reduction mechanism of Ir in the NaCl-KCl-IrCl3 molten salt was investigated by cyclic voltammetry and chronopotentiometry, and Ir film was deposited effectively on platinum in potentiostatic mode. The morphology and constitution of Ir film were examined by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. It is found that the reduction mechanism of Ir（III） is a three-electron step and electro reaction is a reversible diffusion controlled process; the diffusion coefficients of Ir（III） at 1083, 1113, 1143 and 1183 K are 1.56×10-4, 2.23×10-4, 2.77×10-4 and 4.40×10-4 cm2/s, respectively, while the activation energy of the electrode reaction is 102.95 kJ/mol. The compacted Ir film reveals that the applied potential greatly affects the deposition of Ir, the thickness of Ir film deposited at the potential of reduction peak is the highest, the temperature of the molten salt also exerts an influence on deposition, the film formed at a lower temperature is thinner, but more micropores would occur on film when the temperature went too high.

Combustion synthesis of FeAl−Al2O3 composites with TiB2 and TiC additions via metallothermic reduction of Fe2O3 and TiO2

Combustion synthesis involving metallothermic reduction of Fe2O3 and TiO2 was conducted in the mode of self-propagating high-temperature synthesis(SHS)to fabricate FeAl-based composites with dual ceramic phases,TiB2/Al2O3 and TiC/Al2O3.The reactant mixture included thermite reagents of 0.6Fe2O3+0.6TiO2+2Al,and elemental Fe,Al,boron,and carbon powders.The formation of xFeAl−0.6TiB2−Al2O3 composites with x=2.0−3.6 and yFeAl−0.6TiC−Al2O3 composites with y=1.8−2.75 was studied.The increase of FeAl causes a decrease in the reaction exothermicity,thus resulting in the existence of flammability limits of x=3.6 and y=2.75 for the SHS reactions.Based on combustion wave kinetics,the activation energies of Ea=97.1 and 101.1 kJ/mol are deduced for the metallothermic SHS reactions.XRD analyses confirm in situ formation of FeAl/TiB2/Al2O3 and FeAl/TiC/Al2O3 composites.SEM micrographs exhibit that FeAl is formed with a dense polycrystalline structure,and the ceramic phases,TiB2,TiC,and Al2O3,are micro-sized discrete particles.The synthesized FeAl−TiB2−Al2O3 and FeAl−TiC−Al2O3 composites exhibit the hardness ranging from 12.8 to 16.6 GPa and fracture toughness from 7.93 to 9.84 MPa·m1/2.

Effect of sodium carbonate addition on carbothermic reduction of ilmenite concentrate

The enhanced reduction mechanism and kinetics of different Na_(2)CO_(3) additions in the carbothermic reduction of ilmenite concentrate were investigated.The reduction process was carried out at different heating rates in a thermogravimetry facility,and the kinetics was studied using the Starink method.The results indicate that Na_(2)CO_(3) addition enhanced the reduction effect as well as reduced the initial temperature of the reaction and the activation energy by increasing reactant activity in reactant form;however,it deteriorated the late-stage kinetic conditions by generating a molten phase,thereby reducing the reaction rate in the late stages of reduction.The average apparent activation energies of ilmenite concentrate with 0%,3%,and 6%Na_(2)CO_(3) are 447,289,and 430 kJ/mol,respectively.The results from kinetics parameters confirm that Na_(2)CO_(3) addition accelerated the reduction kinetics;however,excessive addition worsened the reduction kinetics.

Solar-heating boosted catalytic reduction of CO_(2） under full-solar spectrum

Catalytic converting CO2 into fuels with the help of solar energy is regarded as‘dream reaction’,as both energy crisis and environmental issue can be mitigated simultaneously.However,it is still suffering from low efficiency due to narrow solar-spectrum utilization and sluggish heterogeneous reaction kinetics.In this work,we demonstrate that catalytic reduction of CO2 can be achieved over Au nanoparticles(NPs)deposited rutile under full solar-spectrum irradiation,boosted by solar-heating effect.We found that UV and visible light can initiate the reaction,and the heat from IR light and local surface-plasmon resonance relaxation of Au NPs can boost the reaction kinetically.The apparent activation energy is determined experimentally and is used to explain the superior catalytic activity of Au/rutile to rutile in a kinetic way.We also find the photo-thermal synergy in the Au/rutile system.We envision that this work may facilitate understanding the kinetics of CO2 reduction and developing feasible catalytic systems with full solar spectrum utilization for practical artificial photosynthesis.

Rational design of viologen redox additives for high-performance supercapacitors with organic electrolytes

Introducing redox species into the electrolytes of traditional electric double layer capacitors(EDLCs)is an efficient strategy to enhance their energy density owing to Faradic reactions.However,few studies have elucidated the effect of the molecular structures of organic redox species on the performance of relative supercapacitors,which is important in the development of redox additives for super-capacitors.In this context,we synthesized several viologens and used them as new organic redox additives for super-capacitors with organic electrolytes.The detailed experimental analysis and theoretical calculation results show that the electrochemical performance of viologens relies heavily on their side chains and conjugated cores.Specifically,the side chains of the viologens affect their electronic structures and are consistent with behaviours between the molecules and the electrode pores due to the size effect,thus influencing their specific capacities.In addition,a larger conjugated aromatic core endows viologens with a smaller band gap and a higher degree of electron delocalization,resulting in better rate performance and cycling stability.Consequently,aπ-conjugated viologen derivative is selected as a favourable additive and enables an EDLC-type supercapacitor to exhibit a high energy density(34.0 W h kg^−1 at 856 W kg^−1)and good cycling performance.

Effective enhancement of electrochemical energy storage of cobalt-based nanocrystals by hybridization with nitrogen-doped carbon nanocages

Cobalt-based oxygenic compounds Co(OH)2,CoO and Co3 O4 are attractive for electrochemical energy storage owing to their high theoretical capacities and pseudocapacitive properties.Despite the great efforts to their compositional and morphological regulations,the performances to date are still quite limited owing to the low active surface area and sluggish charge transfer kinetics.Herein,different Co-based nanocrystals(Co-NCs)were conveniently anchored on the hierarchical nitrogen-doped carbon nanocages(hNCNCs)with high specific surface area and coexisting micro-meso-macropores to decrease the size and facilitate the charge transfer.Accordingly,a high specific capacity of1170 Fg^-1 is achieved at 2 Ag^-1 for the Co(OH)2/hNCNCs hybrid,in which the capacitance of Co(OH)2(2214 F gco(OH)2)is approaching to its theoretical maximum(2595 Fg^-1),demonstrating the high utilization of active materials by the hybridization with N-doped nanocarbons.This study also reveals that these Co-NCs store/release electrical energy via the same reversible redox reaction despite their different pristine compositions.This insight on the energy storage of Co-based nanomaterials suggests that the commonly-employed transformation of the Co-NCs from Co(OH)2 to CoO and Co3 O4 on carbon supports is unnecessary and even could be harmful to the energy storage performance.The result is instructive to develop high-energy-density electrodes from transition metal compounds.

Regulating the electronic structure of NiFe layered double hydroxide/reduced graphene oxide by Mn incorporation for high-efficiency oxygen evolution reaction

The development of highly efficient and costeffective oxygen evolution reaction(OER)electrocatalysts for renewable energy systems is vitally essential.Modulation of the electronic structure through heteroatom doping is considered as one of the most potential strategies to boost OER performances.Herein,a rational design of Mn-doped NiFe layered double hydroxide/reduced graphene oxide(Mn-NiFe LDH/rGO)is demonstrated by a facile hydrothermal approach,which exhibits outstanding OER activity and durability.Experimental results and density functional theory(DFT)calculations manifest that the introduction of Mn can reprogram the electronic structure of surface active sites and alter the intermediate adsorption energy,consequently reducing the potential limiting activation energy for OER.Specifically,the optimal Mn-NiFe LDH/rGO composite shows an enhanced OER performance with an ultralow overpotential of 240 mV@10 mA cm^(-2),Tafel slope of 40.0 mV dec^(-1) and excellent stability.Such superior OER activity is comparable to those of the recently reported state-of-the-art OER catalysts.This work presents an advanced strategy for designing electrocatalysts with high activity and low cost for energy conversion applications.

Black phosphorus-hosted single-atom catalyst for electrocatalytic nitrogen reduction

Designing highly selective and efficient singleatom electrocatalysts is essential for ammonia production under ambient conditions. This paper describes a density functional theory study on exploring the performance trends of transition metal complexes with P-based ligands in nitrogen reduction reaction(NRR) and further develops a design principle for high-performance single-atom catalysts(SACs)of NRR. Among the explored catalysts, W@BP(0.40 eV),Ta@BP(0.47 eV), and Nb@BP(0.53 eV) are identified as remarkable candidates with low free energy change in the potential-limiting step, high stability and high electrical conductivity for NRR. It is worth noting that almost all SACs with P-based ligands exhibit high NRR selectivity, due to the fact that they adsorb *N_(2) more strongly than *H. The adsorption free energy of *N_(2) H can be considered as a descriptor for the intrinsic activity trends in NRR. Furthermore, by constructing a volcano plot of the activity against the electronic charge on metal centers, it is demonstrated that the metal center with a moderate amount of positive charge can promote the catalytic performance of NRR.

A Li-rich layered-spinel cathode material for high capacity and high rate lithium-ion batteries fabricated via a gas-solid reaction

Lithium-rich layered oxide(LLO)cathode materials have drawn extensive attention due to their ultrahigh specific capacity and energy density.However,their commercialization is still restricted by their low initial coulombic efficiency,slow intrinsic kinetics and structural instability.Herein,a facile surface treatment strategy via gaseous phosphine was designed to improve the rate performance and capacity stability of LLOs.During the solid-gas reaction,phosphine reacted with active oxygen at the surface of LLOs due to its reductivity,forming oxygen vacancies and spinel phase at the surface region.As a result,Li ion conductivity and structural stability were greatly enhanced.The phosphinetreated LLOs(LLO@P)showed a layered-spinel hybrid structure and delivered an outstanding rate performance of156.7 mA h g^-1 at 10 C and a high capacity retention of 74%after 300 cycles at 5 C.