Promotion effects of alkali metals on iron molybdate catalysts for CO_(2)catalytic hydrogenation

CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons.Iron-molybdenum catalysts have found numerous applications in catalysis,but have been never evaluated in the CO_(2)hydrogenation.In this work,the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal(Li,Na,K,Rb,or Cs)were characterized using X-ray diffraction,hydrogen temperatureprogrammed reduction,CO_(2)temperature-programmed desorption,in-situ^(57)Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy.Their catalytic performance was evaluated in the CO_(2)hydrogenation.During the reaction conditions,the catalysts undergo the formation of an iron(Ⅱ)molybdate structure,accompanied by a partial reduction of molybdenum and carbidization of iron.The rate of CO_(2)conversion and product selectivity strongly depend on the promoting alkali metals,and electronegativity was identified as an important factor affecting the catalytic performance.Higher CO_(2)conversion rates were observed with the promoters having higher electronegativity,while low electronegativity of alkali metals favors higher light olefin selectivity.

Study of Spectral Character of Alkali Metals Using Microwave Plasma Torch Simultaneous Spectrometer

A microwave plasma torch （MPT） simultaneous spectrometer was used to study the spectral character and the matrix effect on alkali metal ions in solution. The main parameters were optimized. The microwave forward power was 100 W. The argon flow rate that was used to sustain the Ar-MPT included the flow rate of carrier gas and the flow rate of support gas, which were 0. 8 and 1.0 L/min, respectively. The HC1 concentration in the solution was 0.02 mol/L. The observation height was 9. 0 ram. The detection limits of Li, Na, K, Rb, and Cs were 0. 0003, 0. 0004, 0. 009, 0.07 and 2.4 mg/L, respectively, and the resuhs obtained by the Ar-MPT were compared with those obtained by argon inductively coupled plasma（Ar-ICP） and argon microwave induced plasma（Ar-MIP）. The interference effects of several matrix elements were also studied.

Field emission properties of capped carbon nanotubes doped by alkali metals:a theoretical investigation

The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable.In addition,the adsorption energies increase with the introduction of the electric field.The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function.Furthermore,the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.

Effect of alkali metals on the performance of CoCu/TiO_2 catalysts for CO_2 hydrogenation to long-chain hydrocarbons

CoCu/TiO_2 catalysts promoted using alkali metals（Li, Na, K, Rb, and Cs） were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO_2 catalysts and the catalytic performance for CO_2 hydrogenation to long-chain hydrocarbons（C_（5＋））were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO_2 temperature-programmed desorption（TPD）, and H_2-TPD, the introduction of alkali metals could increase the CO_2 adsorption and decrease the H_2 chemisorption, which could suppress the formation of CH_4, enhance the production of C_（5＋）, and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO_2 catalyst provided the maximum C_（5＋） yield of 5.4%, with a CO_2 conversion of 18.4% and C_（5＋） selectivity of42.1%, because it showed the strongest basicity and a slight decrease in the amount of H_2 desorption;it also exhibited excellent catalytic stability of more than 200 h.

Evolution and deformability of inclusions in Al-killed steel with rare earth-alkali metals(Ca or Mg) combined treatment

The quality of stainless steel is closely related to the deformability of inclusions,which is significantly affected by their compositions.The present study first inve stigated the evolution of inclusion compositions in AI-killed steel with rare earth-alkali metals(Ca or Mg)combined treatme nt through four laboratory-scale experiments.The Ce contents in the final steel are 0.0080 wt%,0.015 wt%,0.016 wt%and 0.010 wt%,respectively.The Mg content is 0.0014 wt%in Ce-Mg combined treated steel,and the Ca content is0.0015 wt%in Ce-Ca combined treated steel.The deformability of inclusions in both Ce_(2)O_(3)-Al_(2)O_(3)-CaO and Ce_(2)O_(3)-Al_(2)O_(3)-MgO systems was subsequently evaluated by calculating their Young's modulus at low temperature.The results show that irregular Al_(2)O_(3)and MgAl_(2)O_(4)with poor deformability are modified to CeAlO_(3)and Ce_(2)O_(3)by Ce treatment,resulting in the decrease of Young's modulus of inclusions.The deformability of inclusions is further improved due to the transformation from lumped-like CeAlO_(3)to spherical CaO-Al_(2)O_(3)-Ce_(2)O_(3)caused by Ca treatment,and some of these inclusions are the ones with low liquidus temperature.Thermodynamic analysis was used to discuss the control condition of the formation and evolution of inclusions.Accordingly,the appropriate addition amounts of Al,Mg,Ce,and Ca are expected to control inclusion compositions and properties,including deformability and liquidus temperature,thereby improving the steel performance.

Synergistic Effect of Alkali Metals in Coal and Introduced CaO during Steam Gasification

The steam gasification kinetics of Zhundong raw coal and the washed coal by deionized water or hydrochloric acid with/without addition of CaO were tested by thermogravimetric analyzer(TGA)at medium temperatures(650℃ to 800℃).The cation contents of potassium and sodium in samples were determined by Inductively Coupled Plasma Optical Emission Spectrometer(ICP-OES).The Brunauer-Emmett-Teller(BET)surface area of the samples was tested by N2 adsorption,and the morphologies of the samples were characterized by scanning electron microscopy(SEM).Experimental results showed that the organic sodium was the main catalyst for the gasification of the pyrolysis char,and the gasification rate of the char could be enhanced further with the introduction of CaO.The inherent alkali metals in coal and the introduced CaO showed a synergistic effect that occurred obviously above 735℃.The char conversion curves with or without CaO were fitted by the modified volumetric model(MVM).The calculated results indicated that the addition of CaO increased the pre-exponential factor obviously,but made little changes on the activation energy.It was proposed that the synergistic effect was resulted from the co-melting of the sodium and CaO,which facilitated the migration of the catalyst ions and the generation of C(O)intermediates for the gasification.

Transformation of alkali and alkaline-earth metals during coal oxy-fuel combustion in the presence of SO_2 and H_2O

The occurrence modes of alkali and alkaline-earth metals（AAEMs） in coal relate to their release behavior and ash formation during combustion. To better understand the transformation of AAEMs,the release behavior of water-soluble,HCl-soluble,HCl-insoluble AAEMs during Shenmu coal（SM coal） oxy-fuel combustion in the presence of SO2 and H2O in a drop-tube reactor was investigated through serial dissolution using H2O and HCl solutions. The results show that the release rates of AAEMs increase with an increase in temperature under the three atmospheres studied. The high release rates of Mg and Ca from SM coal are dependent on the high content of soluble Mg and Ca in SM coal. SO2 inhibits the release rates of AAEMs,while H2O promotes them. The effects of SO2 and H2O on the Na and K species are more evident than those on Mg and Ca species. All three types of AAEMs in coal can volatilize in the gas phase during coal combustion. The W-type AAEMs release excessively,whereas the release rates of I-type AAEMs are relatively lower. Different types of AAEM may interconvert through different pathways under certain conditions. Both SO2 and H2O promote the transformation reactions. The effect of SO2 was related to sulfate formation and the promotion by H2O occurs because of a decrease in the melting point of the solid as well as the reaction of H2O.

Emerging Carbon Nanotube-Based Nanomaterials for Stable and Dendrite-Free Alkali Metal Anodes:Challenges,Strategies,and Perspectives

Alkali metals(Li,Na,and K)are promising candidates for high-performance rechargeable alkali metal battery anodes due to their high theoretical specific capacity and low electrochemical potential.However,the actual application of alkali metal anodes is impeded by the challenges of alkali metals,including their high chemical reactivity,uncontrolled dendrite growth,unstable solid electrolyte interphase,and infinite volume expansion during cycling processes.Introducing carbon nanotube-based nanomaterials in alkali metal anodesis an effective solution to these issues.These nanomaterials have attracted widespread attention owing to their unique properties,such as their high specific surface area,superior electronic conductivity,and excellent mechanical stability.Considering the rapidly growing research enthusiasm for this topic in the last several years,we review recent progress on the application of carbon nanotube-based nanomaterials in stable and dendrite-free alkali metal anodes.The merits and issues of alkali metal anodes,as well as their stabilizing strategies are summarized.Furthermore,the relationships among methods of synthesis,nano-or microstructures,and electrochemical properties of carbon nanotube-based alkali metal anodes are systematically discussed.In addition,advanced characterization technologies on the reaction mechanism of carbon nanotube-based nanomaterials in alkali metal anodes are also reviewed.Finally,the challenges and prospects for future study and applications of carbon nanotube-based AMAs in high-performance alkali metal batteries are discussed.

A comprehensive overview of the electrochemical mechanisms in emerging alkali metal-carbon dioxide batteries

Alkali metal-carbon dioxide(Li/Na/K-CO_(2))batteries are emerging electrochemical energy storage technologies in the context of the energy crisis and the urgent demand for carbon neutrality.Alkali metal-CO_(2) batteries offer a new strategy for CO_(2) fixation and utilization,and thus has been receiving considerable attention in recent years.Considerable progress has been achieved since alkali metal-CO_(2) batteries were invented,especially in terms of development of new electrode materials,and yet,research is lacking on the underlying mechanisms of the systems.This is the first typical review focusing on the electrochemical mechanisms of metal-CO_(2) batteries that summarizes the current understanding of and provides insights into the thermodynamic reaction pathways,the kinetic characteristics,and the crucial factors determining the reaction mechanisms in alkali metal-CO_(2) batteries.The review starts with the fundamental concepts of alkali metal-CO_(2) batteries,followed by a comprehensive discussion of the working mechanisms on cathodes and anodes.Moreover,the operation mechanisms of state-of-the-art electrolytes,including liquid and(quasi-)solid-state electrolytes,are also described.Finally,we identify the unsolved problems in current alkali metal-CO_(2) batteries and propose potential topics for future research.

Designing Advanced Liquid Electrolytes for Alkali Metal Batteries:Principles,Progress,and Perspectives

The ever-growing pursuit of high energy density batteries has triggered extensive efforts toward developing alkali metal(Li,Na,and K)battery(AMB)technologies owing to high theoretical capacities and low redox potentials of metallic anodes.Typically,for new battery systems,the electrolyte design is critical for realizing the battery electrochemistry of AMBs.Conventional electrolytes in alkali ion batteries are generally unsuitable for sustaining the stability owing to the hyper-reactivity and dendritic growth of alkali metals.In this review,we begin with the fundamentals of AMB electrolytes.Recent advancements in concentrated and fluorinated electrolytes,as well as functional electrolyte additives for boosting the stability of Li metal batteries,are summarized and discussed with a special focus on structure-composition-performance relationships.We then delve into the electrolyte formulations for Na-and K metal batteries,including those in which Na/K do not adhere to the Li-inherited paradigms.Finally,the challenges and the future research needs in advanced electrolytes for AMB are highlighted.This comprehensive review sheds light on the principles for the rational design of promising electrolytes and offers new inspirations for developing stable AMBs with high performance.

Molecular Dynamics, Diffusion Coefficients and Activation Energy of the Electrolyte (Anode) in Lithium (Li and Li+), Sodium (Na and Na+) and Potassium (K and K+)

This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studied;with and without gap. In this work, we present the structural, physical and chemical properties of the lithium, sodium and potassium electrodes. For the structural properties, the cohesive energy and the mesh parameters were calculated, revealing that, whatever the chemical element selected, the compact hexagonal hcp structure is the most stable, followed by the face-centred cubic CFC structure, and finally the BCC structure. The most stable structure is lithium, with a cohesion energy of -6570 eV, and the lowest bcc-hcp transition energy of -0.553 eV/atom, followed by sodium. For physical properties, kinetic and potential energies were calculated for each of the sectioned chemical elements, with lithium achieving the highest value. Finally, for the chemical properties, we studied the diffusion coefficient and the activation energy. Only potassium followed an opposite order to the other two, with the quantities with lacunae being greater than those without lacunae, whatever the multiplicity. The order of magnitude of the diffusion coefficients is given by the relationship DLi > DNa > Dk for the multiplicity 6*6*6, while for the activation energy the order is reversed.

Penetrative and migratory behavior of alkali metal in different binder based TiB_2-C composite cathodes

In electrolyte melts containing K at low temperature, the penetrative and migratory path of alkali metals （K and Na） in pitch, furan, phenolic aldehyde and epoxy based TiB2-C composite cathodes during the electrolysis process were studied by EDS and self-made modified Rapoport apparatus. The electrolysis expansion rates, the diffusion coefficients of the alkali metals and the corrosion rates of the composite cathode were also calculated and discussed. The results show that no matter what kind of binder is used, alkali metals have the same penetrative path in composite cathodes：firstly in pore, then in binder and finally in carbonaceous aggregates. K and Na penetrate into both binder and carbonaceous aggregates, which leads to the expansion of composite cathodes, and K has stronger penetration ability than Na. Electrolysis expansion rate of resin based composite cathode is smaller than that of pitch based composite cathodes, and so do the diffusion coefficient and corrosion rate. Resin based composite cathode has better resistance ability to the penetration of alkali metals than pith based composite cathode, and phenolic aldehyde based composite cathode exhibits the strongest resistance ability. The penetration rate, the diffusion coefficient of alkali metals in phenolic aldehyde based TiB2-C composite cathode and the corresponding corrosion rate are 4.72 mm/h, 2.24×10^-5 cm^2/s and 2.31 mm/a, respectively.

DFT Study of Alkali Metal Atom Adsorption on Defect-Free MgO（001）Surface

The adsorption of isolated alkali metal atoms （Li, Na, K, Rb, and Cs） on defect-free sur- face of MgO（001） has been systemically investigated with density functional theory using a pseudopotential plane-wave approach. The adsorption energy calculated is about -0.72 eV for the lithium on top of the surface O site and about one third of this value for the other alkali metals. The relatively strong interaction of Li with the surface O can be explained by a more covalent bonding involved, evidenced by results of both the projected density of states and the charge density difference. The bonding mechanism is discussed in detail for all alkali metals.

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Metal-organic frameworks （MOFs） have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I（also named Cu-BTC or MOF-199） was chemically reduced by doping it with alkali metals （Li, Na and K） and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction （XRD）, thermo-gravimetric analysis （TGA） and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li＋, Na＋ and K＋, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST- 1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.

Nano-baskets of Calix[4]-l,3-crown in Emulsion Membranes for Selective Extraction of Alkali Metal Cations

Nano-assisted inclusion separation of alkali metals from basic solutions was reported by inclu sion-facilitated emulsion liquid membrane process. The novelty of this study is application of nano-baskets of calixcrown in the selective and efficient separation of alkali metals as both the carrier and the surfactant. For this aim, four derivatives of diacid calix[4]-1,3-crowns-4,5 were synthesized, and their inclusion-extraction parameters were optimized including the calixcrown scaffold （4.4%, by mass） as the carrier/demulsifier, the commercial kero sene as diluent in membrane, sulphonic acid （0.2 mol.L-1） and ammonium carbonate （0.4 mol.L-1） as the strip and the feed phases, the phase and the treat ratios of 0.8 and 0.3, mixing speed （300 r.min-1）, and initial solute concentration （100 mg.L-1）. The selectivity of membrane over more than ten interfering cations was examined and the re sults reveled that under the optimized operating condition, the degree of inclusion-extraction of alkali metals was as high as 98%-99%.

Alkali-metal-modified ZSM-5 zeolites for improvement of catalytic dehydration of lactic acid to acrylic acid

Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）. The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, tempera- ture-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities （LHSVs） to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions （40 wt% LA aqueous solution, 365 ℃, and LHSV 2 h-1）.

Recent progress in rechargeable alkali metal-air batteries

Rechargeable alkali metal-air batteries are considered as the most promising candidate for the power source of electric vehicles(EVs) due to their high energy density. However, the practical application of metal-air batteries is still challenging. In the past decade, many strategies have been purposed and explored, which promoted the development of metal-air batteries. The reaction mechanisms have been gradually clarified and catalysts have been rationally designed for air cathodes. In this review, we summarize the recent development of alkali metal-air batteries from four parts: metal anodes, electrolytes, air cathodes and reactant gases, wherein we highlight the important achievement in this filed. Finally problems and prospective are discussed towards the future development of alkali metal-air batteries.

A comparison study of alkali metal-doped g-C_3N_4 for visible-light photocatalytic hydrogen evolution

Photocatalytic hydrogen production based on semiconductor photocatalysts has been considered as one of the most promising strategies to resolve the global energy shortage.Graphitic carbon nitride(g‐C3N4)has been a star visible‐light photocatalyst in this field due to its various advantages.However,pristine g‐C3N4usually exhibits limited activity.Herein,to enhance the performance of g‐C3N4,alkali metal ion(Li+,Na+,or K+)‐doped g‐C3N4are prepared via facile high‐temperature treatment.The prepared samples are characterized and analyzed using the technique of XRD,ICP‐AES,SEM,UV‐vis DRS,BET,XPS,PL,TRPL,photoelectrochemical measurements,photocatalytic tests,etc.The resultant doped photocatalysts show enhanced visible‐light photocatalytic activities for hydrogen production,benefiting from the increased specific surface areas(which provide more active sites),decreased band gaps for extended visible‐light absorption,and improved electronic structures for efficient charge transfer.In particular,because of the optimal tuning of both microstructure and electronic structure,the Na‐doped g‐C3N4shows the most effective utilization of photogenerated electrons during the water reduction process.As a result,the highest photocatalytic performance is achieved over the Na‐doped g‐C3N4photocatalyst(18.7?mol/h),3.7times that of pristine g‐C3N4(5.0?mol/h).This work gives a systematic study for the understanding of doping effect of alkali metals in semiconductor photocatalysis.

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.

Selective exchange of alkali metal ions on EAB zeolite

EAB zeolite was successfully prepared and applied to selective adsorption of Li^(+),Na^(+)and K^(+)ions.The physical and chemical properties of the adsorbent were characterized by X-ray diffraction(XRD),X-ray fluorescence(XRF),scanning electron microscope(SEM)and thermogravimetry(TG)methods.The ion exchange behaviours for Li^(+),Na^(+)and K^(+)ions in monomcomponent and multicomponent solutions were studied.In independent ion exchange,the ion exchange capacities ratiosα(/Na/Li)andα(K/Li)were 3.8 and 6.2,respectively.In competitive ion exchange,the selectivitiesβ(Na/Li)andβ(K/Li)increased with the initial concentrations and reached 409 and 992 when the initial concentrations was 100 mmol/L.The thermodynamic study results showed that Gibbs free energy change(ΔGΘ)of ion exchange reaction between Li-EAB and K^(+)was-34.96 kJ/mol,indicating that ion exchange of K^(+)ions was more energetically favourable than Li^(+)ions.The calculation results showed that the energy barriers of ion exchange increased in the order K^(+)Na^(+)<Li^(+).The study shows that EAB zeolite is potential to be used in the separation of alkali ions.