Industrial application prospects and key issues of the pure-hydrogen reduction process

The industrial application prospect and key issues in basic theory and application are discussed by the methods of theoretical analysis and calculation to promote the development of the pure-hydrogen reduction process.According to the discussion of thermodynamics and kinetics of pure-hydrogen reduction reaction,the reduction reaction of iron oxide by pure hydrogen is an endothermic reaction,and the reaction rate of hydrogen reduction is significantly faster than that of carbon reduction.To explore the feasibility of the industrial applications of pure-hydrogen reduction,we design the hydrogen reduction reactor and process with reference to the industrialized hydrogen-rich reduction process and put forward the methods of appropriately increasing the reduction temperature,pressure,and temperature of iron ore into the furnace to accelerate the reaction rate and promote the reduction of iron oxide.The key technical parameters in engineering applications,such as hydrogen consumption,circulating gas volume,and heat balance,are discussed by theoretical calculations,and the optimized parameter values are proposed.The process parameters,cost,advantages,and disadvantages of various current hydrogen production methods are compared,and the results show that hydrogen production by natural gas reforming has a good development prospect.Through the discussion of the corrosion mechanism of high-temperature and high-pressure hydrogen on heat-resistant steel materials and the corrosion mechanism of H_2S in the hydrogen gas on steel,the technical ideas of developing new metal temperature-resistant materials,metal coating materials,and controlling gas composition are put forward to provide guidance for the selection of heater and reactor materials.Finally,the key factors affecting the smooth operation of the hydrogen reduction process in engineering applications are analyzed,offering a reference for the industrial application of the purehydrogen reduction process.

Fluidization behavior and reduction kinetics of pre-oxidized magnetite-based iron ore in a hydrogen-induced fluidized bed

The influence of different pre-oxidation temperatures and pre-oxidation degrees on the reduction and fluidization behaviors of magnetite-based iron ore was investigated in a hydrogen-induced fluidized bed.The raw magnetite-based iron ore was pre-oxidized at 800 and1000℃ for a certain time to reach a partly oxidation and deeply oxidation state.The structure and morphology of the reduced particles were analyzed via optical microscope and scanning electron microscopy(SEM).The reaction kinetic mechanism was determined based on the double-logarithm analysis.The results indicate that the materials with higher oxidation temperature and wider particle size range show better fluidization behaviors.The lower oxidation temperature is more beneficial for the reduction rate,especially in the later reduction stage.The pre-oxidation degree shows no obvious influence on the fluidization and reduction behaviors.Based on the kinetic analysis,the reduction progress can be divided into three stages.The reduction mechanism was discussed combing the surface morphology and phase structure.

Preparation of spherical ultrafine copper powder via hydrogen reduction-densification of Mg(OH)_2-coated Cu_2O powder

A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors （MLCC）. Spherical ultrafine cuprous oxide （Cu20） powder was prepared by glucose reduction of Cu（OH）2. The Cu20 particles were coated by Mg（OH）2 and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, tap density, and thermogravimetry （TG）. It is found that the shape and size distribution of the copper powder are determined by the Cu20 powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg（OH）2 coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm3 and the initial oxidation temperature rises from 125 to 150~C.

Hydrogen Reduction of Tungsten Oxides Part Ⅰ:Reduction of WO_(2.90),W_(20)O_(58) and WO_3

The hydrogen reduction of tungsten oxides WO_(2.90),W_(20)O_(58) and WO_3 were directly studied using high temperature X-ray diffraction analysis.The differences between tetragonal WO_(2.90) and monoclinic W_(20)O_(58) were discussed.Pure β-W was obtained from oxide WO_(2.90),while there appears small amount of WO_2 during the reduction of W_(20)O_(58) to β-W.

Hydrogen Reduction of Tungsten Oxides Part Ⅱ:Reduction of WO_(2.72) and WO_2,Transformation of β-W

The hydrogen reduction of tungsten oxides WO_(272)and WO_2 were studied directly using high-temperature X-ray diffraction analysis,The pure β-W was obtained from the reduction of WO_(272)The transformation of β-W to x-W was also studied in both hydrogen and nitrogen.The forming condition of β-W from WO_2 was discussed.Finally.a complete schematic diagram of reduction of tungsten oxides was given in this paper.

Simultaneous recovery of carbon and sulfur resources from reduction of CO_2 with H_2S using catalysts

An approach to the simultaneous reclamation of carbon and sulfur resources from CO2 and H2S has been proposed and effectively implemented with the aid of catalysts. A brief thermodynamic study reveals the potential of direct reduction of CO2 with H2S（15：15 mol% balanced with N2） for selective production of CO and elemental sulfur. The experiments carried out in a fixed-bed flow reactor over the temperature range of 400–800 °C give evidence of the importance of the employment of catalysts. Both the conversions of the reactants and the selectivities of the target products can be substantially promoted over most catalysts studied. Nevertheless, little difference appears among their catalytic performance. The results also prove that the presence of CO2 can remarkably enhance H2S conversion and the sulfur yield in comparison with H2S direct decomposition. A longtime reaction test on Mg O catalyst manifests its superior durability at high temperature（700 °C） and huge gas hourly space velocity（100,000 h-1）. Free radicals initiated by catalysts are supposed to dominate the reactions between CO2 and H2S.

Synthesis and Characterization of Ultra-fine Cr_2O_3 from Hydrogen Reduction of K_2CrO_4

As a part of the green process for manufacturing chromium compounds, two steps are involved in the synthesis of ultra-fine Cr2O3 powders： the first is the hydrogen reduction of K2CrO4 into intermediate trivalent （Cr^3＋） or tetravalent （Cr^4＋） chromium compounds; the second is the decomposing of the intermediate into Cr2O3 by heat treating. The intermediate is well characterized by means of SEM, XRD, and XPS. The possible reaction mechanism of the process is analyzed.

Kinetics of hydrogen reduction and the influence of gas composition on hot- rolled steel scale after temper rolling

For replacing the presently employed pickling method with a more environmentally friendly descaling method, hydrogen reduction of oxide scale formed during hot rolling was studied at 800℃ under a varied atmosphere. The hydrogen level and water vapor content in the reducing atmosphere were found to influence the reduction rate wherein increasing hydrogen level as well as decreasing water vapor content resulted in faster oxide reduction. The reduction reaction substantially obeyed a parabolic rate law. Oxide scale of a usual thickness （approximately 7 micrometer） could be reduced almost completely in an atmosphere of 20 vol. % hydrogen with a water vapor content corresponding to a -40℃ dew point at 800℃. When lowering the hydrogen level to 10% and increasing the water vapor content to a 10℃ dew point,quite a large extent of the oxide scale was retained,which might be attributable to the formation of an outermost dense layer of pure iron at the early stage of reduction.

Synthesis of High Purity Lithium Sulfide for Sulfide Solid Electrolyte Applications through Hydrogen Reduction of Lithium Sulfate

This paper is aimed to present a clean,inexpensive and sustainable method to synthesize high purity lithium sulfide(Li_(2)S)powder through hydrogen reduction of lithium sulfate(Li_(2)SO_(4)).A three-step reduction process has been successfully developed to synthesize well-crystallized and single-phase Li_(2)S powder by investigating the melting,sintering and reduction behavior of the mixtures of Li_(2)SO_(4)-Li_(2)S.High purity alumina was found to be the most suitable crucible material for producing high purity Li_(2)S,because it was not attacked by the Li_(2)SO_(4)-Li_(2)S melt during heating,as compared with other materials,such as carbon,mullite,quartz,boron nitride and stainless steel.The use of synthesized LizS resulted in higher purity and substantially higher room temperature ionic conductivity(2.77 mS·cm^(-1))for the argyrodite sulfide electrolyte Li_(6)PS_(5)Cl than commercial Li_(2)S(1.12 mS·cm^(-1)).This novel method offers a great opportunity to produce battery grade Li_(2)S for sulfide solid electrolyte applications.

Investigation of Refractory Bricks and Oxide Materials Heated in Hydrogen Reduction Conditions

This study aims to provide the basic knowledge for furnace refractory design by investigating refractory property changes occurred in a hydrogen atmosphere.Since refractory bricks are thermodynamically stable in a hydrogen atmosphere at 1100°C,we tried to find out the minute changes.In this experiment,a refractory brick was prepared by andalusite,mullite chamotte,and clay as raw materials and heated to 1100°C in a 100%hydrogen atmosphere for 72 h.It was found that the strength of the brick was decreased and the color was changed to black by the reduction of impurities.And in addition,this study covered research on the slaking risk of MgO raw materials because the minimum temperature is expected to 400°C in fluidized reduction furnaces unlike shaft furnaces.

Structure evolution of oxygen removal from porous carbon for optimizing supercapacitor performance

The presence of oxygen functional groups is detrimental to the capacitive performance of porous carbon electrode in organic electrolyte. In this regards, hydrogen thermal reduction has been demonstrated effective approach in removing the unstable surface oxygen while maintaining the high porosity of carbon matrix. However, the exact evolution mechanism of various oxygen species during this process, as well as the correlation with electrochemical properties, is still under development. Herein, biomass-based porous carbon is adopted as the model material to trace its structure evolution of oxygen removal under hydrogen thermal reduction process with the temperature range of 400–800 °C. The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700°C. XPS, TPRMS and Boehm titration results indicate that the oxygen elimination undergoes three distinctive stages(intermolecular dehydration, hydrogenation and decomposition reactions). The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700 °C. Benefiting from the stable electrochemical interface and the optimized porous structure, the as-obtained HAC-700 exhibit significantly suppressed self-discharge and leak current, with improved cycling stability, which is attributable to the stabilization of electrochemical interface between carbon surface and electrolyte. The result provides insights for rational design of surface chemistry for high-performance carbon electrode towards advanced energy storage.

Recycle of valuable products from oily cold rolling mill sludge

Oily cold rolling mill （CRM） sludge contains lots of iron and alloying elements along with plenty of hazardous organic components, which makes it as an attractive secondary source and an environmental contaminant at the same time. The compound methods of ＂vacuum distillation ＋ oxidizing roasting＂ and ＂vacuum distillation ＋ hydrogen reduction＂ were employed for the recycle of oily cold rolling mill sludge. First, the sludge was dynamically vacuum distilled in a rotating furnace at 50 r/rain and 600℃ for 3 h, which removed almost hazardous organic components, obtaining 89.2wt% ferrous resultant. Then, high purity ferric oxide powders （99.2wt%） and reduced iron powders （98.9wt%） were obtained when the distillation residues were oxidized and reduced, respectively. The distillation oil can be used for fuel or chemical feedstock, and the distillation gases can be collected and reused as a fuel.

Synthesis and Characterization of Oxide Dispersion Strengthened Ferritic Steel via a Sol-Gel Route

Nanocrystalline oxide dispersion strengthened （ODS） ferritic steel powders with nominal composition of Fe-14Cr-3W-0.3Ti-0.4Y2O3 are synthesized using sol-gel method and hy- drogen reduction. At low reduction temperature the impurity phase of CrO is detected. At higher reduction temperature the impurity phase is Cr2O3 which eventually disappears with increasing reduction time. A pure ODS ferritic steel phase is obtained after reducing the sol-gel resultant products at 1200℃ for 3 h. The HRTEM and EDS mapping indicate that the Y2O3 particles with a size of about 15 nm are homogenously dispersed in the alloy matrix. The bulk ODS ferritic steel samples prepared from such powders exhibit good mechanical performance with an ultimate tensile stress of 960 MPa.

Microbe-derived carbon materials for electrical energy storage and conversion

Microbes are microscopic living organisms that surround us which include bacteria, archaea, most protozoa, and some fungi and algae. In recent years, microbes have been explored as novel precursors to synthesize carbon-based（nano）materials and as substrates or templates to produce carbon-containing（nano）composites. Being greener and more affordable, microbe-derived carbons（MDCs） offer good potential for energy applications. In this review, we describe the unique advantages of MDCs and outline the common procedures to prepare them. We also extensively discuss the energy applications of MDCs including their use as electrodes in supercapacitors and lithium-ion batteries, and as electrocatalysts for processes such as oxygen reduction, oxygen evolution, and hydrogen evolution reactions which are essential for fuel cell and water electrochemical splitting cells. Based on the literature trend and our group＇s expertise, we propose potential research directions for developing new types of MDCs. This review, therefore, provides the state-of-the-art of a new energy chemistry concept. We expect to stimulate future research on the applications of MDCs that may address energy and environmental challenges that our societies are facing.

The effect of hydrogen reduction of α-MnO_(2) on formaldehyde oxidation: The roles of oxygen vacancies

A series of α-MnO_(2) catalysts with various Mn valence states were treated by hydrogen reduction for different periods of time. Their catalytic capacity for formaldehyde(HCHO) oxidation was evaluated. The results indicated that hydrogen reduction dramatically improves the catalytic performance of α-MnO_(2) in HCHO oxidation. The α-MnO_(2) sample reduced by hydrogen for 2 h possessed superior activity and could completely oxidize 150 ppm HCHO to CO_(2) and H_(2)O at 70℃. Multiple characterization results illustrated that hydrogen reduction contributed to the production of more oxygen vacancies. The oxygen vacancies on the catalyst surface enhanced the adsorption, activation and mobility of O_(2) molecules, and thereby enhanced HCHO catalytic oxidation. This study provides novel insight into the design of outstanding MnO_x catalysts for HCHO oxidation at low temperature.

Recent progress in cathodic reduction-enabled organic electrosynthesis: Trends, challenges, and opportunities

Compared with general redox chemistry,electrochemistry using the electron as a potent,controllable,yet traceless alternative to chemical oxidants/reductants usually offers more sustainable options for achieving selective organic synthesis.With its environmentally benign features gradually being uncovered and studied,organic electrosynthesis is currently undergoing a revival and becoming a rapidly growing area within the synthetic community.Among the electrochemical transformations,the anodically enabled ones have been far more extensively exploited than those driven by cathodic reduction,although both approaches are conceptually attractive.To stimulate the development of cathodically enabled organic reactions,this review summarizes the recently developed reductive electrosynthetic protocols,discussing and highlighting reaction features,substrate scopes,applications,and plausible mechanisms to reveal the recent trends in this area.Herein,cathodic reduction-enabled preparative organic transformations are categorized into four types:reduction of(1)unsaturated hydrocarbons,(2)heteroatom-containing carbon-based unsaturated systems,(3)saturated C-hetero or C–C polar/strained bonds,and(4)hetero-hetero linkages.Apart from net electroreductive reactions,a few examples of reductive photo-electrosynthesis as well as paired electrolysis are also introduced,which offer opportunities to overcome certain limitations and improve synthetic versatility.The electrochemically driven,transition metal-catalyzed reductive cross-couplings that have been comprehensively discussed in several other recent reviews are not included here.

Catalytic bubble-free hydrogenation reduction of azo dye by porous membranes loaded with palladium nanoparticles

Catalytic bubble-free hydrogenation reduction of azo dye by porous membranes loaded with palladium （Pd） nanoparticles was studied for the first time. The effects of Pd loading, dye concentration and reuse repetitions of membranes were investigated. In reduction, the dye concentration decreased whereas the pH rose gradually. An optimal Pd loading was found. The catalytic membranes were able to be reused more than 3 times.

Study on hydrogen adsorption on WO_(3)(001) surface by density functional theory calculation

Hydrogen reduction of tungsten oxide is currently the most widely used technology to produce metal tungsten for its simplicity and pollution-free nature.The computer simulation is a powerful tool for exploring the mechanism of hydrogen reduction of tungsten oxide from a microscopic view.The density functional theory(DFT) is applied to investigate the adsorption characteristic of hydrogen molecule on the surface and inside the lattice of WO_(3).The adsorption energy of hydrogen on the WO_(3)(001) surface is 66.56 kJ.mol^(-1) which is larger than the adsorption energy of hydrogen molecule inside the lattice of WO3 which indicates that once the hydrogen diffuses inside the lattice,it is easier to adsorb on the O atom to break W-O bond.And The diffusion process of a hydrogen molecule from the WO-terminated WO_(3)(001) surface to the inside of the WO_(3) lattice and hydrogen molecule adsorption inside the lattice was investigated.The activation energy of hydrogen molecule diffusion from the surface down to the first interstitial and diffusion from the first interstitial down to the second interstitial is 195.41 and 172.81 kJ·mol^(-1),respectively.The controlling step of hydrogen reduction of tungsten oxide may be the hydrogen molecule diffusion inside the oxides lattice through the interstitial.

Effect of Y_(2)O_(3)doping on preparation ultrafine/nano-tungsten powder and refinement mechanism

In this study,ultrafine/nano W-Y_(2)O_(3)composite powders were synthesized by spray drying,roasting and two-step hydrogen reduction using ammonium metatungstate and yttrium nitrate as raw materials.The mechanism of the influence of Y_(2)O_(3)on the growth of WO_(2.72)and the particle refinement of tungsten powder is discussed.The effect of Y_(2)O_(3)particles on the reduction behavior of tungsten powder was investigated using scanning electron microscopy to study the near surface morphology and X-ray diffraction for phase ID(composition)and crystal structural changes for the reduced powders at each step.The results show that the doping of 0.3 wt.%Y_(2)O_(3)can significantly increase the aspect ratio of WO_(2.72)in the first step of hydrogen reduction.Moreover,Y_(2)O_(3)can effectively inhibit the growth of tungsten particles in the hydrogen reduction process.Therefore,The Y_(2)O_(3)-doped tungsten powders have finer particles and a narrower particle size distribution range than the undoped powders.The average particle diameter of 0.3 wt.%Y_(2)O_(3)doping tungsten powder was in the range of 90-120 nm.

Effects of Al contents on microstructure and properties of hot-dip Zn-Al alloy coatings on hydrogen reduced hot-rolled steel without acid pickling

A new hot-dip galvanizing method was employed on hot-rolled low carbon steel.The effects of Al contents on microstructure,micro-hardness and corrosion resistance of Zn-Al alloy coatings were systematically investigated.Phase composition,microstructure and element distribution in Zn-Al alloy coatings were analyzed using X-ray diffraction（XRD）and electron probe micro analysis（EPMA）,respectively.It is found that Al content（0.6-6.0 wt.%）in galvanizing zinc affects surface quality and adhesion between coatings and matrix in the newly developed method.In addition,with increasing Al content,micro-hardness significantly increased due to the increase in Zn-Al eutectoid phases.Potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）also revealed that increase in Al plays a noticeable role in improving the corrosion resistance of Zn-Al alloy coatings.