Pre-reduction Temperature Research Articles

In-Line Co-Processing of Stainless Steel Pickling Sludge Using Argon Oxygen Decarburization Slag Bath: Behavior and Mechanism

Stainless steel pickling sludge (SSPS) is classified as hazardous solid waste, while Argon Oxygen Decarburization (AOD) slag is challenging to utilize due to the leaching toxicity of Cr. This study introduces a novel in-line co-processing technique for AOD slag and SSPS, parallel to the steelmaking process, aimed at metal recovery, sulfur fixation, and slag detoxification: pre-treatment-AOD slag bath approach. The transformations and migrations of sulfur and metal elements, such as Fe and Cr, in the co-processed mixture were analyzed using thermogravimetric–mass spectrometry (TG-MS) and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS). The results indicated that sulfur in SSPS could be transformed from CaSO4 to CaS under controlled low pre-reduction temperatures (below 800 °C), facilitating its stabilization in the slag and achieving a sulfur fixation rate of over 99%. Metal elements, including iron and chromium, first formed a small portion of spinel (FeCr2O4) during the pre-reduction phase, then Fe-Cr or Fe-Cr-C-based alloy particles were rapidly formed at high temperatures and in the presence of reducers in the slag bath (1550 °C), aggregating and growing spontaneously, ultimately achieving a metal recovery rate of over 95%. Furthermore, a reaction model for SSPS briquettes in the AOD slag bath was established to further reveal the mechanisms of sulfur, iron, and chromium stabilization and migration, thereby providing a basis for the harmless disposal of both materials. The product alloys are expected to be used as additives in stainless steel production, while the harmless slag could be safely utilized in the preparation of cementitious auxiliary materials.

Design of high-temperature shift using waste-derived synthesis gas: Thermodynamic approach and practical reaction optimization

Herein, we verify pre-reduction conditions and H2O/CO ratio to increase activity in the HTS using Fe-Cr catalyst. It was determined that the optimal H2O/CO ratio was 2.5 through the result of calculated thermodynamic equilibrium analysis and performed HTS reaction. In the Fe-Cr catalyst, HTS reaction was performed at 350 ∼ 550 °C to find the condition that Fe2O3 convert Fe3O4 without over-reduction after reduced using 2% H2/N2, 5% H2/N2, and reactant gas at various temperature (400, 500, and 600 °C). The lower the pre-reduction temperature, the higher CO conversion, but the effect of the pre-reduction gas was not significant. In addition, as a result of performing a stability test that reduced using reactant gas at 400, 500, and 600 °C, all of which maintained stability without deactivation even though had a large range of CO conversion for 50 h. Thus, we identify that the appropriate H2O/CO ratio for HTS reaction using gas produced from waste gasification is judged to be 2.5. And during the reaction using Fe-Cr, the CO conversion showed high activity when pre-reduction temperature is 400 °C. In the case of the pre-reduction gas, the activity was insignificantly affecting the pre-reduction at 400 °C, thus it is considered appropriate to use reactant gas for practical use without the need to connect the pre-reduction gas separately.

Efficient pre-reduction of chromite ore with biochar under microwave irradiation

Pre-reduction of chromite ore is crucial for producing ferrochromium alloy by submerged arc furnace (SAF) smelting. In this study, an efficient method for low-temperature pre-reduction of chromite ore using biochar under microwave irradiation was explored to produce good burden for subsequent SAF smelting. The thermodynamic analysis proved the feasibility of the easy decomposition of the main phase in the ore, FeCr2O4 to Cr2O3, and finally to ferrochromium, mainly (Fe,Cr)7C3, in the commonly examined temperature range for pre-reduction. The characterizations of electromagnetic properties, microwave absorption capabilities, and temperature rising behaviors of the main raw materials and their mixtures showed that microwave heating could greatly improve the carbothermic reduction of chromite ore. Under the condition of C/O molar ratio of 1.2, addition of 2 wt% Na2B4O7, pre-reduction temperature of 1100 °C, and dwell time of 3 h, the chromite ore-biochar composite briquettes had efficient pre-reduction, producing pre-reduced briquettes with (Fe,Cr)7C3 as the main alloy phase. The iron and chromium metallization degrees (ηFe and ηCr) reached 98.1% and 86.8%, respectively. Compared with the conventional pre-reduction, they were increased by 15.9% and 51.7%, respectively. The results proved the feasibility of using microwave for efficent pre-reduction of chromite ore.

Effects of carbothermal prereduction temperature and Co content on mechanical properties of WC–Co cemented carbides

AbstractWC–Co cemented carbides were prepared via an in situ synthesis method, including the carbothermal prereduction of WO3 and Co2O3 to remove all oxygen and a subsequent carbonization‐vacuum sintering process. The experimental results revealed that as the prereduction temperature increased from 1000 to 1200°C, the grain sizes of WC in WC–6Co and WC–12Co cemented carbides increased from .91 to 1.09 and .97 to 1.19 μm, respectively. Further, the fracture toughness of the sintered WC–6Co and WC–12Co cemented carbides increased from 9.97 to 10.83 and 11.11 to 18.30 MPa m1/2, respectively. In contrast, the hardness of the WC–6Co and WC–12Co cemented carbides decreased from 1477 to 1368 and 1351 to 1184 HV30, respectively. For a given prereduction temperature, an increase in Co content can improve the fracture toughness while lowering the hardness. In addition, an increase in the prereduction temperature or Co content led to an increase in the grain size of WC, which resulted in a transgranular fracture as the dominant mode.

Pre-reduction of United Manganese of Kalahari Ore in CO/CO2, H2/H2O, and H2 Atmospheres

The incorporation of hydrogen, which is a relatively unexplored reductant used during ferromanganese (FeMn) production, is an attractive approach to lessen atmospheric gaseous carbon release. The influence of hydrogen on the pre-reduction of carbonate-rich United Manganese of Kalahari (UMK) ore from South Africa was investigated. Experiments were performed in 70 pct CO 30 pct CO2 (reference), 70 pct H2 30 pct H2O, and 100 pct H2 gas atmospheres at 700 °C, 800 °C, and 900 °C. Calculated phase stability diagrams and experimental results showed good correlation. The pre-reduction process involved two reactions proceeding in parallel, i.e., the pre-reduction of higher oxides and the decomposition of carbonates present in the ore. A thermogravimetric (TG) furnace was employed for the pre-reduction of the ore in various atmospheres. The calculated weight loss percentage was used to determine the degree and rate of pre-reduction. It was found that the oxidation state of higher Fe- and Mn-oxides was lowered when treated in 70 pct H2 30 pct H2O and 70 pct CO 30 pct CO2, whereas FeO was metalized when using 100 pct H2. As for the intrinsic carbonates, the majority thereof were decomposed in the CO/CO2 atmosphere at 900 °C, and ≥ 700 °C in the H2/H2O and H2 atmospheres. Additionally, the degree and rate of reduction were accelerated by increasing the pre-reduction temperature and by employing a hydrogen-containing gas atmosphere (70 pct H2 30 pct H2O, and 100 pct H2). Scanning electron microscopy and electron microprobe analysis revealed the presence of three phases in the pre-reduced ore: (i) Mn- and Fe-rich, (ii) Mg- and Ca-rich, and (iii) Mg-, Si-, K-, and Na-rich. It was also found that there were no appreciable differences in porosity and decrepitation of the ores treated in the CO/CO2 and hydrogen-containing atmospheres. The use of a hydrogen atmosphere showed potential for the pre-reduction of carbonate-containing manganese ores as it accelerated the decomposition of the carbonates as well as facilitated the metallization of Fe-oxides present in the ore.

Pre-reduction of carbon-containing pellets of high chromium vanadium–titanium magnetite at different temperatures

Abstract The effect of temperature on phase transformation, metallization rate, carbon residue and agglomeration of metal Fe after the pre-reduction of carbon-containing pellets in high-chromium vanadium–titanium magnetite (HCVTM) was investigated. The results indicated that titanomagnetite was finally reduced to metal Fe and (Mg, Fe)Ti2O5 without low valence titanium oxide with increasing pre-reduction temperature from 950 to 1,250℃; Vanadium magnetite produces Fe, VO and VC0.88 without V, and chromite magnetite produces Fe, Cr2O3, CrC x and a small amount of Cr. With an increase in the pre-reduction temperature, the metallization rate in the metallized pellets gradually increases, while the content of the residual carbon gradually decreases. Meanwhile, the iron particles precipitated on the surface of ore particles begin to soften into strips and finally agglomerate to form spherical iron particles, which leads to the diameter of iron particles increasing from 8.23 to 182.35 μm. When the pre-reduction temperature is 1,250℃, the maximum metallization rate in the metallized pellets is 92.49 wt% and the minimum content of residual carbon is 10.37 wt%.

Pd/BN catalysts for highly efficient hydrogenation of maleic anhydride to succinic anhydride

A 0.33 wt% Pd/BN catalyst has been proved highly active for the liquid-phase selective hydrogenation of maleic anhydride (MA) to succinic anhydride (SA) at room temperature and highly selective to SA within a wide temperature range, far beyond the Pd/Al2O3 and Pd/MgO catalysts. An SA productivity of 6000 KgSA KgPd−1 h−1 and a high TOF value of 9.0 s−1 can be achieved at room temperature on the Pd/BN, and the high SA selectivity over 99.7% can be retained at the reaction temperature up to 150 ºC. Detailed structural characterizations and reactant-adsorption/desorption tests have demonstrated that the support effect on MA hydrogenation is related not only to the adsorption configurations of MA on Pd, which exhibits the indirect effect of the support via the electronic interaction with Pd, but also to the direct adsorption of MA on the support itself. In particular, for our catalysts with the low Pd loading, the difference of metal centers is largely masked by the adsorption of the support itself. For the Pd/BN, the predominant MA adsorption on Pd through a di-σ mode, the weak MA adsorption with a small amount on BN, and a high H-spillover ability are responsible for its high activity and selectivity. Moreover, it has been also revealed that the catalyst prereduction temperature can change the catalytic performance of the Pd/BN through an integrated effect including the removal of residual chlorine on Pd and the growth of Pd particles.

Enrichment Characteristics of Cr in Chromium Slag after Pre-Reduction and Melting/Magnetic Separation Treatment

Concentrating the chromium in chromium slag and improving the chromium–iron ratio is beneficial for the further utilization of chromium slag. In this paper, chromium slag obtained from a chromite lime-free roasting plant was used as the raw material. Pellets made of the chromium slag and pulverized coal were reduced at different pre-reduction temperatures and then separated by a melting separation process or magnetic separation process, respectively. The mass and composition of the metallized pellets before separation, along with the alloy and tail slag after separation, were comprehensively analyzed. The experimental results showed that the output yield of alloy, iron recovery rate, and chromium content in the alloy were all higher when using melting separation than when using magnetic separation, because of the further reduction during the melting stage. More importantly, a relatively low pre-reduction temperature and selection of magnetic separation process were found to be more beneficial for chromium enrichment in slag; the highest chromium–iron ratio in tail slag can reach 2.88.

Hydrogen pre–reduction determined Co–silica interaction and performance of cobalt catalysts for propane dehydrogenation

[email protected]–41 catalysts with and without hydrogen pre–reduction treatments are prepared for catalyzing non–oxidative propane dehydrogenation (PDH) to propylene. Multi–stage migration of framework Co2+ into extra–framework Co0 species can be achieved by the pre–reduction. The location and chemical states of Co species in catalysts are related to the pre–reduction temperature and time duration. The catalysts reduced at 650–700 °C are consisting of both framework Co2+ ions and small–size Co0 nanoclusters confined in the MCM–41 channels, displaying 2–3 times higher reaction rates in the selective PDH reactions in comparison with the unreduced catalyst. A higher pre–reduction temperature of 750–800 °C causes the formation of large Co particles that are responsible for significantly declined reaction rates and propylene selectivity as well as severe coke deposition. Hydrogen pre–reduction tunes the interaction between Co species and silica support, determining the performances of propane activation, propylene desorption and coke formation for the Co–catalyzed PDH reactions.

Methane thermocatalytic decomposition to COx-free hydrogen and carbon nanomaterials over Ni–Mn–Ru/Al2O3 catalysts

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce COx-free hydrogen and carbon nanomaterials. In this work, the catalytic performance of Ni–Mn–Ru/Al2O3 catalyst under different reaction parameters (such as, pre-reduction temperature, reaction temperature, space velocity, etc.) were investigated to obtain optimum reaction conditions. The catalysts were characterized by N2 adsorption/desorption, X-ray diffraction, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. For the 60 wt% Ni-5 wt% Mn-10 wt% Ru/Al2O3 catalyst using Ru(NO)(NO3)x(OH)y(x + y = 3) as Ru precursor, the methane conversion rate obtained is high as 93.76% under optimum reaction conditions (reduction at 700 °C for 1 h, reaction at 750 °C, GSHV = 36,000 mL/gcat h). Carbon nanomaterials formed during the process of methane thermocatalytic decomposition were characterized by scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon nanofibers were formed over all the Ni–Mn–Ru/Al2O3 catalysts.

Highly Efficient Hydrogenation of Nitrobenzene to Aniline over Pt/CeO2 Catalysts: The Shape Effect of the Support and Key Role of Additional Ce3+ Sites

Pt/CeO2 catalysts with different support shapes and prereduction temperatures were prepared and tested in the liquid-phase hydrogenation of nitrobenzene. Detailed characterizations reveal that the ...

Coprocessing of Stainless-Steel Pickling Sludge with Laterite Ore via Rotary Kiln-Electric Furnace Route: Enhanced Desulfurization and Metal Recovery

Stainless-steel pickling sludge (SSPS) is a hazardous solid waste, which mainly contains CaSO4, CaF2 and a high level of metals such as Fe, Cr and Ni. The high-content of sulfur in the SSPS hinders its adequate treatment and deteriorates the quality of hot ferronickel when the SSPS was used as a feed to the rotary kiln-electrical furnace process (RKEF). Thus, the desulfurization behaviors of the SSPS, including thermodynamics, phase transformation and off-gas emission characteristics during pre-reduction were primarily investigated in this work. Pre-reduction temperature and carbon content were essential for the desulfurization, and the reduction temperature should be higher than 850°C for sufficient sulfur removal. The presence of laterite ore enhanced the desulfurization of SSPS, and on the other hand, the presence of SSPS facilitated the subsequent reduction smelting. Under optimal conditions, almost all of the sulfur within SSPS could be removed by pre-reduction, and 94.72% Fe, 81.90% Ni and 46.14% Cr were recovered by reduction smelting.

Efficient Synthesis of 5-Amino-1-pentanol from Biomass-Derived Dihydropyran over Hydrotalcite-Based Ni–Mg3AlOx Catalysts

The reductive amination (RA) of 2-hydroxytetrahydropyran (2-HTHP) produced from biofurfural-derived dihydropyran provides a new efficient process for the clean synthesis of valuable 5-amino-1-pentanol (5-AP). Among various solid catalysts tested, the inexpensive Ni–Mg3AlOx catalysts derived from hydrotalcite precursors were found to be very active and selective, especially at Ni loadings above 20 wt %. A 85% total yield of 5-AP was obtained from dihydropyran on 40Ni–Mg3AlOx, the catalyst with the highest 2-HTHP RA activity among the Ni–Mg3AlOx catalysts, under mild conditions of 60 °C and 2 MPa H2. Characterization results showed that the reducibility of the calcined NiO-Mg3AlOx samples increased with increasing Ni loading from 5 to 50 wt %, while the Ni0 crystallite sizes exhibited a minimum of 4.8 nm on 40Ni–Mg3AlOx after reduction in H2 at 750 °C. The volcanic changes of 5-AP generation rate/yield with increasing Ni loading of the Ni–Mg3AlOx catalysts and with rising prereduction temperature of 30Ni–Mg3AlOx catalyst in 2-HTHP RA indicate that the balance of the reducibility and Ni0 particle size of the catalysts played an important role in obtaining high 5-AP yields. The 30Ni–Mg3AlOx catalyst showed a good stability in 2-HTHP RA examined in a continuous flow reactor over a 90 h time-on stream.

Alloying Effect of Nickel–Cobalt Based Binary Metal Catalysts Supported on α-Alumina for Ammonia Decomposition

The development of a base metal catalyst which shows high performance for the ammonia (NH3) decomposition have been conducted. For the Ni and Co based catalysts using α-Al2O3 as a support, the performance of the single metal catalysts was lower than that of the γ-Al2O3 supported catalysts. However, its performance was greatly improved by using a binary metal catalyst system. Based on the XRD analysis, it was found that Ni and Co supported on α-Al2O3 were alloyed. TEM observation confirmed that the metal particle size in the α-Al2O3 supported Ni-Co catalyst is smaller than that of the single metal catalysts (Ni/α-Al2O3 or Co/α-Al2O3). Furthermore, in-situ XRD and H2-TPR measurements revealed that the Ni-Co alloy forms during the reduction process. The optimum mixing ratio of Ni and Co components was 1:1, and the optimum pre-reduction temperature before the performance test was 600 °C. Studies on the differences of support oxides proved that the improvement effect by alloying can be similarly obtained with the SiO2 supported catalyst, indicating that the catalyst using the support with less interaction between the active metal and the support is more likely to obtain the performance improvement effect by alloying.

On the nature of spillover hydrogen species on platinum/nitrogen-doped mesoporous carbon composites: A temperature-programmed nitrobenzene desorption study

Spillover hydrogen species were generated by dissociative H2 adsorption on Pt nanoparticles supported on nitrogen-doped mesoporous carbon. The spillover hydrogen species on the support can migrate back to the Pt nanoparticles and hydrogenate subsequently adsorbed nitrobenzene to aniline at 80 °C, which was detected during temperature-programmed desorption experiments from 80 to 300 °C in pure He. The amount of spillover hydrogen can be tuned mainly by the pre-reduction temperature rather than by other parameters. The absence of aniline formation during nitrobenzene desorption experiments in the presence of CO indicates that hydrogenation occurs exclusively on Pt and that the spillover hydrogen species are present on the carbon support in a chemically inactive state. Most likely, spillover hydrogen is reversibly stored on the carbon support as adsorbed protons on the surface and as electrons in the bulk. These findings provide a new perspective on Pt/C-based hydrogen storage materials and fuel cell catalysts.

Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts.

Methods for the hydrogenation of CO2 into valuable chemicals are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over non-noble cobalt catalysts (CoAlOx ), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the composition of the catalysts through the use of different prereduction temperatures, the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g-1 h-1 . Operando FT-IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx , a key intermediate in the production of ethanol by CO2 hydrogenation.

Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts

AbstractMethods for the hydrogenation of CO2 into valuable chemicals are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over non‐noble cobalt catalysts (CoAlOx), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the composition of the catalysts through the use of different prereduction temperatures, the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g−1 h−1. Operando FT‐IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx, a key intermediate in the production of ethanol by CO2 hydrogenation.

Hydrogenolysis of glycerol to propylene glycol over Cu/oxide catalysts: influence of the support and reaction conditions

The syntheses, physicochemical properties and catalytic activity of Cu-containing catalysts in the hydrogenolysis of glycerol are reported in the present paper. The investigated catalysts contained various amounts of Cu deposited by wet impregnation over two oxide supports: Al2O3 and TiO2. The catalysts were characterized by the following techniques: XRD, H2-TPR, BET/BJH and N2O adsorption. The catalytic activity of the prepared catalysts was studied in the selective hydrogenolysis of glycerol to 1,2-propanediol in order to understand the role of the support as well as to select the most active and selective catalyst. The influence of the following parameters was carefully studied: pre-reduction temperature, hydrogen pressure during pre-reduction and hydrogenolysis and reaction time. In addition, the influence of tungstophosphoric acid and sodium hydroxide additives was also studied. The best catalytic systems were identified in terms of glycerol conversion and 1,2-propanediol selectivity.

Rhodium‐Catalyzed Methanation and Methane Steam Reforming Reactions on Rhodium–Perovskite Systems: Metal–Support Interaction

AbstractMetal–support interaction in rhodium–perovskite systems was studied using LSF (La0.6Sr0.4FeO3−δ) and STF (SrTi0.7Fe0.3O3−δ) supports to disentangle different manifestations of strong or reactive metal–support interaction. Electron microscopy and catalytic characterization in methane steam reforming/CO2 methanation reveal that reduction in hydrogen at 673 K and 873 K causes different extents of Fe exsolution. Depending on the perovskite reducibility, Fe–Rh alloy particles are observed. No signs of strong metal–support interaction (i.e., encapsulation of metal particles) by reduced oxide species were observed. As re‐oxidation in oxygen at 873 K did not fully restore the initial structures, the interaction between Rh and the perovskites manifests itself in irreversible alloy formation. Catalytic effects are the suppression of methane reactivity with increasing prereduction temperature. The results show the limits of the strong metal–support interaction concept in complex metal–oxide systems.

CO2 Hydrogenation Over Ni-Based Zeolites: Effect of Catalysts Preparation and Pre-reduction Conditions on Methanation Performance

In this work, CO2 methanation reaction was studied on Ni-based zeolite catalysts, which were prepared by incipient wetness impregnation of USY zeolite with 5 wt% Ni. The effects of the drying method after impregnation, the calcination temperature and the pre-reduction temperature on the catalysts performances were evaluated. The catalysts were characterized by N2 adsorption, hydrogen temperature programmed reduction, diffuse reflectance UV–Vis spectroscopy (DRS UV–Vis), transmission electron microscopy and X-ray diffraction. Drying under microwaves irradiation induced remarkable changes on the type, location and reducibility of Ni species at the same time that leaded to effects in the structural and textural properties of the support and in the average nickel particle size. As a result, changes in the catalytic performances were observed. The calcination temperature changed the location and reducibility of the Ni species being concluded that calcining at 300 °C leads to higher conversions and selectivities. At high reduction temperatures the amount of reduced Ni species (active sites) was greater, but the impact of sintering processes was also stronger. For catalysts with 5 % Ni, the reduction at 550 °C was observed as the most favourable. However for 14 % Ni sample no remarkable effects were observed by reducing at higher temperatures. Thus, it was proved that CO2 conversion and CH4 selectivity can be maximised through the proper choice of both preparation and pre-reduction conditions.