Enhancement of the ammonia synthesis activity of a Cs- or Ba-promoted ruthenium catalyst supported on barium niobate.

Barium niobates with different crystalline structures and morphologies were prepared via a hydrothermal method and applied as a support for a ruthenium catalyst in ammonia synthesis. The sample synthesized with a nominal Ba/Nb ratio = 2.0, having a pure Ba5Nb4O15 crystalline phase and uniform flake-like structure, exhibited the best performance as a support in ammonia synthesis. The flake-like substrate favored the uniform distribution of ruthenium on its surface, which could promote ruthenium to expose more B5 sites. Addition of a Ba- or Cs-promoter enhanced the activity of the Ru/Ba5Nb4O15 catalyst markedly. The highest rate of ammonia synthesis over 2Cs- and 1Ba-4 wt% Ru/Ba5Nb4O15 was 4900 and 3720 (µmol g-1 cat h-1) at 0.1 MPa and 623 K, respectively. Both catalysts were stable during the reaction for 72 h at 673 K and 0.1 MPa. Thus, the synthesized Ba5Nb4O15 is expected to be a promising oxide support for ruthenium catalysts for ammonia synthesis.

Promoted wet peroxide oxidation of chlorinated volatile organic compounds catalyzed by FeOCl supported on macro-microporous biomass-derived activated carbon.

Chlorinated volatile organic compounds (CVOCs) are a recalcitrant class of air pollutants, and the strongly oxidizing reactive oxygen species (ROS) generated in advanced oxidation processes (AOPs) are promising to degrade them. In this study, a FeOCl-loaded biomass-derived activated carbon (BAC) has been used as an adsorbent for accumulating CVOCs and catalyst for activating H2O2 to construct a wet scrubber for the removal of airborne CVOCs. In addition to well-developed micropores, the BAC has macropores mimicking those of biostructures, which allows CVOCs to diffuse easily to its adsorption sites and catalytic sites. Probe experiments have revealed HO• to be the dominant ROS in the FeOCl/BAC + H2O2 system. The wet scrubber performs well at pH 3 and H2O2 concentrations as low as a few mM. It is capable of removing over 90% of dichloroethane, trichloroethylene, dichloromethane and chlorobenzene from air. By applying pulsed dosing or continuous dosing to replenish H2O2 to maintain its appropriate concentration, the system achieves good long-term efficiency. A dichloroethane degradation pathway is proposed based on the analysis of intermediates. This work may provide inspiration for the design of catalyst exploiting the inherent structure of biomass for catalytic wet oxidation of CVOCs or other contaminants.

Selective nitridation-corrosion process to recover vanadium, titanium, chromium, and iron from vanadium slag.

Vanadium slag (V-slag) is an important secondary V source, but other valuable elements are discarded in the tailings in industry. Herein, a green nitridation-corrosion process is proposed for the comprehensive recovery of valuable elements (V, Ti, Cr, Fe) from V-slag without producing hazardous waste. Thermodynamic results indicate that ammonia gas (NH3) can selectively reduce Fe and nitride V, Cr, and Ti. The main phase composition of the nitrided V-slag included metallic Fe, nitrides, and diopside under optimal conditions, and their relative contents were 42.5, 26.2, and 31.3%, respectively, after roasting at 1000 °C for 6 h. The effects of the main parameters on corrosion test were investigated, and the highest weight-gain ratio attained was 19.6%. FeOOH crystallizes on the surface of the nitrided V-slag due to the oxidization of metallic Fe. The phase evolution during the entire process is spinel/olivine/diopside → Fe/nitrides/diopside → FeOOH/nitrides/diopside. Owing to finer particle sizes, most FeOOH is separated by wet sieving (<1400 mesh). The purity of the enriched nitrides attained was 43% after pickling to remove excess Fe. The total recovery rates of Fe, V, Ti, Cr were 87.76%, 95.92%, 92.92%, 92.11%, respectively. This paper provides a sustainable strategy for the comprehensive utilization of V-slag, and guides the cleaner treatment of other similar minerals.

Use of Hydrogen-Rich Gas in Blast Furnace Ironmaking of V-bearing Titanomagnetite: Mass and Energy Balance Calculations.

The iron and steel industry is a major CO2 emitter and an important subject for the implementation of carbon emission reduction goals and tasks. Due to the complex ore composition and low iron grade, vanadium-bearing titanomagnetite smelting in a blast furnace consumes more coke and emits more carbon than in an ordinary blast furnace. Injecting hydrogen-rich gas into blast furnace can not only partially replace coke, but also reduce the carbon emission. Based on the whole furnace and zonal energy and mass balance of blast furnace, the operation window of the blast furnace smelting vanadium-bearing titanomagnetite is established in this study on the premise that the thermal state of the blast furnace is basically unchanged (raceway adiabatic flame temperature and top gas temperature). The effects of different injection amounts of hydrogen-rich gases (shale gas, coke oven gas, and hydrogen) on raceway adiabatic flame temperature and top gas temperature, and the influence of blast temperature and preheating temperature of hydrogen-rich gases on operation window are calculated and analyzed. This study provides a certain theoretical reference for the follow-up practice of hydrogen-rich smelting of vanadium-bearing titanomagnetite in blast furnace.

Pyrolysis Behavior of Pyrite under a CO-H2 Atmosphere.

The transformation behavior of pyrite (FeS2) in the blast furnace process is critical to control the formation and emission of gaseous sulfides in the top gas of ironmaking but has seldom been explored. In present work, the pyrolysis of pyrite from 200 to 900 °C under a CO-H2 atmosphere was investigated by thermal-gravimetric and mass spectrometry. The thermodynamic theoretical calculations were carried out to further understand the transformation process. The results show that FeS2 is almost completely reduced to FeS under various CO-H2 atmospheres. H2S and carbonyl sulfide (COS) are the main gaseous sulfides formed through the pyrolysis reactions of FeS2 under a CO-H2 atmosphere. A higher H2 concentration can reduce the pyrolysis reaction temperature of FeS2, which is favorable for the conversion of sulfides to H2S, while a higher CO concentration promotes the conversion of sulfides to COS. Besides, the pyrolysis products of FeS2 by order from the former to latter under a strong reductive atmosphere (CO-H2) with increasing temperature are as follows: COS → S → H2S → S2 → CS2.

Adsorption-enforced Fenton-like process using activated carbon-supported iron oxychloride catalyst for wet scrubbing of airborne dichloroethane.

Wet scrubbing is a low-cost process for disposing of air pollutants. Nevertheless, this method is rarely used for the treatment of volatile organic compounds (VOCs) because of their poor water solubility. In this study, we used a unique wet scrubbing system containing H2O2 and activated carbon (AC)-supported iron oxychloride (FeOCl) nanoparticles to remove airborne dichloroethane (DCE). The operating conditions of the wet scrubber were optimized, and the mechanism was explored. The results showed that the adsorption of dissolved DCE onto AC promoted its transfer from air to water, while the accumulation of DCE on AC facilitated its oxidation by •OH generated on FeOCl catalyst. The wet scrubber performed well at pH 3 and low H2O2 concentrations. By pulsed or continuous dosing H2O2, the cooperative adsorption-catalytic oxidation allowed long-term DCE removal from air. Benefiting from satisfactory cost-effectiveness, avoidance of toxic byproduct formation, and less corrosion and catalyst poisoning, wet scrubbers coupled with cooperative adsorption and heterogeneous advanced oxidation processes could have broad application potentials in VOC control.

Oxide of porous graphitized carbon as recoverable functional adsorbent that removes toxic metals from water.

The numerous oxygenated functional groups on graphite oxide (GO) make it a promising adsorbent for toxic heavy metals in water. However, the GO prepared from natural graphite is water-soluble after exfoliation, making its recovery for reuse extremely difficult. In this study, porous graphitized carbon (PGC) was oxidized to fabricate a GO-like material, PGCO. The PGCO showed an O/C molar ratio of 0.63, and 8.4% of the surface carbon species were carboxyl, exhibiting enhanced oxidation degree compared to GO. The small PGCO sheets were intensely aggregated chemically, yielding an insoluble solid easily separable from water by sedimentation or filtration. Batch adsorption experiments demonstrated that the PGCO afforded significantly higher removal efficiencies for heavy metals than GO, owing to the former's greater functionalization with oxygenated groups. An isotherm study suggested that the adsorption obeyed the Langmuir model, and the derived maximum adsorption capacities for Cr3+, Pb2+, Cu2+, Cd2+, Zn2+, and Ni2+ were 119.6, 377.1, 99.1, 65.2, 53.0, and 58.1 mg/g, respectively. Furthermore, the spent PGCO was successively regenerated by acid treatment. The results of the study indicate that PGCO could be an alternative adsorbent for remediating toxic metal-contaminated waters.

Generation of atomic hydrogen by Ni-Fe hydroxides: Mechanism and activity for hydrodechlorination of trichloroethylene.

Atomic hydrogen (H•) is highly reactive for the hydrodechlorination of trichloroethylene (TCE). In this work, we found that the coprecipitation of Ni2+ and Fe2+ at neutral pH led to an unprecedented catalytic generation of H•. The generated H• effectively dechlorinate TCE to nontoxic ethylene and ethane, and Fe2+ is the only electron donor. The abundant adsorbed H• produced with a Ni/Fe ratio of 0.4 enhances hydrogen evolution reaction causing a low efficiency for hydrodechlorination. In contrast, the active absorbed H• is generated in the crystal lattice of Ni-Fe hydroxides with a Ni/Fe ratio of 3.0 causing highly efficient hydrodechlorination of TCE. This work not only reveals the mechanism of catalytic hydrodechlorination by Ni-Fe hydroxides at neutral pH, but also provides a novel approach to detoxify TCE in contaminated water using facile precipitated Ni-Fe hydroxides.

Metal-support interactions on Ru/CaAlOx catalysts derived from structural reconstruction of Ca-Al layered double hydroxides for ammonia decomposition.

Strong metal-support interaction (SMSI) over Ru/CaAlOx was constructed by utilizing the surface structural reconstruction of Ca-Al layered double hydroxides (LDHs) in aqueous solution and their subsequent hydroxide-to-oxide transformations. Ru nanoparticles were found to uniformly embed with CaAlOx. The electronic interactions and changes in CO adsorption behavior confirmed the SMSI state between Ru and CaAlOx. Owing to SMSI, the as-prepared Ru/CaAlOx showed improved catalytic activity in the decomposition of ammonia, especially at a relatively low temperature.

Segregation and Morphological Evolution of Si Phase during Electromagnetic Directional Solidification of Hypereutectic Al-Si Alloys.

Understanding the Si segregation behavior in hypereutectic Al-Si alloys is important for controlling the micro- and macrostructures of ingots. The macrosegregation mechanism and morphological evolution of the primary Si phase were investigated during electromagnetic directional solidification (EMDS). Both numerical simulations and experimental results strongly suggested that the severe macrosegregation of the primary Si phase was caused by fluid flow and temperature distribution. Microscopic analysis showed that the morphological evolution of the Si crystal occurred as follows: planar → cellular → columnar → dendritic stages during EMDS. Based on constitutional supercooling theory, a predominance area diagram of Si morphology was established, indicating that the morphology could be precisely controlled by adjusting the values of temperature gradient (G), crystal growth rate (R), and solute concentration (C0). The results provide novel insight into controlling the morphologies of primary Si phases in hypereutectic Al-Si alloys and, simultaneously, strengthen our understanding of the macrosegregation mechanism in metallic alloys.

Improving the property of calcium ferrite using a sonochemical method.

Power ultrasonic vibration was applied to the solidification of calcium ferrite (CF) melt in this study. The results indicated that power ultrasound can promote the formation of CF by accelerating the solidification process. Ultrasonic vibration greatly refined the CF grains, resulting the grain size decreased from 1893 to 437 µm. Meanwhile, ultrasonic vibration significantly enhanced the compressive strength, reduced the reduction time and improved the reducibility of CF slags. With ultrasonic treatment, the ultimate compressive strength of samples increased from 37.5 to 67.8 MPa, and the reduction time decreased from 225 to 136 min.