Search

Abstract: Barium hexaaluminate (BHA) with large surface area (49 m2 g−1) is synthesized by microemulsion-mediated synthesis technique and examined as a support promoting ammonia synthesis by particulate Ru. The Ru/BHA catalyst exhibits higher activity and stability than Ba-promoted Ru/MgO, the previously most active oxide-supported catalyst system for ammonia synthesis. The rate of ammonia synthesis over Ru/BHA is 5426 μmol g−1 cat h−1 (653 K, 1.1 MPa), more than twice of that of Ba–Ru/MgO, and no decrease in the rate is observed over reaction for 80 h at 653 K and 0.1 MPa. Characterization of this catalyst system by various techniques reveals that the electronic and structural interactions between BHA and Ru particles are key factors responsible for the elevated activity and stability of this catalyst. [Copyright &y& Elsevier]

[Display omitted] 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 H 2 O 2 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 + H 2 O 2 system. The wet scrubber performs well at pH 3 and H 2 O 2 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 H 2 O 2 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. [ABSTRACT FROM AUTHOR]

[Display omitted] 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. [ABSTRACT FROM AUTHOR]

• Sr 2 Ta 2 O 7 was used for the first time to support Ru catalyst for ammonia synthesis. • Hydrogen poisoning of Ru species was alleviated through hydrogen spillover. • Loading promoter Cs remarkably improved ammonia synthesis activity of Ru/Sr 2 Ta 2 O 7. • Both promoters and the oxygen vacancies can donate electrons to the Ru. In this work, strontium tantalate (Sr 2 Ta 2 O 7) nanowires were used for the first time as a support of ruthenium catalysts for ammonia synthesis. The highest ammonia synthesis activity of 1582 μmol g−1 cat h−1 was observed with Ru/Sr 2 Ta 2 O 7 catalysts prepared with molar ratio of Sr(OH) 2 /Ta 2 O 5 at 4. After loading promoters, the ammonia synthesis activity was significantly improved to 4856, 5004 and 5038 μmol g−1 cat h−1 for K-, Rb- and Cs- modified Ru/Sr 2 Ta 2 O 7 catalysts. Characterization and kinetic experiments indicate that the improved ammonia synthesis rate of promoters-Ru/Sr 2 Ta 2 O 7 catalysts was attributable to the combined effect of alleviated hydrogen poisoning through the promotion of hydrogen spillover from Ru species to support of Sr 2 Ta 2 O 7 and enhanced activation of N 2 due to increased electron density of Ru sites because of electron donation from introduced oxygen vacancies and promoters. The study not only clarifies the role of promoters in ammonia synthesis, but also provides an excellent Ru catalyst on Sr 2 Ta 2 O 7 nanowires for ammonia synthesis. [ABSTRACT FROM AUTHOR]

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 (NH 3) 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. [Display omitted] • The NH 3 -based nitridation–corrosion process to recover V, Ti, Cr, and Fe from V-slag is proposed. • The reaction mechanism of reduction–nitridation process is revealed. • The optimal parameters during the nitridation–corrosion processes are investigated. • Enrichment of V, Ti, Cr nitrides and separation of Fe are realized. [ABSTRACT FROM AUTHOR]