Sufang He

The optimization of As(V) removal over mesoporous alumina by using response surface methodology and adsorption mechanism

The Box-Behnken Design of the response surface methodology was employed to optimize four most important adsorption parameters (initial arsenic concentration, pH, adsorption temperature and time) and to investigate the interactive effects of these variables on arsenic(V) adsorption capacity of mesoporous alumina (MA). According to analysis of variance (ANOVA) and response surface analyses, the experiment data were excellent fitted to the quadratic model, and the interactive influence of initial concentration and pH on As(V) adsorption capacity was highly significant. The predicted maximum adsorption capacity was about 39.06 mg/g, and the corresponding optimal parameters of adsorption process were listed as below: time 720 min, temperature 52.8 °C, initial pH 3.9 and initial concentration 130 mg/L. Based on the results of arsenate species definition, FT-IR and pH change, As(V) adsorption mechanisms were proposed as follows: (1) at pH 2.0, H₃AsO₄ and H₂AsO₄(-) were adsorbed via hydrogen bond and electrostatic interaction, respectively; (2) at pH 6.6, arsenic species (H₂AsO₄(-) and HAsO₄(2-)) were removed via adsorption and ion exchange, (3) at pH 10.0, HAsO₄(2-) was adsorbed by MA via ion exchange together with adsorption, while AsO₄(3-) was removed by ion exchange.

Ni/SiO 2 catalyst prepared with nickel nitrate precursor for combination of CO 2 reforming and partial oxidation of methane: characterization and deactivation mechanism investigation

The performance of Ni/SiO2 catalyst in the process of combination of CO2 reforming and partial oxidation of methane to produce syngas was studied. The Ni/SiO2 catalysts were prepared by using incipient wetness impregnation method with nickel nitrate as a precursor and characterized by FT-IR, TG-DTA, UV-Raman, XRD, TEM, and H2-TPR. The metal nickel particles with the average size of 37.5 nm were highly dispersed over the catalyst, while the interaction between nickel particles and SiO2 support is relatively weak. The weak NiO-SiO2 interaction disappeared after repeating oxidation-reduction-oxidation in the fluidized bed reactor at 700°C, which resulted in the sintering of metal nickel particles. As a result, a rapid deactivation of the Ni/SiO2 catalysts was observed in 2.5 h reaction on stream.

Investigation of the reaction pathway for synthesizing methyl mercaptan (CH3SH) from H2S-containing syngas over K–Mo-type materials

The reaction pathway for synthesizing methyl mercaptan (CH3SH) using H2S-containing syngas (CO/H2S/H2) as the reactant gas over SBA-15 supported K–Mo-based catalysts prepared by different impregnation sequences was investigated. The issue of the route to produce CH3SH from CO/H2S/H2 has been debated for a long time. In light of designed kinetic experiments together with thermodynamics analyses, the corresponding reaction pathways in synthesizing CH3SH over K–Mo/SBA-15 were proposed. In the reaction system of CO/H2S/H2, COS was demonstrated to be generated firstly via the reaction between CO and H2S, and then CH3SH was formed via two reaction pathways, which were both the hydrogenation of COS and CS2. The resulting CH3SH was in a state of equilibrium of generation and decomposition. Decomposition of CH3SH was found to occur via two reaction pathways; one was that CH3SH first transformed into two intermediates, CH3SCH3 and CH3SSCH3, which were then further decomposed into CH4 and H2S; another was the direct decomposition of CH3SH into C, H2S and H2. Moreover, the catalyst (K–Mo/SBA-15) prepared with co-impregnation exhibits higher catalytic activities than the catalysts (K/Mo/SBA-15 and Mo/K/SBA-15) prepared by the sequence of impregnation. Based on characterization of the oxidized, sulfided and spent catalysts via N2 adsorption–desorption isotherms, XRD, Raman, XPS and TPR, it was found that two K-containing species, K2Mo2O7 and K2MoO4, were oxide precursors, which were then converted into main K-containing MoS2 species. The CO conversion was closely related to the amount of edge reactive sulfur species that formed the sulfur vacancies over MoS2 phases.

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

Waste adsorbents generated from treating Cr(VI)-containing wastewater are hazardous materials and generally landfilled or treated by acid or base desorption, with concomitant high cost and toxic effects. The present work shows that these Cr adsorbents can be reused as highly efficient catalysts for treating sulfur-containing VOCs (CH3SH), not only avoiding the economic and environmental impact from the conventional approaches, but also achieving the efficient treatment of sulfur-containing waste gas. Importantly, these reused Cr adsorbents exhibit enhanced activity and stability compared with the catalysts reported elsewhere, indicating a new avenue of green chemistry. The highly toxic adsorbed Cr(VI) species are reduced to a Cr2O3 crystalline phase by calcination and finally immobilized as a Cr2S3 solid phase while converting and eliminating CH3SH. Still, the presence of Cr(VI) species on the reused Cr adsorbent provides enough reactive sites for reaction, but high concentration of Cr(VI) species causes serious accumulation of coke deposit on the catalyst, leading to fast deactivation of the catalyst.

A novel and facile method to rapidly synthesize Ce0.8Zr0.2O2 nanoparticles for CO preferential oxidation in H2-rich stream

A novel urea grind combustion (UGC) route was reported in this paper to rapidly prepare the ceria-zirconia nanoparticles (Ce0.8Zr0.2O2). For comparison, the conventional surfactant-assisted (SA) and sol-gel (SG) methods were also employed to prepare Ce0.8Zr0.2O2 nanoparticles. CO preferential oxidation in H2-rich stream (CO-PROX) was chosen as probe reaction to investigate the catalytic performance of these Ce0.8Zr0.2O2 catalysts prepared with different methods to highlight the superiority of UGC. It was found that Ce0.8Zr0.2O2-UGC showed the better reducibility and oxygen mobility than the Ce0.8Zr0.2O2 prepared by SA and SG, because the UGC route favored the more incorporation of zirconia into CeO2, leading to more serious distortion of the structure, and more defective sites in the Ce0.8Zr0.2O2. As a result, Ce0.8Zr0.2O2-UGC exhibited the higher CO conversion, better O2 selectivity, and excellent catalytic stability without any deactivation during 72-h reaction on stream. More importantly, the UGC method, as compared to the relatively complex and time-consuming SA and SG method, is simple, facile, low-cost, time-saving (within 30 minutes) and scalable, thereby, might be very promising for the application in many fields.