Promoter Effects on Nickel-Supported Magnesium Oxide Catalysts for the Carbon Dioxide Reforming of Methane

The nickel catalysts supported on bare MgO and its binary Mg–Al, Mg–La, and Mg–Fe metal oxides were prepared and used for carbon dioxide reforming of methane to syngas. The effects of Al, La, and Fe metal oxides on the structural properties, reducibility, and metal–support interaction of the Ni catalysts supported on MgO-based binary metal oxide were investigated. The X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H₂-TPR) analyses show that the nickel nanoparticles were highly dispersed on the supports. It is found that the Al ions can be well-incorporated into the MgO lattice to form uniform Mg–Al oxides, while isolated lanthanum oxides and iron oxides were observed in the Mg–La and Mg–Fe binary systems by TEM, respectively. Ni/Mg–Al metal oxide exhibits greatly improved catalytic activity, owing to the formation of a homogeneous Mg–Al oxide matrix with small particle sizes of Ni nanoparticles compared to bare Ni/MgO. Very low conversions for both CH₄ and CO₂ were obtained on Ni/Mg–La and Ni/Mg–Fe metal oxides, even at a high temperature of 800 °C, as a result of the incomplete reduction of the nickel nanoparticles

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

Uptake of Arsenic(V) Using Alumina Functionalized Highly Ordered Mesoporous SBA-15 (Al_<i>x</i>‑SBA-15) as an Effective Adsorbent

The SBA-15 (a mesoporous SiO₂ material) decorated with 10% aluminum (Al₁₀-SBA-15) was found to be an excellent adsorbent to remove As­(V) from water. The highly dispersed aluminum species have been obtained over the well-ordered mesoporous Al₁₀-SBA-15 adsorbent and act as the active adsorption sites for arsenic­(V) removal instead of SiO₂. The adsorption behavior of As­(V) onto Al₁₀-SBA-15 was investigated in aqueous solution using various experimental parameters. The adsorption data of As­(V) could be fitted more successfully by the Langmuir isotherm than the Freundlich isotherm model, and the pseudo-second-order equation described this entire adsorption process well. It is found from the analysis of kinetic data with the intraparticle diffusion mode that both the boundary layer (film) diffusion and intraparticle diffusion may contribute to the rate-limiting steps. Importantly, Al₁₀-SBA-15 exhibits high arsenic­(V) removal in the wide pH range of 2.0–8.2 and can remove As­(V) from water containing arsenate of ≤2.235 mg·L^–1 to reach levels in accordance with the regulations for drinking water purposes (<10 μg·L^–1). Consequently, Al₁₀-SBA-15 is believed to be an effective adsorbent for treating arsenate contaminated wastewater

Removal of NO_<i>x</i> from Flue Gas Using Yellow Phosphorus and Phosphate Slurry as Adsorbent

A composite slurry containing yellow phosphorus and phosphate slurry was used to remove NO_<i>x</i> from flue gas, where yellow phosphorus is considered to promote generation of ozone from oxygen. The latter can oxidize NO to form more water-soluble N_<i>x</i>O_<i>y</i> species, finally converted to HNO₂ and HNO₃. These acids can react with phosphate slurry to form PO₄^3–. Thus, the final solution containing NO₃^– and PO₄^3– can be potentially used as raw material for the production of nitrogen phosphorus compound fertilizer. Moreover, effects of various parameters on NO_<i>x</i> removal efficiency were optimized, and single-factor experiments together with response surface optimization were applied for optimizing these parameters. It was indicated that the removal efficiency of NO_<i>x</i> can obtain 99.2% under optimal conditions. Subsequently, the corresponding reaction mechanisms were discussed. Therefore, using the mixtures of yellow phosphorus and phosphate slurry as absorbent not only obtains high NO_<i>x</i> removal efficiency, but can avoid the need to dispose of spent liquid wastes, which provides an attractive approach for controlling NO_<i>x</i>. Moreover, the present slurry system can eliminate NO_<i>x</i> and SO₂ simultaneously with high removal efficiency