Xinfa Dong

Selective catalytic methanation of CO in hydrogen-rich gases over Ni/ZrO2 catalyst

Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol% CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h−1 and a temperature range of 260 °C to 280 °C. The X-ray diffraction (XRD) and temperature programmed reduction (TPR) measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.

Effect of CeO2 on the catalytic performance of Ni/Al2O3 for autothermal reforming of methane

Abstract The effect of promoter Ce on the catalytic performance of Ni/Al 2 O 3 catalyst for autothermal reforming of methane to hydrogen was investigated. The catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The results indicated that the catalytic performance of the catalysts was improved with the addition of Ce. Ni/Ce 30 Al 70 O δ showed the highest CH 4 conversion in operation temperatures ranging from 650 °C to 850 °C. At the same time, the decrease in H 2 /CO ratio with increasing reaction temperature was consistent with the fact that water-gas shift reaction was thermodynamically unfavorable at higher temperatures. The XRD result indicated that adding Ce to Ni/Al 2 O 3 catalyst prevented the formation of NiAl 2 O 4 and facilitated the formation of NiO. The formation of NiO increased the number of active sites, resulting in higher activity. Comparing the TPR profiles of Ni/Ce 30 Al 70 O δ with Ni/Al 2 O 3 , it could be clearly observed that with the addition of Ce, the total reduction peak areas in the middle and low temperatures increased. It was most probably that the addition of Ce inhibited the stronger interaction between Ni and Al 2 O 3 to form the phase of NiAl 2 O 4 , and favored the formation of the strong interaction between NiO species and CeO 2 . Therefore, the addition of Ce to the Ni/Al 2 O 3 catalyst increased the active surface that promoted the activity of the catalyst.

Effect of ZrO2 Crystalline Phase on the Performance of Ni-B/ZrO2 Catalyst for the CO Selective Methanation

Amorphous Ni-B/ZrO2 catalysts were prepared by coprecipitation-chemical reduction with KBH4 aqueous solution, and various crystalline phase ZrO2 (amorphous-ZrO2, tetragonal-ZrO2 and monoclinic-ZrO2) supported Ni-B catalysts were obtained by thermal treatment in 5%H2-N2 stream at different temperature. The effect of ZrO2 polymorphs and the treatment temperature on the catalytic performance for the CO selective methanation were investigated, and the catalysts were characterized by N2 physisorption, Powder X-ray diffraction (XRD), Temperature-Programmed Desorption (CO-TPD and H2-TPD), and Differential Scanning Calorimeter (DSC). The treatment temperature affected strongly the crystalline structure of ZrO2, and the CO methanation activity and selectivity of the Ni-B/ZrO2 catalysts were significantly influenced by the crystalline phase of ZrO2. Of the three forms of ZrO2 polymorphs (amorphou-ZrO2, tetragonal-ZrO2 and monoclinic-ZrO2), the amorphous-ZrO2 supported nickle catalyst showed highest CO methanation activity, attributing in large part to the largest specific surface area and the optimum CO/H2 absorption intensity of the Ni-B/amorphous-ZrO2 catalyst.

CO selective methanation in hydrogen-rich gas mixtures over carbon nanotube supported Ru-based catalysts

Abstract Series of carbon nanotube supported Ru-based catalysts were prepared by impregnation method and applied successfully for complete removal of CO by CO selective methanation from H 2 -rich gas stream conducted in a fixed-bed quartz tubular reactor at ambient pressure. It was found that the metal promoter, reduction temperature and metal loading affected the catalytic properties significantly. The most excellent performance was presented by 30 wt% Ru-Zr/CNTs catalyst reduced at 350 °C. Since it decreased CO concentration to below 10 ppm from 12000 ppm by CO selective methanation at the temperature range of 180–240 °C, and kept CO selectivity higher than 85% at the temperature below 200 °C. Characterization using XRD, TEM, H 2 -TPR and XPS suggests that Zr modification of Ru/CNTs results in the weakening of the interaction between Ru and CNTs, a higher Ru dispersion and the oxidization of surface Ru. Amorphous and high dispersed Ru particles with small size were obtained for 30 wt% Ru-Zr/CNTs catalyst reduced at 350 °C, leading to excellent catalytic performance in CO selective methanation.

Enhancing the photocatalytic H2 evolution activity of red phosphorous by using noble-metal-free Ni(OH)2 under photoexcitation up to 700 nm

Ni(OH)2 nanoparticles are demonstrated to be cost-efficient alternatives to Pt co-catalysts for enhancing the visible-light photocatalytic H2 evolution activity of red phosphorous (P) when deposited onto its surface. Ni(OH)2-modified red P exhibits 1.12 times higher photocatalytic activity for H2 evolution than that of Pt-deposited red P under a wide range of visible light.

Selective Oxidation of CO in Excess H2 over Ru/Al2O3 Catalysts Modified with Metal Oxide

Abstract The Ru/Al2O3 catalysts modified with metal oxide (K2OandLa2O3) were prepared via incipient wetness impregnation method from RuCl3·nH2O mixed with nitrate loading on Al2O3 support. The activity of catalysts was evaluated under simulative conditions for the preferential oxidation of CO (CO-PROX) from the hydrogen-rich gas streams produced by reforming gas, and the performances of catalysts were investigated by XRD and TPR. The results showed that the activity temperature of the modified catalysts Ru-K2O/Al2O3 and Ru-La2O3/Al2O3 were lowered approximately 30 °C compared with pure Ru/Al2O3, and the activity temperature range was widened. The conversion of CO on Ru-K2O/Al2O3 and Ru-La2O3/Al2O3 was above 99% at 140–160 °C, suitable to remove CO in a hydrogen-rich gas and the selectivity of Ru-La2O3/Al2O3 was higher than that of Ru-K2O/Al2O3 in the active temperature range. Slight methanation reaction was detected at 220 °C and above.

Fabrication and Water Treatment Application of Carbon Nanotubes (CNTs)-Based Composite Membranes: A Review

Membrane separation technology is widely explored for various applications, such as water desalination and wastewater treatment, which can alleviate the global issue of fresh water scarcity. Specifically, carbon nanotubes (CNTs)-based composite membranes are increasingly of interest due to the combined merits of CNTs and membrane separation, offering enhanced membrane properties. This article first briefly discusses fabrication and growth mechanisms, characterization and functionalization techniques of CNTs, and then reviews the fabrication methods for CNTs-based composite membranes in detail. The applications of CNTs-based composite membranes in water treatment are comprehensively reviewed, including seawater or brine desalination, oil-water separation, removal of heavy metal ions and emerging pollutants as well as membrane separation coupled with assistant techniques. Furthermore, the future direction and perspective for CNTs-based composite membranes are also briefly outlined.

Hydrogen production by glycerol reforming in supercritical water over Ni/MgO-ZrO2 catalyst

Abstract Nano ZrO 2 and MgO-ZrO 2 were prepared by a self-assembly route and were employed as the support for Ni catalysts used in hydrogen production from glycerol reforming in supercritical water (SCW). The reforming experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 600–800 °C. The influences of process variables such as temperature, contact time, and water to glycerol ratio on hydrogen yield were investigated and the catalysts were charactered by ICP, BET, XRD and SEM. The results showed that high hydrogen yield was obtained from glycerol by reforming in supercritical water over the Ni/MgO-ZrO 2 catalysts in a short contact time. The MgO in the catalyst showed significant promotion effect for hydrogen production likely due to the formation of the alkaline active site. Even when the glycerol feed concentration was up to 45 wt%, glycerol was completely gasified and transfered to the gas products containing hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At a diluted feed concentration of 5 wt%, near theoretical yield of 7 mole of H 2 /mol of glycerol could be obtained.

Removal of CO from reformed fuels by selective methanation over Ni-B-Zr-Oδ catalysts

The Ni-B-Oδ and Ni-B-Zr-Oδ catalysts were prepared by the method of chemical reduction, and the deep removal of CO by selective methanation from the reformed fuels was performed over the as-prepared catalysts. The results showed that zirconium strongly influenced the activity and selectivity of the Ni-B-Zr-Oδ catalysts. Over the Ni-B-Oδ catalyst, the highest CO conversion obtained was only 24.32% under the experimental conditions studied. However, over the Ni-B-Zr-Oδ catalysts, the CO methanation conversion was higher than 90% when the temperature was increased to 220 °C. Additionally, it was found that the Ni/B mole ratio also affected the performance of the Ni-B-Zr-Oδ catalysts. With the increase of the Ni/B mole ratio from 1.8 to 2.2, the CO methanation activity of the catalyst was improved. But when the Ni/B mole ratio was higher than 2.2, the performance of the catalyst for CO selective methanation decreased instead. Among all the catalysts, the Ni29B13Zr58Oδ catalyst investigated here exhibited the highest catalytic performance for the CO selective methanation, which was capable of reducing the CO outlet concentration to less than 40 ppm from the feed gases stream in the temperature range of 230–250 °C, while the CO2 conversion was kept below 8% all along. Characterization of the Ni-B-Oδ and Ni-B-Zr-Oδ catalysts was provided by XRD, SEM, DSC, and XPS.

Selective CO methanation over amorphous Ni-Ru-B/ZrO2 catalyst for hydrogen-rich gas purification

Abstract Amorphous Ni-Ru-B/ZrO2 catalysts were prepared by chemical reduction method. The effects of Ni-Ru-B loading and Ru/Ni mole ratio on the catalytic performance for selective CO methanation from reformed fuel were studied, and the catalysts were characterized by BET, ICP, XRD and TPD. The results showed that Ru strongly affected the catalytic activity and selectivity by increasing the thermal stability of amorphous structure, promoting the dispersion of the catalyst particle, and intensifying the CO adsorption. For the catalysts with Ru/Ni mole ratio under 0.15, the CO methanation conversion and selectivity increased significantly with the increasing Ru/Ni mole ratio. Among all the catalysts investigated, the 30 wt% Ni-Ru-B loading amorphous Ni61Ru9B30/ZrO2 catalyst with 0.15 Ru/Ni mole ratio presented the best catalytic performance, over which higher than 99.9% of CO conversion was obtained in the temperature range of 230°C∼250°C, and the CO2 conversion was kept under the level of 0.9%.