Xingfu Shang

Facile strategy for synthesis of mesoporous crystalline γ-alumina by partially hydrolyzing aluminum nitrate solution

The facile synthesis of mesoporous γ-alumina is developed through the partial hydrolysis of Al(NO3)3 aqueous solution with (NH4)2CO3 without organic surfactants. In this synthesis, the stable NH4NO3/Al species (AN/Al) hybrid containing Keggin-Al13 polycations is first prepared, which is the key for the successful formation of mesoporous γ-alumina. XRD, 27Al MAS NMR, TEM, and N2 adsorption and desorption results demonstrate that the as-prepared AN/Al hybrid can be transformed to γ-alumina by treatment at 200 °C and exhibit a wormhole-like mesoporous structure with large surface area up to ∼450 m2 g−1, pore volume of ∼0.3 cm3 g−1 and narrow pore size distribution peaked at ∼3.9 nm after completely removing NH4NO3 at 300 °C. The obtained mesoporous γ-aluminas have high thermal stabilities up to 900 °C and excellent hydrothermal stability. The investigation shows that the synergetic effect of NH4NO3 and Al13 species promotes crystallization of Al species to γ-alumina, which may have a unique mechanism distinct from the mesoporous aluminas reported previously. CO2 adsorption measurements indicate that these mesoporous γ-aluminas have a much higher CO2 adsorption capacity than ordered mesoporous alumina synthesized by the surfactant-templating method and conventional γ-alumina derived from aluminum oxyhydroxides. We believe that this research should be useful for providing new insights into the transformation of transition alumina phases and for synthesizing mesoporous γ-alumina with promising properties for various chemical applications.

Influence of nickel content on structural and surface properties, reducibility and catalytic behavior of mesoporous γ-alumina-supported Ni–Mg oxides for pre-reforming of liquefied petroleum gas

Mesoporous γ-alumina-supported Ni–Mg oxides (xNiO–MgO/γ-MA) with various mass percentage contents of nickel (x = 0, 5, 10, 15, 18 and 21) were prepared through one-pot hydrolysis of metal nitrate salts without surfactants. The influences of nickel content on the catalyst structure, surface properties, interaction between Ni species and the support, reducibility of Ni2+ ions and Ni particle dispersion were investigated in detail using XRD, N2 sorption, TEM, XPS, CO2-TPD, H2-TPR, hydrogen chemisorption and TG techniques. The xNiO–MgO/γ-MA materials showed wormhole-like mesoporous structures with large surface areas and narrow pore size distributions. The dominant NiO species were homogeneously dispersed and had an attenuated interaction with the support with the increase in Ni content, producing uniform Ni nanoparticles throughout γ-alumina frameworks after H2 reduction. The Ni particle sizes decreased with increasing Ni content and showed a minimum at 18 wt%, likely due to Ni crystallite growth by Ostwald ripening rather than by migration of Ni nanoparticles. The reduced xNi–MgO/γ-MA catalysts were investigated for their catalytic behaviors in pre-reforming of liquefied petroleum gas. The results demonstrated that the Ni surface areas were mainly responsible for their catalytic activities; smaller Ni nanoparticles promoted steam reforming of hydrocarbons, methanation of carbon oxides and water gas shift reaction, but inhibited hydrocracking of hydrocarbons and lowered the rate of coke deposition, improving the catalytic activity and stability.

High Performance and Active Sites of a Ceria‐Supported Palladium Catalyst for Solvent‐Free Chemoselective Hydrogenation of Nitroarenes

Cerium oxide‐supported palladium catalysts (Pd/CeO2) prepared by a simple impregnation method exhibit exciting catalytic activity and high chemoselectivity for the solvent‐free hydrogenation of a variety of substituted nitroarenes including the reducible functional groups to the corresponding aromatic amines under mild reaction conditions. Taking nitrobenzene as an example, the Pd/CeO2 catalyst can afford aniline yields of >99 % with turnover frequencies as high as 11 411 h−1 and 69 824 h−1 at 40 °C and 100 °C, respectively. Pd2+ ion species exist as isolated single atoms with −Pd2+−O2−−Ce4+− linkages on the surface of PdxCe1−xO2−σ solid solution and are found to be active sites for the selective hydrogenation of nitroarenes in the absence of solvent. The superior catalytic performance can be attributed to the cooperative effect between Pd2+ ions and unique surface sites of CeO2. A possible mechanism is proposed for the hydrogenation of nitroarenes with H2 over the Pd/CeO2. The Pd/CeO2 catalyst can be recovered easily and reused for at least seven recycling reactions without loss of catalytic properties.

Nitrogen-doped graphene-activated metallic nanoparticle-incorporated ordered mesoporous carbon nanocomposites for the hydrogenation of nitroarenes

Herein, nanoscale metallic nanoparticle-incorporated ordered mesoporous carbon catalysts activated by nitrogen-doped graphene (NGr) were fabricated via an efficient multi-component co-assembly of a phenolic resin, nitrate, acetylacetone, the nitrogen-containing compound 1,10-phenanthroline, and Pluronic F127, followed by carbonization. The obtained well-dispersed nitrogen-doped graphene-activated transition metal nanocatalysts possess a 2-D hexagonally arranged pore structure with a high surface area (∼500 m2 g−1) and uniform pore size (∼4.0 nm) and show excellent activity for the selective hydrogenation–reduction of substituted nitroarenes to anilines in an environmentally friendly aqueous solution. The high catalytic performance and durability is attributed to the synergistic effects among the components, the unique structure of the nitrogen-doped graphene layer-coated metallic nanoparticles, and electronic activation of the doped nitrogen.

Investigation of mesoporous NiAl2O4/MOx (M = La, Ce, Ca, Mg)–γ-Al2O3 nanocomposites for dry reforming of methane

One-pot synthesized mesoporous NiAl2O4/γ-Al2O3 and NiAl2O4/MOx (M = La, Ce, Ca, Mg)–γ-Al2O3 nanocomposites with excellent textural properties were employed for the dry reforming of methane (DRM). NiAl2O4/La2O3/γ-Al2O3-imp prepared via a traditional impregnation method was used for comparison. The promotion effect of modifiers on the physicochemical properties and catalytic performance of the catalysts was systematically investigated. Characterization and evaluation results indicated that the modified catalysts showed higher activities and better coking-resistance than Ni/γ-Al2O3, and Ni/La2O3–γ-Al2O3 was found to be the most effective one. All the catalysts with or without modifiers presented similar Ni particle sizes due to the enhanced metal–support interaction derived from the reduction of the NiAl2O4 precursor. However, more medium-strength basic sites on the catalyst surface were obtained by adding promoters, which could facilitate the adsorption/activation of CO2 and the gasification of amorphous carbon, improving the catalytic properties and accelerating the coke elimination rate. Additionally, the incorporation of promoters also prevented the phase transformation of γ-alumina.

Low Temperature Synthesis of Mesoporous γ-Alumina supported Nickel Oxides and their Catalytic Application for CO2 Methanation

The mesoporous γ-alumina supported nickel oxides with different Ni/Al molar ratios (x = 0.05, 0.10, 0.125, 0.25, 0.50) have been prepared by a simple partial hydrolysis of aqueous solution of Al(NO3)3 and Ni(NO3)2 with (NH4)2CO3 without templates or organic surfactants at low calcination temperature of 400 o C. The as-prepared materials possessed wormhole-like mesoporous structures with large specific surface areas of 252-477 m 2 /g and narrow pore size distributions in the range of 3-4 nm. The specific surface areas and pore volumes of the materials gradually decreased with the increase in the Ni/Al molar ratio and the nickel species were highly dispersed in the materials. Among the catalysts tested for the methanation of CO2, the mesoporous γ-alumina supported nickel oxides with the Ni/Al molar ratios of 0.25 revealed the best catalytic performance and showed the similar catalyst activity to the counterpart with ordered mesoporous alumina supported nickel oxide synthesized through templating approach.

Pre-reforming of Liquefied Petroleum Gas over Magnesium Aluminum Mixed Oxide Supported Nickel Catalysts: Pre-reforming of Liquefied Petroleum Gas over Magnesium Aluminum Mixed Oxide Supported Nickel Catalysts

The catalytic performance of Ni catalysts supported on magnesium aluminum mixed oxide (Ni/MgmAl) for the pre-reforming of liquefied petroleum gas (LPG) was studied, and the catalysts were prepared by the co-precipitation-impregnation method and calcined in the lower temperature range of 400–700 oC. The X-ray diffraction and H2 temperature-programmed reduction results showed that Ni species were highly dispersed on the catalyst surface without NiAl2O4 spinel formation. The Ni/MgmAl catalysts could be reduced to metallic Ni nanoparticles at 650 oC, which showed excellent catalytic activity and stability for LPG pre-reforming at 400 oC and a low steam/carbon molar ratio of 2.0. The effects of Mg/Al molar ratios, Ni loading, and calcination temperature of the support and catalyst on the catalytic behavior of the Ni/MgmAl catalysts were investigated in detail. The results revealed that the 15%Ni/Mg1.25Al catalyst with both support and catalyst calcined at 500 oC had the optimal catalytic performance for LPG pre-reforming. Compared with Ni/MgmAl catalysts calcined at high temperature (≥ 800 oC), the present catalysts showed easier coke deposition and a slight decrease in catalytic activity and stability. However, it may be more promising candidate for LPG pre-reforming for the use of hydrogen fuel cells in transportation and small stationary application due to lower reduction temperature.