Xiujing Zou

Effect of CeO2 addition on Ni/Al2O3 catalysts for methanation of carbon dioxide with hydrogen

Abstract The Ni-CeO2/Al2O3 catalysts with a nickel content of 15 wt% prepared via impregnating boehmite were found to be highly active and stable for methanation of carbon dioxide with hydrogen at a H2/CO2 molar ratio of 4. The effects of CeO2 content and reaction temperature on the performance of the Ni-CeO2/Al2O3 catalysts were studied in detail. The results showed that the catalytic performance was strongly dependent on the CeO2 content in Ni-CeO2/Al2O3 catalysts and that the catalysts with 2 wt% CeO2 had the highest catalytic activity among the tested ones at 350 °C. The XRD and H2-TPR characterizations revealed that the addition of CeO2 decreased the reduction temperature by altering the interaction between Ni and Al2O3, and improved the reducibility of the catalyst. Preliminary stability test of 120 h on stream over the Ni-2CeO2/Al2O3 catalyst at 350 °C revealed that the catalyst was much better than the unpromoted one.

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.

Highly chemoselective reduction of nitroarenes over non-noble metal nickel-molybdenum oxide catalysts

The chemoselective reduction of nitroarenes is an important transformation for the production of arylamines, which are the primary intermediates in the synthesis of pharmaceuticals, agrochemicals and dyes. Heterogeneous non-noble metal nickel-molybdenum oxide catalysts supported on ordered mesoporous silica SBA-15 (Ni-MoO3/CN@SBA-15) were prepared for the first time by treating SBA-15-supported nickel-molybdenum oxide materials with 1,10-phenanthroline, and exhibited unprecedented catalytic activity and chemoselectivity for the reduction of various substituted nitroarenes to the corresponding aromatic amines in ethanol with hydrazine hydrate as a hydrogen donor under mild conditions owing to the synergistic effect of metal Ni and MoO3 species, affording excellent yields of >99% within very short reaction periods (≤60 min). The Ni-MoO3/CN@SBA-15 catalysts were highly stable and could easily be recovered by simple filtration or by an external magnetic field for at least ten recycling reactions without any observable loss of catalytic performance or leaching of metal components.

Solvent-Free Selective Hydrogenation of Nitroarenes Using Nanoclusters of Palladium Supported on Nitrogen-Doped Ordered Mesoporous Carbon

The selective hydrogenation of nitroarenes is a key transformation for the production of aromatic amines, which are primary intermediates in the synthesis of pharmaceuticals, agrochemicals, and dyes. However, most reaction processes require toxic organic solvents and suffer from poor selectivity in the presence of other reducible groups. Herein, we report a successful example of nanoclusters of ultrafine Pd supported on N‐modified ordered mesoporous CMK‐3 carbon (Pd/N‐CMK‐3) prepared by a facile two‐step impregnation route with aqueous solutions of 1,10‐phenanthroline and H2PdCl4 that hydrogenated various nitroarenes highly efficiently and selectively to the corresponding aromatic amines with hydrogen in the absence of solvent. The Pd/N‐CMK‐3 catalyst could be recovered easily for multiple recycling reactions without a loss of catalytic performance.

Highly Efficient Ni/CeO2/Al2O3 Catalyst for Pre-reforming of Liquefied Petroleum Gas under a Low Molar Ratio of Steam to Carbon

Abstract The pre-reforming of commercial liquefied petroleum gas (LPG) over Ni-based catalysts at a low steam to carbon molar ratio was investigated. Ni/CeO 2 /Al 2 O 3 catalysts were prepared by impregnating boehmite with an aqueous solution of cerium and nickel nitrates. These catalysts were found to be highly efficient in LPG pre-reforming at 300–400°C and a low molar ratio of steam to carbon of 1.0. The effect of nickel content and reaction temperature on the performance of the Ni/CeO 2 /Al 2 O 3 catalysts was evaluated and the 15%Ni/CeO 2 /Al 2 O 3 catalyst was selected for a stability test in the pre-reforming of LPG. The results showed that the conversion of LPG and the composition of the products in the exit gas were almost unchanged for the steam reforming of commercial LPG after about 105 h of reaction time on stream at 350°C and GHSV of the inlet gas of 3∼000 ml/(g·h) with a steam to carbon molar ratio of 1.0, indicating that the catalyst exhibited excellent stability. After the reaction, no obvious carbon was observed on the catalyst surface. Ni/CeO 2 /Al 2 O 3 catalysts show good catalytic performance for the low temperature steam reforming of LPG, which may potentially be used in commercial fuel cells.

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.

High catalytic performance and sustainability of the Ni/La2O3 catalyst for daily pre-reforming of liquefied petroleum gas under a low steam/carbon molar ratio

The Ni/La2O3 catalyst first shows not only high catalytic activity and long-term stability but also excellent sustainability in the daily start-up and shut-down operation for the pre-reforming of LPG at a low S/C molar ratio of 1.0 due to new synergistic active sites consisting of metal Ni nanoparticles and La2O2CO3 species.

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.