Minghua Qiao

FexOy@C Spheres as an Excellent Catalyst for Fischer−Tropsch Synthesis

We demonstrate a one-pot hydrothermal cohydrolysis-carbonization process using glucose and iron nitrate as starting materials for the fabrication of carbonaceous spheres embedded with iron oxide nanoparticles. It is verified by TEM, (57)Fe Mossbauer, and Fe K-edge XAS that iron oxide nanoparticles are highly dispersed in the carbonaceous spheres, leading to a unique microstructure. A formation mechanism is also proposed. This route is also applicable to a range of other naturally occurring saccharides and metal nitrates. A catalytic study revealed the remarkable stability and selectivity of the reduced Fe(x)O(y)@C spheres in the Fischer-Tropsch synthesis, which clearly exemplifies the promising application of such materials.

A general chelate-assisted co-assembly to metallic nanoparticles-incorporated ordered mesoporous carbon catalysts for Fischer-Tropsch synthesis.

The organization of different nano objects with tunable sizes, morphologies, and functions into integrated nanostructures is critical to the development of novel nanosystems that display high performances in sensing, catalysis, and so on. Herein, using acetylacetone as a chelating agent, phenolic resol as a carbon source, metal nitrates as metal sources, and amphiphilic copolymers as a template, we demonstrate a chelate-assisted multicomponent coassembly method to synthesize ordered mesoporous carbon with uniform metal-containing nanoparticles. The obtained nanocomposites have a 2-D hexagonally arranged pore structure, uniform pore size (~4.0 nm), high surface area (~500 m(2)/g), moderate pore volume (~0.30 cm(3)/g), uniform and highly dispersed Fe(2)O(3) nanoparticles, and constant Fe(2)O(3) contents around 10 wt %. By adjusting acetylacetone amount, the size of Fe(2)O(3) nanoparticles is readily tunable from 8.3 to 22.1 nm. More importantly, it is found that the metal-containing nanoparticles are partially embedded in the carbon framework with the remaining part exposed in the mesopore channels. This unique semiexposure structure not only provides an excellent confinement effect and exposed surface for catalysis but also helps to tightly trap the nanoparticles and prevent aggregating during catalysis. Fischer-Tropsch synthesis results show that as the size of iron nanoparticles decreases, the mesoporous Fe-carbon nanocomposites exhibit significantly improved catalytic performances with C(5+) selectivity up to 68%, much better than any reported promoter-free Fe-based catalysts due to the unique semiexposure morphology of metal-containing nanoparticles confined in the mesoporous carbon matrix.

Preparation of the Ni-B amorphous alloys with variable boron content and its correlation to the hydrogenation activity

Some ultrafine Ni-B amorphous alloys with variable B contents were prepared by chemical reduction under different conditions. The effect of the B content on their activities was evaluated by using the liquid phase cyclohexene hydrogenation as a probe. Both the specific activity and the TOF value increased with the increase of the B content, showing the promoting effect of the alloying B on the hydrogenation activity, which was mainly attributed to its modification of the nature of the Ni active sites. Concerning the structural effect, the XRD patterns revealed that the amorphous degree of the as-prepared Ni-B alloy increased with the increase of the B content. Meanwhile, the DSC analysis demonstrated that increase of the B content could increase the thermal stability of the Ni-B amorphous alloy and in turn, delay its crystallization during the cyclohexene hydrogenation. Furthermore, the EXAFS also demonstrated that the Ni active sites became more highly unsaturated at higher B content. These structural modifications were favorable for the hydrogenation activity. Concerning the electronic effect, the XPS spectra demonstrated the electronic interaction between Ni and B in the Ni-B amorphous alloy, making Ni electron-enriched while B became electron-deficient. According to the DFT calculations, more electrons may transfer from the alloying B to Ni with the increase of the B content. Such electronic modifications may also facilitate the cyclohexene hydrogenation.

Preparation of amorphous NiCoB alloys and the effect of cobalt on their hydrogenation activity

Abstract The bimetallic amorphous alloys Ni Co B were prepared by the chemical reduction of the solution containing both nickel and cobalt salts with aqueous potassium borohydride. Those samples were thoroughly characterized by ICP, BET, DSC, XRD, EXAFS, XPS, TEM and TPR. Superior to the rapid quenching techniques, the content of Co in Ni Co B alloys could be adjusted in a wide range by changing the initial concentration of cobalt salt in the solution. The catalytic activities of the asprepared materials were measured through the hydrogenation of benzene under moderate pressure in liquid phase. By comparing with the activities of the corresponding pure Ni B, Co B and their mixture as well as the Ni Co B amorphous alloys with different contents of Co, both the inhibiting and promoting effects of Co on the hydrogenation activities in Ni Co B amorphous alloys have been observed and discussed according to the amount of the effective metal in the alloys and their structural characters, especially their surface properties.

In-Situ Crystallization Route to Nanorod-Aggregated Functional ZSM-5 Microspheres

Herein, we develop a reproducible in situ crystallization route to synthesize uniform functional ZSM-5 microspheres composed of aggregated ZSM-5 nanorods and well-dispersed uniform Fe(3)O(4) nanoparticles (NPs). The growth of such unique microspheres undergoes a NP-assisted recrystallization process from surface to core. The obtained magnetic ZSM-5 microspheres possess a uniform size (6-9 μm), ultrafine uniform Fe(3)O(4) NPs (~10 nm), good structural stability, high surface area (340 m(2)/g), and large magnetization (~8.6 emu/g) and exhibit a potential application in Fischer-Tropsch synthesis.

Kinetics of hydrogen evolution in alkali leaching of rapidly quenched Ni-Al alloy

Abstract The caustic leaching kinetics of the rapidly quenched Ni–Al alloys has been studied by measuring the evolution of H 2 during the leaching process. The effects of various parameters, such as the composition and the particle size of the Ni–Al alloys, the concentration of the NaOH aqueous solution, and the temperature have been systematically investigated. It is found that the leaching process of the rapidly quenched Ni–Al alloys can be well fitted by a reaction-controlled shrinking core model, which is attributed to the uniform microstructure of the alloys prepared by the rapid quenching technique.

Preparation and Catalysis of Carbon‐Supported Iron Catalysts for Fischer–Tropsch Synthesis

Fischer–Tropsch synthesis (FTS) is essential for the transformation of natural gas, coal, and biomass to clean transportation fuels and value‐added chemicals. Traditionally, iron catalysts for FTS are predominantly fused iron catalysts and precipitated iron catalysts using silica as the support. Owing to an intense surge in interest in carbon materials during recent years, along with the unique properties of these materials, such as high surface area, high porosity, and ample structures, carbon‐supported iron‐based FTS catalysts have attracted increasing attention. In this detailed review of the progress of the Fe/C catalysts for FTS in the last three decades, particular emphasis is put on their preparation, characterization, and catalytic performance relevant to the characteristics of carbon materials. This review is intended to be a valuable resource to researchers interested in this exciting field of catalysis, as well as the foundation for those investigating applications of novel carbon materials. A brief discussion is also devoted to the challenges and opportunities regarding the future development of Fe/C FTS catalysts.

ε -Iron carbide as a low-temperature Fischer–Tropsch synthesis catalyst

ε-Iron carbide has been predicted to be promising for low-temperature Fischer-Tropsch synthesis (LTFTS) targeting liquid fuel production. However, directional carbidation of metallic iron to ε-iron carbide is challenging due to kinetic hindrance. Here we show how rapidly quenched skeletal iron featuring nanocrystalline dimensions, low coordination number and an expanded lattice may solve this problem. We find that the carbidation of rapidly quenched skeletal iron occurs readily in situ during LTFTS at 423-473 K, giving an ε-iron carbide-dominant catalyst that exhibits superior activity to literature iron and cobalt catalysts, and comparable to more expensive noble ruthenium catalyst, coupled with high selectivity to liquid fuels and robustness without the aid of electronic or structural promoters. This finding may permit the development of an advanced energy-efficient and clean fuel-oriented FTS process on the basis of a cost-effective iron catalyst.

Fischer–Tropsch Synthesis over Molecular Sieve Supported Catalysts

For sustainable fuel production from alternative energy sources, it is important to design and develop Fischer–Tropsch synthesis (FTS) catalysts for hydrocarbons that deviate from the Anderson‐Schulz–Flory distribution. The introduction of a molecular sieve to a conventional FTS catalyst system offers the opportunity to confine spatially the chain length of the hydrocarbons, and to convert long‐chain hydrocarbons to molecules more suitable as transportation fuels. The incorporation of metal nanoparticles in a variety of molecular sieves with different methods allows a versatile means to modulate the distribution of the FTS hydrocarbons for different purposes.

Study on the deactivation of amorphous NiB/SiO2 catalyst during the selective hydrogenation of cyclopentadiene to cyclopentene

The deactivation of the silica supported NiB amorphous catalyst during the selective hydrogenation of cyclopentadiene (CPD) to cyclopentene (CPE) in a fixed-bed reactor was studied. According to the characterizations of the initial and used catalysts by ICP, BET, SEM, XRD and XPS, no significant sintering of the active component or crystallization of the amorphous structure was observed, while severe surface oxidation occurred after the deactivation of the catalyst. Those results demonstrated that such a deactivation should mainly be attributed to the oxidation of the active component. Water promoted the deactivation because the surface oxidation of elemental Ni was accelerated by forming Ni(OH)2 in the presence of water. The deactivation resulted from sulfication and carboneous species deposition was not observed in the present conditions, although it really occurred at high sulfur concentration and low CPD conversion.