Kongyong Liew

SBA-16-Supported Cobalt Catalyst with High Activity and Stability for Fischer–Tropsch Synthesis

SBA‐16 molecular sieves were used as support to prepare cobalt catalyst for Fischer–Tropsch synthesis (FTS). The catalysts were characterized by using TEM, power XRD, temperature‐programmed reduction, and N2 adsorption–desorption. The analyses indicate that most of the Co3O4 nanoparticles were introduced into the SBA‐16 cages, and the SBA‐16 mesostructure was retained after cobalt impregnation. The Co/SBA‐16 catalyst exhibited higher cobalt dispersion compared to the Co/SiO2 catalyst. The catalytic properties of the catalysts in FTS were evaluated in a fixed‐bed reactor. The effect of the addition of water was measured in a continuously stirred tank reactor. High FTS activity and stability were observed on the SBA‐16‐supported catalyst. The SBA‐16‐supported cobalt catalyst shows low mobility of cobalt particles in the SBA‐16 cages. Unlike silica, the SBA‐16 support can efficiently prevent the aggregation and sintering of cobalt nanoparticles.

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes (CNT) on the activity and product selectivity of Fischer-Tropsch synthesis (FTS) reaction. Three types of CNT with average pore sizes of 5, 11, and 17 nm were used as the supports. The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT. The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT, and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing. The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT. Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.

An environmentally friendly method for the synthesis of nano-alumina with controllable morphologies

The relatively high price of aluminum alkoxides as an alumina source and organic surfactants as morphology control or structure directing agents are less attractive for practical applications to the synthesis of nanostructured alumina. Moreover, some of these synthesis processes may generate large masses of salt by-products. A highly efficient synthesis of nano-alumina from ammonium carbonate aqueous solution and aluminum nitrate ethanol solution without the use of a template and complicated processes has been achieved. The Al(NO3)3·9H2O reagent can be completely converted to nano-alumina without a by-product and the ethanol solutions can be reused. In addition, the CO2 and NH3 produced can also be recycled to the reagent (NH4)2CO3. The nano-alumina synthesized is of γ-alumina structure. Moreover, the simple and environmentally friendly route described could enhance the synthesis technology for nano-alumina and its applications.

Al‐SBA‐16‐Supported Cobalt Catalysts for the Fischer–Tropsch Production of Gasoline‐Fraction Hydrocarbons

The Fischer–Tropsch synthesis (FTS) is an important technology for the production of clean transportation fuels and chemicals from syngas (CO+H2). Although it was first developed 90 years ago, some challenges still remain. The development of FTS catalysts with high activity, high stability, and, in particular, high selectivity, remains one of the key goals of current research in this area. Over conventional FT catalysts, the hydrocarbon products generally follow the wide and unselective Anderson–Schulz– Flory (ASF) distribution. The statistical distribution of these hydrocarbons is one of the most-significant drawbacks to the direct synthesis of liquid fuels from FTS, which limits the maximum attainable selectivity for a given fuel [about 45 % for gasoline (C5–C12) and 30 % for diesel (C13–C20)] . To obtain the ideal gasoline component from syngas, zeolites, which have uniform molecular-sized pores, strong surface acidity, and large amount of active sites, have been employed to hydrocrack the FTS hydrocarbons. However, the small micropores of zeolites are not suitable for the conversion of large organic molecules, which cause the deactivation of zeolites with time-on-stream (TOS) owing to the deposition of wax. Another key problem in using zeolites as supports is their extremely low degree of reduction, owing to strong interactions between the metal and the zeolites, and, thus, very low CO conversion. Meanwhile, higher temperatures (>300 8C) are required to promote efficient secondary reactions, which is not suitable for cobalt catalysts. The successful design and application of a bifunctional catalyst system that consists of a FTS-active metal and a molecular sieve, which functions both as a support and as an acid catalyst, has the potential to spark a significant revolution in FTS catalysis. Previously, we reported that the SBA-16 silica support, with its cage-like structure, can impede the agglomeration of metal particles, enhance the stability of the catalyst, increase the distribution of cobalt particles, and allow the fast transportation of the reactants and products. Herein, aluminum was introduced into the framework of SBA-16. The introduction of aluminum into the framework of mesoporous silica modified the surface acidity of the material whilst also retaining the SBA-16 mesopores. The performance of Al-SBA-16-supported cobalt catalysts, with unique particle size and pore size, in the FTS was investigated and we found that the acidity of the Al-SBA-16 support played a crucial role in tuning the product selectivity in the FT synthesis. The N2-physisorption isotherms of the Al-SBA-16 supports have a type-IV isotherm pattern with a H2 hysteresis loop (see the Supporting Information, Figure S1), thus indicating that the mesopores adopt cage-like structure. The diameters of the pore entrance and the cage (see the Supporting Information, Table S1), which were calculated from the adsorption branches of the isotherms by using nonlocal density functional theory (NLDFT), were about 2.8 nm and 10 nm, respectively, and they did not change significantly during the synthesis and subsequent calcination steps, thus indicating that the pore structure of the Al-SBA-16 support was well-preserved, regardless of the amount of incorporated aluminum. The N2-physisorption isotherms and pore-size distributions of the Co/SBA-16 and AlCo/SBA-16 catalysts are shown in Figure 1. The pore diameter did not change significantly after being impregnated with 15 wt. % Co; however, the BET surface areas and pore volumes clearly decreased (see the Supporting Information, Table S1), thus indicating that the cobalt species were introduced into the support cages. This conclusion was also supported by TEM analysis (see below). The small-angle X-ray diffraction (XRD) patterns of the AlSBA-16 supports with different amounts of aluminum incorporation (see the Supporting Information, Figure S2) were similar to each other and showed a very strong (110) reflection, which indicates that the uniform pore structure of SBA-16 was retained. TEM images of the Al-SBA-16 supports (see the Supporting Information, Figure S3) show well-ordered cubic mesopores along the (111) directions. The pore diameter was about 10 nm, which was unchanged after the incorporation of the aluminum species, in agreement with the N2-physisorption isotherms. Wide-angle XRD patterns of the SBA-16 and Al-SBA-16 supports (see the Supporting Information, Figure S4) showed a very broad peak at around 2q= 238, which is typical of amorphous silica. No extra peaks were observed in the XRD patterns. The wide-angle XRD patterns of the Co/SBA-16 and AlCo/ SBA-16 catalysts (Figure 2) indicate that cobalt is present in the form of a Co3O4 crystalline phase on all of the catalysts after calcination at 350 8C. The average particle sizes of the Co3O4 phase (see the Supporting Information, Table S1), as estimated from the Scherrer equation by using the most-intense reflection at 2q= 36.98, indicates that the crystallite size is similar in [a] Dr. Y. Zhao, Dr. Y. Zhang, Dr. S. Chen College of Chemistry Chemical Engineering and Materials Science Soochow University Suzhou 215123 (P.R. China) [b] Dr. Y. Zhao, Prof. J. Li, Dr. Y. Zhang, Prof. K. Liew Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and the Ministry of Education South-Central University for Nationalities Wuhan 430074 (P.R. China) Fax: (+ 86) 27-67842752 E-mail : jinlinli@yahoo.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200394.

Ru catalysts supported on Al–SBA-15 with high aluminum content and their bifunctional catalytic performance in Fischer–Tropsch synthesis

Highly ordered mesoporous Al–SBA-15 materials with high Al/Si ratios (0.2, 0.5 and 1.0) have been synthesized by a modified “pH-adjusting” method, and ruthenium catalysts supported on the Al–SBA-15 were prepared by incipient wetness impregnation and tested in a fixed bed reactor at high temperature (250 °C) in order to study their bifunctional catalytic performance in Fischer–Tropsch synthesis. The samples were characterized by ICP-AES, XRD, 27Al MAS NMR, N2 physisorption, NH3-TPD, TEM, TPR and IR spectroscopy of adsorbed pyridine. The results showed that the selectivities of hydrocarbons were significantly influenced by Al/Si ratio in the support. The 4Ru(1.0) catalyst with Al/Si ratio of 1.0 exhibited typical bifunctional properties in Fischer–Tropsch synthesis, lower selectivity (24.9%) of heavy hydrocarbons (C13+) and much higher selectivities of olefins and iso-paraffins were found in the products.

Cobalt catalysts supported on silica nanotubes for Fischer-Tropsch synthesis

Silica nanotubes (SNT) have been synthesized using carbon nanotubes (CNT) as a template. Silica-coated carbon nanotubes (SNT-CNT) and SNT were loaded with a cobalt catalyst for use in Fischer-Tropsch synthesis (FTS). The catalysts were prepared by incipient wetness impregnation and characterized by N2 physisorption, X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR) and transmission electron microscopy (TEM). FTS performance was evaluated in a fixed-bed reactor at 493 K and 1.0 MPa. Co/CNT and Co/SNT catalysts showed higher activity than Co/SNT-CNT in FTS because of the smaller cobalt particle size, higher dispersion and stronger reducibility. The results also showed that structure of the support affects the product selectivity in FTS. The synergistic effects of cobalt particle size, catalytic activity and diffusion limitations as a consequence of its small average pore size lead to medium selectivity to C5+ hydrocarbons and CH4 over Co/SNT-CNT. On the other hand, the Co/CNT showed higher CH4 selectivity and lower C5+ selectivity than Co/SNT, due to its smaller average pore size and cobalt particle size.