Yanxi Zhao

Shape-controlled synthesis of palladium nanocrystals by microwave irradiation

The controlled synthesis of Pd icosahedra in tetraethylene glycol (TEG) with H2PdCl4 as a precursor and poly(vinylpyrrolidone) (PVP) as a stabilizer in the presence of an appropriate amount of KOH under microwave irradiation was demonstrated. TEG served as both solvent and reducing agent, and stable Pd icosahedra with uniform sizes and well-defined shapes could be prepared in a yield of over 90 % by microwave heating for 60 s. The sizes of Pd icosahedra can be well controlled by adjusting the concentration of the precursor H2PdCl4.

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.

Controlled synthesis of hierarchical tetrapod Pd nanocrystals and their enhanced electrocatalytic properties

Well-defined highly branched hierarchical tetrapod Pd nanocrystals with mutually embedded metameres were successfully synthesized with Pd(acac)2 as a precursor and CO as a reducing agent in the presence of SDS. SDS played an essential role in controlling the hierarchical tetrapod morphologies of the final products. The formation of the hierarchical Pd tetrapods was ascribed to the SDS-confined growth from the four tips along the directions. The as-prepared hierarchical Pd nanostructures demonstrated outstanding electrocatalytic activity.

Effect of Textural Structure on the Catalytic Performance of LaCoO3 for CO Oxidation

Bulk, supported, and porous perovskite LaCoO3 were prepared and their catalytic performances for CO oxidation were investigated. XRD, FTIR spectroscopy, SEM, TEM, and N2 physisorption measurements were performed to identify their structure, and temperature‐programmed desorption of oxygen, temperature‐programmed reduction by hydrogen, and X‐ray photoelectron spectroscopy were conducted to study their physicochemical properties. With the change from bulk to nanoparticles and further to a porous structure, the series of LaCoO3 samples showed increased oxygen vacancies and improved oxidizing ability, which led to enhanced catalytic performances for CO oxidation. The correlation of the CO oxidation activity with the amount of exposed metal sites indicated that the Co ions should be the active site of the reaction. Comparison of the activation energy supported the changes observed in the activities.

Metal-free mesoporous carbon nitride catalyze the Friedel–Crafts reaction by activation of benzene

Mesoporous graphitic carbon nitride (mpg-C3N4) was synthesized and studied as a metal-free catalyst for Friedel–Crafts acylation of benzene. The synthesis was done by a template method using SiO2 as template and organic chemicals including guanidine hydrochloride (GndCl), dicyandiamide and urea as precursors. Characterizations by XRD, FT-IR, XPS, N2 physisorption and TEM indicated that the assumed mpg-C3N4 is synthesized irrespective of the precursor used. However, the surface chemistry of mpg-C3N4, evaluated from TGA and CO2-TPD, varied with the precursors and the mass ratio (r) of SiO2 to precursor. Catalytic results showed that the sample prepared using GndCl as precursor and at mass ratio of SiO2 to GndCl equals to 0.7, defined as mpg-C3N4_G(0.7), exhibits the best activity for the reactions, due to its rich surface basic sites and high surface area. Thus 89% conversion was obtained within 30 min using hexanoyl chloride as electrophile at 90 °C. Even at room temperature (27 °C), 75% conversion can be observed within 30 min. The catalyst is also reusable with ca. 80% activities recoverable after washing with ethanol. The excellent catalytic performances, as well as its low cost, straightforward synthesis and metal-free characters, make mpg-C3N4_G(0.7) a potential catalyst for Friedel–Crafts acylation of benzene in industry with a “green” route.

Nickel catalysts supported on MgO with different specific surface area for carbon dioxide reforming of methane

In this paper, three kinds of MgO with different specific surface area were prepared, and their effects on the catalytic performance of nickel catalysts for the carbon dioxide reforming of methane were investigated. The results showed that MgO support with the higher specific surface area led to the higher dispersion of the active metal, which resulted in the higher initial activity. On the other hand, the specific surface area of MgO materials might not be the dominant factor for the basicity of support to chemisorb and activate CO2, which was another important factor for the performance of catalysts. Herein, Ni/MgO(CA) catalyst with proper specific surface area and strong ability to activate CO2 exhibited stable catalytic property and the carbon species deposited on the Ni/MgO(CA) catalyst after 10 h of reaction at 650 °C were mainly activated carbon species.

Controlled synthesis of Pd–Pt alloy nanohypercubes under microwave irradiation

Pd–Pt alloy hypercubic nanostructures were successfully fabricated by reducing Pd and Pt precursors simultaneously in a one step process under microwave irradiation for only 100 s without using any sacrificial templates. Together with the use of tetraethylene glycol (TEG) as both a solvent and a reducing agent, the presence of KI was critical to the formation of Pd–Pt alloy nanohypercubes. The as-prepared Pd–Pt alloy nanohypercubes improved the electrocatalytic activities.

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.

Controlled synthesis of tetrapod/Mitsubishi-like palladium nanocrystals

Well-defined tetrapod/Mitsubishi-like Pd nanocrystals with uniform dimensions were successfully synthesized by using Pd(acac)2 as a precursor and CO as a reducing agent in the presence of sodium acetate. Carboxylate anions such as acetate anions played an essential role in controlling the tetrapod morphologies of the final products.

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.