Showing papers by "Tewodros Asefa published in 2013"

Enhanced catalytic activity in strained chemically exfoliated WS 2 nanosheets for hydrogen evolution

Abstract: Efficient evolution of hydrogen via electrocatalysis at low overpotentials is promising for clean energy production. Monolayered nanosheets of chemically exfoliated WS2 are shown to be efficient catalysts for hydrogen evolution at very low overpotentials. The enhanced catalytic performance is associated with the high concentration of the strained metallic octahedral phase in the exfoliated nanosheets.

Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction

Abstract: We report chemically exfoliated MoS2 nanosheets with a very high concentration of metallic 1T phase using a solvent free intercalation method. After removing the excess of negative charges from the surface of the nanosheets, highly conducting 1T phase MoS2 nanosheets exhibit excellent catalytic activity toward the evolution of hydrogen with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS2, we found that the activity of 2H MoS2 is significantly reduced after oxidation, consistent with edge oxidation. On the other hand, 1T MoS2 remains unaffected after oxidation, suggesting that edges of the nanosheets are not the main active sites. The importance of electrical conductivity of the two phases on the hydrogen evolution reaction activity has been further confirmed by using carbon nanotubes to increase the conductivity of 2H MoS2.

Efficient metal-free electrocatalysts for oxygen reduction: polyaniline-derived N- and O-doped mesoporous carbons.

Abstract: The oxygen reduction reaction (ORR)—one of the two half-reactions in fuel cells—is one of the bottlenecks that has prevented fuel cells from finding a wide range of applications today. This is because ORR is inherently a sluggish reaction; it is also because inexpensive and sustainable ORR electrocatalysts that are not only efficient but also are based on earth-abundant elements are hard to come by. Herein we report the synthesis of novel carbon-based materials that can contribute to solving these challenges associated with ORR. Mesoporous oxygen- and nitrogen-doped carbons were synthesized from in situ polymerized mesoporous silica-supported polyaniline (PANI) by carbonization of the latter, followed by etching away the mesoporous silica template from it. The synthetic method also allowed the immobilization of different metals such as Fe and Co easily into the system. While all the resulting materials showed outstanding electrocatalytic activity toward ORR, the metal-free, PANI-derived mesoporous carbon ...

Efficient noble metal-free (electro)catalysis of water and alcohol oxidations by zinc-cobalt layered double hydroxide.

Abstract: Replacing rare and expensive noble metal catalysts with inexpensive and earth-abundant ones for various renewable energy-related chemical processes as well as for production of high value chemicals is one of the major goals of sustainable chemistry Herein we show that a bimetallic Zn–Co layered double hydroxide (Zn–Co–LDH) can serve as an efficient electrocatalyst and catalyst for water and alcohol oxidation, respectively In the electrochemical water oxidation, the material exhibits a lower overpotential, by ∼100 mV, than monometallic Co-based solid-state materials (eg, Co(OH)2 and Co3O4)-catalytic systems that were recently reported to be effective for this reaction Moreover, the material’s turnover frequency (TOF) per Co atoms is >10 times as high as those of the latter at the same applied potentials The Zn–Co–LDH also catalyzes oxidation of alcohols to the corresponding aldehydes or ketones at relatively low temperature, with moderate to high conversion and excellent selectivity

Nanocatalysis : synthesis and applications

Abstract: Foreword vii Graham Hutchings Preface ix List of Contributors xiii 1 INTRODUCTION TO NANOCATALYSIS 1 Vivek Polshettiwar and Tewodros Asefa 2 NANOCATALYSTS FOR THE HECK COUPLING REACTIONS 11 T. Asefa, A. V. Biradar, S. Das, K. K. Sharma, and R. Silva 3 NANOCATALYSTS FOR THE SUZUKI COUPLING REACTIONS 51 Liane M. Rossi, Natalia J. S. Costa, Jones Limberger, and Adriano L. Monteiro 4 SONOGASHIRA REACTIONS USING NANOCATALYSTS 89 Rafael Chinchilla and Carmen N'ajera 5 NANOCATALYSTS FOR HIYAMA, STILLE, KUMADA, AND NEGISHI C C COUPLING REACTIONS 133 Abhinandan Banerjee and Robert W. J. Scott 6 ARYL CARBON HETEROATOM COUPLING REACTIONS USING NANOMETAL CATALYST 189 Brindaban C. Ranu, Debasree Saha, Debasish Kundu, and Nirmalya Mukherjee 7 NANOSTRUCTURED CATALYSTS FOR THE ALDOL, KNOEVENAGEL, AND HENRY REACTIONS 221 T. Asefa, A. V. Biradar, S. Das, and R. Silva 8 NANOCATALYSTS FOR REARRANGEMENT REACTIONS 251 Joaqu'yn Garc'ya-A'lvarez, Sergio E. Garc'ya-Garrido, and Victorio Cadierno 9 OXIDATION OF ALCOHOLS USING NANOCATALYSTS 287 Takato Mitsudome and Kiyotomi Kaneda 10 TUNING THE MORPHOLOGY OF METAL OXIDES FOR CATALYTIC APPLICATIONS 333 Yong Li and Wenjie Shen 11 NANOCATALYSTS FOR HYDROGENATION REACTIONS 405 Radha Narayanan 12 HYDROGENOLYSIS REACTIONS USING NANOCATALYSTS 443 Aziz Fihri and Vivek Polshettiwar 13 NANOMATERIAL-BASED PHOTOCATALYSTS 469 Biswajit Mishra and Deepa Khushalani 14 NANOCATALYSTS FOR WATER SPLITTING 495 Xu Zong, Gaoqing Lu, and Lianzhou Wang 15 PROPERTIES OF NANOCATALYTIC MATERIALS FOR HYDROGEN PRODUCTION FROM RENEWABLE RESOURCES 561 Zhong He and Xianqin Wang 16 NANOCATALYSTS FOR BIOFUELS 595 Vitaliy Budarin, Peter S. Shuttleworth, Brigid Lanigan, and James H. Clark 17 NANOMATERIAL-BASED BIOCATALYST 615 Jin Hyung Lee, Soo Youn Lee, Zhi-Kang Xu, and Jeong Ho Chang 18 ROLE OF NANOCATALYSIS IN CHEMICAL INDUSTRY 643 Anirban Ghosh, K. S. Nagabhushana, Debabrata Rautaray, and Rajiv Kumar 19 NANOCATALYSIS: ACTIVATION OF SMALL MOLECULES AND CONVERSION INTO USEFUL FEEDSTOCK 679 Suresh Babu Kalidindi and Balaji R. Jagirdar Index 713

Hierarchical macrochanneled layered titanates with “house-of-cards”-type titanate nanosheets and their superior photocatalytic activity

Abstract: Novel three-dimensional (3D) hierarchical macroporous–mesoporous layered titanates were synthesized by self-assembly of interconnected “house-of-cards”-type nanosheets with a facile template-free solvothermal method in presence of hydrazine. Prolonging the time of solvothermal treatment led to the enlargement in size and thickness of the titanate nanosheets in the materials. When the solvothermal temperature was increased, diamond-shaped nanoparticles without macrochannels were formed. Stability of the unique 3D architectures in the materials was attained by post-thermal treatment of the materials in temperatures ranging between 500 and 900 °C. During the post-thermal treatment, a gradual transformation from flake-like titanates with porous structures to anatase/rutile crystalline particles was also observed. Such changes in the hierarchical morphology significantly altered the porosity, crystallinity, and optical and photoelectrochemical properties of the layered titanate materials. Owing to their hierarchical 3D porous structures, large surface area and appropriate band gap energy, these novel layered titanate materials exhibited higher adsorption capacity and more efficient photodegradation catalytic activity towards organic contaminants in wastewater compared with the commercially available P25 TiO2 (Degussa/Evonik) and many other previously reported hierarchical TiO2 materials.

New polyoxomolybdate compounds synthesized in situ using ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate as green solvent

Abstract: Herein we report the facile, green syntheses of three new polyoxomolybdate-based inorganic–organic hybrid materials using room temperature ionic liquid (RTIL), 1-butyl-3-methyl-imidazolium tetrafluoroborate (bmim)[BF4], as a green and reactive solvent. The organic imidazolium component of the RTIL was incorporated into all three structures, the μ5-oxo octamolybdate cluster compound (bmim)3NH4[Mo8O26] (1) and two Keggin-type cluster compounds, one being a charge transfer salt (bmim)4[PMoVMo11O40] (2) and the other having the unreduced anion (bmim)3[PMo12O40] (3). Phase pure and highly crystalline samples were obtained. In 1 the Mo8O26 moiety is a tetranionic cluster in its β phase. Compound 1 contains three bmim cations and an NH4+ molecule to complement the −4 charge on the octamolybdate anion. The α-phase Keggin-type anion in 2, [PMoVMo11O40]4−, contains one Mo atom in the +5 oxidation state, indicating that 2 is a charge transfer complex. The α-phase Keggin-type anion in 3, [PMo12O40]3−, has 12 fully-oxidized Mo atoms. Compound 3 has a band gap ∼3.5 eV. The catalytic nature of compound 3 in the oxidation of styrene to benzaldehyde was investigated. The maximum styrene conversion was 83%, while the maximum selectivity to benzaldehyde was 96.5%. The catalyst was successfully used for five cycles without significant loss in activity or selectivity. The structure of the catalyst remains unchanged after repeated use. Our work points to the feasibility of generating a wide variety of new and useful POM-based compounds through a ‘green’ synthesis route.

Efficient Tertiary Amine/Weak Acid Bifunctional Mesoporous Silica Catalysts for Michael Addition Reactions

Abstract: SBA-15-NMe2-IPA, the silanol groups of which were not passivated by trimethysilyl (SiMe3) groups. Compared with ExtSBA-15-NMe2-Tol, the Ext-SBA-15-NMe2-IPA material (whose the amine groups were grafted in polar-protic solvents), in particular, demonstrated an effective cooperative bifunctional catalysis because of its optimized proportions of tertiary amine groups and a significant number of surface silanol groups that were judiciously left behind on the material with this optimized synthetic strategy. The catalytic activity of this material was found to be significantly higher than that of the corresponding material that was grafted in toluene and that contained less optimized proportions of these two catalytic groups (i.e., amine and silanol groups). The bifunctional catalysts also showed good recyclability upon washing with acetone, which offered an effective way of regenerating the catalyst free from any undesired product/substrate bound on the surface of the catalysts.

Introduction to Nanocatalysis

Abstract: Catalysis provides sustainable and cost-effective methods to transform raw materials into valuable chemicals. Thus, catalytic processes have long become essential to solving the energy and environmental challenges that we currently face around the globe. Catalysis can be broadly divided into homogeneous and heterogeneous catalysis. Homogeneous catalysis involves catalysts and reactants in the same phase.1 As homogeneous catalysts are generally soluble molecular or ionic compounds, they have more easily accessible active catalytic sites, and thus often exhibit good catalytic activity. Moreover, their structures and functional groups can easily be changed to result in chemo-, regio-, and enantioselectivity. However, despite their many advantages and being widely used in industry, homogeneous catalysts do have some disadvantages, which is mainly to do with the fact that they are difficult to separate from the final products or reaction mixtures. Furthermore, even with the use of numerous techniques, such as chromatography, distillation, or extraction, the removal of trace amounts of residual catalytic species from the reaction mixture is always challenging in the case of homogeneous catalysis. This is an important issue that requires attention, given the fact that the presence of trace amounts of catalytic moieties, especially metallic ones, is strictly regulated in the commodity chemicals and pharmaceutical products, which are often produced using catalysts. All of these issues together, therefore, pose major hurdles for homogeneous catalysts, making many of them to have only limited applications.

Biocompatibility of calcined mesoporous silica particles with ventricular myocyte structure and function

Abstract: In vivo and in vitro systems were employed to investigate the biocompatibility of two forms of calcined mesoporous silica microparticles, MCM41-cal and SBA15-cal, with ventricular myocytes. These particles have potential clinical use in delivering bioactive compounds to the heart. Ventricular myocytes were isolated from 6 to 8 week male Wistar rats. The distribution of the particles in ventricular myocytes was investigated by transmission electron microscopy and scanning electron microscopy. The distribution of particles was also examined in cardiac muscle 10 min after intravenous injection of 2.0 mg/mL MCM41-cal. Myocyte shortening and the Ca(2+) transient were determined following exposure to 200 μg/mL MCM41-cal or SBA15-cal for 10 min. Within 10 min of incubation at 25 °C, both MCM41-cal and SBA15-cal were found attached to the plasma membrane, and some particles were observed inside ventricular myocytes. MCM41-cal was more abundant inside the myocytes than SBA15-cal. The particles had a notable affinity to mitochondrial membranes, where they eventually settled. Within 10 min of intravenous injection (2.0 mg/mL), MCM41-cal traversed the perivascular space, and some particles entered ventricular myocytes and localized around the mitochondrial membranes. The amplitude of shortening was slightly reduced in myocytes superperfused with MCM41-cal or SBA15-cal. The amplitude of the Ca(2+) transient was significantly reduced in myocytes superperfused with MCM41-cal but was only slightly reduced with SBA15-cal. Overall, the results show reasonable bioavailability and biocompatibility of MCM41-cal and SBA15-cal with ventricular myocytes.

Lung toxicities of core-shell nanoparticles composed of carbon, cobalt, and silica.

Abstract: We present here comparative assessments of murine lung toxicity (biocompatibility) after in vitro and in vivo exposures to carbon (C-SiO2-etched), carbon-silica (C-SiO2), carbon-cobalt-silica (C-Co-SiO2), and carbon-cobalt oxide-silica (C-Co3O4-SiO2) nanoparticles. These nanoparticles have potential applications in clinical medicine and bioimaging, and thus their possible adverse events require thorough investigation. The primary aim of this work was to explore whether the nanoparticles are biocompatible with pneumatocyte bioenergetics (cellular respiration and adenosine triphosphate content). Other objectives included assessments of caspase activity, lung structure, and cellular organelles. Pneumatocyte bioenergetics of murine lung remained preserved after treatment with C-SiO2-etched or C-SiO2 nanoparticles. C-SiO2-etched nanoparticles, however, increased caspase activity and altered lung structure more than C-SiO2 did. Consistent with the known mitochondrial toxicity of cobalt, both C-Co-SiO2 and C-Co3O4-SiO2 impaired lung tissue bioenergetics. C-Co-SiO2, however, increased caspase activity and altered lung structure more than C-Co3O4-SiO2. The results indicate that silica shell is essential for biocompatibility. Furthermore, cobalt oxide is the preferred phase over the zerovalent Co(0) phase to impart biocompatibility to cobalt-based nanoparticles.

Nanocrafting Iron–Cobalt for Fischer–Tropsch Catalysis

Abstract: The world energy consumption continues to grow unabated, and fossil fuels, especially petroleum, remain the prominent source of the energy supply. Massive worldwide efforts are needed to find low-CO2-emitting and sustainable-energy technologies based on alternative feedstocks, such as natural gas and biomass. This issue can be addressed by developing improved or better catalysts or catalytic processes that might allow efficient conversion of natural gas and biomass feedstock into portable energy sources. Recently, this has, once again, revived interest in the Fischer–Tropsch synthesis (FTS)—catalytic technology that has long been successfully used for the production of ultraclean liquid fuels from coal and natural gas through so-called coal-to-liquid (CTL) and gas-to-liquid (GTS) processes. The renewed interest in FTS stems also from the fact that it has already been well utilized by countries such as South Africa, Qatar, and China. The burgeoning worldwide interest in FTS comes also at a time when 1) more countries want to exploit their recently discovered large reserve of natural gas, methane hydrate, or shale gas that has been proven to be extractable through a new, so-called “hydraulic fracturing” process, and 2) the need for the utilization of sustainable feedstocks such as biomass as our energy sources is gaining momentum. Yet, despite its appeal, the FTS has drawbacks: At the heart of the problem lies inherent complications associated with the ironand cobalt-based materials that are commonly used as catalysts for it. Although both iron and cobalt can catalyze FTS effectively, they are more active towards different types of feedstocks, and they lead to different products. Thus, choosing an FTS catalyst depends on what the desired product is (i.e. , fuel or chemical product), besides the cost of the catalyst. For instance, cobalt is the preferred catalyst for natural gas derived feedstock containing 1:2 CO/H2 syngas, whereas iron is chosen for biomass-derived CO-rich syngas. In comparison to iron, cobalt gives higher conversion and higher selectivity to paraffins and middle distillates. It is also more active and more stable in slurry bubble column reactors. Hence, cobalt is deemed a more suitable catalyst for converting syngas into liquid fuels. Unfortunately, however, cobalt is more expensive and much less earth abundant than iron, and yet, it is needed in large scales in typical FTS reactors, often in hundreds of tons. This is exacerbated by the fact that many conventional synthetic methods used to prepare FTS catalysts give big cobalt particles, in which most of the cobalt atoms are not on the surface of the catalysts and are therefore unavailable for catalysis. This thus begs for new design and new synthetic approaches to state-of-the-art catalysts, which can leave most of the cobalt atoms on the surface of the catalysts, that is, nanostructured catalysts. As most of the atoms in nanocatalysts reside on the surface of the materials, they can be exposed to reactants and thereby take part in catalysis. Hence, one of the goals in the development of efficient nanocatalysts is finding ways to maximize the number of atoms available to catalyze the reaction without compromising other attributes. This, however, is easier said than done, because it often compromises the catalytic activities and selectivity of the materials; for example, FTS nanocatalysts cannot produce diesel fractions at high conversion unless the size of the nanocatalysts is within the 5–10 nm range. Thus, the preparation of nanostructured FTS catalysts that perform as efficiently as pure cobalt but that use the maximum possible number of cobalt atoms, if not all, within the material in the catalytic reaction in a cost-effective and scalable manner for large-scale production is tricky. Rothenberg and co-authors recently took this issue front and center and successfully developed a new rational design and synthetic approach to a cobaltand iron-based core–shell nanocatalyst that consists of a minimum number of cobalt atoms but that still catalyzes FTS efficiently. Because both activity and selectivity in FTS depend on the topology of the active phase in the catalyst, the authors meticulously designed the nanomaterial in such a way that only an optimum amount of the more expensive and active phase (i.e. , cobalt) resides on the very outer shell of the material, whereas the cheaper material (i.e. , iron) fills in the rest of it. They showed that the resulting material was not only an effective catalyst for FTS but also the most cost effective overall. The authors’ accomplishment can be appreciated by first noting their simulation result or graph on the relationship between the price/performance of various hypothetical core/ cobalt core–shell-type catalysts (Figure 1). The price of a core– shell nanocatalyst is a function of many parameters such as precursor type, stoichiometry, density, and ratio of core to shell. Simulating this, the authors showed that a significant portion (50 %) of savings on the cost of the catalyst could easily be achieved by making the core from an inexpensive material such as Fe, Ti, or Si oxide and the shell from the active materials with an optimum size (only 10–20 % of the radius of the particle). With this in mind and by using Figure 1 as a “master guide”, they systematically approached the issue and [a] Prof. Dr. T. Asefa Department of Chemistry and Chemical Biology Department of Chemical and Biochemical Engineering Rutgers, The State University of New Jersey 610 Taylor Road, Piscataway, NJ 08854 (USA) Fax: (+ 1) 732-445-5312 E-mail : tasefa@rci.rutgers.edu Homepage: http ://chem.rutgers.edu/asefa_teddy