/pdf/toward-greener-nanosynthesis-1hoe86e9k0.pdf

Toward Greener Nanosynthesis

This review considers cases in which a discrete transition-metal complex is used as a precatalyst for reductive catalysis; it focuses on the problem of determining if the true catalyst is a metal-complex homogeneous catalyst or if it is a soluble or other metal-particle heterogeneous catalyst. The various experiments that have been used to distinguish homogeneous and heterogeneous catalysis are outlined and critiqued. A more general method for making this distinction is then discussed. Next, the circumstances that make heterogeneous catalysis probable, and the telltale signs that a heterogeneous catalyst has formed, are outlined. Finally, catalytic systems requiring further study to determine if they are homogeneous or heterogeneous are listed. The major findings of this review are: (i) the in situ reduction of transition-metal complexes to form soluble-metal-particle heterogeneous catalysts is common; (ii) the formation of such a catalyst is easy to miss because colloidal solutions often appear homogeneous to the naked eye; (iii) a variety of experiments have been used to distinguish homogeneous catalysis from heterogeneous catalysis, but there is no single definitive experiment for making this distinction; (iv) experiments that provide kinetic information are key to the correct identification of the true catalyst; and (v) a more general approach for distinguishing homogeneous catalysis from heterogeneous catalysis has been developed. Additionally, (vi) the conditions under which a heterogeneous catalyst is likely to form include: (a) when easily reduced transition-metal complexes are used as precatalysts; (b) when forcing reaction conditions are employed; (c) when nanocluster stabilizers are present; and (d) when monocyclic arene hydrogenation is observed. Finally, (vii) the telltale signs of heterogeneous catalysis include the formation of dark reaction solutions, metallic precipitates, and the observation of induction periods and sigmoidal kinetics.

A review of the problem of distinguishing true homogeneous catalysis from soluble or other metal-particle heterogeneous catalysis under reducing conditions

Oils and fats of vegetable and animal origin have been the most important renewable feedstock of the chemical industry in the past and in the present. A tremendous geographical and feedstock shift of oleochemical production has taken place from North America and Europe to southeast Asia and from tallow to palm oil. It will be important to introduce and to cultivate more and new oil plants containing fatty acids with interesting and desired properties for chemical utilization while simultaneously increasing the agricultural biodiversity. The problem of the industrial utilization of food plant oils has become more urgent with the development of the global biodiesel production. The remarkable advances made during the last decade in organic synthesis, catalysis, and biotechnology using plant oils and the basic oleochemicals derived from them will be reported, including, for example, ω-functionalization of fatty acids containing internal double bonds, application of the olefin metathesis reaction, and de novo synthesis of fatty acids from abundantly available renewable carbon sources.

Oils and Fats as Renewable Raw Materials in Chemistry

A sol-gel chemistry approach was used to fabricate nanoparticles of TiO(2) in its anatase form. The particle size is shown to be sensitive to the use of HClO(4) or HNO(3) as acid catalyst. The gold-capped TiO(2) nanocomposites were processed by the reduction of gold on the surface of the TiO(2) nanoparticles via a chemical reduction or a photoreduction method. Different percentages of vanadium-doped TiO(2) nanoparticles, which extended the TiO(2) absorption wavelength from the ultraviolet to the visible region, were successfully prepared. The synthesized nanocomposites have a size of about 12-18 nm and an anatase phase as characterized by XRD, TEM, AFM, and UV-vis spectroscopy. The TiO(2) nanocomposite coatings have been applied on glass slide substrates. The antibacterial activity of TiO(2) nanocomposites was investigated qualitatively and quantitatively. Two types of bacteria, Escherichia coli (DH 5alpha) and Bacillus megaterium (QM B1551), were used during the experiments. Good inhibition results were observed and demonstrated visually. The quantitative examination of bacterial activity for E. coli was estimated by the survival ratio as calculated from the number of viable cells, which form colonies on the nutrient agar plates. The antimicrobial efficiency and inhibition mechanisms are illustrated and discussed.

Anatase TiO2 Nanocomposites for Antimicrobial Coatings

Process gas discharged from a bypass pipe to a gas exhaust system can be prevented from diffusing back to the inside of a process chamber without having to install a dedicated vacuum pump at the downstream side of the bypass pipe. The substrate processing apparatus includes a process chamber accommodating a substrate, a gas supply system supplying process gas from a process gas source to the process chamber for processing the substrate, a gas exhaust system configured to exhaust the process chamber, two or more vacuum pumps installed in series at the gas exhaust system, and a bypass pipe connected between the gas supply system and the gas exhaust system. The most upstream one of the vacuum pumps is a mechanical booster pump, and the bypass pipe is connected between the mechanical booster pump and the rest vacuum pumps located at a downstream side of the mechanical booster pump.

Substrate Processing Apparatus

The liquid-phase deoxygenation of stearic, oleic, and linoleic acids employing a 5 wt% Pd/C catalyst was investigated using on-line quadrupole mass spectrometry (QMS). Catalytic deoxygenation of stearic acid (SA) under He occurs primarily via decarboxylation; the liquid products are n-heptadecane and heptadecenes. On-line QMS revealed concomitant CO2 and H2 evolution which can explain the greater than expected heptadecene yields at low to intermediate conversions. After essentially complete SA conversion, hydrogenation of heptadecenes via hydrogen transfer from the dodecane solvent results in 98% n-heptadecane yield. The initial rate of SA decarboxylation under 10% H2 is lower than under He; however, by avoiding the formation of unsaturated products the reaction requires much less time to reach completion. The SA decarboxylation rate under 10% H2 is 6-fold slower in heptadecane than in dodecane. This apparent solvent effect is explained by the lower vapor pressure of heptadecane resulting in greater H2 inhibition of the decarboxylation reaction. Our results demonstrate that the unsaturated C18 free fatty acids, oleic and linoleic, must be hydrogenated to SA before decarboxylation can proceed at a significant rate. Oleic acid (OA) deoxygenation under He occurs very slowly and primarily via decarbonylation. In contrast, OA deoxygenation under 10% H2 occurs facilely via hydrogenation to SA followed by decarboxylation. Since hydrogenation is complete during heating to reaction temperature, the decarboxylation kinetics and product yields are not affected by the initial unsaturation of the reactant.

Catalytic reaction pathways in liquid-phase deoxygenation of C18 free fatty acids

The present invention is directed to processes for the direct conversion of lipidic biomass fuelstock to combustible fuels. In particular, the invention provides a process for the direct conversion of animal fats to transportations fuels suitable as replacement for petroleum-derived transportation fuels. In one embodiment, the method comprises the steps of hydrolyzing a lipidic biomass to form free fatty acids, catalytically deoxygenating the free fatty acids to form n-alkanes, and reforming at least a portion of the n-alkanes into a mixture of compounds in the correct chain length, conformations, and ratio to be useful transportation fuels. Particularly, the product prepared according to the invention comprises mixtures of hydrocarbon compounds selected from the group consisting of n-alkanes, isoalkanes, aromatics, cycloalkanes, and combinations thereof.

Process for conversion of biomass to fuel

Metal carbonyls react on metal oxide surfaces to give a wide range of structures analogous to those of known compounds. The reactions leading to formation of surface-bound metal carbonyls are explained by known molecular organometallic chemistry and the functional group chemistry of the surfaces. The reaction classes include formation of acid-base adducts as the oxygen of a carbonyl group donates an electron pair to a Lewis acidic center; nucleophilic attack at CO ligands by basic surface hydroxyl groups or O2⊖ ions; ion-pair formation by deprotonation of hydrido carbonyls to give carbonylate ions; interaction of bifunctional complexes with surface acid-base pair sites such as [Mg2⊕O2⊖]; and oxidative addition of surface hydroxyl groups to metal clusters. The reactions of surface-bound organometallic species include redox condensation and cluster formation on basic surfaces (paralleling the reactions in basic solution) as well as oxidation of mononuclear metal complexes and oxidative fragmentation of metal clusters by reaction with surface hydroxyl groups. Most supported metal carbonyls are unstable at high temperatures, but some, including osmium carbonyl cluster anions on the basic MgO surface, are strongly stabilized in the presence of CO and are precursors of catalysts for CO hydrogenation at 550 K.

Molecular Organometallic Chemistry on Surfaces: Reactivity of Metal Carbonyls on Metal Oxides

Low-temperature nitridation of SiO2 thin films by Ar/N2 remote plasma processing was investigated using on-line Auger electron spectroscopy, angle-resolved x-ray photoelectron spectroscopy (ARXPS), and optical emission spectroscopy (OES). Nitridation experiments were performed at 300 °C using 30 W Ar/N2 remote plasmas at 0.1 and 0.3 Torr. Ar/N2 remote plasma exposure of 5 nm SiO2 films for 30 min results in nitrogen incorporation throughout the films, independent of process pressure and plasma reactor configuration (i.e., upstream versus downstream N2 injection). ARXPS indicates a N–Si3 local bonding configuration with second nearest neighbor oxygen atoms. Ar/N2 remote plasma exposure at 0.1 Torr results in higher nitrogen concentrations (8–10 at. %). Reactor configuration has a negligible effect at 0.1 Torr; conversely, downstream N2 injection results in higher nitrogen concentrations (5–6 at. %) than upstream injection (3–4 at. %) at 0.3 Torr. OES indicates that the Ar/N2 remote plasmas contain N2 triplet excited states and ground-state N atoms. The Ar emission intensities and the saturation N concentrations in the resultant films follow similar trends with processing pressure and reactor configuration; the N2 first positive emission intensities run counter to these trends. We infer that low-temperature SiO2 nitridation by Ar/N2 remote plasmas is a two-step process: O removal by Ar+ ion bombardment and N insertion by plasma-generated active N species. Moreover, the first step appears to be rate limiting under the conditions employed in this study. Annealing the oxynitride films in N2 at 900 °C decreases the N concentration and results in a more uniform nitrogen distribution.

Low-temperature Ar/N2 remote plasma nitridation of SiO2 thin films

Fed-batch catalytic deoxygenation of C18 free fatty acids (FFAs) to n-heptadecane was demonstrated in a 50 mL stirred autoclave reactor with continuous FFA injection via a high-pressure syringe pump. High selectivity to the hydrogen-neutral decarboxylation pathway was achieved using a 5 wt % Pd/C catalyst at 300 °C under 5% H2 (15 atm total pressure); the maximum quasi-steady-state deoxygenation rate under these conditions was 0.46 mmol gcat−1 min−1 [0.083 s−1 turnover frequency (TOF)] with 95% CO2 selectivity. In a separate experiment, quasi-steady-state SA deoxygenation activity was maintained for >24 h at 0.29 mmol gcat−1 min−1 (0.053 s−1 TOF) with 92% CO2 selectivity. When higher H2 partial pressures were employed, an abrupt switchover in reaction pathway and product selectivity from decarboxylation (CO2) to decarbonylation (CO) was observed. Higher CO selectivity leads to increased H2 consumption because of hydrogenation of heptadecenes, the primary products of the decarbonylation pathway. We infer t...

H. Henry Lamb

Papers

Catalytic reaction pathways in liquid-phase deoxygenation of C18 free fatty acids

Process for conversion of biomass to fuel

Molecular Organometallic Chemistry on Surfaces: Reactivity of Metal Carbonyls on Metal Oxides

Low-temperature Ar/N2 remote plasma nitridation of SiO2 thin films

Fed-Batch Catalytic Deoxygenation of Free Fatty Acids