Ryan M. Richards

Nanoscopic Metal Particles − Synthetic Methods and Potential Applications

Mono- and bimetallic colloidal particles have gained increasing attention in science and application throughout the last several years. In this contribution, we present a synopsis of the wet chemical syntheses of these materials and survey potential applications in catalysis and materials science. Methods for the characterization of these particles and their surfaces are not reviewed here.

Controlled selectivity for palladium catalysts using self-assembled monolayers

The selective reaction of one part of a bifunctional molecule is a fundamental challenge in heterogeneous catalysis and for many processes including the conversion of biomass-derived intermediates. Selective hydrogenation of unsaturated epoxides to saturated epoxides is particularly difficult given the reactivity of the strained epoxide ring, and traditional platinum group catalysts show low selectivities. We describe the preparation of highly selective Pd catalysts involving the deposition of n-alkanethiol self-assembled monolayer (SAM) coatings. These coatings improve the selectivity of 1-epoxybutane formation from 1-epoxy-3-butene on palladium catalysts from 11 to 94% at equivalent reaction conditions and conversions. Although sulphur species are generally considered to be indiscriminate catalyst poisons, the reaction rate to the desired product on a catalyst coated with a thiol was 40% of the rate on an uncoated catalyst. Interestingly the activity decreased for less-ordered SAMs with shorter chains. The behaviour of SAM-coated catalysts was compared with catalysts where surface sites were modified by carbon monoxide, hydrocarbons or sulphur atoms. The results suggest that the SAMs restrict sulphur coverage to enhance selectivity without significantly poisoning the activity of the desired reaction.

Sunflower and rapeseed oil transesterification to biodiesel over different nanocrystalline MgO catalysts

The catalytic activity for the production of biodiesel with three morphologically different nanocrystalline MgO materials prepared using simple, green and reproducible methods was investigated. The nanocrystalline samples studied were MgO(111) nanosheets (MgO (I)), conventionally prepared MgO (MgO (II)) and aerogel prepared MgO (MgO (III)). The methods to produce the catalysts included: (a) 4-methoxy-benzyl alcohol templated sol-gel process followed by supercritical drying and calcination in air at 773 K (MgO (I)), (b) from a commercial MgO that was boiled in water, followed by drying at 393 K, and dehydration under vacuum at 773 K (MgO (II)), and (c) viahydrolysis of Mg(OCH3)2 in a methanol–toluene mixture, followed by supercritical solvent removal with the formation of a Mg(OH)2 aerogel that was dehydrated under vacuum at 773 K (MgO (III)). These catalysts were characterized by TEM, DRIFT, and DR-UV-Vis and tested in the transesterification of sunflower and rapeseed vegetable oils at low temperatures, under different experimental conditions: autoclave, microwave and ultrasound. Working with these materials under microwave conditions provided higher conversions and selectivities to methylesters compared to autoclave or ultrasound conditions. Under ultrasound, a leaching of the magnesium has been evidenced as a direct consequence of a saponification reaction. These systems also allow working with much lower ratios of methanol to vegetable oil than reported in the literature for other heterogeneous systems. The activation temperature providing the most active catalysts was found to vary depending on the exposed facet: for MgO(111) structures (i.e.MgO (I)) this was 773 K, while for MgO (110) and (100) (i.e.MgO (II) and MgO (III)) this was 583 K.

Phase evolution for conversion reaction electrodes in lithium-ion batteries.

The performance of battery materials is largely governed by structural and chemical evolutions during electrochemical reactions. Therefore, resolving spatially dependent reaction pathways could enlighten mechanistic understanding, and enable rational design for rechargeable battery materials. Here, we present a phase evolution panorama via spectroscopic and three-dimensional imaging at multiple states of charge for an anode material (that is, nickel oxide nanosheets) in lithium-ion batteries. We reconstruct the three-dimensional lithiation/delithiation fronts and find that, in a fully electrolyte immersion environment, phase conversion can nucleate from spatially distant locations on the same slab of material. In addition, the architecture of a lithiated nickel oxide is a bent porous metallic framework. Furthermore, anode-electrolyte interphase is found to be dynamically evolving upon charging and discharging. The present study has implications for resolving the inhomogeneity of the general electrochemically driven phase transition (for example, intercalation reactions) and for the origin of inhomogeneous charge distribution in large-format battery electrodes.

NiO(111) nanosheets as efficient and recyclable adsorbents for dye pollutant removal from wastewater

Semiconductor single-crystalline polar NiO(111) nanosheets with well-defined hexagonal holes have been investigated for application in dye adsorption and combustion processes. With regard to adsorption technologies, high surface area metal oxides have an advantage over activated carbon in that the adsorbed species can be combusted and the adsorbent reused in the case of metal oxides while regeneration of activated carbon remains challenging and thus the adsorbent/adsorbate system must be disposed of. Here, three typical textile dyes, reactive brilliant red X-3B, congo red and fuchsin red, were studied for removal from wastewater with two NiO systems and activated carbon. These studies revealed that the NiO(111) nanosheets exhibited much more favorable adsorptive properties than conventionally prepared nickel oxide powder (CP-NiO) obtained from thermal decomposition of nickel nitrate. The maximum adsorption capabilities of the three dyes on NiO(111) nanosheets reached 30.4 mg g(-1), 35.15 mg g(-1) and 22 mg g(-1) for reactive brilliant red X-3B, congo red and fuchsin acid, respectively, while the maximum adsorption capabilities of the three dyes on CP-NiO were only 8.4, 13.2 and 12 mg g(-1) for reactive brilliant red X-3B, congo red and fuchsin acid. To simulate the adsorption isotherm, two commonly employed models, the Langmuir and the Freundlich isotherms, were selected to explicate the interaction of the dye and NiO(111). The isotherm evaluations revealed that the Langmuir model demonstrated better fit to experimental equilibrium data than the Freundlich model. The maximum predicted adsorption capacity was 36.1 mg g(-1). In addition, adsorption kinetic data of NiO(111) followed a pseudo-second-order rate for congo red. These studies infer that NiO(111) nanosheets possess desirable properties for application in adsorption and combustion applications.

Surface and nanomolecular catalysis

Characterization of Heterogeneous Catalysts Z. Ma and F. Zaera Catalysis by Metal Oxides K.T. Ranjit and K.J. Klabunde Colloidal Nanoparticles in Catalysis H. Bonnemann and K.S. Nagabhushana Microporous and Mesoporous Catalysts W. Schmidt Skeletal Catalysts A.J. Smith A Scientific Method to Prepare Supported Metal Catalysts J.R. Regalbuto Catalysis and Chemical Reaction Engineering S. Hocevar Structure and Reaction Control at Catalyst Surfaces M. Tada and Y. Iwasawa Texturology V. Fenelonov and M. Melgunov Understanding Catalytic Reaction Mechanisms: Surface Science Studies of Heterogeneous Catalysts W.T. Wallace and D.W. Goodman High-Throughput Experimentation and Combinatorial Approaches in Catalysis S.A. Schunk, O. Busch, D.G. Demuth, O. Gerlach, A. Haas, J. Klein, and T. Zech Heterogeneous Photocatalysis V.I. Parvulescu and V. Marcu Liquid-Phase Oxidations Catalyzed by Polyoxometalates N. Mizuno, K. Kamata, and K. Yamaguchi Asymmetric Catalysis by Heterogeneous Catalysts S.M. Coman, G. Poncelet, and V.I. Parvulescu

Hole doping in Al-containing nickel oxide materials to improve electrochromic performance.

Electrochromic materials exhibit switchable optical properties that can find applications in various fields, including smart windows, nonemissive displays, and semiconductors. High-performing nickel oxide electrochromic materials have been realized by controlling the material composition and tuning the nanostructural morphology. Post-treatment techniques could represent efficient and cost-effective approaches for performance enhancement. Herein, we report on a post-processing ozone technique that improves the electrochromic performance of an aluminum-containing nickel oxide material in lithium-ion electrolytes. The resulting materials were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, and X-ray absorption spectroscopy (XAS). It was observed that ozone exposure increased the Ni oxidation state by introducing hole states in the NiO(6) octahedral unit. In addition, ozone exposure gives rise to higher-performing aluminum-containing nickel oxide films, relative to nickel oxide containing both Al and Li, in terms of switching kinetics, bleached-state transparency, and optical modulation. The improved performance is attributed to the decreased crystallinity and increased nickel oxidation state in aluminum-containing nickel oxide electrochromic films. The present study provides an alternative route to improve electrochromic performance for nickel oxide materials.

Organo-Ruthenium Supported Heteropolytungstates: Synthesis, Structure, Electrochemistry, and Oxidation Catalysis

The reaction of [Ru(arene)Cl(2)](2) (arene = benzene, p-cymene) with [X(2)W(22)O(74)(OH)(2)](12-) (X = Sb(III), Bi(III)) in buffer medium resulted in four organo-ruthenium supported heteropolytungstates, [Sb(2)W(20)O(70)(RuC(6)H(6))(2)](10-) (1), [Bi(2)W(20)O(70)(RuC(6)H(6))(2)](10-) (2), [Sb(2)W(20)O(70)(RuC(10)H(14))(2)](10-) (3), and [Bi(2)W(20)O(70)(RuC(10)H(14))(2)](10-) (4), which have been characterized in solution by multinuclear ((183)W, (13)C, (1)H) NMR, UV-vis spectroscopy, electrochemistry, and in the solid state by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Polyanions 1, 2, and 4 crystallize in the triclinic system, space group P1 with the following unit cell parameters: K(5)Na(5)[Sb(2)W(20)O(70)(RuC(6)H(6))(2)] x 22 H(2)O (KNa-1), a = 12.1625(2) A, b = 13.1677(2) A, c = 16.0141(3) A, alpha = 78.9201(7) degrees, beta = 74.4442(8) degrees, gamma = 78.9019(8) degrees, and Z = 1; Cs(2)Na(8)[Bi(2)W(20)O(70)(RuC(6)H(6))(2)] x 30 H(2)O (CsNa-2), a = 11.6353(7) A, b = 13.3638(7) A, c = 16.7067(8) A, alpha = 79.568(2) degrees, beta = 71.103(2) degrees, gamma = 80.331(2) degrees, and Z = 1; Na(10)[Bi(2)W(20)O(70)(RuC(10)H(14))(2)].35H(2)O (Na-4), a = 15.7376(12) A, b = 15.9806(13) A, c = 24.2909(19) A, alpha = 92.109(4) degrees, beta = 101.354(4) degrees, gamma = 97.365(3) degrees, and Z = 2. Polyanions 1-4 consist of two (L)Ru(2+) (L = benzene or p-cymene) units linked to a [X(2)W(20)O(70)](14-) (X = Sb(III), Bi(III)) fragment via Ru-O(W) bonds resulting in an assembly with idealized C(2h) symmetry. Polyanions 1-4 are stable in solution as indicated by the expected (183)W, (13)C, and (1)H NMR spectra. The electrochemistry of 1-4 is described by considering the reduction and the oxidation processes. The nature of the arene in Ru(arene) has practically no influence on the formal potentials of the W-centers, which are more sensitive to the Sb or Bi hetero atoms. The results suggest that the respective Sb- and Bi derivatives have very different pK(a) values, with the reduced form of 1 being the most basic, thus permitting the observation of two well-developed voltammetric waves at pH 6. In contrast, the identity of the arene influences the oxidation processes, thus permitting to distinguish them. A strong electrocatalytic water oxidation peak is observed that is more positive than the one corresponding to the Ru(arene) oxidation process. Also a stepwise oxidation of the Ru(benzene) group could be observed at pH 3. The catalytic efficiency, on the other hand, of 1-4 toward the oxidation of n-hexadecane and p-xylene illustrated the effect of ruthenium substitution on the polyanion catalytic performance.

Heterogeneous Gold Catalysts for Efficient Access to Functionalized Lactones

A novel class of heterogeneous gold catalysts supported on zeolite beta-NH4+ was prepared by the deposition-precipitation method. This new class of catalyst showed interesting catalytic activities for the intramolecular cycloisomerization of gamma-acetylenic carboxylic acids leading to functionalized gamma-alkylidene gamma-butyrolactones. Analysis of the supported gold species with in situ X-ray photoelectron spectroscopy (in situ XPS) suggests that cationic Au (possibly AuIII) can play an important role in such reactions. The high discrepancy in catalyst stability in favor of the Au supported on the zeolite system over bulk Au2O3 is explained by 1) the size of the particles and 2) the reversibility of the redox deactivating process (AuIII-->AuI) in the presence of oxygen for the supported system. The efficiency of this system allowed reaction under mild heterogeneous conditions. The potential for catalyst recycling was also highlighted.

Real-time monitoring of the deactivation of HZSM-5 during upgrading of pine pyrolysis vapors.

The conversion of pine pyrolysis vapors over fixed beds of HZSM-5 catalyst was studied as a function of deactivation of the catalyst, presumably by coking. Small laboratory reactors were used in this study in which the products were identified using a molecular beam mass spectrometer (MBMS) and gas chromatography mass spectrometry (GCMS). In all of these experiments, real-time measurements of the products formed were conducted as the catalyst aged and deactivated during upgrading. The results from these experiments showed the following: (1) Fresh catalyst produces primarily aromatic hydrocarbons and olefins with no detectable oxygen-containing species. (2) After pyrolysis of roughly the same weight of biomass as weight of catalyst, oxygenated products begin to appear in the product stream. This suite of oxygen containing products appears different from the products formed when the catalyst is fresh and when the catalyst is completely deactivated. In particular, phenol and cresols are measured while upgrading pine, cellulose and lignin pyrolysis vapors, suggesting that these products are intermediates or side products formed during upgrading. (3) After the addition of more pyrolysis vapors, the product stream consists of primary vapors from pine pyrolysis. Catalyst samples collected at various points during deactivation were analyzed using a variety of tools. The results show that carbon build-up is correlated with catalyst deactivation, suggesting that deactivation is due to coking. Further, studies of nitrogen adsorption on the used catalyst suggest that coking initially occurs on the outside of the catalyst, leaving the micropores largely intact. From a practical point of view, it appears that based upon this study and others in the literature, the amount of oxygen in the upgraded products can be related to the level of deactivation of the HZSM-5 catalyst, which can be determined by how much pyrolysis vapor is run over the catalyst.