Theory of the Kinetics of Chemical Potentials in Heterogeneous Catalysis

Simple and powerful: The reaction kinetics at surfaces of heterogeneous catalysts is reformulated in terms of the involved chemical potentials. Based on this formulism, an approach of searching for good catalysts is proposed without recourse to extensive calculations of reaction barriers and detailed kinetic analyses. (see picture; R=reactant, I=surface intermediate, P=product, and =standard chemical potential).

Complex fiber bundle model for optimization of heterogeneous materials

We propose a complex fiber bundle model for the optimization of heterogeneous materials, which consists of many simple bundles. We also present an exact and compact recursion relation for the failure probability of a simple fiber bundle model with local load sharing, which is more efficient than the ones reported previously. Using a ''renormalization method'' and the recursion relation developed for the simple bundle, we calculate the failure probabilities of the complex fiber bundle. When the total number of fibers is given, we find that there exists an optimum way to organize the complex bundle, in which one gets a stronger bundle than in other ways.

Electrochemistry of Sulfur and Polysulfides in Ionic Liquids

The electrochemistry of elemental sulfur (S-8) and the polysulfides Na2S4 and Na2S6 has been studied for the first time in nonchloroaluminate ionic liquids. The cyclic voltammetry of S-8 in the ionic liquids is different to the behavior reported in some organic solvents, with two reductions and one oxidation peak observed. Supported by in situ UV-vis spectro-electrochemical experiments, the main reduction products of S-8 in [C(4)mim][DCA] ([C(4)mim] = 1-butyl-3-methylimidazolium; DCA = dicyanamide) have been identified as s(6)(2-) and S-4(2-), and plausible pathways for the formation of these species are proposed. Dissociation and/or disproportionation of the polyanions S-6(2-) and S-4(2-) appears to be slow in the ionic liquid, with only small amounts of the blue radical species S3(center dot-) formed in the solutions at r.t., in contrast with that observed in most molecular solvents.

Miniaturization of heterogeneous catalytic reactors: Prospects for new developments in catalysis and process engineering

This paper gives an overview of the research done since 1999 at Eindhoven University of Technology in the Netherlands in the field of miniaturization of heterogeneous catalytic reactors. It is described that different incentives exist for the development of these microstructured reaction systems. These include the need for efficient research instruments in catalyst development and screening, the need for small-scale reactor devices for hydrogen production for low-power electricity generation with fuel cells, and the recent quest for intensified processing equipment and novel process architectures (as in the fine chemicals sector). It is demonstrated that also in microreaction engineering, catalytic engineering and reactor design go hand-in-hand. This is illustrated by the design of an integrated microreactor and heat-exchanger for optimum performance of a highly exothermic catalytic reaction, viz. ammonia oxidation. It is argued that future developments in catalytic microreaction technology will depend on the availability of very active catalysts (and catalyst coating techniques) for which microreactors may become the natural housing.

Blue bottle light: lecture demonstrations of homogeneous and heterogeneous photo-induced electron transfer reactions

The classic, non-photochemical blue bottle experiment involves the reaction of methylene blue (MB) with deprotonated glucose, to form a bleached form of the dye, leuco-methylene blue (LMB), and subsequent colour recovery by shaking with air. This reaction is a popular demonstrator of key principles in kinetics and reaction mechanisms. Here it is modified so as to highlight features of homogenous and heterogeneous photoinduced electron transfer (PET) (Pure Appl. Chem., 2007, 79, 293-465) reactions, i.e. blue bottle light experiments. The homogeneous blue bottle light experiment uses methylene blue, MB, as the photo-sensitizer and triethanolamine as the sacrificial electron donor. Visible light irradiation of this system leads to its rapid bleaching, followed by the ready restoration of its original colour upon shaking away from the light source. The heterogeneous blue bottle light experiment uses titania as the photo-sensitizer, MB as a redox indicator and glucose as the sacrificial electron donor. UVA light irradiation of this system leads to the rapid bleaching of the MB and the gradual restoration of its original colour with shaking and standing. The latter 'dark' step can be made facile and more demonstrator-friendly by using platinised titania particles. These two photochemical versions of the blue bottle experiment are used to explore the factors which underpin homogeneous and heterogeneous PET reactions and provide useful demonstrations of homogeneous and heterogeneous photochemistry.

HETEROGENEOUS REDOX CATALYSIS - A NOVEL ROUTE FOR REMOVING BROMATE IONS FROM WATER

The oxidation of water to oxygen by bromate ions is mediated by the heterogeneous redox catalyst ruthenium-Adams, a high surface area and very stable form of ruthenium(IV) oxide. The initial kinetics of catalysis are investigated as a function of [BrO3-], [Ru-Adams], temperature and [anion], where ''anion'' = ClO4- Cl- or Br-. An electrochemical model of heterogeneous redox catalysis, in which the two participating redox couples are both electrochemically irreversible, is used to interpret most of the kinetic data. The observed inhibition of the initial rate of the redox reaction by Cl- and, especially, Br- ions is tentatively attributed to competitive adsorption. In the presence of organic species, such as methanol, ethanol and propan-1-ol, which are more easily oxidised than water by bromate ions, the rate of BrO3- ion reduction is significantly faster, i.e. ca 24-34 times.

OXIDATION OF RUTHENIUM(II) TRIS(2,2'-BIPYRIDINE) IONS BY THALLIC IONS IN NITRIC-ACID, MEDIATED BY RUTHENIUM DIOXIDE HYDRATE - AN EXAMPLE OF REVERSIBLE HETEROGENEOUS REDOX CATALYSIS

The kinetics of the oxidation of Ru(bpy)32+ to Ru(bpy)33+ by T13+ ions, catalyzed by a dispersion of RuO2-xH2O in 3 mol dm-3 HNO3, are reported as a function of [Ru(bpy)32+], [Tl3+], [Tl+], [RuO2.xH2O], and temperature. The kinetics of Ru(bpy)32+ oxidation fit an electrochemical model of redox catalysis involving electron transfer between the two electrochemically reversible redox couples, i.e. Ru(bpy)33+/Ru(bpy)32+ and Tl3+/Tl+, mediated by the dispersion of microelectrode particles of RuO2.xH2O. In this model, the rate of reaction is assumed to be controlled by the diffusion of Ru(bpy)32+ toward, and Ru(bpy)33+ away from, the catalyst particles. The Arrhenius activation energy for the catalyzed reaction is 25.9 +/- 0.7 kJ mol-1, and the changes in enthalpy and entropy for the reaction are 36 +/- 2 kJ mol-1 and 127 +/- 6 J mol-1 K-1, respectively. This work describes a rare example of reversible heterogeneous redox catalysis.

COMPARATIVE-STUDY OF NEW AND ESTABLISHED HETEROGENEOUS OXYGEN CATALYSTS

The kinetics of catalysis of a number of new and established heterogeneous O2 catalysts have been studied using Ce(IV) as the oxidant via both the disappearance of the Ce(IV) ions and concomitant appearance of O2. The most active of the catalysts tested utilised a PGM(IV) oxide, usually Ru or Ir, prepared by the Adams method, which appears to generate microcrystalline powders with high surface areas and optimum activities per unit area.

Targeting heterogeneous architectures via macro data flow

We propose a data flow based run time system as an efficient tool for supporting execution of parallel code on heterogeneous architectures hosting both multicore CPUs and GPUs. We discuss how the proposed run time system may be the target of both structured parallel applications developed using algorithmic skeletons/parallel design patterns and also more "domain specific" programming models. Experimental results demonstrating the feasibility of the approach are presented. © 2012 World Scientific Publishing Company.