Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Conversion of Biomass into Chemicals over Metal Catalysts

Unsaturated alcohols, widely used in the flavouring, perfume and pharmaceutical industries, are produced by selectively hydrogenating CO groups over CC groups present in suitable starting aldehyde molecules. Developing efficient catalysts for this transformation is challenging. Here Zhiyong Tang and colleagues describe a new type of highly selective catalyst in which platinum nanoparticles are sandwiched between a core and a shell of a metalorganic framework. This arrangement results in stable catalysts that selectively hydrogenate CO groups to produce a range of value-added unsaturated alcohols. The design strategy underpinning the work should be applicable to other selective catalysts for important yet challenging chemical reactions.

Metal–organic frameworks as selectivity regulators for hydrogenation reactions

Metal nanoparticles stabilized on a support material catalyse many major industrial reactions. Metal-support interactions in these nanomaterials can have a substantial influence on the catalysis, making metal-support interaction modulation one of the few tools able to enhance catalytic performance. This topic has received much attention in recent years, however, a systematic rationalization of the field is lacking due to the great diversity in catalysts, reactions and modification strategies. In this review, we cover and categorize the recent progress in metal-support interaction tuning strategies to enhance catalytic performance for various reactions. Furthermore, we quantify the productivity enhancements resulting from metal-support interaction control that have been achieved in C1 chemistry in recent years. Our analysis shows that up to fifteen-fold productivity enhancement has been achieved, and that metal-support interaction is most impactful for metal nanoparticles smaller than four nanometres. These findings demonstrate the importance of metal-support interaction to improve performance in catalysis. Methods to control the performance of heterogeneous catalysts are extremely relevant to the success of industrial processes. This review provides a rationalization of the effects that metal support interactions have on the reactivity of different catalytic systems, emphasizing strategies to tune such effects.

Control of metal-support interactions in heterogeneous catalysts to enhance activity and selectivity

Selective oxidation of alcohols and aldehydes over supported metal nanoparticles

The selective hydrogenation of unsaturated ketones (methyl vinyl ketone and benzalacetone) and unsaturated aldehydes (crotonaldehyde and cinnamaldehyde) was carried out with H2 at 2 bar absolute over Pd/C, Pt/C, Ru/C, Au/C, Au/TiO2, or Au/Fe2O3 catalysts in ethanol or water solvent at 333 K. Comparison of the turnover frequencies revealed Pd/C to be the most active hydrogenation catalyst, but the catalyst failed to produce unsaturated alcohols, indicating hydrogenation of the C═C bond was highly preferred over the C═O bond on Pd. The Pt and Ru catalysts were able to produce unsaturated alcohols from unsaturated aldehydes, but not from unsaturated ketones. Although Au/Fe2O3 was able to partially hydrogenate unsaturated ketones to unsaturated alcohols, the overall hydrogenation rate over gold was the lowest of all of the metals examined. First-principles density functional theory calculations were therefore used to explore the reactivity trends of methyl vinyl ketone (MVK) and benzalacetone (BA) hydrogenati...

Mechanistic insights on the hydrogenation of α,β-unsaturated ketones and aldehydes to unsaturated alcohols over metal catalysts

Although gold is generally considered to be a relatively inert metal, supported gold nanoparticles have demonstrated exceptionally high catalytic activity for the oxidation of carbon monoxide and alcohols at modest temperatures. In both cases, the presence of hydroxyl groups substantially promotes the reaction rate, presumably by participating in the reaction. Direct comparisons of CO oxidation to alcohol oxidation over gold catalysts have been difficult for scientists to explain. The former reaction is usually performed with gas phase reagents, whereas the latter reaction is often performed in the condensed phase. In this Account, we discuss the important role of hydroxyl for these two oxidation reactions catalyzed by gold, in terms of its influence on the turnover frequency. During CO oxidation over gold, a hydroxyl can directly react with CO to form COOH, which eventually decomposes to CO2. The gas phase CO oxidation reaction likely occurs at the gold-support interface, where adsorbed hydroxyl groups can be found after the addition of water to the feed. When we perform CO oxidation in liquid water, increasing the pH substantially promotes the reaction rate by providing an external source of hydroxyl. Likewise, we can also promote alcohol oxidations over gold catalysts in aqueous media by increasing the pH of the system. Since the hydroxyl groups are supplied through the reaction medium instead of on the support surface, the gold-support interface is much less important in the aqueous phase reactions. Even bulk gold powder becomes an active oxidation catalyst in alkaline water. The role of O2 in both CO and alcohol oxidation in aqueous media is to remove electrons from the gold surface that are deposited during oxidation, maintaining electroneutrality. Thus, the oxidation of CO and alcohols in water at high pH is analogous to the electrochemical oxidation reactions performed on gold electrodes. As the field of chemistry continues to encourage the development of sustainable chemical processes utilizing environmentally benign reaction conditions, the use of water as a "green" solvent becomes an attractive choice. In general, however, heterogeneous catalysts that scientists have developed over the last century for the petrochemical industry have not been optimized for use in aqueous media. Given the active role of water in oxidation reactions catalyzed by gold, additional research is needed to understand how water affects other catalytic transformations on traditional transition metal catalysts.

Matthew S. Ide

Papers

Selective oxidation of alcohols and aldehydes over supported metal nanoparticles

Mechanistic insights on the hydrogenation of α,β-unsaturated ketones and aldehydes to unsaturated alcohols over metal catalysts

The important role of hydroxyl on oxidation catalysis by gold nanoparticles.

On the deactivation of supported platinum catalysts for selective oxidation of alcohols

Perspectives on the kinetics of diol oxidation over supported platinum catalysts in aqueous solution