Towards the sustainable use of Europe’s forests: a centre for European forest science! – Some missing catalytic elements?

The Symposium, “Towards the sustainable use of Europe’s forests”, with sub-title “Forest ecosystem and landscape research: scientific challenges and opportunities” lists three fundamental substantive areas of research that are involved: Forest management and practices, Ecosystem processes and functional ecology, and Environmental economics and sociology. This paper argues that there are essential catalytic elements missing! Without these elements there is great danger that the aimed-for world leadership in the forest sciences will not materialize. What are the missing elements? All the sciences, and in particular biology, environmental sciences, sociology, economics, and forestry have evolved so that they include good scientific methodology. Good methodology is imperative in both the design and analysis of research studies, the management of research data, and in the interpretation of research finding. The methodological disciplines of Statistics, Modelling and Informatics (“SMI”) are crucial elements in a proposed Centre of European Forest Science, and the full involvement of professionals in these methodological disciplines is needed if the research of the Centre is to be world-class. Distributed Virtual Institute (DVI) for Statistics, Modelling and Informatics in Forestry and the Environment (SMIFE) is a consortium with the aim of providing world-class methodological support and collaboration to European research in the areas of Forestry and the Environment. It is suggested that DVI: SMIFE should be a formal partner in the proposed Centre for European Forest Science.

General rules for predicting where a catalytic reaction should occur on metal surfaces: A density functional theory study of C-H and C-O bond breaking/making on flat, stepped, and kinked metal surfaces

To predict where a catalytic reaction should occur is a fundamental issue scientifically. Technologically, it is also important because it can facilitate the catalyst's design. However, to date, the understanding of this issue is rather limited. In this work, two types of reactions, CH4 CH3 + H and CO C + 0 on two transition metal surfaces, were chosen as model systems aiming to address in general where a catalytic reaction should occur. The dissociations of CH4 - CH3 + H and CO --> C + O and their reverse reactions on flat, stepped, and kinked Rh and Pd surfaces were studied in detail. We find the following: First, for the CH4 Ch(3) + H reaction, the dissociation barrier is reduced by similar to0.3 eV on steps and kinks as compared to that on flat surfaces. On the other hand, there is essentially no difference in barrier for the association reaction of CH3 + H on the flat surfaces and the defects. Second, for the CO C + 0 reaction, the dissociation barrier decreases dramatically (more than 0.8 eV on Rh and Pd) on steps and kinks as compared to that on flat surfaces. In contrast to the CH3 + H reaction, the C + 0 association reaction also preferentially occurs on steps and kinks. We also present a detailed analysis of the reaction barriers in which each barrier is decomposed quantitatively into a local electronic effect and a geometrical effect. Our DFT calculations show that surface defects such as steps and kinks can largely facilitate bond breaking, while whether the surface defects could promote bond formation depends on the individual reaction as well as the particular metal. The physical origin of these trends is identified and discussed. On the basis of our results, we arrive at some simple rules with respect to where a reaction should occur: (i) defects such as steps are always favored for dissociation reactions as compared to flat surfaces; and (ii) the reaction site of the association reactions is largely related to the magnitude of the bonding competition effect, which is determined by the reactant and metal valency. Reactions with high valency reactants are more likely to occur on defects (more structure-sensitive), as compared to reactions with low valency reactants. Moreover, the reactions on late transition metals are more likely to proceed on defects than those on the early transition metals.

Catalytic Water Formation on Platinum: A First-Principles Study

The study of catalytic behavior begins with one seemingly simple process, namely the hydrogenation of O to H2O on platinum. Despite the apparent simplicity its mechanism has been much debated. We have used density functional theory with,gradient corrections to examine microscopic reaction pathways for several elementary steps implicated in this fundamental catalytic process. We find that H2O formation from chemisorbed O and H atoms is a highly activated process. The largest barrier along this route, with a value of similar to1 eV, is the addition of the first H to O to produce OH. Once formed, however, OH groups are easily hydrogenated to H2O with a barrier of similar to0.2 eV. Disproportionation reactions with 1:1 and 2:1 stoichiometries of H2O and O have been examined as alternative routes for OH formation. Both stoichiometries of reaction produce OH groups with barriers that are much lower than that associated with the O + H reaction. H2O, therefore, acts as an autocatalyst in the overall H O formation process. Disproportionation with a 2:1 stoichiometry is thermodynamically and kinetically favored over disproportionation with a l:I stoichiometry. This highlights an additional (promotional) role of the second H2O molecule in this process. In support of our previous suggestion that the key intermediate in the low-temperature H2O formation reaction is a mixed OH and H2O overlayer we find that then is a very large barrier for the dissociation of the second H2O molecule in the 2:1 disproportionation process. We suggest that the proposed intermediate is then hydrogenated to H2O through a very facile proton transfer mechanism.

Catalytic Role of Metal Oxides in Gold-Based Catalysts: A First Principles Study of CO Oxidation on TiO2 Supported Au

CO oxidation on TiO2 supported Au has been studied using density functional theory calculations. Important catalytic roles of the oxide have been identified: (i) CO oxidation occurs at the interface between Au and the oxide with a very small barrier; and (ii) O-2 adsorption at the interface is the key step in the reaction. The physical origin of the oxide promotion effect has been further investigated: The oxide enhances electron transfer from the Au to the antibonding states of O-2, giving rise to (i) strong ionic bonding between the adsorbed O-2, Au, and the Ti cation; and (ii) a significant activation of O-2 towards CO oxidation.

In vitro study of the efficacy of acrylic bone cement loaded with supplementary amounts of gentamicin: Effect on mechanical properties, antibiotic release, and biofilm formation

Background: Infection remains a severe complication following a total hip replacement. If infection is suspected when revision surgery is being performed, additional gentamicin is often added to the cement on an ad hoc basis in an attempt to reduce the risk of recurrent infection.

Methods and results: In this in vitro study, we determined the effect of incorporating additional gentamicin on the mechanical properties of cement. We also determined the degree of gentamicin release from cement, and also the extent to which biofilms of clinical Staphylococcus spp. isolates form on cement in vitro. When gentamicin was added to unloaded cement (1–4 g), there was a significant reduction in the mechanical performance of the loaded cements compared to unloaded cement. A significant increase in gentamicin release from the cement over 72 h was apparent, with the amount of gentamicin released increasing significantly with each additional 1 g of gentamicin added. When overt infection was modeled, the incorporation of additional gentamicin did result in an initial reduction in bacterial colonization, but this beneficial effect was no longer apparent by 72 h, with the clinical strains forming biofilms on the cements despite the release of high levels of gentamicin.

Interpretation: Our findings indicate that the addition of large amounts of gentamicin to cement is unlikely to eradicate bacteria present as a result of an overt infection of an existing implant, and could result in failure of the prosthetic joint because of a reduction in mechanical performance of the bone cement.

A review of the effect of the addition of hydrogen in the selective catalytic reduction of NOx with hydrocarbons on silver catalysts

Research is progressing fast in the field of the hydrogen assisted hydrocarbon selective catalytic reduction (HC-SCR) over Ag-based catalysts: this paper is a review of the work to date in this area. The addition of hydrogen to the HC-SCR reaction feed over Ag/Al2O3 results in a remarkable improvement in NO (x) conversion using a variety of different hydrocarbon feeds. There is some debate concerning the role that hydrogen has to play in the reaction mechanism and its effect on the form of Ag present during the reaction. Many of the studies use in situ UV-Vis spectroscopy to monitor the form of Ag in the catalyst and appear to indicate that the addition of hydrogen promotes the formation of small Ag clusters which are highly reactive for NO (x) conversion. However, some authors have expressed concern about the use of this technique for these materials and further work is required to address these issues before this technique can be used to give an accurate assessment of the state of Ag during the SCR reaction. A study using in situ EXAFS to probe the H-2 assisted octane-SCR reaction has shown that small Ag particles (containing on average 3 silver atoms) are formed during the SCR reaction but that the addition of H-2 to the feed does not result in any further change in the Ag particle size. This points to the direct involvement of H-2 in the reaction mechanism. Clearly the addition of hydrogen results in a large increase in the number and variety of adsorbed species on the surface of the catalyst during the reaction. Some authors have suggested that conversion of cyanide to isocyanate is the rate-determining step and that hydrogen promotes this conversion. Others have suggested that hydrogen reduces nitrates to more reactive nitrite species which can then activate the hydrocarbon; activation of the hydrocarbon to form acetates has been proposed as the key step. It is probable that all these promotional effects can take place and that it very much depends on the reaction temperature and feed conditions as to which one is most important.

Trends in C-O and C-N bond formations over transition metal surfaces: An insight into kinetic sensitivity in catalytic reactions

Transition metal catalyzed bond formation is a fundamental process in catalysis and is of general interest throughout chemistry. To date, however, the knowledge of association reactions is rather limited, relative to what is known about dissociative processes. For example, surprisingly little is known about how the bond-forming ability of a metal, in general, varies across the Periodic Table. In particular, the effect of reactant valency on such trends is poorly understood. Herein, the authors examine these key issues by using density functional theory calculations to study CO and CN formations over the 4d metals. The calculations reveal that the chemistries differ in a fundamental way. In the case of CO formation, the reaction enthalpies span a much greater range than those of CN formation. Moreover, CO formation is found to be kinetically sensitive to the metal; here the reaction barriers (E-a) are found to be influenced by the reaction enthalpy. CN formation, conversely, is found to be relatively kinetically insensitive to the metal, and there is no correlation found between the reaction barriers and the reaction enthalpy. Analysis has shown that at the final adsorbed state, the interaction between N and the surface is relatively greater than that of O. Furthermore, in comparison with O, relatively less bonding between the surface and N is observed to be lost during transition state formation. These greater interactions between N and the surface, which can be related to the larger valency of N, are found to be responsible for the relatively smaller enthalpy range and limited variation in E-a for CN formation. (C) 2007 American Institute of Physics.