Directory scheelin Alexander Scheeline. More Department News Postdoctoral Research series features seven researchers. Organized by the Department of Chemistry's ACS Women Chemist Committee, this year's annual event will be virtual and feature a poster session, two seminar speakers and a reception for networking opportunities with all seven researchers.
Read full story. Jeff Moore wins campus award for distinguished leaders. Beckman Director Jeff Moore has been awarded the Campus Executive Officer Distinguished Leadership Award, which recognizes outstanding academic leadership and vision by an executive officer within a college or campus unit. Hee-Sun Han part of team developing rapid, point-of-care device for detecting sepsis. Pt3Sc and Pt3Y electrodes is enhanced relative to pure Pt by a factor of 1.
B , , — DOI: Norskov, J. A method to obtain the stability of reaction intermediates of electrochem. This method is used in combination with detailed d. O redn. This allowed identification of the origin of the overpotential of this reaction. Adsorbed O and hydroxyl are stable intermediates at potentials close to equil. From a database of calcd. O and hydroxyl adsorption energies, the trends in the O redn. O were also considered, and this peroxide mechanism dominates for most noble metals.
The model suggests ways to improve the electrocatalytic properties of fuel cell cathodes. The authors extend the activity volcano for O redn. Using d. Using this fact, the authors show the existence of a universal activity volcano to describe O redn. Specifically, the facet of Pt is found to bind O intermediates too strongly and is not active for O redn. In contrast, Au is predicted to be more active than Au and comparable in activity to Pt alloys. Using this activity volcano, the authors further predict that Au alloys that bind OH more strongly could display improved ORR activity on the facet.
The authors carry out a computational search over candidate alloys and suggest that alloying Au with early transition metals could lead to materials that exhibit enhanced ORR activity. The authors also prescribe a simple principle in the choice of nanoparticle catalysts in which the chosen catalyst should have its dense facet on the weak binding leg of the volcano so that its more open facets and defects could also be active.
Science , , — DOI: C , , — DOI: Elsevier B. Mass transport, which is a function of a particular system, may also limit the rate of peroxide formation. Halide ions Cl- or Br- and protons derived from H2SO4 in this study are essential for limiting the combustion reaction; i.
Bromide is particularly useful as the halide because it inhibits the loss of Pd from the support. The net formation rate for H2O2 was found to be first order with respect to H2 and zero order with respect to O2. The effects of changing the temp. These results further establish the complexity of this three-phase system that involves a network of reactions and the possibility that the catalyst undergoes change with time. An overall rate expression for the formation of hydrogen peroxide by direct combination DC of H2 and O2 is required for a rational design of a microreactor and for the detn.
Since the formation of H2O2 by the DC process involves four simultaneous reactions synthesis of H2O2, synthesis of water, decompn. In this work, we investigate the mechanism and the rate expression for redn. Kinetic expts. The reaction was shown to be free of mass transfer limitations at the conditions of the kinetic expts.
A Langmuir-Hinshelwood mechanism for the redn. A rate expression based on this mechanism was shown to accurately correlate exptl. Elsevier Ltd. Direct combination DC of hydrogen and oxygen over a heterogeneous catalyst in a microreactor is a novel method of producing hydrogen peroxide with significant economic advantages over the currently dominant anthraquinone autoxidn.
A kinetic rate expression for this reaction is required for design and modeling of a microreactor for the DC process. Since the formation of H2O2 by the DC process involves four simultaneous reactions synthesis of H2O2, synthesis of water, redn. In this work, we describe a reactor model that involves the four component reactions as well as mass transfer effects. The model is verified by comparing the predicted reactor performance with exptl.
In addn. Today , , 40 — 47 DOI: Hydrogen peroxide is an industrially important oxidant with a growing no. In this work, hydrogen peroxide was safely produced by direct combination of hydrogen and oxygen in a microreactor in the explosive regime. Optimum ranges of the temp.
A plan for obtaining the overall kinetics of direct H2O2 formation is described, which involves the detn. A mechanism for the H2O2 synthesis reaction is proposed on the basis of past research and kinetic data. A rate expression is derived based on the proposed mechanism, and kinetic data were used to calc.
This is the first step toward the detn. A review is given. Reducing O content in biomass-derived feedstocks via hydrodeoxygenation HDO is a key step in their upgrading to fuels and valuable chems. Although it is practiced far less frequently than mol. We present a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation.
On acid-base catalysts, Lewis acid-base pair sites, rather than a single acid or base site, mediate hydrogenation of carbonyl groups with alcs. While acid-base catalysts typically only catalyze the hydrogenation of carbonyl groups with alcs. Several model reactions involving platform chems. Because alcs. Therefore, solvent effects are discussed primarily in the context of sugar isomerization and reactions with formic acid as the H donor, in which the solvent and H donor are 2 sep.
Current challenges and opportunities of future research to develop CTH into a competitive and complementary strategy of the conventional mol. Elsevier Science B. Catalytic systems for the direct prodn. The use of low metal loadings, an org. London, Ser. A , , DOI: Today , , — DOI: Ham, Hyung Chul; Stephens, J. Adam; Hwang, Gyeong S. The calcns. In particular, on isolated Pd monomers surrounded by less active Au atoms, the activation barrier to form H2O2 is appreciably lowered due to the suppression of O-O bond cleavage.
In contrast, the reactivity to H2O on the Pd dimer is predicted to be enhanced compared with pure Pd. Using Monte Carlo simulations the authors also predict Pd ensemble populations in the AuPd surface layer as a function of temp. Due to the favorability of Au-Pd interactions over Pd-Pd, small ensembles, particularly monomers, preferentially exist.
This study highlights how theor. Functional Theory calcns. Three formation steps and their competing decompn. O2 dissocn. OOH dissocn. H2O2 dissocn. We have found that as we change the surface from Pd to Pt to Au, the step which governs the non-selective formation of water shifts from O2 dissocn.
Centomo, P. The direct synthesis of hydrogen peroxide is catalyzed by palladium catalysts supported over different solids.
With the aid of a suitable plug-flow reaction cell, we carried out a preliminary X-ray absorption fine structure spectroscopy EXAFS characterization of a palladium catalyst supported on the com. Whereas the catalyst, which in the dry catalyst presents metal Pd and PdO when fresh, is practically unaffected by the reaction medium methanol or by the reaction mixt.
These findings suggest the role of bromide ions as enhancers of the selectivity of palladium catalysts in the direct synthesis of hydrogen peroxide could not be limited to the selective blocking of the sites responsible for the undesired formation of water, but could also entail phase modifications of the active metal. An exptl. A simple theor.
This test may be used when heterogeneous catalysis is carried out in batch, continuous stirred tank, and tubular plug-flow reactors, and is best suited to be used with supported metal catalysts. Absence of phys. If the reaction is exothermic, the test should be repeated at another temp. Energy Environ. Stephens, Ifan E. Royal Society of Chemistry. A review.
The high cost of low temp. Arguably the most viable route to decrease the Pt loading, and to hence commercialize these devices, is to improve the ORR activity of Pt by alloying it with other metals. In this perspective paper we provide an overview of the fundamentals underlying the redn.
We employ angle resolved XPS and d. Nano Lett. The use of heterogeneous catalysts in liq. For porous silica-based oxides, one strategy to address these issues is to design or functionalize oxide surfaces with hydrophobic moieties or domains.
Hydrophobic moieties can be present either at external crystallite surfaces or within the internal porous voids where most active sites typically reside. Both extracryst. As a result, hydrophobic environments at both external and internal crystallite surfaces can have fundamentally different consequences for reactivity, in spite of the phenomenol.
The conceptual distinction between these two forms of hydrophobicity, together with accurate assessments of transport and kinetic contributions to measured reaction rates, can inform the placement of hydrophobic domains at appropriate locations in porous solids to cause predictable changes in reactivity.
This mini-review discusses these concepts within the context of recent studies that have used hydrophobic Bronsted and Lewis acidic microporous and mesoporous oxides in catalytic reactions of biomass-derived mols. Despite being considered a mature field, recent developments in exptl. One area of particular interest is the effect of co-adsorbed species on reactivity in heterogeneous systems. We begin by classifying adsorbate-adsorbate interactions that have been shown to alter the reactivity of a metal surface.
We then review numerous systems where such effects have been obsd. Systems such as the hydrogenation of olefins with other carbonaceous adsorbates present, the chiral templating of surfaces, and the co-adsorption of alkalis, halides, and other inorg.
Finally, future directions of study and outstanding questions are addressed. Direct synthesis of H2O2 from its elements was carried out in an acidic aq. Given that platinum is rare and extremely expensive, current research is aimed at the development of structural and functional models for oxygen activation and reduction to water via proton-coupled electron transfer. Similar strategies are also being exploited to drive the energetically uphill reverse reaction, in which hydrogen is produced from water using solar energy.
The success of both these areas of work may ultimately prove crucial to the development and sustainability of a global hydrogen economy. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.
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