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In-operando surface-sensitive probing of electrochemical reactions on nanoparticle electrocatalysts: Spectroscopic characterization of reaction intermediates and elementary steps of oxygen reduction reaction on Pt
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Abstract Despite the advances in discovering new nuclei, modeling microscopic nuclear structure, nuclear reactors, and stellar nucleosynthesis, we still lack a systemic tool, such as a network approach, to understand the structure and dynamics of over 70 thousands reactions compiled in JINA REACLIB. To this end, we develop an analysis framework, under which it is simple to know which reactions generally are possible and which are not, by counting neutrons and protons incoming to and outgoing from any target nucleus. Specifically, we assemble here a nuclear reaction network in which a node represents a nuclide, and a link represents a direct reaction between nuclides. Interestingly, the degree distribution of nuclear network exhibits a bimodal distribution that significantly deviates from the common power-law distribution of scale-free networks and Poisson distribution of random networks. Based on the dynamics from the cross section parameterizations in REACLIB, we surprisingly find that the distribution is universal for reactions with a rate below the threshold, λ < e − T γ , where T is the temperature and γ ≈ 1.05. Moreover, we discover three rules that govern the structure pattern of nuclear reaction network: (i) reaction-type is determined by linking choices, (ii) network distances between the reacting nuclides on 2D grid of Z vs N of nuclides are short, and (iii) each node in- and out-degrees are close to each other. By incorporating these three rules, our model universally unveils the underlying nuclear reaction patterns hidden in a large and dense nuclear reaction network regardless of nuclide chart expansions. It enables us to predict missing links that represent possible new nuclear reactions not yet discovered.more » « less
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Role of surface phenomena in the reaction of molecular solids: the Diels–Alder reaction on pentaceneReactivity trends for molecular solids cannot be explained exclusively through the topochemical phenomenon ( i.e. diffusivity, reaction cavities) or electronic structure of the molecules. As an example of this class, Diels–Alder reactions of small molecules with pentacene thin films are examined to elucidate the importance of surface phenomena to reactivity. Polarization modulation-infrared reflection–absorption spectroscopy (PM-IRRAS) has revealed that vapors from the small molecules condense on the surface, in a non-covalent manner, to form a coating 2–3 molecules thick. The phase of this layer can provide increased surface diffusion (both reactant and product) which rapidly accelerates the reaction rate. Kinetic studies of pentacene thin film reactions demonstrate the importance of this condensed state to trends in reactivity, with layers in a quasi-liquid state showing a rate acceleration of 13–30 times compared to those in a quasi-solid state. Scanning electron microscopy provides further evidence of this phase behavior, while solid-state UV-vis confirms the kinetic results.more » « less
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The growing global plastic waste challenge requires development of new plastic waste management strategies, such as pyrolysis, that will help to enable a circular plastic economy. Developing optimized, scalable pyrolysis reactors capable of maximizing the yield of desired products requires a fundamental understanding of plastic pyrolysis chemistry. Accordingly, the intrinsic reaction kinetics of polypropylene pyrolysis have been evaluated by the method of pulse-heated analysis of solid reactions (PHASR), which enables time-resolved measurement of pyrolysis kinetics at high temperature absent heat and mass transfer limitations on the millisecond scale. Polypropylene pyrolysis product evolution curves were generated at 525°C–625°C, and the overall reaction kinetics were described by a lumped first-order model with an activation energy of 242.0 ± 2.9 kJ mol−1 and a pre-exponential factor of 35.5 ± 0.6 ln(s−1). Additionally, the production of solid residues formed during polypropylene pyrolysis was investigated, revealing a secondary kinetic regime.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.jcat.2021.02.009
