Stable Reaction Intermediates Research Articles

Deciphering the bridge oxygen vacancy-induced cascading charge effect for electrochemical ammonia synthesis.

Oxygen vacancy engineering has recently been gaining much interest as the charging effect it induces in a material can be used for varied applications. Usually, semiconductor materials act poorly in electrocatalysis, particularly in the nitrogen reduction reaction (NRR), owing to their inherent charge deficit and huge band gap. Vacancy introduction can be a viable material engineering route to make use of these materials for the NRR. However, a detailed investigation of the vacancy-type and its role for the structural reorientation and charge redistribution of a material is lagging in the field of NRRs. This work thus focuses on the synthesis of oxygen vacancy-engineered SnO2 with a gradual structural transformation from in-plane (iov) to bridge-type oxygen vacancy (bov) density. Consequently, the electron occupancy of the sp3d hybrid orbital changes, leading to an upshifted valence band maxima towards the Fermi level. This has a profound effect on the nature of N2 adsorption and the extent of NN bond polarization. Sn atoms adjacent to the bov are found to have a fair density of dangling charges that accomplish the NRR process at a comparatively low overpotential and determine the binding strength of the intermediates on the active site. The obscured yet stable reaction intermediates are thereby identified with in situ ATR-IR studies. A restricted hydrogen evolution reaction Faradaic on the Sn-site (favored over O-atoms) results in a Faradaic efficiency of 48.5%, which is better than that reported in all the literature reports on SnO2 for the NRR. This study thus unveils sufficient insights into the role of oxygen vacancies in a crystal as well as electronic structural alteration of SnO2 and the effect of active sites on the rate kinetics of the NRR.

Plasmon induced decarboxylation of aromatic carboxylic acids on bipolar electrodeposited Au- and Ag-film monitored by SERS

This study delves into the intersection of plasmonics and catalysis, offering insights into tailoring nanoscale chemical reactions. Employing Surface Enhanced Raman Spectroscopy (SERS), we track the decarboxylation process of 4-mercaptobenzoic acid (4-MBA) and its isomers. Using a specially designed thin film platform of gold and silver, prepared via bipolar electrodeposition (BP-ED), we investigate the influence of laser-power, solution pH, and exposure duration. Decarboxylation predominantly occurs in alkaline pH environments, attributed to deprotonation. Notably, 2-MBA exhibits swift decarboxylation, even without alkaline conditions, likely due to its closer proximity to the nanostructured surface. The significance of the carboxylate anion (–COO–) is underscored, as experiments with ester forms of 2- and 3-MBA exhibit similar behavior. Additionally, experiments with linear chain thiocarboxylic acids highlight the necessity of a benzene ring for stable reaction intermediates. A key finding lies in the effectiveness of the bipolar electrodeposition technique for monitoring decarboxylation reactions across various compositions on a unified platform. This research sheds light on the potential of SERS in understanding chemical reactions near metal nanostructures, ultimately advancing our grasp of reaction pathways and the identification of new reactive species.

Concerted versus stepwise proton transfer reactions in the [2, 2'-bipyridyl]-3-3'-diol molecule: A static and dynamic ab-initio investigation.

The double proton transfer (PT) reaction has been investigated in the [2,2'-bipyridyl]-3-3'-diol, a complex molecule where the proton movements is coupled to significant rearrangement of the electronic structure. Moreover, the reaction could be concerted, that is the two protons are exchanged simultaneously, or stepwise, where the two protons are transferred sequentially. To this end, a static exploration of the potential energy surface (PES) was carried together with the analysis of the free-energy surface (FES), both surfaces being evaluated at density functional theory level and different exchange-correlation functionals. While the concerted mechanism has been clearly discharged, the characteristics of the stepwise PT significantly depends on the chosen functionals, some suggesting a clear stepwise mechanism characterized by a stable reaction intermediates and two transitions states, whereas other approaches propend for a asynchronous PT, with a single TS. These features appear on both PES and FES, albeit some differences appears due to their different nature.

(Keynote) Insights into the CO2 Reduction Pathway through the Electrolysis of Aldehydes

Investigating the electrochemical reduction of aldehydes to alcohols provides insights into the mechanistic pathways of converting CO2 to alcohols electrochemically. Both acetaldehyde and propionaldehyde were electrochemically reduced on a polycrystalline Cu catalyst to illustrate that it is a viable pathway to ethanol and 1-propanol, respectively, supporting the mechanistic route previously proposed in the literature. 13C and 1H NMR analysis on isotopically labeled acetaldehyde was utilized to trace the reduction process. In an aqueous solution, acetaldehyde is at equilibrium with ethanediol, and propionaldehyde with propanediol. The dissociation of adsorbed ethanediol to acetaldehyde and water was also found to be favorable on both Cu and Au surfaces. Experimental observations were also supported with DFT calculations, indicating a higher-energy reaction intermediate on Au (111) over Cu (100). In summary, the results from this study support previously proposed mechanisms and provide a framework for testing other stable CO2 reaction intermediates to gain insights into the overall CO2 reaction pathway. Figure 1

Influence of Ionic Coordination on the Cathode Reaction Mechanisms of Al/S Batteries

The lack of knowledge on electrochemical reaction pathways for Al/S batteries prevents the development of practical approaches to mitigate the irreversibility and poor cycling performances of this appealing secondary battery system, which is, in theory, scalable, inexpensive, and energy-dense. Different from the Li/S system, Al/S batteries use ionic liquids (ILs) as electrolytes. The choice of the IL, i.e., whether the IL is based on a conventional EMImCl-based electrolyte or in a deep eutectic mixture of aluminum chloride with urea (or any of its derivatives), strongly affects the electrochemical energy-storage performance of the cell. To shed some light on the Al/S battery chemistry, here, we present the computational electrochemistry research work to determine the most favorable reaction pathways and thermodynamically stable reaction intermediates. We also discuss the effect of the coordination of ionic species (originated from aluminum-containing deep eutectic electrolytes) with polysulfide intermediates, which lead to alterations in the reaction pathway and electrochemical behavior of the Al/S system. The spectroscopic signatures from various reaction intermediates are also reported and validated via comparison with experimental observations.

Engineering the Cu/Mo2CTx (MXene) interface to drive CO2 hydrogenation to methanol

Development of efficient catalysts for the direct hydrogenation of CO2 to methanol is essential for the valorization of this abundant feedstock. Here we show that a silica-supported Cu/Mo2CTx (MXene) catalyst achieves a higher intrinsic methanol formation rate per mass Cu than the reference Cu/SiO2 catalyst with a similar Cu loading. The Cu/Mo2CTx interface can be engineered due to the higher affinity of Cu for the partially reduced MXene surface (in preference to the SiO2 surface) and the mobility of Cu under H2 at 500 °C. With increasing reduction time, the Cu/Mo2CTx interface becomes more Lewis acidic due to the higher amount of Cu+ sites dispersed onto the reduced Mo2CTx and this correlates with an increased rate of CO2 hydrogenation to methanol. The critical role of the interface between Cu and Mo2CTx is further highlighted by density functional theory calculations that identify formate and methoxy species as stable reaction intermediates.

Mechanistic Insights into Hydrogen Evolution by Photocatalytic Reforming of Naphthalene

Heterogeneous photocatalysis has been widely considered, among other applications, for environmental remediation and hydrogen production. While these applications have been traditionally seen as well-separated areas, recent examples have highlighted the possibility of coupling them. Here, we demonstrate the simultaneous production of H2 and naphthalene removal from aqueous solutions with (unoptimized) photonic efficiencies of 0.97 and 0.33%, respectively, over Pt–TiO2 under simulated sunlight. Photocatalytic and spin-trapping experiments in the presence of a hydroxyl radical and hole scavengers evinced that only the photogenerated holes play a significant role in the oxidation of naphthalene. Isotopic labeling analyses showed that the evolved H2 isotopologues match those of the solvent and that deuterated water (but not deuterated naphthalene) decreases the reaction rate, suggesting its involvement in the rate-determining step. Moreover, the use of Ti18O2 does not lead to the significant formation of 18O-enriched CO2, suggesting that water is the source of the oxygen atoms. Ultimately, by considering the stable and transient reaction intermediates, we propose a plausible reaction pathway. Our work illustrates that environmental remediation can be effectively coupled to solar fuel production, providing a double purpose to photocatalytic reactions, while the mechanistic insights will be of use for the further development of this strategy.

Jim Hyde and the ENDOR Connection: A Personal Account

In this minireview, we report on our year-long EPR work, such as electron–nuclear double resonance (ENDOR), pulse electron double resonance (PELDOR) and ELDOR-detected NMR (EDNMR) at X-band and W-band microwave frequencies and magnetic fields. This report is dedicated to James S. Hyde and honors his pioneering contributions to the measurement of spin interactions in large (bio)molecules. From these interactions, detailed information is revealed on structure and dynamics of macromolecules embedded in liquid-solution or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultra-fast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy and its multi-frequency extensions to new horizons concerning sensitivity of detection, selectivity of molecular interactions and time resolution. Among the most important advances is the upgrading of EPR to high magnetic fields, very much in analogy to what happened in NMR. The ongoing progress in EPR spectroscopy is exemplified by reviewing various multi-frequency electron–nuclear double-resonance experiments on organic radicals, light-generated donor–acceptor radical pairs in photosynthesis, and site-specifically nitroxide spin-labeled bacteriorhodopsin, the light-driven proton pump, as well as EDNMR and ENDOR on nitroxides. Signal and resolution enhancements are particularly spectacular for ENDOR, EDNMR and PELDOR on frozen-solution samples at high Zeeman fields. They provide orientation selection for disordered samples approaching single-crystal resolution at canonical g-tensor orientations—even for molecules with small g-anisotropies. Dramatic improvements of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Thus, unique structural and dynamic information is revealed that can hardly be obtained by other analytical techniques. Micromolar concentrations of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems—offering exciting applications for physicists, chemists, biochemists and molecular biologists.

Kinetics of Electrocatalytic Reactions from First-Principles: A Critical Comparison with the Ab Initio Thermodynamics Approach.

Multielectron processes in electrochemistry require the stabilization of reaction intermediates (RI) at the electrode surface after every elementary reaction step. Accordingly, the bond strengths of these intermediates are important for assessing the catalytic performance of an electrode material. Current understanding of microscopic processes in modern electrocatalysis research is largely driven by theory, mostly based on ab initio thermodynamics considerations, where stable reaction intermediates at the electrode surface are identified, while the actual free energy barriers (or activation barriers) are ignored. This simple approach is popular in electrochemistry in that the researcher has a simple tool at hand in successfully searching for promising electrode materials. The ab initio TD approach allows for a rough but fast screening of the parameter space with low computational cost. However, ab initio thermodynamics is also frequently employed (often, even based on a single binding energy only) to comprehend on the activity and on the mechanism of an electrochemical reaction. The basic idea is that the activation barrier of an endergonic reaction step consists of a thermodynamic part and an additional kinetically determined barrier. Assuming that the activation barrier scales with thermodynamics (so-called Brønsted-Polanyi-Evans (BEP) relation) and the kinetic part of the barrier is small, ab initio thermodynamics may provide molecular insights into the electrochemical reaction kinetics. However, for many electrocatalytic reactions, these tacit assumptions are violated so that ab initio thermodynamics will lead to contradictions with both experimental data and ab initio kinetics. In this Account, we will discuss several electrochemical key reactions, including chlorine evolution (CER), oxygen evolution reaction (OER), and oxygen reduction (ORR), where ab initio kinetics data are available in order to critically compare the results with those derived from a simple ab initio thermodynamics treatment. We show that ab initio thermodynamics leads to erroneous conclusions about kinetic and mechanistic aspects for the CER over RuO2(110), while the kinetics of the OER over RuO2(110) and ORR over Pt(111) are reasonably well described. Microkinetics of an electrocatalyzed reaction is largely simplified by the quasi-equilibria of the RI preceding the rate-determining step (rds) with the reactants. Therefore, in ab initio kinetics the rate of an electrocatalyzed reaction is governed by the transition state (TS) with the highest free energy Grds#, defining also the rate-determining step (rds). Ab initio thermodynamics may be even more powerful, when using the highest free energy of an reaction intermediate Gmax(RI) rather than the highest free energy difference between consecutive reaction intermediates, ΔGloss, as a descriptor for the kinetics.

Experimental and kinetic modeling study of 2-methyltetrahydrofuran oxidation under engine-relevant conditions

The oxidation of 2-methyltetrahydrofuran (2-MTHF) has been experimentally studied in a rapid compression machine. The ignition delays of stoichiometric 2-MTHF/O2/inert mixtures were measured for a wide range of conditions: Top dead center pressure ranging from 0.3 to 2.1 MPa and core gas temperatures between 640 K and 900 K. Two-stage ignition is observed for temperatures between 685 K and 790 K, leading to a deviation from Arrhenius behavior of the evolution of ignition delays with temperature. Sampling of the reacting mixture was performed for different times between the top dead center and the ignition. Stable reaction intermediates were separated by gas chromatography, identified by mass spectrometry and quantified with a flame ionization detector. More than 20 species were identified and used to identify major reaction pathways. Among species of importance, 2-methyl-dihydrofurans, 2-methylfuran, methyldihydrofuranones, 1-cyclopropanylethanone, 3-penten-2-one and methylvinylketone were detected. Mole fraction profiles were obtained and used alongside first stage and total ignition delays to validate a detailed kinetic model for the oxidation of 2-MTHF. The resulting model takes in account 507 species involved in 2425 reactions. The validity of this model was extended to the high temperature range using existing ignition delays and low pressure laminar flame speciation data.

Transition-metal-decorated germanene as promising catalyst for removing CO contamination in H2

Single-layer germanene was proposed as substrate for single-atom transition metal catalysts with much larger adsorption energies and higher thermal migration barriers than graphene. By density functional theory calculations, the electronic properties, thermal stabilities and catalytic abilities of Au, Fe, Ni, Pd, Pt and Ru adatoms on single-layer germanene were theoretically investigated. The results indicate that the CO contamination in H2 could be transformed into HCHO under the catalysis of Fe and Ru adatoms. For Fe and Ru adatoms, the three-step catalytic reactions were found both thermodynamically and kinetically favorable, with stable reaction intermediates and low potential barriers. Furthermore, Fe and Ru adatoms could be stably adsorbed on germanene with large adsorption energies and high thermal migration barriers, preventing the aggregation of Fe and Ru on germanene. However, for Au, Ni, Pd and Pt adatoms, the reaction intermediates are thermodynamically unfavorable so that the catalytic reactions should be difficult to proceed. By contrast, Fe and Ru adatoms on single-layer germanene should be excellent catalysts for removing the CO contamination from H2 feed gas of fuel cells.

Full Kinetics from First Principles of the Chlorine Evolution Reaction over a RuO2(110) Model Electrode

AbstractCurrent progress in modern electrocatalysis research is spurred by theory, frequently based on ab initio thermodynamics, where the stable reaction intermediates at the electrode surface are identified, while the actual energy barriers are ignored. This approach is popular in that a simple tool is available for searching for promising electrode materials. However, thermodynamics alone may be misleading to assess the catalytic activity of an electrochemical reaction as we exemplify with the chlorine evolution reaction (CER) over a RuO2(110) model electrode. The full procedure is introduced, starting from the stable reaction intermediates, computing the energy barriers, and finally performing microkinetic simulations, all performed under the influence of the solvent and the electrode potential. Full kinetics from first‐principles allows the rate‐determining step in the CER to be identified and the experimentally observed change in the Tafel slope to be explained.

Full Kinetics from First Principles of the Chlorine Evolution Reaction over a RuO2 (110) Model Electrode.

Current progress in modern electrocatalysis research is spurred by theory, frequently based on ab initio thermodynamics, where the stable reaction intermediates at the electrode surface are identified, while the actual energy barriers are ignored. This approach is popular in that a simple tool is available for searching for promising electrode materials. However, thermodynamics alone may be misleading to assess the catalytic activity of an electrochemical reaction as we exemplify with the chlorine evolution reaction (CER) over a RuO2 (110) model electrode. The full procedure is introduced, starting from the stable reaction intermediates, computing the energy barriers, and finally performing microkinetic simulations, all performed under the influence of the solvent and the electrode potential. Full kinetics from first-principles allows the rate-determining step in the CER to be identified and the experimentally observed change in the Tafel slope to be explained.

Recent advances in biosynthetic modeling of nitric oxide reductases and insights gained from nuclear resonance vibrational and other spectroscopic studies.

This Forum Article focuses on recent advances in structural and spectroscopic studies of biosynthetic models of nitric oxide reductases (NORs). NORs are complex metalloenzymes found in the denitrification pathway of Earth’s nitrogen cycle where they catalyze the proton-dependent two-electron reduction of nitric oxide (NO) to nitrous oxide (N2O). While much progress has been made in biochemical and biophysical studies of native NORs and their variants, a clear mechanistic understanding of this important metalloenzyme related to its function is still elusive. We report herein UV–vis and nuclear resonance vibrational spectroscopy (NRVS) studies of mononitrosylated intermediates of the NOR reaction of a biosynthetic model. The ability to selectively substitute metals at either heme or nonheme metal sites allows the introduction of independent 57Fe probe atoms at either site, as well as allowing the preparation of analogues of stable reaction intermediates by replacing either metal with a redox inactive metal. Together with previous structural and spectroscopic results, we summarize insights gained from studying these biosynthetic models toward understanding structural features responsible for the NOR activity and its mechanism. The outlook on NOR modeling is also discussed, with an emphasis on the design of models capable of catalytic turnovers designed based on close mimics of the secondary coordination sphere of native NORs.

A mechanistic investigation of anti-elimination in (Z)-1,2-bis(arylseleno)-1-alkenes and their sulfur analogs.

The oxidation of (Z)-1,2-bis(arylseleno)-1-alkenes is known to afford alkynyl selenoxides via a unique selenoxide anti-elimination mechanism; however, to date, there have been no mechanistic studies of this reaction. During our studies of this transformation, monoselenoxides 6 and 7 were unexpectedly isolated as stable reaction intermediates. In addition, (77)Se NMR studies of the reaction mixture revealed the presence of an intramolecular Se···O interaction and the formation of alkynyl selenoxides. Meanwhile, even at higher temperatures, the reaction of a (Z)-1,2-bis(arylsulfinyl)-1-alkene, the sulfur analog of (Z)-1,2-bis(arylseleninyl)-1-alkenes, did not proceed via sulfoxide elimination but proceeded via isomerization and disproportionation. Therefore, the intramolecular Se···O interaction can be concluded to play a pivotal role in the anti-elimination reaction.

Studies on the Key Aroma Compounds in Raw (Unheated) and Heated Japanese Soy Sauce

An investigation using the aroma extract dilution analysis (AEDA) technique of the aroma concentrate from a raw Japanese soy sauce and the heated soy sauce revealed 40 key aroma compounds including 7 newly identified compounds. Among them, 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone and 3-hydroxy-4,5-dimethyl-2(5H)-furanone exhibited the highest flavor dilution (FD) factor of 2048, followed by 3-(methylthio)propanal, 4-ethyl-2-methoxyphenol, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone having FD factors from 128 to 512 in the raw soy sauce. Furthermore, comparative AEDAs, a quantitative analysis, and a sensory analysis demonstrated that whereas most of the key aroma compounds in the raw soy sauce were common in the heated soy sauce, some of the Strecker aldehydes and 4-vinylphenols contributed less to the raw soy sauce aroma. The model decarboxylation reactions of the phenolic acids during heating of the raw soy sauce revealed that although all reactions resulted in low yields, the hydroxycinnamic acid derivatives were much more reactive than the hydroxybenzoic acid derivatives due to the stable reaction intermediates. Besides the quantitative analyses of the soy sauces, the estimation of the reaction yields of the phenolic compounds in the heated soy sauce revealed that although only the 4-vinylphenols increased during heating of the raw soy sauce, they might not mainly be formed as decarboxylation products from the corresponding hydroxycinnamic acids but from the other proposed precursors, such as lignin, shakuchirin, and esters with arabinoxylan.

Structure Sensitivity in Pt Nanoparticle Catalysts for Hydrogenation of 1,3-Butadiene:In SituStudy of Reaction Intermediates Using SFG Vibrational Spectroscopy

The product selectivity during 1,3-butadiene hydrogenation on monodisperse, colloidally synthesized, Pt nanoparticles was studied under reaction conditions with kinetic measurements and in situ sum frequency generation (SFG) vibrational spectroscopy. SFG was performed with the capping ligands intact in order to maintain nanoparticle size by reduced sintering. Four products are formed at 75 °C: 1-butene, cis-2-butene, trans-2-butene, and n-butane. Ensembles of Pt nanoparticles with average diameters of 0.9 and 1.8 nm exhibit a ∼30% and ∼20% increase in the full hydrogenation products, respectively, as compared to Pt nanoparticles with average diameters of 4.6 and 6.7 nm. Methyl and methylene vibrational stretches of reaction intermediates observed under working conditions using SFG were used to correlate the stable reaction intermediates with the product distribution. Kinetic and SFG results correlate with previous DFT predictions for two parallel reaction pathways of 1,3-butadiene hydrogenation. Hydrogenation of 1,3-butadiene can initiate with H-addition at internal or terminal carbons leading to the formation of 1-buten-4-yl radical (metallocycle) and 2-buten-1-yl radical intermediates, respectively. Small (0.9 and 1.8 nm) nanoparticles exhibited vibrational resonances originating from both intermediates, while the large (4.6 and 6.7 nm) particles exhibited vibrational resonances originating predominately from the 2-buten-1-yl radical. This suggests each reaction pathway competes for partial and full hydrogenation and the nanoparticle size affects the kinetic preference for the two pathways. The reaction pathway through the metallocycle intermediate on the small nanoparticles is likely due to the presence of low-coordinated sites.

Kinetics and mechanisms in flow systems: reduction of SO2 on carbons

Surface‐science studies of some reactions have allowed postulating the mechanisms using a variety of techniques. The surface chemistry of Group IV elements has been particularly studied recently because Si, Ge, and C are semiconductors, and the surface organic chemistry to functionalize these elements has seen immense progress in recent years. In this review article we describe the methodology used to study the mechanism of a solid–gas reaction, the reduction of SO2 on carbons, and the necessary conditions that allowed the measurement of the solid conversion and product distribution when the kinetics was chemically controlled and the reaction had reached the steady state. The reaction was first‐order with respect to SO2 and with respect to carbon and the stoichiometry was determined from the product distribution. The reaction proceeds through two thermally stable reaction intermediates bound to the surface, a six‐membered ring 1,3,2‐dioxathiolane and a five‐membered ring 1,2‐oxathietene 2‐oxide or γ‐sultine, both species being in equilibrium. The reaction was shown to be reversible. The primary product is an episulfide that, after a series of consecutive reactions of atomic sulfur, is able to free sulfur. The reactivity of the intermediates and the episulfide was studied for several reactions and consistent mechanisms were postulated from the X‐ray photoelectron spectroscopy and solid state nuclear magnetic resonance spectra. Aminolysis and the reaction with alkyl halides resulted on the insertion of the alkyl moiety in the episulfide primary product, while the thiolysis and photolytic alcoholysis resulted in the insertion of the alkyl moiety in the oxidized intermediates. Copyright © 2012 John Wiley & Sons, Ltd.

Experimental and Theoretical Analyses of Azulene Synthesis from Tropones and Active Methylene Compounds: Reaction of 2-Methoxytropone and Malononitrile

A representative azulene formation from an active troponoid precursor (2-methoxytropone) and an active methylene compound (malononitrile) has been analyzed both experimentally and theoretically. (2)H-Tracer experiments using 2-methoxy[3,5,7-(2)H(3)]tropone (2-d(3)) and malononitrile anion give 2-amino-1,3-dicyano[4,6,8-(2)H(3)]azulene (1-d(3)) in quantitative yield. New and stable (2)H-incorporated reaction intermediates have been isolated, and main intermediates have been detected by careful low-temperature NMR measurements. The detection has been guided by mechanistic considerations and B3LYP/6-31(+)G(d) calculations. The facile and quantitative one-pot formation of azulene 1 has been found to consist of a number of consecutive elementary processes: (a) The troponoid substrate, 2-methoxytropone (2), is subject to a nucleophilic substitution by the attack of malononitrile anion (HC(CN)(2)(-)) to form a Meisenheimer-type complex 3, which is rapidly converted to 2-troponylmalononitrile anion (5). (b) The anion 5 is converted to an isolable intermediate, 2-imino-2H-cyclohepta[b]furan-3-carbonitrile (6), by the first ring closure in the reaction. (c) A nucleophilic addition of the second HC(CN)(2)(-) toward the imine 6 at the C-8a position produces the second Meisenheimer-type adduct 7. (d) The second ring closure leads to 1-carbamoyl-1,3-dicyano-2-imino-2,3-dihydroazulene (11). A base attacks the imine 11, which results in generation of a conjugate base 12 of the final product, azulene 1.

Methanol decomposition on Ru(0001) during continuous exposure at room temperature

Using infrared vibrational spectroscopy, we have studied the chemical reactivity of methanol on Ru(0001) under experimental conditions closer to real catalysts than those existing in most of the literature. We have performed experiments in the pressure range from 10−8 to 10−3mbar, exposing the surface to large gas doses at room temperature. We show the co-existence of two active paths: one involves the complete dehydrogenation of methanol into CO, the other one promotes the scission of the CO bond of methanol, leaving carbon and oxygen on the surface, which, after large exposures, deactivate the surface towards a further evolution of the molecular adlayer. In no case, the presence of stable reaction intermediates is detected along either of the two reaction paths. We have compared the behavior of flat ruthenium surfaces with those having a variable concentration of controlled surface defects. Surface defects, mainly steps, seem to accelerate the rate of both reaction paths, but do not activate any new reaction path or stabilize intermediates.