Extra Proton Research Articles

Tuning the Interfacial Reaction Environment for CO2 Electroreduction to CO in Mildly Acidic Media.

A considerable carbon loss of CO2 electroreduction in neutral and alkaline media severely limits its industrial viability as a result of the homogeneous reaction of CO2 and OH- under interfacial alkalinity. Here, to mitigate homogeneous reactions, we conducted CO2 electroreduction in mildly acidic media. By modulating the interfacial reaction environment via multiple electrolyte effects, the parasitic hydrogen evolution reaction is suppressed, leading to a faradaic efficiency of over 80% for CO on the planar Au electrode. Using the rotating ring-disk electrode technique, the Au ring constitutes an in situ CO collector and pH sensor, enabling the recording of the Faradaic efficiency and monitoring of interfacial reaction environment while CO2 reduction takes place on the Au disk. The dominant branch of hydrogen evolution reaction switches from the proton reduction to the water reduction as the interfacial environment changes from acidic to alkaline. By comparison, CO2 reduction starts within the proton reduction region as the interfacial environment approaches near-neutral conditions. Thereafter, proton reduction decays, while CO2 reduction takes place, as the protons are increasingly consumed by the OH- electrogenerated from CO2 reduction. CO2 reduction reaches its maximum Faradaic efficiency just before water reduction initiates. Slowing the mass transport lowers the proton reduction current, while CO2 reduction is hardly influenced. In contrast, appropriate protic anion, e.g., HSO4- in our case, and weakly hydrated cations, e.g., K+, accelerate CO2 reduction, with the former providing extra proton flux but higher local pH, and the latter stabilizing the *CO2- intermediate.

Protonation of Homocitrate and the E1 State of Fe-Nitrogenase Studied by QM/MM Calculations.

Nitrogenase is the only enzyme that can cleave the strong triple bond in N2, making nitrogen available for biological life. There are three isozymes of nitrogenase, differing in the composition of the active site, viz., Mo, V, and Fe-nitrogenase. Recently, the first crystal structure of Fe-nitrogenase was presented. We have performed the first combined quantum mechanical and molecular mechanical (QM/MM) study of Fe-nitrogenase. We show with QM/MM and quantum-refinement calculations that the homocitrate ligand is most likely protonated on the alcohol oxygen in the resting E0 state. The most stable broken-symmetry (BS) states are the same as for Mo-nitrogenase, i.e., the three Noodleman BS7-type states (with a surplus of β spin on the eighth Fe ion), which maximize the number of nearby antiferromagnetically coupled Fe-Fe pairs. For the E1 state, we find that protonation of the S2B μ2 belt sulfide ion is most favorable, 14-117 kJ/mol more stable than structures with a Fe-bound hydride ion (the best has a hydride ion on the Fe2 ion) calculated with four different density-functional theory methods. This is similar to what was found for Mo-nitrogenase, but it does not explain the recent EPR observation that the E1 state of Fe-nitrogenase should contain a photolyzable hydride ion. For the E1 state, many BS states are close in energy, and the preferred BS state differs depending on the position of the extra proton and which density functional is used.

Sequential Modification Strategy to Construct Crystalline Benzimidazole Covalent Organic Frameworks with Extraordinary Stability and Polymerization Degree

The intriguing proton-conducting and catalytic properties of benzimidazole-functionalized covalent organic frameworks (BIM-COFs) largely depend on their material quality. Here, we report a novel sequential modification (SM) strategy that enables the preparation of extraordinarily stable BIM-COFs with high polymerization degree. As a “proof of principle”, the designed TpBD-BIMSM was successfully synthesized using the SM strategy, which exhibited superior chemical stability (slight structural change after treatment in 6 M HCl or 6 M NaOH). Compared with the counterpart produced by the conventional direct condensation approach (TpBD-BIMDC), TpBD-BIMSM exhibited a higher Brunauer–Emmett–Teller (BET) surface area (213 m2 g–1 vs 52 m2 g–1) and significantly enhanced CO2, CH4, C2H6, and C2H4 uptake capacities. Furthermore, the proton conductivity of TpBD-BIMSM was measured to be 1.2 × 10–2 S cm–1, which is 2 orders of magnitude higher than that of TpBD-BIMDC (7.2 × 10–4 S cm–1) under identical conditions (80 °C and 98% RH) and also ranks it among the highest in all COF-based proton conductors. In addition, TpBD-BIMSM showed a lower activation energy (Ea) value than TpBD-BIMDC (0.16 eV vs 0.20 eV). Such high proton conductivity and low Ea value of TpBD-BIMSM can be attributed to its large surface area and high polymerization degree, which could provide extra proton transfer paths and accelerate proton movement. Furthermore, such a strategy can be readily extended to construct other BIM-COFs (TpOMe-BIMSM) that thus highlights the generality of sequential modification strategy. And this strategy thus paves a new way for constructing stable and highly polymerized BIM-COFs for related applications.

Composite proton exchange membranes based on inorganic proton conductor boron phosphate functionalized multi-walled carbon nanotubes and chitosan

Super inorganic proton conductor boron phosphate (BPO4) was utilized to functionalize the multi-walled carbon nanotubes (MWNTs) through a convenient sol-gel method with the assist of polydopamine (PDA) to yield BPO4 coated MWNTs (BPO4@MWNTs). Then the BPO4@MWNTs was dispersed in dilute chitosan (CTS) solution to fabricate CTS/BPO4@MWNTs composite membrane. The CTS/BPO4@MWNTs composite membranes showed superior performances in thermal stability, mechanical property and oxidation stability due to the well-dispersed BPO4@MWNTs in CTS matrix and the optimized interface compatibility between the BPO4@MWNTs and the CTS matrix. Moreover, BPO4 coated on the surface of MWNTs can provide an extra proton conducting pathway render the CTS/BPO4@MWNTs-2 composite membrane showed the proton conductivity of 0.040 S cm−1 at 80 °C and the maximum power density of 49.0 mW cm−2 at 70 °C and 2 M methanol concentration much higher than that for original CTS membranes.

Synergistically promoted proton conduction of proton exchange membrane by phosphoric acid functionalized carbon nanotubes and graphene oxide

One dimensional (1D) and two dimensional (2D) nanomaterials with suitable functional groups possess great potential as proton conduction accelerators due to their long-range proton conductive feature. Herein, two outstanding proton conduction accelerators, phosphoric acid functionalized 1D carbon nanotubes and 2D graphene oxide (PCNT and PGO) were prepared, and then incorporated into Nafion matrix to obtain the codoped proton exchange membrane (PEM). Compared with common sulfonation, phosphorylation exhibits the prospect of more efficient proton conduction due to the amphoteric characteristic, large hydration energy and polarizability of phosphoric acid group (–PO3H2). Introduction of PCNT and PGO provided extra excellent proton conductive sites and improved water retention capacity. More importantly, codoping of PCNT and PGO made their 1D and 2D proton conduction pathways combine as hierarchical proton conduction pathways for better interconnecting ionic clusters, which further generated synergistic effect to form more consecutive proton transfer channels in the codoped PEM, whose proton conductivity climbed to 0.282 S/cm under 90 °C, 95% RH, distinctly greater than that of the recast Nafion (0.130 S/cm). Meanwhile, the codoped PEM attained a peak power density of 493.8 mW/cm2, which was approximately 72% larger than that of the recast Nafion (286.8 mW/cm2).

Unidirectional Double- and Triple-Hydrogen Rearrangement Reactions Probed by Infrared Ion Spectroscopy.

Unidirectional double-hydrogen (2H) and triple-hydrogen (3H) rearrangement reactions occur upon electron-ionization-induced fragmentation of trans-2-(4-N,N-dimethylaminobenzyl)-1-indanol (1), trans-2-(4-methoxybenzyl)-1-indanol (2), 4-(4-N,N-dimethylaminophenyl)-2-butanol (3), and related compounds, as reported some 35 years ago (Kuck, D.; Filges, U. Org. Mass Spectrom. 1988, 23, 643-653). These unusual intramolecular redox processes were found to dominate the mass spectra of long-lived, metastable ions. The present report provides independent evidence for the structures of the product ions formed by the 2H and 3H rearrangement in an ion trap instrument. The radical cations 1•+ and 3•+ as well as ionized 1-(4-N,N-dimethylaminophenyl)-5-(4-methoxyphenyl)-3-pentanol, 5•+, were generated by electrospray ionization from anhydrous acetonitrile solutions. The 2H and 3H fragment ions were obtained by collision-induced dissociation and characterized by IR ion spectroscopy and density functional theory calculations. Comparison of the experimental and calculated infrared ion spectra enabled the identification of the 2H rearrangement product ion, C9H14N+ (m/z 136), as an N,N-dimethyl-para-toluidinium ion bearing the extra proton ortho to the amino group, a tautomer which was calculated to be 31 kJ/mol less stable than the corresponding N-protonated form. The 3H rearrangement product ion, C8H13N•+ (m/z 123), formerly assumed to be a distonic ammonium ion bearing a cyclohexadienyl radical, was now identified as a conventional radical cation, ionized N,N-dimethyl-2,3-dihydro-para-toluidine. Thus, the 3H rearrangement represents an intramolecular transfer hydrogenation between a secondary alcohol and an ionized aromatic ring. Based on these structural assignments, more detailed mechanisms for the unidirectional 2H and 3H rearrangement reactions are proposed.

Experimental evidence for extra proton exchange in ribulose 1,5-bisphosphate carboxylase/oxygenase catalysis

ABSTRACT Despite considerable advances in the past 50 y, the mechanism of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalysis is still not well understood. In particular, the movement and exchange of protons within the active site is not well documented: typically, kinetics of H exchange during the first steps of catalysis, i.e. abstraction of the H3 atom of ribulose 1,5-bisphosphate (RuBP) and enolization, are not clearly established. Here, we took advantage of reaction assays run in heavy water (2H2O) to monitor the appearance of deuterated RuBP and deuterated products (3-phosphoglycerate and 2-phosphoglycolate) with exact mass LC-MS. Enolization was reversible such that de-enolization generated not only monodeuterated RuBP (2H-[H-3]-ribulose 1,5-bisphosphate) but also dideuterated RuBP (2H2-[H-3,O-3]-ribulose 1,5-bisphosphate). Carboxylation yielded about one half deuterated 3-phosphoglycerate (2H-[H-2]-3-phosphoglycerate) and also a small proportion of dideuterated 3-phosphoglycerate (2H2-[H-2,O-2]-3-phosphoglycerate). Oxygenation generated a small amount of monodeuterated, but no dideuterated, products. (Di)deuterated isotopologue abundance depended negatively on gas concentration. We conclude that in addition to the first step of proton exchange at H3 occurring before gas addition (and thus influenced by the competition between de-enolization and gas addition), there is another proton exchange step between solvent water, active site residues, and the 2,3-enediol(ate) leading to deuterated OH groups in products.

Mechanistic Insights into the Thermal Decomposition of Ammonium Perchlorate: The Role of Amino-Functionalized Magnetic Nanoparticles.

This work reports the characterization and application of two promising nanocatalysts for the thermal decomposition of ammonium perchlorate (AP). To obtain these composite materials, magnetite nanoparticles (Fe3O4 NPs) were functionalized with two different amine derivative groups, tertiary amine (Fe3O4 NPs-A1) and quaternary amine. X-ray photoelectron spectroscopy and differential scanning calorimetry provided mechanistic insights into the thermal decomposition of AP. Furthermore, tertiary and quaternary amine groups play a critical role, where the presence of an extra proton could favor an electron-proton transfer as the rate-determining step. Moreover, Fe3O4 NPs-A1 causes a diminution of the high-temperature decomposition of AP positively to 335 °C, increasing the energy release by 278 J g-1 and consequently affording the lowest activation energy (102 kJ mol-1), indicating a low degree of thermal stability, and accelerating the thermal decomposition of AP.

Double-filler composite sulfonated poly(aryl ether ketone) membranes with graphite carbon nitride and graphene oxide as polyelectrolyte for fuel cells

Composite polymer electrolyte membranes are exhibiting their bright prospect especially in the field of fuel cell now. We prepared a series of double-filler composite proton exchange membranes from sulfonated poly(aryl ether ketone)s (SPAEK), graphene oxide (GO) and graphite carbon nitride (g-C3N4) with the total filler loading of 0.75 wt%. Facile solution blending provides homogeneous, strong and flexible composite SPAEK/GO/g-C3N4 membranes readily. Characterizations and measurements including membrane morphology, water absorption and dimensional swelling, thermal and mechanical properties, chemical and electrical performance are investigated in detail. Both GO and g-C3N4 nano-fillers can offer extra proton hopping sites via the H2N…HO3S interactions and hydrogen bond networks, which promote the proton conduction and membrane stability. Attributing to the interactions between the two nano-fillers and their interactions with SPAEK polymers, the double-filler compositing system exhibits better physicochemical stability, higher proton conductivity than the corresponding single-filler ones. The SPAEK/GO/g-C3N4(2/2) membrane shows the proton conductivity of 228 mS/cm@90 °C and power output of 675 mW/cm2@80 °C in a H2/O2 fuel cell. This work provides a significative way in the development of multi-component composite polymer electrolyte membranes applied for fuel cells.

Molecular and Supramolecular Structures of Cd(II) Complexes with Hydralazine-Based Ligands; A New Example for Cyclization of Hydrazonophthalazine to Triazolophthalazine

Molecular and supramolecular structures of two polymeric and one trinuclear Cd(II) complex with hydralazine-type ligands were presented. Self-assembly of E-1-(2-(thiophen-2-ylmethylene)hydrazinyl)phthalazine (HL) and CdCl2 gave the 1D coordination polymer [Cd(H2L)Cl3]n*H2O, 1, in which the Cd(II) ion is hexa-coordinated with one cationic monodentate ligand (H2L+) and five chloride ions, two of them acting as connectors between Cd(II) centers, leading to the formation of a 1D coordination polymer along the a-direction. Using DFT calculations, the cationic ligand (H2L+) could be described as a protonated HL with an extra proton at the hydrazone moiety. Repeating the same reaction by heating under reflux conditions in the presence of 1 mL saturated aqueous KSCN solution, the ligand HL underwent cyclization to the corresponding [1,2,4]triazolo[3,4-a]phthalazine-3(2H)-thione (TPT) followed by the formation of [Cd(TPT)(SCN)2]n*H2O, 2, a 1D coordination polymer. In this complex, the Cd(II) is coordinated with one NS-donor TPT bidentate chelate and two bridged μ(1,3)-thiocyanate ions connecting the Cd(II) centers forming the 1D polymer array along the b-direction. Heating E-2-(1-(2-(phthalazin-1-yl)hydrazono)ethyl)phenol HLOH with CdCl2 under reflux condition gave the trinuclear complex [Cd3(Hydralazine)2(H2O)2Cl6], 3, indicating the hydrolysis of the hydrazonophthalazine ligand HLOH during the course of the reaction. Due to symmetry considerations, there are only two different Cd(II) centers having CdN2Cl3O and CdN2Cl4 coordination environments. Hirshfeld topology analysis was used to analyze the solid-state supramolecular structure of the studied complexes.

Non-recovery moisture sensor for breach integrity using the degenerate mode of planar microwave ring resonator

A non-recovery moisture sensor (NMS) based on a planar-microwave resonator for breach integrity is presented. The NMS consists of a microwave ring transducer (MRT), a non-recovery hydrophilic film, and expected to be patterned in the infrastructures transporting the target content. Though PVA and PANI are organic polymers with switchable conductivity, they are incapable of withholding water indefinitely. As PVA conductivity permits switching between p-, n-type semiconductor states, and insulator; a certain concentration of PANI is infused. Because PANI exhibits an extra proton from an acid attached to the nitrogen group, the non-recovery change occurs as it accepts hydronium ions from water, and changes to a more conductive form. The concentration of the acidity results in the degree of permittivity variance. The MRT is configured to see the permittivity variance and convert it into electrical quantities.

Bidirectional Superionic Conduction in Surface-Engineered 2D Hexagonal Boron Nitrides.

We designed functionalized hexagonal boron nitride (FhBN) nanoflakes with high proton conductivity in both in- and through-plane directions as next generation polymer electrolyte membranes (PEMs) for energy storage and conversion systems. The synthesis and functionalization of hBN nanoflakes with sulfonic acid (SA) groups are obtained by one-step and in situ liquid-phase exfoliation with excellent dispersibility and stability over a period of three months. The physico/chemical properties of FhBN nanoflakes were investigated by different spectroscopic and microscopic characterization, confirming chemical interactions between hBN lattice and SA groups. High concentrations (65 and 75 wt %) of FhBN nanoflakes composed with Nafion solution formed stable FhBN-Nafion nanocomposite PEMs, offering extra proton conduction sites, doubling ion-exchange capacity, and reducing the swelling ratio compared to those of Nafion. Our results demonstrate that both the in-plane and through-plane proton conductivities of FhBN-Nafion PEMs significantly improve under various conditions comparative to that of Nafion. The maximum values of both in- and through-plane conductivities for FhBN75%-Nafion PEM at 80% of humidity and 80 °C are 0.41 and 0.1 S·cm-1, respectively, which are 7 and 14 times higher than those of Nafion. The bidirectional superionic transport in highly concentrated FhBN PEMs is responsible for outstanding properties, useful for electrochemical energy devices.

New insights into the mechanism of Schiff base synthesis from aromatic amines in the absence of acid catalyst or polar solvents

Extensive computational studies of the imine synthesis from amines and aldehydes in water have shown that the large-scale structure of water is needed to afford appropriate charge delocalization and enable sufficient transition state stabilization. These insights cannot, however, be applied to the understanding of the reaction pathway in apolar solvents due their inability to form extensive hydrogen-bonding networks. In this work, we perform the first computational studies of this reaction in nonpolar conditions. This density-functional study of the reaction of benzaldehyde with four closely related aromatic amines (aniline, o-toluidine, m-toluidine and p-toluidine) shows that, although an additional molecule of amine may provide some stabilization of the first transition state even in the absence of a hydrogen bonding network, this is insufficient to achieve high reaction rates. Our computations also show that when an extra proton is added to the spectator amine, the activation energies become so low that even picomolar amounts of protonated base are enough to achieve realistic rates. Additional computations show that those minute amounts of protonated base may be obtained under reaction conditions without the addition of extraneous acid through the auto-protolysis of the amines themselves. To our knowledge, this is the first report of a role for the auto-protolysis of anilines in their extensive reactional repertoire.

Preparing proton exchange membranes via incorporating silica-based nanoscale ionic materials for the enhanced proton conductivity

Proton exchange membranes (PEMs) have triggered growing attention in energy-related applications due to their fundamental and technological significance. In this work, silica-based nanoscale ionic materials (NIMs-SiO2) were synthesized and incorporated into sulfonated poly (ether-ether-ketone) (SPEEK) to prepare nanocomposite membranes. NIMs-SiO2 could not only provide extra proton transfer sites, but also enhanced the hydrophilicity of the membranes, leading to decrease of the activation energy. The nano-scale size (7 nm) and the functional groups of the NIMs-SiO2 lead to good interfacial adhesion with SPEEK, improving the mechanical properties of the membranes. Consequently, SPEEK/NIMs-SiO2(5) exhibited the highest proton conductivity and peak power density, which were 1.92 and 1.51 folds higher than the pristine SPEEK membranes, respectively. The results showed the nanocomposite membranes had potential as alternative proton exchange membranes for corresponding devices.

The structure of the oxidized state of cytochrome c oxidase - experiments and theory compared

Cytochrome c oxidase (CcO), the terminal enzyme in the respiratory chain, reduces molecular oxygen to water. Experimental data on the midpoint potentials of the heme iron/copper active site cofactors do not match the overall reaction energetics, and are also in conflict with the observed efficiency of energy conservation in CcO. Therefore it has been postulated that the ferric/cupric intermediate (the oxidized state) exists in two forms. One form, labelled OH, is presumably involved during catalytic turnover, and should have a high CuB midpoint potential due to a metastable high energy structure. When no more electrons are supplied, the OH state supposedly relaxes to the resting form, labelled O, with a lower energy and a lower midpoint potential. It has been suggested that there is a pure geometrical difference between the OH and O states, obtained by moving a water molecule inside the active site. It is shown here that the difference between the two forms of the oxidized state must be of a more chemical nature. The reason is that all types of geometrically relaxed structures of the oxidized intermediate have similar energies, all with a high proton coupled reduction potential in accordance with the postulated OH state. One hypothesized chemical modification of the OH state is the transfer of an extra proton, possibly internal, into the active site. Such a protonated state has several properties that agree with experimental data on the relaxed oxidized state, including a decreased midpoint potential.

Study of Sub-barrier Fusion of \(^{36}\)S+\(^{50}\)Ti,\(^{51}\)V Systems

A detailed comparative study of the sub-barrier fusion of the two nearby systems 36S+50Ti,51V was performed at the National Laboratories of Legnaro (INFN). The experiment aimed to evidence possible effects of the non-zero spin of the ground state of the 51V nucleus on the sub-barrier excitation function and on the shape of the barrier distribution. The comparison of both excitation functions and barrier distributions showed a very similar behavior, down to the level of 20–30 µb. Coupled-channels calculations have been performed including the low-energy excitations of both projectile and the two targets, and the results are in very good agreement with the data. This indicates that the low-lying levels in 51V can be interpreted in the weak-coupling scheme and that the extra proton in the f7/2 shell does not have a significant influence on sub-barrier fusion.

Proton Acceptor near the Active Site Lowers Dramatically the O-O Bond Formation Energy Barrier in Photocatalytic Water Splitting.

The O–O bond formation process via water nucleophilic attack represents a thermodynamic and kinetic bottleneck in photocatalytic water oxidation because of the considerably high activation free energy barrier. It is therefore of fundamental significance and yet challenging to find strategies to facilitate this reaction. The microscopic details of the photocatalytic water oxidation step involving the O–O bond formation in a catalyst–dye supramolecular complex are here elucidated by density functional theory-based Car–Parrinello molecular dynamics simulations in the presence of an extra proton acceptor. Introducing a proton acceptor group (OH–) in the hydration shell near the catalytic active site accelerates the rate-limiting O–O bond formation by inducing a cooperative event proceeding via a concerted proton-coupled electron-transfer mechanism and thus significantly lowering the activation free energy barrier. The in-depth insight provides a strategy for facilitating the photocatalytic water oxidation and for improving the efficiency of dye-sensitized photoelectrochemical cells.

Sub-barrier fusion involving odd mass nuclei: The case of 36S + 50Ti, 51V

Sub-barrier fusion of the two near-by systems 36S + 50Ti, 51V has been measured at the Laboratori Nazionali di Legnaro (INFN). Motivation for the experiment came from the possible effect of the non-zero spin of the ground state of the 51V nucleus on the sub-barrier excitation function, and in particular on the shape of the barrier distribution. No previous data were available for these two systems near the barrier. Our results show that the two measured excitation functions are very similar down to the level of 20-30μb. The same is true for the two barrier distributions. Coupled-channel calculations have been performed including the low energy excitations of both projectile and the two targets. We have indication that the low-lying levels in 51V can be interpreted in the weak-coupling scheme, that is, 51V (I) = 50Ti(2+) ⊗ p(1f7/2) and that the extra proton in the $ 1f_{7/2}$ shell does not have a significant influence on sub-barrier fusion.

Studying effects of different protonation states of His11 and His102 in ribose-5-phosphate isomerase of Trypanosoma cruzi: an example of cooperative behavior

The Trypanosoma cruzi ribose-5-phosphate isomerase B (TcRpiB) is a crucial piece in the pentose phosphate pathway and thus is a potential drug target for treatment of Chagas’ disease. TcRpiB residues, such as Cys69, Asp45, Glu149 and Pro47, have confirmed their roles in substrate recognition, catalytic reaction and binding site conformation. However, the joint performance of His11 and His102, in the D-ribose-5-phosphate (R5P) in the catalysis is not well understood. In this work, we probed the influence of different protonation states of His11 and His102 on the behavior of the ligand R5P using molecular dynamics simulations, network analysis and thermodynamic integration. Simulations revealed that a protonated His11 combined with a neutral His102 (His11+‒His102) was able to stabilize the ligand R5P in the binding site. Moreover, calculated relative free energy differences showed that when protonated His11 was coupled to a neutral His102 an exergonic process takes place. On the other hand, neutral His11 combined with a protonated His102 (His11‒His102+), sampled conformations that resembled the catalyzed product D-ribulose-5-phosphate (Ru5P). Network analysis also demonstrated some peculiarities for these systems with some negatively correlated nodes in the binding site for His11‒His102+, and exclusive suboptimal paths for His11+‒His102. Therefore, the combined approach presented in this paper proposes two suitable protonation states for the TcRpiB catalytic mechanism, where an extra proton in either histidines might favor R5P binding or influence isomerization reaction to Ru5P. Our results may guide further in silico drug discovery studies. Communicated by Ramaswamy H. Sarma

Identifying the presence of [V=O]2+ during SCR using in-situ Raman and UV Vis spectroscopy

Abstract Combining UV Vis and Raman spectrosocopy allows for V O, oxo vanadium(IV) surface species to be identified during operando SCR on V2O5/TiO2 catalysts. V4+ is formed by a one electron reduction pathway by NO and NH3 and it exhibits a V O stretch which is red shifted slightly compared to its V5+ counterpart. This is due to an extra proton charge balancing the reduced entity in form of an OH group. This red shift is similar in nature to the effect of hydration, which is a function of water partial pressure in the gas stream and the temperature. It is shown that the red shift cannot solely be due to changes in the water contents, and that it is related to a reduction of vanadium. Furthermore, exposing the oxidized catalyst to 1.5% H2O, which is more than an order of magnitude higher than the residual water level present after the NO and NH3 reduction, induces less red shift as observed after reduction of the catalyst in the apparent dry conditions. It is further observed with UV Vis spectroscopy that NO and NH3 reduction forms a V(IV) band at 15,000 cm−1.