Department of Chemistry

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IIT Hyderabad

There has been a major interest in the development of efficient catalysts for the electrochemical reduction of CO2 into useful chemicals and fuels. In this work, the thermochemical and electrochemical CO2 reduction pathways are systematically studied on the (1 1 1) facet of an octahedral copper (Cu85) nanocluster (NC) using density functional theory (DFT) calculations. An investigation is carried out to understand the catalytic activity of the Cu NC towards CO2 reduction to explore its activity and product selectivity (CH3OH vs. CH4; i.e., six-electron vs. eight-electron reduction reaction). Interestingly, CO2 adsorbs strongly the (1 1 1) facet of the Cu NC, as opposed to the previous reports on the periodic Cu(1 1 1) surfaces. Furthermore, such NC shows excellent catalytic activity towards direct C–O bond dissociation, which is again in contrary to what was reported in the literatures. Besides, the CO2 hydrogenation reaction has been investigated using different proton transfer mechanisms (surface-hydrogenation, water-assisted, and water solvated) with/without the help of a solvent water molecule. We find that the water-assisted H-shuttling mechanism lowers the activation barrier significantly and thus favours the CO2 hydrogenation. However, the direct C–O bond dissociation is very competing with respect to indirect C–O bond dissociation. Based on our reaction free energy calculations, activation barrier calculations, and simulated Pourbaix calculations, we find that the Cu NC shows excellent catalytic activity and selectivity over any catalysts studied to date. Besides, the Cu NC requires a lower overpotential (0.53 V) compared to the periodic Cu(1 1 1) surface (0.71 V) and thus can be a promising catalyst for CO2 reduction reaction. © 2017 Elsevier Inc.

World University root node

Journal of Catalysis

Thermochemical and electrochemical CO2 reduction on octahedral Cu nanocluster: Role of solvent towards product selectivity

Stanene is a quantum spin Hall insulator and a promising material for electronic and optoelectronic devices. Density functional theory (DFT) calculations are performed to study the band gap opening in stanene by elemental mono-doping (B, N) and co-doping (B-N). Different patterned B-N co-doping is studied to change the electronic properties of stanene. A patterned B-N co-doping opens the band gap in stanene and its semiconducting nature persists under strain. Molecular dynamics (MD) simulations are performed to confirm the thermal stability of such a doped system. The stress-strain study indicates that such a doped system is as stable as pure stanene. Our work function calculations show that stanene and doped stanene have a lower work function than graphene and thus are promising materials for photocatalysts and electronic devices. © the Owner Societies 2017.

Fulltext

Physical Chemistry Chemical Physics

Band gap opening in stanene induced by patterned B-N doping

There is a need for investigating new electrode materials for solid oxide electrolysis cells (SOEC) as conventional electrodes for solid oxide fuel cells (SOFC) have some limitations when they are used in SOEC mode. Sr substituted LaMnO3 (LSM) is reported to have some demerits when it is used as an anode material in SOEC. With the intention of finding new anode material for SOEC, a series of materials, where Sr of LSM was either partially or fully substituted by Ca, were synthesized via combustion synthesis method. The synthesized material was found to be phase pure with orthorhombic symmetry. Thermal expansion coefficients (TEC) of all the samples were found to be in the range of 11–12×10−6 K−1. Electrical conductivity was found to increase with increasing Ca-content for the samples where Sr was fully replaced by Ca (LCM) but the same was found to decrease with increasing Ca-content for the partially Sr substituted samples (LSCM). The materials with either partial or total substitution of Sr by Ca were used as an anode material of a coupon cell and tested in SOEC mode. These anode materials were found to be better than LSM in terms of hydrogen production. Also, LCM and YSZ did not react with each other even after a prolonged annealing of 100 h at 1000 °C. © 2016 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Synthesis and characterization of Ca doped LaMnO3 as potential anode material for solid oxide electrolysis cells

Exploring suitable electrode materials is a fundamental step toward developing Al batteries with enhanced performance. In this work, we explore using density functional theory calculations the feasibility of single-walled carbon nanotubes (SWNTs) as a cathode material for Al batteries. Carbon nanotubes with hollow structures and large surface area are able to overcome the difficulty of activating the opening of interlayer spaces as observed in graphite electrode during the first intercalation cycle. Our results show that AlCl4 binds strongly with the SWNT to result in an energetically and thermally stable AlCl4-adsorbed SWNT system. Diffusion calculations show that the SWNT system allows ultrafast diffusion of AlCl4 with a more favorable inner surface diffusion than outer surface diffusion. Our charge-density difference and Bader atomic charge analysis confirm the oxidation of SWNT upon adsorption of AlCl4, which shows a similar behavior to the previously studied graphite cathode. The average open-circuit voltage and AlCl4 storage capacity increases with increasing SWNT diameter and can be as high as 1.96 V and 275 mA h g−1 in (25,25) SWNT relative to graphite (70 mA h g−1). All of these properties show that SWNTs are a potential cathode material for high-performance Al batteries and should be explored further. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chemistry - An Asian Journal

A Computational Study of a Single-Walled Carbon-Nanotube-Based Ultrafast High-Capacity Aluminum Battery

This study is aimed at characterising the structure, dynamics and thermophysical properties of five alkylammonium carboxylate ionic liquids (ILs) from classical molecular dynamics simulations. The structural features of these ILs were characterised by calculating the site-site radial distribution functions, g(r), spatial distribution functions and structure factors. The structural properties demonstrate that ILs show greater interaction between cations and anions when alkyl chain length increases on the cation or anion. In all ILs, spatial distribution functions show that the anion is close to the acidic hydrogen atoms of the ammonium cation. We determined the role of alkyl group functionalization of the charged entities, cations and anions, in the dynamical behavior and the transport coefficients of this family of ionic liquids. The dynamics of ILs are described by studying the mean square displacement (MSD) of the centres of mass of the ions, diffusion coefficients, ionic conductivities and hydrogen bonds as well as residence dynamics. The diffusion coefficients and ionic conductivity decrease with an increase in the size of the cation or anion. The effect of alkyl chain length on ionic conductivity calculated in this article is consistent with the findings of other experimental studies. Hydrogen bond lifetimes and residence times along with structure factors were also calculated, and are related to alkyl chain length. © the Owner Societies 2017.

Protic ammonium carboxylate ionic liquids: Insight into structure, dynamics and thermophysical properties by alkyl group functionalization

Steady state spectroscopy, femtosecond transient absorption spectroscopy (fsTA), and femtosecond stimulated Raman spectroscopy (FSRS) of DNA mini-hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker and 1-3 adenine-thymine (A-T) or guanine-cytosine (G-C) base pairs have been investigated. Ultraviolet and circular dichroism (UV and CD) spectra are consistent with ground state conformations that are predominantly base-paired and π-stacked for conjugates possessing two or three base pairs; however, they offer no information concerning the conformation of conjugates possessing a single base pair. fsTA spectra are indicative of π-stacked structures excepted in the case of the conjugate possessing a single G-C base pair. All of the conjugates display transient absorption bands characteristic of the DPA-. anion radical. Conjugates possessing two or three G-C base pairs display a transient absorption band characteristic of the short-lived G+• cation radical. The mini-hairpins with 1-3 A-T base pairs do not display the transient absorption band characteristic of the (An+•) polaron. This implies that an A-tract with three base pairs is too short to support polaron formation. © 2017 American Chemical Society.

Journal of Physical Chemistry B

Dynamics of Charge Injection and Charge Recombination in DNA Mini-Hairpins

In this work, a series of porous CeO2 stabilized PdCu nanoparticles are synthesized by a modified hydrothermal method and applied for catalytic reductive degradation of azo dyes. For the synthesis of CeO2 support a simple precipitation method is adopted using ammonium oxalate as precipitant. Synthesized support and nanoparticles are characterized by XRD, TGA, BET surface area, SEM/EDX, TEM, Raman, UV-visible DRS, FTIR and XPS analyses. Catalytic studies show that the synthesized nanoparticles can efficiently reduce model azo dyes, methyl orange (MO) and congo red (CR) with good recyclability. Among various PdCu compositions, Pd1Cu9/CeO2 exhibits superior catalytic activity towards reductive degradation of MO and CR at room temperature. Thus, PdCu/CeO2 nanoparticles can be accepted as potential component for the application in wastewater treatment. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

ChemistrySelect

PdCu nanoparticles stabilized on porous CeO2 for catalytic degradation of Azo dyes: Structural characterization and kinetic studies

Understanding the role of nanointerface structures in supported bimetallic nanoparticles is vital for the rational design of novel high-performance catalysts. This study reports the synthesis, characterization, and the catalytic application of Co-Mn oxide nanoparticles supported on CeO2 nanocubes with the specific aim of investigating the effect of nanointerfaces in tuning structure-activity properties. High-resolution transmission electron microscopy analysis reveals the formation of different types of Co-Mn nanoalloys with a range of 6 ± 0.5 to 14 ± 0.5 nm on the surface of CeO2 nanocubes, which are in the range of 15 ± 1.5 to 25 ± 1.5 nm. High concentration of Ce3+ species are found in Co-Mn/CeO2 (23.34%) compared with that in Mn/CeO2 (21.41%), Co/CeO2 (15.63%), and CeO2 (11.06%), as evidenced by X-ray photoelectron spectroscopy (XPS) analysis. Nanoscale electron energy loss spectroscopy analysis in combination with XPS studies shows the transformation of Co2+ to Co3+ and simultaneously Mn4+/3+ to Mn2+. The Co-Mn/CeO2 catalyst exhibits the best performance in solvent-free oxidation of benzylamine (89.7% benzylamine conversion) compared with the Co/CeO2 (29.2% benzylamine conversion) and Mn/CeO2 (82.6% benzylamine conversion) catalysts for 3 h at 120 °C using air as the oxidant. Irrespective of the catalysts employed, a high selectivity toward the dibenzylimine product (97-98%) was found compared with the benzonitrile product (2-3%). The interplay of redox chemistry of Mn and Co at the nanointerface sites between Co-Mn nanoparticles and CeO2 nanocubes as well as the abundant structural defects in cerium oxide plays a key role in the efficiency of the Co-Mn/CeO2 catalyst for the aerobic oxidation of benzylamine. © 2017 American Chemical Society.

Langmuir

Nanoscale Cobalt-Manganese Oxide Catalyst Supported on Shape-Controlled Cerium Oxide: Effect of Nanointerface Configuration on Structural, Redox, and Catalytic Properties

The oxidation of cyclohexene was studied using nanostructured CeO2, CeO2/SiO2, CeO2-Sm2O3, and CeO2-Sm2O3/SiO2 catalysts. The CeO2-Sm2O3/SiO2 catalyst shows ~ 96% cyclohexene conversion and ~ 91% selectivity to allylic products, namely, 2-cyclohexen-1-one (~ 53%) and 2-cyclohexen-1-ol (~ 38%) owing to favorable redox (oxygen vacancies) and acid sites stimulated by synergistic interactions of dopant (Sm) and support (SiO2) with CeO2. In contrast, only ~ 40, ~ 55, and ~ 78% of cyclohexene conversions were observed, respectively, over CeO2, CeO2/SiO2, and CeO2-Sm2O3 catalysts. With the increase of reaction time, temperature, and molar ratio of cyclohexene/oxidant, the conversion of cyclohexene and the selectivity of 2-cyclohexen-1-one are increased considerably. © 2017 Elsevier B.V.

Catalysis Communications

Selective allylic oxidation of cyclohexene catalyzed by nanostructured Ce-Sm-Si materials

Hierarchical porous materials are of great interest in various industrial applications because of their potential to overcome the mass transport limitations typically encountered for single-mode porous materials. This report describes the synthesis of a hierarchical trimodal porous silica-based material using a 7.5 molar ratio of a relatively inexpensive nonionic surfactant template, triblock copolymer P123, EO20PO70EO20. The pore size distribution curve shows the presence of three types of pores with average diameters of â8, 25, and 89 nm. Electron microscope images confirm the existence of smaller ordered mesopores (first mode), larger ordered mesopores (second mode), and macropores (third mode). Ni nanoparticles dispersed on this trimodal porous silica produce a material that exhibited excellent catalytic performance for the CO2 reforming of CH4. This research provides new insights that will facilitate the development of trimodal porous silica (TMS) materials for a variety of applications. The results demonstrated that the presence of large pores (second and third mode pores) in TMS material increased the number of accessible active Ni sites, which led to the high activity observed for Ni/TMS catalyst. © 2017 American Chemical Society.