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Jithin John Varghese

Bio: Jithin John Varghese is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Catalysis & Dissociation (chemistry). The author has an hindex of 8, co-authored 13 publications receiving 313 citations. Previous affiliations of Jithin John Varghese include Nanyang Technological University.

Papers
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TL;DR: In this article, the authors discuss the fundamental reasons behind observed solvent effects with suitable examples, and provide an overview of some of these methods and their application and potential to demonstrate their application.
Abstract: Solvents are crucial components in specialty chemical and pharmaceutical industries and in electrochemical and photoelectrochemical processes, and are increasingly being used in catalytic reactions. Solvents significantly influence the kinetics and thermodynamics of reactions and can alter product selectivity markedly. While such solvent effects are observed routinely, identification of the root causes of such effects is less frequent. Solvents can influence reaction rates, conversion and product selectivity by 1) directly participating in the reaction steps and opening alternate reaction pathways, 2) competing with the reactant for interaction with the catalysts, 3) changing the relative stabilization of the reactant, the transition state (TS) and/or the product, 4) altering intra-pore diffusion characteristics in porous catalysts, 5) exhibiting entropic confinement effects altering free energy barriers of reactions, 6) changing the solubility of different components in the reaction mixture, and 7) inhibiting undesired reactions. Their indirect influences may be due to 1) changes brought on to active sites on catalysts and 2) altered structure/stability of catalysts. This article discusses these fundamental reasons behind observed solvent effects with suitable examples. Advances in computational chemistry have led to the development of multiple tools and techniques, considering solvents either as implicit or as explicit molecules, providing molecular insights into complex solvent effects in catalysis. This article provides an overview of some of these methods with suitable examples to demonstrate their application and potential. This mapping of the solvent effects and their origins is believed to aid in the rational selection of solvents for catalytic reactions. The description of the computational tools, their application and their potential is likely to encourage widespread use of these techniques to investigate solvent effects.

94 citations

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TL;DR: In this article, an unconventional strategy for the synthesis of CuO nanoleaves within 5 min of US irradiation was reported, which was found to be selective in the base-free aqueous oxidation of glycerol to dicarboxylic acids (78% yield of tartronic and oxalic acids), in the presence of hydrogen peroxide (H2O2) and under mild reaction conditions.

87 citations

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TL;DR: In this article, it was shown that the under-coordinated lattice Cu-O pair on different CuO surfaces synergistically activated methane with barriers as low as 60.5 kJ mol−1 on the high-energy CuO(010) surface and 76.6 kJmol−1 in the most stable CuO (111) surface.

57 citations

Journal ArticleDOI
TL;DR: The mechanism of glucose ring opening and isomerization to fructose, catalyzed by the Lewis acid catalyst CrCl3 in the presence of water, is investigated using Car-Parrinello molecular dynamics with metadynamics and minimum energy pathways for the reactions are revealed and the corresponding free energy barriers are computed.
Abstract: The mechanism of glucose ring opening and isomerization to fructose, catalyzed by the Lewis acid catalyst CrCl3 in the presence of water, is investigated using Car–Parrinello molecular dynamics with metadynamics. Minimum energy pathways for the reactions are revealed and the corresponding free energy barriers are computed. Addition of glucose replaces two water molecules in the active [Cr(H2O)5OH]+2 complex, with two hydroxyl groups of glucose taking their place. Ring opening and isomerization reactions can only proceed if the first step involving the deprotonation of glucose is accompanied by the protonation of the OH− group in the partially hydrolyzed metal center ([Cr(C6H12O6)(H2O)3OH]+2 → [Cr(C6H11O6)(H2O)4]+2). This provides further evidence that the partially hydrolyzed [Cr(H2O)5OH]+2 is the active species catalyzing ring opening and isomerization reactions and that unhydrolyzed Cr+3 may not be able to catalyze the reactions. After the ring opening, the isomerization reaction proceeds via deprotonation, followed by hydride shift and the back donation of the proton from the metal complex to the sugar. Water molecules outside the first coordination sphere of the metal complex participate in the reaction for mediating the proton transfer. The hydride shift in the isomerization is the overall rate limiting step with a free energy barrier of 104 kJ mol−1. The simulation computed barrier is in agreement with experiments.

54 citations

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TL;DR: Using density functional theory (DFT) calculations, Wang et al. as mentioned in this paper investigated the reactivity of two different crystal facets of NiO and reveal the contribution of the coordinatively unsaturated NiO pairs, nickel and oxygen vacancies, and low valent dopant Li in determining and altering the surface reactivity.
Abstract: For the development of nickel oxide (NiO) as an oxidation catalyst, a fundamental understanding of the role of surface morphology and of nickel and oxygen vacancy defects is essential, since they govern the reactivity of the surface. Using density functional theory (DFT) calculations, we investigated the reactivity of two different crystal facets of NiO and reveal the contribution of the coordinatively unsaturated Ni–O pairs, nickel and oxygen vacancies, and low valent dopant Li in determining and altering the reactivity of the surfaces. The most stable surface, NiO(100), is relatively inactive for methane C–H activation with an activation barrier of 136.6 kJ mol–1. However, the relatively less stable NiO(110) surface is extremely active and can dissociate methane with an activation barrier of 57.1 kJ mol–1. The coordinative unsaturation and comparatively low binding strength of the four-coordinated surface lattice oxygen on the NiO(110) surface leads to strong chemisorption of the dissociated H, facilita...

43 citations


Cited by
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TL;DR: Recent advances and developments in catalytic transformations of the carbohydrate content of lignocellulosic biomass to IPCs (i.e., ethanol, 3-hydroxypropionic acid, isoprene, succinic and levulinic acids, furfural, and 5-hydroxymethylfurfural) are overviewed.
Abstract: The replacement of fossil resources that currently provide more than 90% of our energy needs and feedstocks of the chemical industry in combination with reduced emission of carbon dioxide is one of the most pressing challenges of mankind. Biomass as a globally available resource has been proposed as an alternative feedstock for production of basic building blocks, which could partially or even fully replace the currently utilized fossil-based ones in well-established chemical processes. The destruction of lignocellulosic feed followed by oxygen removal from its cellulose and hemicellulose content by catalytic processes results in the formation of initial platform chemicals (IPCs). However, their sustainable production strongly depends on the availability of resources, their efficient or even industrially viable conversion processes, and replenishment time of feedstocks. Herein, we overview recent advances and developments in catalytic transformations of the carbohydrate content of lignocellulosic biomass ...

784 citations

Journal Article
TL;DR: In this paper, a generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators.
Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

376 citations

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TL;DR: It is highlighted that the ratio and strength of Brønsted and Lewis acid in bifunctional catalyst are critical for maximizing HMF production by selective improvement in the kinetics of desirable reactions over undesirable reactions.

375 citations

Journal ArticleDOI
TL;DR: This review identifies significant parallels and differences in the strategies used by each metallozeolite active sites to achieve high reactivity, highlighting potentially interesting mechanisms to tune the performance of synthetic catalysts.
Abstract: Metal-exchanged zeolites are a class of heterogeneous catalysts that perform important functions ranging from selective hydrocarbon oxidation to remediation of NOx pollutants. Among these, copper and iron zeolites are remarkably reactive, hydroxylating methane and benzene selectively at low temperature to form methanol and phenol, respectively. In these systems, reactivity occurs at well-defined molecular transition metal active sites, and in this review we discuss recent advances in the spectroscopic characterization of these active sites and their reactive intermediates. Site-selective spectroscopy continues to play a key role, making it possible to focus on active sites that exist within a distribution of inactive spectator metal centers. The definition of the geometric and electronic structures of metallozeolites has advanced to the level of bioinorganic chemistry, enabling direct comparison of metallozeolite active sites to functionally analogous Fe and Cu sites in biology. We identify significant pa...

219 citations

Journal ArticleDOI
TL;DR: This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization ofAldoses at C2 and newly uncovered catalytic systems and mechanisms of carbohydrate transformations.
Abstract: Selected aldohexoses (D-glucose, D-mannose, and D-galactose) and aldopentoses (D-xylose, L-arabinose, and D-ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon-efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations.

214 citations