Arumugamangalam V. Ramaswamy

Bio: Arumugamangalam V. Ramaswamy is an academic researcher from Savitribai Phule Pune University. The author has contributed to research in topics: Molecular sieve & Catalysis. The author has an hindex of 34, co-authored 86 publications receiving 2851 citations. Previous affiliations of Arumugamangalam V. Ramaswamy include Indian Institute of Chemical Technology & National Chemical Laboratory.

Nature of Manganese Species in Ce1-xMnxO2-δ Solid Solutions Synthesized by the Solution Combustion Route

Abstract: A series of manganese−cerium oxide composites with Mn concentrations in the range of 1−20 mol % in ceria was prepared by the solution combustion technique using urea as fuel. The nature, type, and oxidation state of Mn species in ceria were investigated by X-ray diffraction (XRD), diffuse reflectance UV−visible spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy, and temperature-programmed reduction techniques. The study reveals that the method of preparation significantly influences the type of manganese species in ceria. Wet-impregnation, coprecipitation, and solid-state synthesis techniques lead to clustered MnOx-like species in the ceria matrix, while the present method of preparation (solution combustion route) yields a highly dispersed form of Mn species. In the reported series of samples, Mn is present mainly in +2 and +3 oxidation states and there is no evidence for the presence of Mn4+ species. Powder X-ray diffraction studies at variable temperatures (298−1323 K...

Insights into the formation of hydroxyl ions in calcium carbonate:temperature dependent FTIR and molecular modelling studies

Abstract: This paper describes the use of temperature dependent FTIR spectroscopy and molecular modelling studies to establish the origin and the nature of surface hydroxyl ions on calcium carbonate. It has been demonstrated that two types (Type I, corresponding to a band at 3690 cm−1 and Type II, corresponding to a band at 3640 cm−1) of hydroxyl ions exist on calcium carbonate surfaces prepared by the carbonation method. Type I hydroxyl ions are ascribed to those of the unreacted calcium hydroxide (portlandite) present due to incomplete carbonation and Type II hydroxyl ions are ascribed to interstitial defects which are strongly associated with the calcium carbonate lattice framework. Interestingly, the calcium carbonate samples prepared by the solution method do not possess Type I/Type II hydroxyl ions. A molecular modelling exercise was carried out to generate the calcite 104 plane, and the different modes of adsorption of water on the calcite 104 plane were derived based on energy minimisation calculations. The possibility of replacement of a carbonate ion either by (i) two hydroxyl ions or (ii) a hydroxyl and a bicarbonate ion has been considered. The replacement of a carbonate ion by one hydroxyl and one bicarbonate ion is indicative of the presence of surface/interstitial defects on calcite (corresponding to Type II hydroxyl ions assigned by FTIR studies). A molecular description of hydroxylating calcite surfaces is discussed in detail and the results from the energy of formation at zero water coverage corroborate the above findings. The calculations also predict the formation of a maximum of two pairs of hydroxyl and bicarbonate ions over a surface area of 1.0 nm2, during chemisorption at low surface coverages.

Synthesis and characterization of tin oxide-modified mesoporous SBA-15 molecular sieves and catalytic activity in trans-esterification reaction

Abstract: Mesoporous silica molecular sieve SBA-15 has been synthesized and incorporated with various amounts of tin via incipient-wetness impregnation using tin chloride in ethanol followed by calcination. Characterization was done by X-ray fluorescence spectrophotometry (XRF), powder X-ray diffraction (PXRD), nitrogen adsorption, diffuse reflectance ultraviolet (DRUV), scanning and transmission electron microscopy (SEM, TEM), FTIR, Si 29 and Sn 119 MAS NMR, and Sn-Mossbauer spectroscopic techniques to understand the chemical nature of incorporated tin. The silanol groups on the internal walls of SBA-15 are suggested to be the sites for tin incorporation. Bulk structural characterization techniques (X-ray diffraction and BET) are used to demonstrate that the hexagonal structure is maintained during impregnation. Tin oxide exists as a thin film anchored inside the mesopores of SBA-15. Complementarily, Sn 119 NMR and Mossbauer spectroscopies are used to investigate the microstructure of the Sn centers grafted to the mesoporous walls. Sn-Mossbauer spectroscopic studies reveal that Sn2+ may form upon reductive treatments and can probably be stabilized atomically in the pore wall, whereas Sn4+ is stabilized as large entities. While SBA-15 itself shows some activity in transesterification of diethyl malonate with various alcohols, Sn-SBA-15 samples are found to possess enhanced catalytic activity for the same.

Heterogeneous catalysts obtained by grafting metallocene complexes onto mesoporous silica

Abstract: THE synthesis of mesoporous siliceous solids with large-diameter channel apertures (25–100 A) has greatly expanded the capabilities of heterogeneous catalysis1–7 The large apertures in such mesoporous silicas can, for example, be modified by framework substitution to create highly selective catalysts4,5 Here we show that direct grafting of an organometallic complex onto the inner walls of mesoporous silica MCM-41 (ref 1) generates a shape-selective catalyst with a large concentration of accessible, well spaced and structurally well defined active sites Specifically, attachment of a titanocene-derived catalyst precursor to the pore walls of MCM-41 produces a catalyst for the epoxidation of cyclohexene and more bulky cyclic alkenes

Heterogeneous Catalysts for Liquid-Phase Oxidations: Philosophers' Stones or Trojan Horses?

Abstract: Introduction In the early seventies one of us1 was involved in the development of the heterogeneous Ti(IV)/SiO2 catalyst which forms the basis of the Shell process for the epoxidation of propylene with ethylbenzene hydroperoxide (reaction 1).2 Halcon3 and ARCO4,5 workers had previously found, independently, that soluble compounds of early transition metals, e.g., Mo, W, Ti, and V, catalyze reaction 1. The mechanism of catalysis involves withdrawal of electrons from a coordinated alkylperoxo moiety, thereby increasing the electrophilic character of the peroxidic oxygens, i.e., the metal ion acts as a Lewis acid. Hence, effective catalysts are both a strong Lewis acid and a weak oxidant in their highest oxidation state. The latter criterion is necessary in order to minimize competing one-electron oxidation of the ROO ligand leading to homolytic decomposition of ROOH (see Scheme 1). These criteria are best met by molybdenum(VI), and soluble molybdenum compounds exhibit the best combination of activity and selectivity.6,7 Soluble titanium(IV) compounds, on the other hand, are rather mediocre catalysts for reaction 1. In contrast, Ti(IV)/SiO2 exhibits selectivities comparable to homogeneous molybdenum and (for a heterogeneous catalyst) high activities.8 The superior catalytic activity of Ti(IV)/SiO2 was attributed to both an increase in Lewis acidity of the Ti(IV), owing to electron withdrawal by silanoxy ligands, and to site isolation of discrete Ti(IV) centers in the silica lattice preventing oligomerization to unreactive μ-oxo species (which readily occurs with soluble Ti(IV) compounds). Furthermore, it was demonstrated that only the combination of titanium(IV) with silica affords a stable heterogeneous catalyst; all other combinations, e.g., Mo(VI), W(VI), V(V), etc., on silica, gave rapid leaching of the metal ion. One property which soluble Ti(IV) compounds and Ti(IV)/SiO2 share is a marked sensitivity toward deactivation by strongly coordinating ligands, especially water.9 For this reason Ti(IV)/ SiO2 is an ineffective catalyst for epoxidations with aqueous hydrogen peroxide. Hence the appearance in the mid-eighties of Enichem patents10 describing the remarkable catalytic activity of titanium(IV) silicalite (generally known as TS-1) in, inter alia, the selective epoxidation of olefins under very mild conditions with 30% aqueous hydrogen peroxide (Figure 1) was greeted with some scepticism. Thus, two materials, Ti(IV)/SiO2 and TS-1, having roughly the same elemental composition, i.e., 2% Ti in SiO2, exhibited totally different catalytic properties. Initial attempts by various groups to reproduce the Enichem results were largely unsuccessful. However, once it became clear that certain parameters in the synthesis