BITS Faculty Publications

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Subject: search.filters.subject.Zeolites

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    Unveiling the dichotomy between cobalt(ii)-exchanged x and y faujasite zeolites via oxidative carboxylation of alkene to cyclic carbonate
    (ACS, 2025-04) Ray, Saumi
    Cobalt(II)-exchanged X and Y zeolites with varying metal loadings were employed to convert CO2 to cyclic carbonates starting from alkenes. The transformation was carried out using O2 as an oxidant in a mixture of O2 and CO2 under atmospheric pressure, and a maximum yield of 35.7% cyclic carbonate was achieved. Studies revealed a stark difference among both the zeolites, primarily arising from a difference in their ion exchange behaviors. Their catalytic and recyclability properties differed as a result of this variation
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    Dual reforming of model biogas for syngas production on Ni/γ-Al2O3 and Ni-C/ZSM-5 cordierite monolith catalysts
    (Elsevier, 2023) Roy, Banasri; Srinivas, Appari
    This work attempts to convert the model biogas on Ni/γ-Al2O3 and Ni-C/ZSM-5 into syngas using a dual-bed catalytic monolith reactor. The monolith is wash-coated with alumina and ZSM-5, respectively, followed by Ni and glucose-assisted Ni (Ni-C) loading using the wet impregnation technique. These two monoliths are loaded in an Inconel reactor and placed in a two-zone heating furnace. In dual reforming, either Ni/γ-Al2O3 or Ni-C/ZSM-5 monolith is used for dry reforming, and then Ni/γ-Al2O3 is used for steam reforming. A distance of ∼ 10 cm is maintained between these two monoliths. The exhaust gases from the first monolith are combined with steam before passing to the second monolith. The biogas reforming is carried out for a feed ratio (CH4:CO2) 1.5, GHSV of 1440 h−1 and 2880 h−1, at 800℃ and 1 atm pressure. The steam to CH4 ratio (S/C) is optimized to maximize the conversions (greater than80 %) of both CH4 and CO2. It was observed that the CH4 conversions increase with an increased S/C ratio due to the steam reforming in the second monolith. The TGA results show 7.6 % carbon formation on Ni-C/ZSM-5 and 35 % on Ni/γ-Al2O3 in dry reforming on the first monolith bed.
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    Encapsulation of Cobalt Phthalocyanine in Zeolite-Y: Evidence for Nonplanar Geometry
    (ACS, 2003-02) Ray, Saumi
    Cobalt (II) phthalocyanine (CoPc) molecules have been encapsulated within the supercage of zeolite-Y. The square-planar complex, being larger than the almost spherical cage, is forced to adopt a distorted geometry on encapsulation. A comparative spectroscopic and magnetic investigation of CoPc encapsulated in zeolite-Y and in the unencapsulated state is reported. These results supported by molecular modeling have been used to understand the nature and extent of the loss of planarity of CoPc on encapsulation. The encapsulated molecule is shown to be the trans-diprotonated species in which the center of inversion is lost due to distortions required to accommodate the square complex within the zeolite. Encapsulation also leads to an enhancement of the magnetic moment of the CoPc. This is shown to be a consequence of the nonplanar geometry of the encapsulated molecule resulting in an excited high-spin state being thermally accessible.
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    Tuning of Catalytic Property Controlled by the Molecular Dimension of Palladium–Schiff Base Complexes Encapsulated in Zeolite Y
    (ACS, 2017) Ray, Saumi
    Planar palladium–Schiff base complexes are synthesized, maintaining the order of their molecular dimensions as PdL1 < PdL2 < PdL3 < PdL4 < PdL5 in free state, as well as encapsulated in zeolite Y, where L1: N,N′-bis(salicylidene)ethylenediamine and L2, L3, L4, and L5 are derivatives of L1. All encapsulated complexes have shown better catalytic activity for the sulfoxidation of methyl phenyl sulfide in comparison to their homogeneous counter parts. These hybrid systems are characterized with the help of different characterization techniques such as X-ray diffraction analysis, scanning electron microscopy–energy-dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared, and UV–visible spectroscopy; all of these studies have suggested that the largest complex deviates by the maximum from its free-state properties, and a radical change in the reactivity of the complex is observed.
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    The Local Hard−Soft Acid−Base Principle:  A Critical Study
    (ACS, 1997) Roy, Ram Kinkar
    The recently proposed local hard−soft acid−base principle characterizes the reactive centers of two systems on the basis of equal Fukui functions or/and equal local softnesses. We make a quantum chemical study of this principle using ab initio and density functional calculations in cases where the global softnesses of the reacting systems are different. We consider reactions of a dimer cluster model of faujasite X-type zeolite with the probe molecules CO, NH3, and H2O.
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    Local reactivity descriptors to predict the strength of Lewis acid sites in alkali cation-exchanged zeolites
    (Elsiever, 2004-05) Roy, Ram Kinkar
    Lewis acidity of alkali cation-exchanged zeolite is studied using local reactivity descriptors based on hard-soft acid–base (HSAB) concept. The local softness for nucleophilic attack (sx+), local softness for electrophilic attack (sx−) and their ratio, which is called `relative electrophilicity' (sx+/sx−), are calculated for the exchanged cations and Lewis acidity of the cations is found to decrease in the order: Li+ > Na+ > K+ > Rb+ > Cs+. Calculated blue shift of CO vibrational frequency (Δν) and interaction energy of CO molecule with alkali cation-exchanged zeolite clusters vary linearly with sx+/sx− values.