@article {44639, title = {Selective oxidation of cyclohexane to cyclohexanone using chromium oxide supported mesoporous MCM-41 nanospheres: probing the nature of catalytically active chromium sites}, journal = {ChemCatChem}, volume = {10}, year = {2018}, month = {AUG}, pages = {3291-3298}, abstract = {

Highly dispersed chromium oxide supported mesoporous MCM-41 nanosphere catalysts have been synthesized using a simple wet impregnation method. This work is devoted to a systematic study to reveal the active Cr sites in chromium oxide supported MCM-41 nanosphere catalysts for the selective oxidation of cyclohexane to cyclohexanone. To probe the nature of the active species, we synthesized 0.5-10wt\% Cr loaded catalysts and characterized them by using XRD, UV/Vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near edge structure analysis, N-2 sorption analysis, FTIR spectroscopy, (SiNMR)-Si-29 spectroscopy, SEM, and TEM. The liquid-phase oxidation of cyclohexane to cyclohexanone (99\% selectivity) was performed under mild reaction conditions, and the results reveal clearly that the 5wt\% Cr loaded catalyst was optimum for the reaction. The initial composition of isolated Cr3+ species in the catalyst is the major factor that influences the enhanced activity for cyclohexane oxidation.

}, keywords = {chromium, heterogeneous catalysis, Nanostructures, Oxidation, supported catalysts}, issn = {1867-3880}, doi = {10.1002/cctc.201800309}, author = {Betsy, Kurisingal J. and Nayak, Chandrani and Lazar, Anish and Krishnan, Athira and Bhattacharyya, Dibyendu and Jha, Shambhu N. and Vinod, Chathakudath P.} } @article {46117, title = {Cu/Cu2O nanoparticles supported on a phenol-pyridyl COF as a heterogeneous catalyst for the synthesis of unsymmetrical diynes via glaser-hay coupling}, journal = {ACS Applied Materials \& Interfaces}, volume = {11}, year = {2019}, month = {MAY }, pages = {15670-15679}, type = {Article}, abstract = {

Covalent organic frameworks (COFs) are a new class of porous crystalline polymers with a modular construct that favors fiinctionalization. COF pores can be used to grow nanoparticles (nPs) with dramatic size reduction, stabilize them as dispersions, and provide excellent nP access. Embedding substrate binding sites in COFs can generate host-guest synergy, leading to enhanced catalytic activity. In this report, Cu/Cu2O nPs (2-3 nm) are grown on a COF, which is built by linking a phenolic trialdehyde and a triamine through Schiff bonds. Their micropores restrict the nP to exceptionally small sizes (similar to 2-3 nm), and the pore walls decorated with strategically positioned hydrogen-bonding phenolic groups anchor the substrates via hydrogen-bonding, whereas the basic pyridyl sites serve as cationic species to stabilize the [CuclusterCl2](2-) type reactive intermediates. This composite catalyst shows high activity for Glaser-Hay heterocoupling reactions, an essential 1,3-diyne yielding reaction with widespread applicability in organic synthesis and material science. Despite their broad successes in homocoupled products, preparation of unsymmetrical 1,3-diynes is challenging due to poor selectivity. Here, our COF-based Cu catalyst shows elevated selectivity toward heterocoupling product(s) (Cu nP loading 0.0992 mol \%; turn over frequency: similar to 4S-50; turn over number: similar to 17S-190). The reversible redox activity at the Cu centers has been demonstrated by carrying out X-ray photoelectron spectroscopy on the frozen reactions, whereas the crucial interactions between the substrates and the binding sites in their optimized configurations have been modeled using density functional theory methods. This report emphasizes the utility of COFs in developing a heterogeneous catalyst for a truly challenging organic heterocoupling reaction.

}, keywords = {Copper nanoparticles, Covalent organic framework, Glaser-Hay heterocoupling, heterogeneous catalysis, unsymmetrical diynes}, issn = {1944-8244}, doi = {10.1021/acsami.9b02860}, author = {Chakraborty, Debanjan and Nandi, Shyamapada and Mullangi, Dinesh and Haldar, Sattwick and Vinod, Chathakudath P. and Vaidhyanathan, Ramanathan} } @article {47319, title = {Boron nitride and oxide supported on dendritic fibrous nanosilica for catalytic oxidative dehydrogenation of propane}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {8}, year = {2020}, month = {NOV }, pages = {16124-16135}, type = {Article}, abstract = {

In this work, we were able to significantly increase the activity of boron nitride (BN) catalysts used for the oxidative dehydrogenation (ODH) of propane by designing and synthesizing BN supported on dendritic fibrous nanosilica (DFNS). DFNS/BN showed a markedly increased catalytic efficiency, accompanied by exceptional stability and selectivity. Textural characterization, together with solid-state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopic analyses, indicates the presence of a combination of unique fibrous morphology of DFNS and various boron sites connected to silica to be the reason for this increase in the catalytic performance. Notably, DFNS/B2O3 also showed catalytic activity, although with more moderate selectivity compared to that of DFNS/BN. Solid-state NMR spectra indicate that the higher selectivity of DFNS/BN might stem from a larger amount of hydrogen-bonded hydroxyl groups attached to B atoms. This study indicates that both boron nitride and oxide are active catalysts and by using high surface area support (DFNS), conversion from propane to propene as well as productivity of olefins was significantly increased.

}, keywords = {Electron microscopy, heterogeneous catalysis, Nanostructures, NMR spectroscopy, propane dehydrogenation, X-ray diffraction, X-ray photoelectron spectroscopy}, issn = {2168-0485}, doi = {10.1021/acssuschemeng.0c04148}, author = {Belgamwar, Rajesh and Rankin, Andrew G. M. and Maity, Ayan and Mishra, Amit Kumar and Gomez, Jennifer S. and Trebosc, Julien and Vinod, Chathakudath P. and Lafon, Olivier and Polshettiwar, Vivek} }