No abstract

Iron-oxide (Fe 2 O 3 ) nanoparticles in the dimension of ∼2.3 nm supported on zeolite-Y appeared as an excellent, reusable heterogeneous catalyst for the chromatography-free selective synthesis of 2,2-di(3-indolyl)-3-indolones, a C2-trimerized product. The zeolite-Y-supported Fe-oxide nanocatalyst showed the catalytic activity better than the Pd-and Au-based catalysts in the synthesis of C2 di-indolyl indolones under the prevailing reaction conditions. Besides, this low-cost catalyst displayed the ability to synthesize the pharmaceutically significant isatin molecules with high selectivity. The nature of the solvent and oxidant played a crucial role in the regioselective trimerization of indoles. The selective formation of the C2-trimerized product was accomplished in acetonitrile with peroxymonosulfate (oxone) as the oxidant, while in a water/acetonitrile mixture, it led to the formation of isatin. Compared to many other high-cost catalysts, the cheaper zeolite-Y-supported iron oxide catalyst promoted the reaction at room temperature with high selectivity. The products were obtained within 15−30 min with ≤95% yield. Different pieces of spectroscopic and electrochemical evidence supported by density functional theory (DFT) studies provided strong evidence for the proposed reaction mechanism. The kinetics of the reaction was studied through UV−vis spectroscopy and found to follow first-order kinetics. The UV−vis spectrum of the C2-trimerized product was further evaluated through time-dependent DFT calculations. The CO 2temperature programmed desorption study indicated the presence of strong basic sites in the Fe 2 O 3 -Y catalyst, favoring the interaction of the acidic indole molecule with the catalyst surface.

Two hybrid electrocatalysts formulated as Rh/RhO x -Ni­(OH)2-rGO and Rh/RhO x -Ni­(OH)2-Y/rGO were synthesized using zeolite-Y and reduced graphene oxide (rGO) as solid support and hard templating agents. The hybrid composites served as effective electrocatalysts for the electrochemical oxidation of both methanol and ethanol. X-ray photoelectron spectroscopic analysis predicted for the creation of metallic rhodium, Rh(0), sites that helped in reducing the CO poisoning during electrocatalytic decomposition of the C1 and C2 alcohols. The zeolite-Y-embedded electrocatalyst, Rh/RhO x -Ni­(OH)2-Y/rGO, showed high CO tolerance in comparison to Rh/RhO x -Ni­(OH)2-rGO and Pt/C. This was further evident from the CO stripping experiment. The zeolite-Y matrix was found to have significant impact in enhancing the current density and durability of the electrocatalysts in both methanol and ethanol oxidation reaction (MOR and EOR) by stabilizing the low valent Rh species. The maximum current density in the case of MOR was found to be 5.6 A/mg, while that in the case of EOR was found to be 7.1 A/mg. The zeolite-Y-supported electrocatalyst exhibited stability up to 1000 cycles, which was retained for 13.8 h during MOR/EOR without any significant loss in the current density. The creation of mesoporous channels in zeolite-Y after its post-modification helped in high mass transfer and allowed to follow a diffusion-controlled mechanism. The linear relationship between current density and the square root of the scan rate also suggested a diffusion-controlled process. The catalysts also exhibited good methanol and ethanol tolerance with the maximum concentration up to 4 and 3 M, respectively.

Non-noble metal-based electrocatalysts have been designed for effective electrochemical oxidation of methanol in basic medium. The catalyst consisting of nickel (Ni) and cobalt (Co) metals was synthesized with a zeolitic imidazolate framework (ZIF) template approach. Such a method leads to the decoration of cylindrically shaped nickel hydroxides, Ni­(OH)2, in nanodimensions within the zeolitic crystals of spinel cobalt oxides, Co3O4. The mixed metal hydroxide and oxide, Ni­(OH)2-Co3O4, represented good activity toward electrochemical oxidation of methanol in 1 M KOH at a low onset potential. When combined with a carboxylate-functionalized multiwalled carbon nanotube (COOH-MWCNT), the same material, Ni­(OH)2-Co3O4, exhibited superior MOR (methanol oxidation reaction) activity, giving a peak current density of 4.2 Amg–1 at similar conditions. The MWCNT-modified catalyst, Ni­(OH)2-Co3O4-MWCNT, also showed high stability up to 500 cycles and 25000 s without a significant loss in the current density. The linear dependency of the current density against the square root of the scan rate indicated a diffusion-controlled MOR process. The decrease in onset potential with increasing scan rate also predicted a kinetically favorable MOR process. Fourier transform infrared and Raman analyses suggested that the MOR mechanism proceeded through the adsorption of methanol (CH3OH) on the catalyst surface, and its deprotonation formed the methoxide ion (CH3O–) which in the later course decomposed to CO2 and H2O. The Raman study also showed that, during the electrochemical oxidation process, Co2+ species in Co3O4 transformed to CoOOH and thereby favored the MOR.

The influence of two different surface matrices, that is, zeolite‐Y and multi‐walled carbon nanotubes (MWCNTs), on the electrocatalytic ability of Ni(OH)2 combined with MnO2 has been studied. The Ni and Mn loaded in different ratio exhibited different current density with respect to the change in the nature of support. The MnO2−Ni(OH)2 catalyst decorated like a fish in a net‐stock at the interface of the zeolite‐Y and the MWCNT with high Ni(II) content provided the highest current density of 3.8 Amg−1 and 3.6 Amg−1 with platinum and graphitic rod as counter electrode, respectively. The study revealed that both the concentration of the Ni(II) as well as the nature of the support influenced the electrochemical behaviour of MnO2−Ni(OH)2. The electrochemical surface area as well as the durability of the catalyst having two different supports showed higher values in comparison to those in single matrix. The plot of current density vs. square root of scan rate showed diffusion control methanol oxidation process. The results predicted that the MnO2−Ni(OH)2 catalyst containing both zeolite‐Y and MWCNT surface indicated that under the highly basic condition it can withstand for long period without significant loss in current density during the methanol oxidation reaction process.