No abstract

Pd–Au nanoalloy supported on zeolite-Y (Pd–Au–Y) matrix was found to be an effective catalyst for C–Cl bond activation and oxidative coupling of 2-naphthol, leading to the formation of various biaryl products and 1,1′-bi-2-naphthol, BINOL. The same catalyst was also highly efficient for selective oxidation of benzylic alcohols to benzaldehydes. Cinnamaldehydes were obtained directly from benzaldehydes by aldol condensation with acetaldehyde generated in situ by partial oxidation of ethanol in the presence of Pd–Au–Y catalyst at 120 °C under basic condition. The biaryl products were also obtained directly from benzylic alcohols in a one-pot system by reacting with phenylboronic acid. The formation of biaryls from benzylic alcohols was believed to occur via one-pot benzylic C–H and C–Cl bond activation. A high % yield of biaryls, BINOL, aldehydes, and cinnamaldehydes was obtained by performing different reactions using the single Pd–Au–Y catalyst. The strong interaction of chloro-benzylic alcohol was predominantly located at active gold species. X-ray photoelectron and diffuse reflectance spectroscopic studies revealed the strong interaction between Pd and Au particles. Electrochemical studies provided proper evidence for the individual role of the nanoparticles (NPs) in one-pot synthesis of biaryls from benzylic alcohols.

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.

Pd–NiO hybridized with zeolite and multiwalled carbon nanotube appeared as highly effective electrocatalyst in methanol oxidation reaction.