Ramana Singuru

Fabrication of Ruthenium Nanoparticles in Porous Organic Polymers: Towards Advanced Heterogeneous Catalytic Nanoreactors.

A novel strategy has been adopted for the construction of a copolymer of benzene-benzylamine-1 (BBA-1), which is a porous organic polymer (POP) with a high BET surface area, through Friedel-Crafts alkylation of benzylamine and benzene by using formaldehyde dimethyl acetal as a cross-linker and anhydrous FeCl3 as a promoter. Ruthenium nanoparticles (Ru NPs) were successfully distributed in the interior cavities of polymers through NaBH4, ethylene glycol, and hydrothermal reduction routes, which delivered Ru-A, Ru-B, and Ru-C materials, respectively, and avoided aggregation of metal NPs. Homogeneous dispersion, the nanoconfinement effect of the polymer, and the oxidation state of Ru NPs were verified by employing TEM, energy-dispersive X-ray spectroscopy mapping, cross polarization magic-angle spinning (13)C NMR spectroscopy, and X-ray photoelectron spectroscopy analytical tools. These three new Ru-based POP materials exhibited excellent catalytic performance in the hydrogenation of nitroarenes at RT (with a reaction time of only ≈ 30 min), with high conversion, selectivity, stability, and recyclability for several catalytic cycles, compared with other traditional materials, such as Ru@C, Ru@SiO2, and Ru@TiO2, but no clear agglomeration or loss of catalytic activity was observed. The high catalytic performance of the ruthenium-based POP materials is due to the synergetic effect of nanoconfinement and electron donation offered by the 3D POP network. DFT calculations showed that hydrogenation of nitrobenzene over the Ru (0001) catalyst surface through a direct reaction pathway is more favorable than that through an indirect reaction pathway.

Strongly coupled Mn3O4–porous organic polymer hybrid: a robust, durable and potential nanocatalyst for alcohol oxidation reactions

Herein we describe a novel strategy for noble-metal-free Mn3O4@POP (porous organic polymer) hybrid synthesis by encapsulation of Mn3O4-NP in the interior cavity of a porous organic polymer which exhibited enhanced catalytic activity and stability for oxidation of diverse activated and nonactivated alcohols relative to the conventional catalysts to demonstrate the benefits of such a nanoarchitecture in heterogeneous nanocatalysis. The use of a non precious catalyst, tremendous recyclability (upto 15 catalytic runs) and exceptional stability make our system innovative in nature, addressing all the profound challenges in the noble-metal-free heterogeneous catalysts development community.

Towards rational design of core–shell catalytic nanoreactor with high performance catalytic hydrogenation of levulinic acid

We have described herein the synthesis and characterization of a uniquely designed mesoporous silica shell@Pd nanoparticle tethered amine functionalized silica core catalyst and its catalytic properties in the hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone, using formic acid as a sustainable H2 source. Monodispersed silica core particles (∼300 nm in diameter) were prepared and further functionalized by amine groups and then the in situ loading of Pd nanoparticles was carried out. Pd0-NPs are sandwiched between the nonporous silica core and the mesoporous silica shell, leading to the exceptional stability of the catalyst. The nanostructured material was thoroughly characterised by means of powder XRD patterns, N2 sorption, FE-SEM, UHR-TEM, TG-DTA, and XPS analysis. Our core–shell nanostructure catalyst encapsulated with Pd nanoparticles exhibited a significant increase in catalytic activity and excellent selectivity towards γ-valerolactone (99%) compared with control catalysts for levulinic acid hydrogenation, including Pd@C and Pd@SiO2 (without a mesoporous SiO2 shell). Our results suggest that the core–shell silica based nanocatalyst offers tremendous recyclability (up to the 10th catalytic run with consistent conversion and selectivity of γ-valerolactone), stability (no leaching of Pd and structure collapsing) and no sign of deactivation.

Palladium Nanoparticles Encaged in a Nitrogen-Rich Porous Organic Polymer: Constructing a Promising Robust Nanoarchitecture for Catalytic Biofuel Upgrading

Robust nanoarchitectures based on surfactant‐free ultrafine Pd nanoparticles (NPs) (2.7–8.2±0.5 nm) have been developed by using the incipient wetness impregnation method with subsequent reduction of PdII species encaged in the 1,3,5‐triazine‐functionalized nitrogen‐rich porous organic polymer (POP) by employing NaBH4, HCHO, and H2 reduction routes. The Pd‐POP materials prepared by the three different synthetic methods consist of virtually identical chemical compositions but have different physical and texture properties. Strong metal–support interactions, the nanoconfinement effect of POP, and the homogeneous distribution of Pd NPs have been investigated by performing 13C cross‐polarization (CP) solid‐state magic angle spinning (MAS) NMR, FTIR, and X‐ray photoelectron spectroscopy (XPS), along with wide‐angle powder XRD, N2 physisorption, high‐resolution (HR)‐TEM, high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM), and energy‐dispersive X‐ray (EDX) mapping spectroscopic studies. The resulting Pd‐POP based materials exhibit highly efficient catalytic performance with superior stability in promoting biomass refining (hydrodeoxygenation of vanillin, a typical compound of lignin‐derived bio‐oil). Outstanding catalytic performance (≈98 % conversion of vanillin with exclusive selectivity for hydrogenolysis product 2‐methoxy‐4‐methylphenol) has been achieved over the newly designed Pd‐POP catalyst under the optimized reaction conditions (140 °C, 10 bar H2 pressure), affording a turnover frequency (TOF) value of 8.51 h−1 and no significant drop in catalytic activity with desired product selectivity has been noticed for ten successive catalytic cycles, demonstrating the excellent stability and reproducibility of this catalyst system. A size‐ and location‐dependent catalytic performance for the Pd NPs with small size (1.31±0.36 and 2.71±0.25 nm) has been investigated in vanillin hydrodeoxygenation reaction with our newly designed Pd‐POP catalysts. The presence of well‐dispersed electron‐rich metallic Pd sites and highly rigid cross‐linked amine‐functionalized POP framework with high surface area is thought to be responsible for the high catalytic activity and improvement in catalyst stability.

Integrated Experimental and Theoretical Study of Shape-Controlled Catalytic Oxidative Coupling of Aromatic Amines over CuO Nanostructures

We have synthesized CuO nanostructures with flake, dandelion-microsphere, and short-ribbon shapes using solution-phase methods and have evaluated their structure–performance relationship in the heterogeneous catalysis of liquid-phase oxidative coupling reactions. The formation of nanostructures and the morphological evolution were confirmed by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, elemental mapping analysis, and Fourier transform infrared spectroscopy. CuO nanostructures with different morphologies were tested for the catalytic oxidative coupling of aromatic amines to imines under solvent-free conditions. We found that the flake-shaped CuO nanostructures exhibited superior catalytic efficiency compared to that of the dandelion- and short-ribbon-shaped CuO nanostructures. We also performed extensive density functional theory (DFT) calculations to gain atomic-level insight into the intriguing reactivity trends observed for the different CuO nanostructures. Our DFT calculations provided for the first time a detailed and comprehensive view of the oxidative coupling reaction of benzylamine over CuO, which yields N-benzylidene-1-phenylmethanamine as the major product. CuO(111) is identified as the reactive surface; the specific arrangement of coordinatively unsaturated Cu and O sites on the most stable CuO(111) surface allows N–H and C–H bond-activation reactions to proceed with low-energy barriers. The high catalytic activity of the flake-shaped CuO nanostructure can be attributed to the greatest exposure of the active CuO(111) facets. Our finding sheds light on the prospective utility of inexpensive CuO nanostructured catalysts with different morphologies in performing solvent-free oxidative coupling of aromatic amines to obtain biologically and pharmaceutically important imine derivatives with high selectivity.

Cu–Pd bimetallic nanoalloy anchored on a N-rich porous organic polymer for high-performance hydrodeoxygenation of biomass-derived vanillin

The structural composition, particle size on the nanoscale, phase state, and surface property have a significant impact on the performance of nanoalloy catalysts. Here we report a bimetallic Cu3Pd nanoalloy anchored on a N-rich porous organic polymer (BBA-1), Cu3Pd@BBA-1, which shows enhanced catalytic activity for the hydrodeoxygenation of vanillin, a typical compound of lignin-derived bio-oil. The prepared Cu3Pd @BBA-1 bimetallic nanocatalyst exhibits highly efficient catalytic performance in promoting biomass refining compared with its monometallic counterparts, providing 99.3% conversion of vanillin with an exclusive selectivity of 93.6% for the hydrogenolysis product 2-methoxy-4-methylphenol. This catalyst is also found to have superior stability (reproducible conversion values upon several cycles), which represents a significant step forward in promoting biomass refining. The Cu3Pd@BBA-1 and related Cu and Pd based catalysts with varying metallic molar ratios were synthesized by a polyol method using NaBH4 as a strong reducing agent. The specific textural and chemical characteristics of the as-synthesized nanohybrid materials were comprehensively investigated by performing X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, synchrotron powder diffraction, X-ray absorption fine structure spectroscopy, 13C cross polarization magic angle spinning nuclear magnetic resonance, nitrogen physisorption, high resolution transmission electron microscopy, and high angle annular dark field scanning transmission electron microscopy with the corresponding elemental mapping. The catalytic performance of Cu3Pd on other commercial supports such as Al2O3, TiO2 and N-doped carbon is found to be inferior to that on BBA-1, revealing the important role of the nitrogen-rich porous organic polymer matrix. The performance of a 3 : 1 mixture of the monometallic nanoalloys was substantially lower than that of Cu3Pd@BBA-1. These results and the inputs from the experimental probes used for the characterization indicate that in Cu3Pd@BBA-1, alloying leads to improved surface conditions on the nanoscale and brings about a synergetic electronic effect, thus enabling an enhanced catalytic activity and good recyclability.