Astha Shukla

Nanocrystalline Pt-CeO2 as an efficient catalyst for a room temperature selective reduction of nitroarenes

We have developed a new synthesis strategy to prepare Pt nanoparticles with size between 2 and 5 nm supported on CeO2 nanoparticles with size between 30 and 60 nm by the hydrothermal method in the presence of the surfactant cetyltrimethyl ammonium bromide (CTAB) and a polymer (PVP). It was found that the catalyst is highly active for the chemoselective hydrogenation of nitro compounds in aqueous medium in the presence of molecular hydrogen at room temperature (25 °C). The catalyst was characterized by XRD, ICP-AES, XPS, BET-surface area measurements, SEM, TEM and EXAFS. Different reaction parameters like reaction time, catalyst ratio, Pt loading etc. were studied in detail. The investigation revealed that the site of Pt plays a crucial role in the activity by favouring the reduction of nitro-compounds. The catalyst shows >99.9% conversion of nitro-compounds with 99% selectivity of amino compounds. The reusability of the catalyst was tested by conducting the experiment with the same catalyst and it was found that the catalyst does not change its activity and selectivity even after five reuses.

Partial oxidation of methane to synthesis gas over Pt nanoparticles supported on nanocrystalline CeO2 catalyst

Pt-nanoparticles supported on CeO2 have been prepared by a post synthesis method (Pt–CeO2PS). In the post synthesis method, CeO2 nanoparticles were prepared by a hydrothermal method, followed by the deposition of Pt nanoparticles over the CeO2. The prepared catalyst was characterized by XRD, BET-surface area, TPR, SEM, TEM, XPS and XAFS. It was observed that the catalyst prepared by the post synthesis method contained Pt nanoparticles with sizes between 2–5 nm supported on CeO2 nanoparticles with sizes between 20–60 nm. The catalytic performance of the Pt–CeO2PS catalyst was evaluated in the partial oxidation of methane for synthesis gas production. The Pt–CeO2PS catalyst could activate methane at 350 °C. We believe that the nanosized Pt particles and the synergy between the Pt particles, the CeO2 nanoparticles and the presence of a strong metal–support interaction play key roles in the activation of methane at such a low temperature. Different reaction parameters, like Pt-loading, reaction temperature, space velocity, and time on stream, were studied in detail. The Pt–CeO2PS catalyst does not deactivate till 100 h with a constant H2/CO mole ratio of 1.9 at 800 °C.

Catalytic oxidation of aromatic amines to azoxy compounds over a Cu–CeO2 catalyst using H2O2 as an oxidant

We have prepared Cu-nanoparticles supported on nanocrystalline CeO2 by a one pot hydrothermal method using cetyltrimethylammonium bromide (CTAB) surfactant. The prepared catalyst was characterised by XRD, SEM, TEM, XPS, TPR, EXAFS, BET-surface area and UV-Vis spectroscopy. This prepared catalyst was highly active for the selective oxidation of aromatic amines to corresponding N-oxides with very high yield. It was observed that 5–10 nm Cu-nanoparticles supported on 20–40 nm CeO2 nanoparticles was formed when Cu loading was 3.8 wt%. 3.8 wt% Cu was the optimum loading to give maximum catalytic activity and above 3.8 wt% Cu loading due to the formation of agglomerated Cu species, catalytic activity decreases. The 3.8% Cu–CeO2 catalyst showed 95% aniline conversion and 92% selectivity towards azoxybenzene formation using H2O2 as an oxidising agent. The effect of different reaction parameters like temperature, reaction time, substrates and H2O2 mole ratio were investigated in detail.

Reaction and Mechanistic Studies of Heterogeneous Hydroamination over Support‐Stabilized Gold Nanoparticles

Highly stable gold nanoparticles (GNPs) around 5–6 nm have been prepared by in situ reduction of chloroauric acid on the surface of nitrogen‐rich mesoporous carbon (MCN) without adding any extra stabilizing agent. The synthesized materials have been efficiently utilized as a catalyst for the truly heterogeneous hydroamination of phenylacetylene with aniline. Large turnover numbers (42×106) were achieved by suitably adjusting the gold/support (w/w) ratio, time, temperature, and solvent, leading to 98 % selectivity towards the Markovnikov product. Density functional theory (DFT) studies have been performed to predict the mechanistic pathway of hydroamination with Au0 in GNP@MCN. To understand the structure–activity relationship, the catalyst was characterized by using different techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption studies (BET), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy.

Pt–CeO2 nanoporous spheres – an excellent catalyst for partial oxidation of methane: effect of the bimodal pore structure

Pt–CeO2 nanoporous spheres were prepared by a two-step synthesis procedure. First, CeO2 nanoporous spheres were prepared by a solvo-thermal method followed by Pt-loading by controlled deposition. The synthesized catalysts were characterized by BET-surface area, H2-chemisorption, XRD, H2-TPR, SEM, TEM, XPS, Raman analysis and EXAFS techniques. The prepared Pt–CeO2NP catalyst showed a bimodal pore structure, which highly influenced its catalytic activity. The catalyst activates methane at 350 °C and was found to be highly active and selective for synthesis gas production via partial oxidation of methane. Pt-nanoparticles of 1.27 nm on average supported on about 150 nm nanoporous spheres comprised of 5–15 nm CeO2 particles were stable for more than 60 h of time-on-stream (TOS) without any significant activity loss, producing synthesis gas with an H2/CO ratio ∼1.95. The high surface area and bimodal pore size distribution played the most important role for the catalysts superior activity.

Nonlinear optical response of germanium nanoparticles

Nonlinear changes of the refractive index are observed by electromagnetic interaction of laser light with germanium nanoparticles. Self-phase modulated optical fringes are used to reveal the nonlinear optical response of germanium nanoparticles at the wavelength of 514.5 nm. The intensity dependence (photo-induced) and size dependence of the refractive index are studied using self-phase modulation of the laser beam. The optical fringe patterns, which are observed due to photo-induced refractive indices, are found to depend on the size of the nanoparticle. The Drude model is also utilized to explore the origin of the photo-induced refractive index of the germanium nanoparticles. It is found that photo-excited electrons contribute appreciably to the nonlinear changes of the refractive index.

Synthesis and catalytic activity of a Pd doped Ni–MgO catalyst for dry reforming of methane

A Pd-doped Ni–MgO catalyst was prepared for synthesis gas production by dry reforming of methane (DRM). The catalyst was prepared by a two-step method; first a high surface area MgO support was prepared by a hydrothermal method then Pd and Ni nanoparticles were deposited by sublimation of the precursor salts. The prepared catalysts were characterized by BET-surface area, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (CO2-TPD), Raman spectroscopy, FT-IR spectroscopy and temperature programmed reduction (H2-TPR) analysis. Both Ni–MgO and Pd/Ni–MgO were highly active for the DRM reaction. Addition of Pd-nanoparticles to the Ni–MgO catalyst decreased the reaction initiation temperature by 90 °C and increased the rate of H2 and CO production during catalysis. The increased activity of the Pd/Ni–MgO catalyst was due to the easily reducible Ni-oxide particles and much smaller Pd-particles, which were active for the DRM reaction at lower temperature. The best feature of the synthesized catalysts was the ability to inhibit the reverse water gas shift (RWGS) reaction, which highly improved the H2/CO ratio. In fact, the Pd/Ni–MgO catalyst almost stopped the RWGS reaction and the presence of water in the reaction product was negligible. A time on stream (TOS) study of both the catalysts showed absolutely no deactivation even after 100 h of reaction at 750 °C. Both catalysts showed production of synthesis gas with a H2/CO ratio of 0.97–0.99 during the TOS study.