Raghunath V. Chaudhari

Development of simple and reliable protocols for the immobilization of catalytically active metal nanoparticles is an important aspect of the nanomaterials field. Amine groups bind very strongly to platinum and palladium nanoparticles; therefore, we have attempted to entrap aqueous platinum and palladium nanoparticles on the surface of micron-sized zeolite particles functionalized with amine groups. In this paper, we demonstrate that platinum and palladium nanoparticles bound at high surface coverage on 3-aminopropyltrimethoxysilane (APTS)-functionalized Na−Y zeolites are excellent heterogeneous catalysts for hydrogenation and Heck reactions. The assembly of platinum or palladium nanoparticles on the zeolite surface occurs via an interaction with the amine groups present in APTS leading to a new class of catalyst. The synthesized catalysts were well-characterized by UV−vis, FTIR, TGA, XRD, XPS, and TEM. TEM images of the fresh and used catalysts indeed show that the platinum and palladium nanoparticles supported on amine-functionalized zeolites remain unchanged at the end of the reactions. The rate of hydrogenation and Heck reactions over these catalysts was much higher than those obtained using conventionally prepared catalysts.

The catalytic hydrogenation of p-nitrophenol to p-aminophenol was investigated in a laboratory-scale batch-slurry reactor. Pt/C catalyst (1%) was chosen for optimization of reaction conditions and kinetic studies because of its higher catalytic activity compared to that of other heterogeneous transition metal catalysts. The average catalytic activity and initial rate of hydrogenation was found to increase with increase in the solvent polarity. To investigate the intrinsic kinetics of the reaction, the effect of catalyst loading, agitation speed, p-nitrophenol concentration, and hydrogen partial pressure on the initial rate of hydrogenation was studied at different temperatures. The analysis of initial rate data indicated that the mass-transfer resistances were not significant under the prevailing reaction conditions. A simple Langmuir−Hinschelwood (L−H)-type model was found to represent the kinetics of hydrogenation of p-nitrophenol to p-aminophenol satisfactorily. The apparent energy of activation was found to be 61 kJ/mol.

The present work describes the preparation of p-aminophenol via single-step catalytic hydrogenation of nitrobenzene in acid medium. A conventional method of synthesis of p-aminophenol is a two-step reaction involving iron−acid reduction of p-nitrophenol. This method causes serious effluent disposal problems due to the stoichiometric use of iron−acid, which leads to the formation of Fe−FeO sludge (≅1.2 kg/kg of product) in the process, which cannot be recycled. The single-step hydrogenation of nitrobenzene was carried out using platinum catalyst, and the process conditions were optimized. Complete conversion of nitrobenzene was achieved with selectivity to p-aminophenol as high as 75% under the best set of conditions. Furthermore, the catalyst can be easily recovered and efficiently recycled giving the TON as high as 1.38 × 10.5 This paper presents studies on the effect of various process parameters such as temperature, hydrogen pressure, and substrate and acid concentration on the rate of reaction and selectivity to p-aminophenol.

Abstract The process of spreading/recoiling of a liquid drop after collision with a flat solid surface was experimentally and computationally studied to identify the key issues in spreading of a liquid drop on a solid surface. The long‐term objective of this study is to gain an insight in the phenomenon of wetting of solid particles in the trickle‐bed reactors. Interaction of a falling liquid drop with a solid surface (impact, spreading, recoiling, and bouncing) was studied using a high‐speed digital camera. Experimental data on dynamics of a drop impact on flat surfaces (glass and Teflon) are reported over a range of Reynolds numbers (550–2500) and Weber numbers (2–20). A computational fluid dynamics (CFD) model, based on the volume of fluid (VOF) approach, was used to simulate drop dynamics on the flat surfaces. The experimental results were compared with the CFD simulations. Simulations showed reasonably good agreement with the experimental data. A VOF‐based computational model was able to capture key features of the interaction of a liquid drop with solid surfaces. The CFD simulations provide information about finer details of drop interaction with the solid surface. Information about gas–liquid and liquid–solid drag obtained from VOF simulations would be useful for CFD modeling of trickle‐bed reactors. © 2004 American Institute of Chemical Engineers AIChE J, 51: 59–78, 2005