Raghunath V. Chaudhari

Hydrogenation of nitrobenzene to p-aminophenol in a four-phase reactor : reaction kinetics and mass transfer effects

The kinetics of catalytic hydrogenation of nitrobenzene in acid medium to p-aminophenol was investigated in a batch slurry reactor in a temperature range of 323-353 K. Aniline was formed as a byproduct (upto 20%). The initial rate data were analyzed to assess the mass transfer effects and it was found that gas-liquid mass transfer resistance was important under certain reaction conditions. A Langmuir-Hinshelwood type rate model has been proposed based on the initial rate data in the kinetic regime and considering the reaction taking place in both organic as well as aqueous phase. Since this was a four-phase system, the rate equation was suitably modified to include gas-liquid and liquid-liquid mass transfer steps. The kinetic parameters evaluated from a semibatch reactor model were found to represent the observed experimental data very well indicating the applicability of the proposed rate model.

Copper-catalyzed amination of aryl halides: single-step synthesis of triarylamines

Abstract A simple and efficient methodology for the synthesis of triarylamines in a single step has been demonstrated using a ligand-free CuI catalyst and potassium tertiary butoxide as the base. Use of chelating ligands leads to the formation of triarylamine derivatives selectively (95% yield) with high catalytic activity.

Activity, selectivity and stability of Ni and bimetallic Ni–Pt supported on zeolite Y catalysts for hydrogenation of acetophenone and its substituted derivatives

Abstract The hydrogenation of acetophenone, p -hydroxy acetophenone ( p -HAP) and p -isobutyl acetophenone was studied using Ni and bimetallic Ni–Pt supported on zeolite Y catalysts. A 10% Ni-supported-on-zeolite Y catalyst showed the optimum activity when compared to other Ni-supported catalysts. The activity of this catalyst decreased very rapidly on recycle; however, the bimetallic Ni–Pt-supported-on-zeolite Y catalyst was highly stable and showed constant activity on recycle. The addition of Pt catalyses the reduction of Ni 2+ to Ni 0 , as characterised by X-ray photoelectron spectroscopy (XPS) and other techniques. For the Ni–Pt bimetallic catalyst, the hydrogen adsorption was found to be higher than that for monometallic catalysts; the adsorbed hydrogen reacts with the activated acetophenone complex to facilitate the catalytic process. The FTIR analysis of adsorbed acetophenone on the catalyst samples indicated that, in both monometallic and bimetallic catalysts supported on zeolite Y, the CO bond of acetophenone is highly activated due to the strong interactions with the acidic sites present on the zeolite. Zeolite interactions with intermediate products and solvent moieties also influenced the selectivity behaviour. A trace amount of a base like NaOH acts as a promoter in improving the selectivity towards alcohol. A plausible reaction mechanism has been proposed for the hydrogenation of acetophenone and its derivatives using monometallic as well as bimetallic catalysts.

Tailoring of activity and selectivity using bimetallic catalyst in hydrogenation of succinic acid

Abstract The liquid phase hydrogenation of succinic acid (SA) to γ-butyrolactone (GBL) and 1,4-butanediol (BDO) was investigated using ruthenium–cobalt bimetallic catalysts in a semi-batch slurry reactor. The doping of ruthenium (up to 1%) with cobalt resulted in increase (3–4 times) in the overall hydrogenation activity indicating a strong synergistic effect. Ru–Co bimetallic catalyst also influenced the product distribution by promoting specific hydrogenation steps in the overall reaction scheme. Based on the observed catalyst activity results, a speculative reaction pathway for cobalt as well as for ruthenium–cobalt catalyzed hydrogenation of succinic acid has been proposed.

A trickle-bed reactor model for hydrogenation of 2,4 dinitrotoluene: experimental verification

Abstract A trickle-bed reactor model has been developed for hydrogenation of 2,4 dinitrotoluene (DNT). This model incorporates the contributions of partial wetting and stagnant liquid hold-up effects in addition to external and intraparticle mass transfer resistances for a complex consecutive/parallel reaction scheme under consideration represented by L-H-type kinetics. As the reaction is highly exothermic, the heat effects have also been incorporated in the model. The reactor performance for complete wetting, partial wetting of catalyst particles and in the presence of stagnant liquid pockets has been compared and the significance of different parameters discussed. Experimental data were obtained for different particles sizes, different gas and liquid velocities in a temperature range 318–328 K. The model predictions were compared with experimental data and were found to agree very well for a wide range of operating conditions. The model proposed here also allowed prediction of maximum temperature rise in the catalyst bed and which was also found to agree well with the steady-state experimental data. Under certain conditions, hysteresis behaviour of the reactor performance has been observed.

On the mechanism of hydroesterification of styrene using an in situ-formed cationic palladium complex

Abstract The mechanism of hydroesterification of styrene using in situ-formed Pd(OTs) 2 (PPh 3 ) 2 from Pd(OAc) 2 , PPh 3 and TsOH in methanol has been investigated by isolation and characterisation of catalytically active intermediates. From reaction mixtures, Pd–hydridocarbonyl and Pd–acyl complexes were isolated and characterised, based on which a Pd hydride mechanism has been proposed. Formation of palladium hydride species has also been confirmed by 31 P-NMR experiments.

Lattice-matched bimetallic CuPd-graphene nanocatalysts for facile conversion of biomass-derived polyols to chemicals.

A bimetallic nanocatalyst with unique surface configuration displays extraordinary performance for converting biomass-derived polyols to chemicals, with potentially much broader applications in the design of novel catalysts for several reactions of industrial relevance. The synthesis of nanostructured metal catalysts containing a large population of active surface facets is critical to achieve high activity and selectivity in catalytic reactions. Here, we describe a new strategy for synthesizing copper-based nanocatalysts on reduced graphene oxide support in which the catalytically active {111} facet is achieved as the dominant surface by lattice-match engineering. This method yields highly active Cu-graphene catalysts (turnover frequency = 33-114 mol/g atom Cu/h) for converting biopolyols (glycerol, xylitol, and sorbitol) to value-added chemicals, such as lactic acid and other useful co-products consisting of diols and linear alcohols. Palladium incorporation in the Cu-graphene system in trace amounts results in a tandem synergistic system in which the hydrogen generated in situ from polyols is used for sequential hydrogenolysis of the feedstock itself. Furthermore, the Pd addition remarkably enhances the overall stability of the nanocatalysts. The insights gained from this synthetic methodology open new vistas for exploiting graphene-based supports to develop novel and improved metal-based catalysts for a variety of heterogeneous catalytic reactions.

Reaction engineering of emerging oxidation processes

A review of the recent developments in emerging multiphase catalytic oxidation processes for the manufacture of various key chemicals, and an overview of reaction engineering principles needed for reactor design and interpretation of performance are presented. The utility of combining a knowledge of the catalytic chemistry through fundamental mechanisms and kinetics with transport effects and hydrodynamics using recent advances in experimental methods is also discussed and reviewed with reference to liquid phase oxidation.

Kinetics of hydroformylation of l-dodecene using homogeneous HRh(CO) (PPh3)3 catalyst

Abstract The kinetics of the HRh(CO(PPh 3 ) 3 catalyzed hydroformylation of l-dodecene has been investigated in a temperature range of 323–343, K. The effect of l-dodecene and catalyst concentration, P H and P CO , on the rate of reaction has been studied. The rate was found to be first order with respect to catalyst concentration and partial pressure of hydrogen. The rate vs. P CO shows a typical case of substrate inhibited kinetics. The rate was found to be first order with respect to l-dodecene in the lower concentration range while at higher concentrations a zero order dependence was observed. A rate equation has been proposed and kinetic parameters evaluated. The activation energy was found to be 57.12 kJ/mol. A batch reactor model has been a used to predict the concentration-time profiles which were found to agree well with the experimental data at different temperatures. This indicates the applicability of the rate model over a wide range of conditions.

Oxidative carbonylation of aniline over Pd/C catalyst: effect of promoters, solvents, and reaction conditions

Oxidative carbonylation of aniline to N,N′-diphenylurea over 5% PdC NaI catalyst has been reported. The effects of promoters, solvents, reaction conditions, and pretreatment of catalyst with reactants have been investigated. Pretreatment of 5% PdC catalyst with O2, CO, and aniline resulted initially in a decrease in the activity of the catalyst. Activity-versus-NaI concentration and activity-versus-O2 pressure curves passed through maxima, indicating inhibition of rates at higher concentrations. CO pressure showed a linear dependence below 35 atm pressure, but zero-order behavior at higher pressures. The variation in activity was 1.6th order with respect to aniline concentration. Higher activity is obtained in polar solvents. Process parameters had a strong influence on the activity of the catalyst, but the selectivity for N,N′-diphenylurea was unaffected.