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• Controllable activity and selectivity of Pd/C hydrogenation catalysts. • Effect of the carbon support on the structure and catalytic properties of Pd NPs. • Effect of the Pd precursor on the structure and catalytic properties of Pd NPs. • Addition of a second metal and the synergistic effect in Pd-based bimetallic catalysts. Carbon-supported palladium catalysts are widely used for hydrogenation of various organic compounds in the fine chemical industry. The nanoscale geometry and electronic structure of supported Pd nanoparticles play a crucial role in providing the necessary catalytic properties. To improve catalytic activity and selectivity of Pd nanoparticles, it is possible to fine tune their intrinsic properties (e.g., size and oxidation state) by controlling the chemical transformations at different stages of catalyst preparation. Recent years have seen considerable advancement in developing new catalyst preparation techniques as well as in understanding the mechanism of active site formation. This review summarizes some of the existing approaches to regulating the catalytic properties of carbon-supported palladium by variation of the carbon support, the composition of palladium precursor and its reduction conditions, as well as the addition of a second active metal. The data presented may be useful for researchers developing efficient Pd/C catalysts for hydrogenation of polyfunctional organic compounds. [ABSTRACT FROM AUTHOR]

• Mechanism of Pd/C-catalyzed hydrogenation of furfural in H 2 O was established. • Deuterium labeling is one of the techniques used to study the reaction mechanism. • Aqueous-phase furfural hydrogenation is realized through four pathways. • Mechanism includes reductive and acid-catalyzed furan ring opening reactions. Catalytic hydrogenation of furfural under hydrothermal conditions is of great importance and has recently attracted huge attention as an approach to obtaining a wide range of valuable chemicals from a renewable source. However, the data concerning the reaction mechanism of aqueous-phase furfural hydrogenation are very scarce, and it is still not clear which reactions lead to various carbonyl compounds, such as cyclopentanone, 4-oxopentanal, 5-hydroxy-2-pentanone. Herein, we present the results of an experimental study of the mechanism of reactions occurring in the furfural hydrogenation under hydrothermal conditions over the 1% Pd/CNTs catalyst. The following approaches have been used to study the reaction mechanism: hydrogenation of key intermediates formed upon the furfural conversion, and isotopic labeling experiments using D 2 O as a tracer in hydrogenation of furfural, which provides direct evidence of the occurring reactions. It was found that the furfural hydrogenation process is realized through four pathways including various reductive and acid-catalyzed furan ring opening reactions. The methods and approaches used in the present work, as well as the results obtained, can be useful in studying the mechanism of aqueous-phase hydrogenation of a wide range of oxygen-containing substrates in the presence of catalysts of different compositions. [ABSTRACT FROM AUTHOR]

The palladium catalysts prepared using carbon nanoglobules (CNGs) as the support and containing no more than 2 wt% Pd were shown to be highly effective for the liquid-phase hydrogenation of ethyl 4-nitrobenzoate under mild conditions. Regardless of the kind of CNGs and the catalyst preparation method, the most of the Pd/CNGs catalysts allow achieving a complete conversion of substrate giving benzocaine in a 100% yield. The Pd/CNGs catalyst is easily recycled many times without loss of its catalytic performance. The results obtained may be useful for the development of effective Pd/C catalysts for chemoselective hydrogenation of various nitroarenes. [ABSTRACT FROM AUTHOR]

The effect of the nature of alkaline agent and pH value of hydrolysis of Pd(II) chloride complex into palladium polynuclear hydroxo complexes, as precursor of active component in Pd/C catalyst, on the dispersion of palladium particles supported on carbon material Sibunit was revealed. It was shown that an increase in the particle size of supported palladium enhances the specific catalytic activity in hydrogenation of 2,4,6-trinitrobenzoic acid and changes the direction of the transformation (increases the fraction of non-aromatic intermediate, cyclohexane-1,3,5-trione trioxime, in the products). The results obtained are essential for optimizing the particle size of supported palladium in selective hydrogenation of polyfunctional organic compounds. [ABSTRACT FROM AUTHOR]

Bimetallic Pd-Ru/C catalysts prepared with different carbon supports were shown to be much more active in the liquid-phase hydrogenation of benzaldehyde in comparison with their monometallic analogs. In the case of systems based on nanoglobular carbon, the synergistic effect manifested itself as an increased selectivity for benzyl alcohol (86–90%) at a complete conversion of benzaldehyde, whereas the catalysts containing carbon nanotubes were highly active in hydrogenolysis of the C O bonds, which caused an increased yield of toluene (up to 56%). The synergistic effect between palladium and ruthenium in the reaction under study can be related to the changes in the electronic and dispersion state of the supported metals upon interaction with each other and formation of Pd-Ru alloy. In terms of the electronic factor, the enhanced catalytic performance of bimetallic systems can be a result of facilitation of electrophilic activation of the C O bond in benzaldehyde owing to an increased fraction of the electron-deficient palladium species. The nature of carbon support was shown to affect the electronic state of supported metals and thus catalytic properties of bimetallic Pd-Ru/C systems. [ABSTRACT FROM AUTHOR]

Results of the catalytic hydrogenation of 2,4,6-trinitrobenzoic acid (TNBA) in the presence of 1% Pd/C catalyst with analysis of the reaction products at the steps corresponding to the consumption of 1, 3, 5, 6, 8 and 9 mols of hydrogen per mol of TNBA are presented. Numerous reaction intermediates were identified using the 1 H and 13 C NMR spectroscopy; the reaction mixture composition was assessed quantitatively at different steps of the hydrogenation. The data obtained were used to propose a scheme of TNBA transformations over the Pd/C catalyst in the aqueous-phase reaction conditions. The data on the component composition at different steps of TNBA hydrogenation are important to understand the process chemistry, to explore the possibility of selective formation of different types of intermediate nitroamino compounds, and to synthesize high-performance catalysts for the hydrogenation of aromatic polynitro compounds. [ABSTRACT FROM AUTHOR]

The study considered the formation and catalytic properties of the active sites in Pd/C and Ru/C catalysts supported on carbon nanotubes (CNT) and carbon black (CB). The nature of carbon support was shown to affect the dispersion of supported metal and its catalytic properties in the aqueous-phase hydrogenation of furfural. The 1.5% Pd/CB catalyst demonstrated a high selectivity (99%) for furfuryl alcohol during hydrogenation of furfural at a temperature of 50 °C and hydrogen pressure of 0.5 MPa. The 1.5% Pd/CNT catalyst was not active under mild conditions of the reaction (50 °C, 0.5 MPa), but had a greater tendency to reduce the furan ring under severe conditions (90 °C, 0.5 or 2.0 MPa) as demonstrated by an increased yield of tetrahydrofurfuryl alcohol. The ruthenium samples showed a low activity in aqueous-phase hydrogenation of furfural irrespective of the support nature and reaction conditions, possibly due to irreversible adsorption of water on the active sites. [ABSTRACT FROM AUTHOR]