Capping agent effect on Pd-supported nanoparticles in the hydrogenation of furfural

The catalytic performance of a series of 1 wt % Pd/C catalysts prepared by the sol-immobilization method has been studied in the liquid-phase hydrogenation of furfural. The temperature range studied was 25\u201375 \ub0C, keeping the H2 pressure constant at 5 bar. The effect of the catalyst preparation using different capping agents containing oxygen or nitrogen groups was assessed. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly (diallyldimethylammonium chloride) (PDDA) were chosen. The catalysts were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization data suggest that the different capping agents affected the initial activity of the catalysts by adjusting the available Pd surface sites, without producing a significant change in the Pd particle size. The different activity of the three catalysts followed the trend: PdPVA/C > PdPDDA/C > PdPVP/C. In terms of selectivity to furfuryl alcohol, the opposite trend has been observed: PdPVP/C > PdPDDA/C > PdPVA/C. The different reactivity has been ascribed to the different shielding effect of the three ligands used; they influence the adsorption of the reactant on Pd active sites

Support acid-base properties as a tool for directing selectivity in the Au-Pt catalyzed base-free glycerol oxidation

Concept Glycerol is a promising chemical building block for the synthesis of fine chemicals from renewable sources [1]. In particular glycerol oxidation shows a complex reaction pathway that can lead to a large number of valuable organic compounds (glyceric acid, tartronic acid, dihydroxyacetone, etc.). Supported noble metal nanoparticles have been used as catalysts for this reaction when molecular oxygen is employed as the oxidant [2]. Depending on the reaction conditions and the noble metal employed, the reaction pathway can be directed either to the oxidation of the primary or the secondary hydroxyl group. In particular Au NPs reveal peculiar properties in terms of both activity and selectivity. However only recently it was found that the catalytic oxidation of glycerol can be carried out without the use of a basic environment, being it a great advantage from an industrial point of view. In this view it has been shown that basic supports greatly enhanced the activity of AuPt alloyed catalysts. In this work AuPt NPs based catalysts were tested in the base-free glycerol aqueous phase oxidation, using supports with different acid/base properties. Experimental results showed that the support surface properties not only influenced the catalyst activity but also greatly affected the selectivity to C3 compounds. Motivations and Objectives Recent studies [3] [4] showed that a careful choice of the support of AuPt alloyed nanoparticle lead to effective catalytic systems in terms of both activity and selectivity, even in the absence of a basic environment. In particular these works opened the way to a new-generation of bifunctional gold-based catalysts where the acid/base properties of the support play a crucial role, affecting activity and selectivity of the reaction. Herein we supported AuPtNPs on a series of supports with different acid-base character in order to clarify the role of the surface properties of the support on catalyst activity/selectivity in the base-free glycerol oxidation. Results and Discussion AuPt nanoparticles were immobilized on, MCM-41, SiO2, NiO and MgO and tested in the base-free glycerol oxidation in a batch reactor (0.3 mol L-1 aqueous glycerol solution, glycerol/metal molar ratio 500, pO2 3 atm, 16 h). Using acidic support (MCM-41, SiO2) a high selectivity to glyceraldehyde/glyceric acid (88-90%) has been obtained. Conversely, using basic supports (NiO, MgO), a low selectivity to glyceric acid was observed (35%) as a consequence of the successive oxidation to tartronic acid/ mesoxalic acids but also to the high occurrence of C-C bond oxidative cleavage. Moreover glyceraldehyde was not detected. References [1] A. Corma, S. Iborra, and A. Velty, Chem. Rev., 107 (2007) 2411-2502 [2] T. Mallat and A. Baiker, Chem. Rev., 104 (2004) 3037-3058. [3] A. Villa, G.M. Veith and L. Prati, Angew. Chem. Int. Ed., 49 (2010) 4499-4502 [4] G. L. Brett, Q. He, C. Hammond, P. J. Miedziak, N. Dimitratos, M. Sankar, A. A. Herzing, M. Conte, J. A. Lopez-Sanchez, C. J. Kiely, D. W. Knight, S. H. Taylor, and G. J. Hutchings et al., Angew. Chem. Int. Ed., 50 (2011) 10136-1013

Base-free glycerol oxidation: studying the effects of structural and acid properties of support in bimetallic catalysts

Glycerol is a highly functionalized bioderived molecule that is recognized as a promising chemical building block for the synthesis of fine chemicals from renewable sources [1]. In particular the selective oxidation of glyce-rol has been shown to produce valuable products such as glyceric acid, hydroxyacetone and tartronic acid. Suppor-ted noble metal nanoparticles have been used as catalysts for this reaction when molecular oxygen is employed as the oxidant [2]. In particular gold nanoparticles reveal peculiar properties in terms of both activity and selectivity. However only recently it was found that the catalytic oxidation of glycerol can be carried out without the use of a basic environment.From an industrial point of view working under non-basic conditions provides a great advantage and a lot of efforts have been devoted to solve this problem. Recent studies showed that alloying gold with a second metal is possible to obtain an effective catalytic systems in terms of activity and selectivity even in the absence of a basic environment. Prati and coworkers [3] demonstrated that by using AuPt bimetallic systems glycerol can be successfully oxidized in pure water. In particu-lar they showed that the support greatly affected the selectivity. Indeed, using an acidic support, H-Mordenite, an enhancement in the selectivity to C3 products (glyceric and tartronic acid) limiting the C-C cleavage can be obtai-ned. Also basic supports such as hydroxy apatite and MgO [4] have been shown to be useful supports. These works opened the way to a new-generation of bifunctional gold-based catalysts where the acid/base properties of the sup-port play a crucial role, affecting activity and selectivity of the reaction. Herein we extended these studies to a series of supports with different acidic character, namely H-Mordenite, SiO2, MCM-41, sulfated ZrO2 in order to clarify the effect of the acid site nature and strength (Lewis and/or Br\uf8nsted) on the activity and selectivity of Au-Pt based catalysts in the base-free glycerol oxidation, particularly for the synthesis of glyceraldehyd