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Herein, we investigated the effect of the support modification (Sibunit carbon) with diazonium salts of Pd and Pd-Au catalysts on furfural hydrogenation under 5 bars of H2 and 50 °C. To this end, the surface of Sibunit (Cp) was modified with butyl (Cp-Butyl), carboxyl (Cp-COOH) and amino groups (Cp-NH2) using corresponding diazonium salts. The catalysts were synthesized by the sol immobilization method. The catalysts as well as the corresponding supports were characterized by Fourier transform infrared spectroscopy, N2 adsorption-desorption, inductively coupled plasma atomic emission spectroscopy, high resolution transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Hammet indicator method and X-ray photoelectron spectroscopy. The analysis of the results allowed us to determine the crucial influence of surface chemistry on the catalytic behavior of the studied catalysts, especially regarding selectivity. At the same time, the structural, textural, electronic and acid–base properties of the catalysts were practically unaffected. Thus, it can be assumed that the modification of Sibunit with various functional groups leads to changes in the hydrophobic/hydrophilic and/or electrostatic properties of the surface, which influenced the selectivity of the process. [ABSTRACT FROM AUTHOR]

We aimed to understand the characteristics of bimetallic systems samples with porous and large surface areas. In doing this we studied in particular the surface structure of the Pd/Ag system. Our cluster models were based on high resolution transmission electron microphotographs of samples with defects. For the modelling of our Pd/Ag nano systems, we combined a variety of experimental and theoretical methods, such as: sputtering, acrylamide sol–gel, high resolution transmission electron microscopy, energy dispersive X-ray spectrometry, and density functional theory. This study explores the connection between nanocrystal structure, electron density distribution, and charge transfer. Charge transfer was determined via density difference analysis. Charge density as a function of the orbital radius was calculated. Vertical electron affinity, vertical first ionization potential, and vertical electronegativity of the Pd18 and Ag24 clusters were calculated. In addition, Voronoi, Bader, Becke, Loewdin, Mulliken, NPA, and NBO population analyses were conducted. [ABSTRACT FROM AUTHOR]

• BiPd and PbPd nanoalloy particles of about 3 nm in size are prepared in aqueous media. • Mass activity of BiPd/C for oxygen reduction is two-fold higher than that of Pd/C. • All the prepared alloy catalysts show excellent methanol tolerance in alkaline media. In this work three PdM/C bimetallic catalysts were prepared with a second metal being either Bi, Pb or Sn. The synthesised Pd-alloy nanoparticles were supported on Vulcan carbon XC-72R. These catalysts were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM) and electrochemically using the rotating disk electrode (RDE) technique. The prepared Pd-based electrocatalysts were compared to pure Pd/C catalyst synthesised using the citrate method. The oxygen reduction reaction (ORR) kinetics on Pd-alloy catalysts in alkaline solution was systematically investigated. Pd content was determined by microwave plasma atomic emission spectroscopy, which was used to calculate the mass activities (MA) for ORR. Mass activities revealed that BiPd had two-fold higher and PbPd showed 1.6-times increase in MA as compared to Pd/C, however SnPd showed lower MA than Pd/C. BiPd/C catalyst showed around 45% increase in specific activity (SA) for ORR, PdSn catalyst showed around 25% increase and PbPd no increase in SA in comparison to the Pd/C catalyst. Methanol tolerance was also studied for the PdM/C alloy catalysts and a higher tolerance was observed for BiPd/C losing 17 mV in the half-wave potential value and even better methanol tolerance was in evidence with the other two catalysts that lost only ∼10 mV in 0.1 M KOH + 0.5 M MeOH. [ABSTRACT FROM AUTHOR]

Oxidation of 5-hydroxymethylfurfural (HMF), a major feedstock derived from waste/fresh biomass, into 2,5-furandicarboxylic acid (FDCA) is an important transformation for the production of biodegradable plastics. Herein, we investigated the effect of the support (unmodified and modified titania, commercial alumina, and untreated and treated Sibunit carbon) of mono- and bimetallic catalysts based on noble metals (Ag, Au, Pd) on selective HMF oxidation with molecular oxygen to FDCA under mild and basic reaction conditions. The higher selectivity to FDCA was obtained when metals were supported on Sibunit carbon (Cp). The order of noble metal in terms of catalyst selectivity was: Ag < Au < Pd < PdAu. Finally, FDCA production on the most efficient PdAu NPs catalysts supported on Sibunit depended on the treatment applied to this carbon support in the order: PdAu/Cp < PdAu/Cp-HNO3 < PdAu/Cp-NH4OH. These bimetallic catalysts were characterized by nitrogen adsorption-desorption, inductively coupled plasma atomic emission spectroscopy, high resolution transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Hammet indicator method and X-ray photoelectron spectroscopy. The functionalization of Sibunit surface by HNO3 and NH4OH led to a change in the contribution of the active states of Pd and Au due to promotion effect of N-doping and, as a consequence, to higher FDCA production. HMF oxidation catalyzed by bimetallic catalysts is a structure sensitive reaction. [ABSTRACT FROM AUTHOR]

Catalytic hydrotreatment is recognized as an efficient method to improve the properties of pyrolysis liquids (PO) to allow co-feeding with fossil fuels in conventional refinery units. The promising catalyst recipes identified so far are catalysts with high nickel contents (38 to 57 wt.%), promoted by Cu, Pd, Mo and/or a combination, and supported by SiO2, SiO2-ZrO2, SiO2-ZrO2-La2O3 or SiO2-Al2O3. To gain insights into the reactivity of the pyrolytic sugar (PS) and pyrolytic lignin (PL) fraction of PO, hydrotreatment studies (350 °C, 120 bar H2 pressure (RT) for 4 h) were performed in a batch autoclave. Catalyst performance was evaluated by considering the product properties (H/C ratio, the charring tendency (TGA) and molecular weight distribution (GPC)) and the results were compared with a benchmark Ru/C catalyst. All Ni based catalysts gave products oils with a higher H/C compared to Ru/C. The Mo promoted catalyst performed best, giving a product with the highest H/C ratio (1.54) and the lowest TG residue (0.8 wt.% compared to 12 wt.% for the fresh PS). The results further revealed that the PS fraction is highly reactive and full conversion was achieved at 350 °C. In contrast, the PL fraction was rather inert, and only part of the PL fraction was converted. The fresh and spent catalysts after the hydrotreatment of the PS and PL fractions were characterized by elemental analysis, powder X-Ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM-EDX). The results revealed that the use of PS as the feed leads to higher amounts of coke deposits on the catalysts, and higher levels of Ni agglomeration when compared to experiments with PL and pure PO. This proofs that proper catalyst selection for the PS fraction is of higher importance than for the PL fraction. The Mo promoted Ni catalysts showed the lowest amount of coke and the lowest tendency for Ni nanoparticle agglomeration compared to the monometallic Ni and bimetallic Ni-Cu catalysts. [ABSTRACT FROM AUTHOR]