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 25–75 °C, 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.

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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.

Furfural is a high-value chemical, being the precursor of compounds such as furfuryl alcohol and tetrahydrofurfuryl alcohol. Pt is known as active for furfural hydrogenation, but the high price limits its exploitation and imposes the search for alternatives. Here we presented a Pt/Mo bimetallic system with enhanced catalytic activity for furfural hydrogenation. For comparison, monometallic Mo-and Ptsupported on activated carbon have been prepared by impregnation and sol-immobilization. The bimetallic Pt/Mo was prepared impregnating the Mo-AC catalyst with Pt, using Na 2 PtCl 4 as a precursor, PVA, and NaBH 4 as reducing agent. HR-TEM analyses on Pt/Mo catalyst showed Mocontaining agglomerates embedded in the carbon matrix, displaying diffraction fringes with spacing typical of Mo 4 O 11 in the orthorhombic phase, as well as Pt nanoparticles more evenly dispersed in the Mo-AC system compared to bare AC. The Pt/Mo catalyst showed higher activity than both monometallic ones, and it converted 92 % of furfural to furfuryl alcohol and ethyl furfuryl ether with 20 % and 80 % selectivity, respectively. However, despite a lower initial activity, the monometallic Mo/AC catalyst showed a complete selectivity to the ether.

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We demonstrate a modified sol‐immobilization procedure using (MeOH)x/(H2O)1‐x solvent mixtures to prepare Pd/TiO2 catalysts that are able to reduce the formation of acid catalyzed products, e. g. ethers, for the hydrogenation of furfural. Transmission electron microscopy found a significant increase in polyvinyl alcohol (PVA) deposition at the metal‐support interface and temperature programmed reduction found a reduced uptake of hydrogen, compared to an established Pd/TiO2 preparation. We propose that the additional PVA hinders hydrogen spillover onto the TiO2 support and limits the formation of Brønsted acid sites, required to produce ethers. Elsewhere, the new preparation route was able to successfully anchor colloidal Pd to the TiO2 surface, without the need for acidification. This work demonstrates the potential for minimizing process steps as well as optimizing catalyst selectivity – both important objectives for sustainable chemistry.

Pt/Al2O3 catalysts with different Pt particle sizes and after phosphorous deposition were studied for liquid phase catalysed furfural hydrogenation. The activity and selectivity were related to various physico-chemical properties studied by scanning transmission electron microscopy, N2 physisorption, 31P nuclear magnetic resonance, diffuse reflectance Fourier transform infrared spectroscopy and attenuated total reflectance infrared spectroscopy. The results indicate that the large particles obtained upon calcination of 1 wt% Pt/Al2O3 at 600 °C exhibited higher turnover frequency per surface Pt; nonetheless, the overall activity decreased due to the loss of surface Pt upon sintering. While in certain cases phosphorous can act as promoter, the addition of this element to Pt/Al2O3 resulted in catalyst poisoning, which was ascribed to Pt encapsulation/blockage effects related to formation of AlPO4. Finally, gradual deactivation of Pt/Al2O3 was observed over five consecutive catalytic cycles which was caused by Pt sintering (from 0.6 to 2.0 nm) as well as by irreversible adsorption of organic reaction intermediates. Graphic Abstract

Light naphtha isomerization is a significant process in a crude oil refinery which is responsible for upgrading low-octane light naphtha to the high-octane and low-aromatic content gasoline. In this work, deactivation of an industrial chlorinated Pt/Al2O3 isomerization catalyst was studied in a laboratory scale plant. Experiments were carried out under temperatures in the range of 120–180 °C, liquid hourly space velocities (LHSV) of 0.7–2 h−1 and hydrogen to hydrocarbon molar ratios (H2/Oil) of 0.7–1.5. Moreover, the total water content of the combined feed, i. e. n-hexane and hydrogen, was 70 ppmwt. During 75 h time on stream (TOS), 42 data sets were collected and applied for training, testing and validating a hybrid-artificial neural network model (hybrid-ANN or HANN) to estimate the activity of the catalyst. Results showed that the activity decreased to 0.56 at the end of the operation mostly due to water poisoning. Furthermore, using the estimated activity, HANN could simulate the conversion and selectivity of the isomerization process with the absolute average deviations (AAD%) of 0.97 % and 0.0766 % and the mean squared errors (MSE) of 0.311 and 0.0156, respectively.