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In this work, four cobalt-based catalysts were obtained using two routes of preparation which differed in the expected degree of interaction with the silica matrix, using salicylic acid as a sacrificial modifier during the synthesis to modulate the interaction between the cobalt phase and the silica support due to its complexing properties. The catalysts were tested for the hydroconversion of guaiacol at 300 °C and 5 MPa of H2, with clear differences between each procedure. It is found that the synthesis route has a deep impact on the catalytic activity, with the catalysts prepared using a one-pot route being less active and having an increased selectivity to cyclohexane. In contrast, the ones prepared using a two-step process have increased yield towards phenol and cyclohexanol under the conditions used herein. Salicylic acid increases the catalytic activity in comparison to the untreated material for both families of materials, without changing the observed selectivity between samples with the same preparation. [ABSTRACT FROM AUTHOR]

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb2O5 with different crystal phases was studied. Nb2O5 particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb2O5 was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb2O5 spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb2O5 favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed. [ABSTRACT FROM AUTHOR]

The increasing CO2 emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal–organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO2 capture applications. In this research, the effect of changing the metal center between Zr(IV), Ce(IV), and Hf(IV), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N2 adsorption. We also report the BET surface area, CO2 adsorption capacities, kinetics, and the adsorption isosteric heat (Qst) of the UiO-66 derivatives mentioned family. The CO2 adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO2 adsorption using various MOFs are in the range 20–65 kJ mol−1 observing differences in adsorption capacities between 1.15 and 4.72 mmol g−1 at different temperatures due to the electrostatic interactions between CO2 and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO2 with the PDC linker and an increase in Qst with defects. [ABSTRACT FROM AUTHOR]

Macroporous resins are employed for the purification of polyphenolic extracts. However, the relationship between the adsorption and desorption and the textural properties remains unexplored. Thus, we evaluated the textural properties of HP-20, XAD-16 and SP-825 resins and their impact on adsorption and desorption of specific polyphenols like gallic acid, epigallocatechin, and procyanidin B2. The HP-20 resin exhibited a type II isotherm with macroporous structure, while XAD-16 and SP-825 resins displayed type IV isotherms, typically associated with mesoporous materials. The HP-20 resin demonstrated superior adsorption capacity and rupture points for epigallocatechin (2.37 mg/g, 124 min) and procyanidin B2 (1.29 mg/g, 136 min) compared to SP-825 and XAD-16. Contrary, the SP-825 resin exhibited the highest adsorption capacity (5.34 mg/g) and rupture point (68 min) for gallic acid. However, the desorption was more efficient when HP-20 resin was used for all specific polyphenols. Therefore, for an efficient purification process is necessary to consider the chemical structure of the polyphenol and the textural properties. [ABSTRACT FROM AUTHOR]

The catalytic performance of Ru impregnated perovskites‐based catalysts (Ru/SrZrO3 and Ru/BaZrO3) in the conversion of levulinic acid (LA) into higher valuable chemicals was carried out at different reaction temperatures. The Ru/SrZrO3 and Ru/BaZrO3 catalysts, with a loading of 2.0 Ru atoms nm−2, were prepared by incipient impregnation, and characterized by different techniques. The characterization results indicate presence of dispersed Ru catalysts, with a crystalline structure, with absence of carbonate species for Ru/SrZrO3 and larger carbonates as segregated phase and with stronger basic sites for Ru/BaZrO3. At higher reaction temperatures (200 °C – 250 °C), the higher strength of the basic sites of Ru/BaZrO3 had a direct influence on the levulinic acid (LA) conversion reaction. Differences in the apparent activation energy (Eap) values follow the same trend. The catalysts produce a 100 % of selectivity towards GVL. The formation of GVL was proposed to proceed via the intermediacy of 4‐hydroxypentanoic acid due to the presence of basic surface sites. [ABSTRACT FROM AUTHOR]

The effect of partial substitution of La by Ca and Sr in the catalytic activity of lanthanum cobaltite (LaCoO3) was studied. Two series of La1−xCaxCoO3 and La1−xSrxCoO3 (x = 0, 0.2, and 0.4) reduced perovskites were prepared, characterized and evaluated in the succinic acid conversion at 200 °C and 6 MPa. The characterization results showed a larger Ca substitution in the La1−xCaxCoO3 series, whereas carbonates as segregated phases up to x = 0.2 of Sr were obtained in the La1−xSrxCoO3 series. In the Sr substituted perovskites, the oxidation of Co3+ to Co4+ neutralizes the electronic instability, whereas in the Ca substituted perovskites the presence of Ca2+ generates oxygen vacancies. The succinic acid conversion forms mainly succinic anhydride and 2-hydroxy-tetrahydrofuran by dehydration and hydrogenation processes. The highest initial rate of the reduced LaCoO3 was attributed to the smallest Co crystal size with no segregated phases, compared to substituted catalysts. [ABSTRACT FROM AUTHOR]