N. Escalona

Hydrodeoxygenation of guaiacol over Ni/carbon catalysts: effect of the support and Ni loading

Commercial carbon nanotubes (CNT), oxidized CNT (CNTox) and activated carbon (AC) were used as supports to prepare Ni/C catalysts with a nominal loading of 15 wt%. In addition, xNi/CNT catalysts with loadings of x: 10, 12, 15, 17, 20 wt% were prepared. The catalysts were characterized by N2 physisorption, temperature-programmed decomposition (TPD), potentiometric titration, H2-temperature programmed reduction (TPR), CO chemisorption and X-ray photoelectron spectroscopy (XPS). The catalysts were evaluated for the conversion of guaiacol at 573 K and 5 MPa H2 pressure for 4 h in a batch reactor. The activity of the xNi/CNT catalysts was related to Ni dispersion, while their selectivity was similar and favored the formation of hydrogenation products. The activity of 15Ni/CNT catalyst was higher than those of 15Ni/CNTox and 15Ni/AC catalysts. The higher activity of the 15Ni/CNT catalyst compared to 15Ni/AC catalyst was possibly due to their different morphologies, while the lower activity of the 15Ni/CNTox catalyst was attributed to the limiting effect of surface oxygen groups on the support. In addition, the higher acidity of the 15Ni/CNTox catalyst enhanced its hydrogenolysis and deoxygenation capacities.

Carbon nanofiber-supported ReOx catalysts for the hydrodeoxygenation of lignin-derived compounds

The effect of ReOx loading (2–13 wt%) and H2 pressure (0–5 MPa) for the hydrodeoxygenation of phenol has been studied for carbon nanofiber-supported ReOx catalysts in a batch reactor at 573 K. Characterization of the supports and catalysts has been obtained from N2 physisorption, TPD, FTIR, XRD, potentiometric titration, TPR and XPS measurements, which revealed the presence of a crystalline and surface ReOx phase whose particle size and surface coverage increased with loading. The reactivity of the catalysts was linked to the in situ partial reduction of ReO3 to form Re4+ and Re6–7+ sites, whose presence and relative amounts were determined by post-reaction XPS analysis. The reaction rate increased with ReOx loading up to 10 wt%, attributed to the increase in Re surface coverage; a decrease in reaction rate at higher loading was ascribed to the formation of aggregates. The study revealed a strong affinity for direct cleavage of the C–O bond to form benzene. The similar relative abundance of the Re species is responsible for the similar trend in product distribution of the catalysts. The dependence of activity and product distribution with respect to H2 pressure has been related to kinetics and thermodynamics. The reactivity of the best catalyst for the HDO of guaiacol (2-methoxyphenol), anisole (methoxybenzene), phenol and o-cresol (2-methylphenol) further demonstrated the catalysts preference for C–O bond scission.

The promoter effect of potassium in CuO/CeO2 systems supported on carbon nanotubes and graphene for the CO-PROX reaction

The effect of K promotion on the CO preferential oxidation (CO-PROX) reaction has been studied over Cu–CeO2 based catalysts supported on carbon nanotubes (CNT) and reduced graphene oxide (G). The catalysts were prepared with 3 wt% Cu and 20 wt% CeO2 loadings and 1 wt% K when promoted. In the CNT series, K loading was varied between 0.5 and 2 wt%. The catalytic performance and the characterization by powder X-ray diffraction (XRD), TEM-STEM, H2-temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) have been presented. TEM analysis showed that the type of carbon support has an important effect on the dispersion of ceria, with the latter being higher for the CNT support. Addition of K to the catalysts improved the conversion of CO at lower temperatures. The characterization results reveal that the observed increases in the Cu+ species proportion and in lattice oxygen are related to the better catalytic performance.

The effect of Cu loading on Ni/carbon nanotubes catalysts for hydrodeoxygenation of guaiacol

Commercial carbon nanotubes (CNT), were used as supports to prepare Ni/CNT catalysts with a 15 wt% Ni loading and NiCux/CNT catalysts with Cu loadings of x: 1.5, 2.25, 3.0 and 3.75 wt% were prepared. The catalysts were characterized by N2 physisorption, H2-temperature programmed reduction (TPR), transmission electron microscopy (TEM), STEM-HAADF and X-ray photoelectron spectra (XPS), and they were evaluated in the conversion of guaiacol at 573 K and 5 MPa H2 pressure for 4 h in a batch reactor. The characterization showed that Ni–Cu alloys were formed which existed along with Ni, Cu and NiO entities. The Ni metallic particle size was lower upon increasing Cu content, however the increased proportion of NiO species and the coverage of Ni sites with Cu diminished the intrinsic activity. The addition of Cu also decreased the hydrogenolysis and deoxygenation ability for the catalysts up to 3 wt% of Cu, which can be related to the lower size of Ni ensembles. Beyond that percentage, the selectivity was modified and it was attributed to changes in the Ni dispersion.

Phenol hydrodeoxygenation: effect of support and Re promoter on the reactivity of Co catalysts

In this work, the reactivity of supported Co catalysts as a function of the oxide support (alumina, silica-alumina, zirconia and titania) and Re promoter for the hydrodeoxygenation of phenol at 300 °C and 3 MPa H2 using a batch autoclave reactor was investigated. The catalyst properties have been obtained from N2 physisorption, X-ray Diffraction (XRD), Atomic Absorption Spectroscopy (AAS), Temperature-Programmed Reduction (TPR), Temperature-Programmed Desorption of ammonia (NH3-TPD), H2 chemisorption and X-ray Photoelectron spectroscopy (XPS). Characterization results revealed the presence of Co particles existing as Co metal and CoO whose surface properties were controlled by the surface behavior of the oxide supports. It was found that phenol conversion proceeded via three major pathways which were dictated by the support. The Co/Al2O3 and Co/SiO2–Al2O3 catalysts preferred the well-documented sequential ring hydrogenation–dehydration–hydrogenation (or dehydrogenation) route while phenol tautomerization, followed by hydrogenation and dehydration was observed in the case of the Co/ZrO2 catalyst. The catalytic activity was governed by a combination of metal sites and acid properties of metal–support interface and decreased in the order: Co/Al2O3 > Co/SiO2–Al2O3 > Co/ZrO2 > Co/TiO2. The markedly low activity of the Co/TiO2 catalyst was attributed to the presence of a thin TiOx layer which partially covered the active metal sites due to the strong metal–support interaction effect. The low activity, however, is offset by this catalysts ability to catalyze the efficient production of benzene directly from phenol. The addition of Re to the supported Co catalysts had a beneficial effect on the activity, attributed to improved reducibility and the presence of additional hydrogenation sites. The strongest effect of Re addition on the activity and selectivity was observed for the TiO2-supported catalyst. The results further highlight the importance of the choice of support in HDO reactions.

Microstructure, vibrational and visible emission properties of low frequency ultrasound (42 kHz) assisted ZnO nanostructures

Size and shape tuneable ZnO nanostructures were prepared by a low frequency ultrasound (42 kHz) route using various organic solvents as the reaction media. The crystalline nature, lattice parameters and microstructural parameters such as microstrain, stress and energy density of the prepared ZnO nanostructures were revealed through X-ray diffraction (XRD) analysis. The organic solvents influenced the size and morphology of the ZnO nanostructures, and interesting morphological changes involving a spherical to triangular shaped transition were observed. The visible emission properties and lattice vibrational characteristics of the nanostructures were drastically modified by the changes in size and shape. Raman spectral measurements revealed the presence of multiphonon processes in the ZnO nanostructures. The intensity of the visible emission band was found to vary with the size and morphology of the structures. The strongest visible emission band corresponded to the structure with the largest surface/volume ratio and could be attributed to surface oxygen vacancies. The control over the size and morphology of ZnO nanostructures has been presented as a means of determining the intensity of the visible emission band.

Environmentally friendly heterogeneous sol–gel La 2 O 3 –Al 2 O 3 mixed oxides for transesterification reaction

Environmentally friendly heterogeneous sol–gel La2O3–Al2O3 materials with no alkaline or alkaline-earth metals were synthesized to be used as catalysts for biodiesel production by a transesterification reaction of canola oil. The effect of the La2O3 content (0, 3, 5, 7, and 10 wt%) on the catalytic performance of the La2O3–Al2O3 mixed oxides, as well as the textural, structural, and surface properties, is reported. It was found that La2O3 loading increases the number and strength of basic sites up to 7% La2O3–Al2O3 catalyst with an La2O3 monolayer formation with 0.23xa0mmol highly dispersed La atoms over Al2O3 is reported. A correlation between catalytic performance, informed as biodiesel production with basicity, carbonation degree, and La2O3 dispersion is obtained. The extent of biodiesel production (45% at 65xa0°C and 5xa0h of reaction time), under mild reactions conditions, for the monolayer La2O3 alumina catalyst is the highest reported up now for nontoxic heterogeneous catalysts.

STUDY OF THE CATALYTIC CONVERSION AND ADSORPTION OF ABIETIC ACID ON ACTIVATED CARBON: EFFECT OF SURFACE ACIDITY

This study reports the adsorption and catalytic conversion of abietic acid as representative compound of tall oil, using activated carbons. Acid functional groups present on CGRAN activated carbons favored the adsorption of abietic acid, probably through a physical adsorption mechanism. In contrast, the conversion of abietic acid was not favored in DARCO activated carbon by increase of acid sites thought HNO3 treatment. The detection of neoabietic, palustric and/or levopimaric acids as reaction products indicate that the transformation of abietic acid was by dehydrogenation and/or isomerization routes. The negative influence of acid sites on the catalytic activity, in addition to the non-detection of volatile products, suggests that the cracking pathway for the conversion of abietic acid over these catalysts can be ruled out. Contrasting effects of the surface groups on the adsorption capacity and the conversion was observed: strong acid sites of CGRAN activated carbon favor the adsorption of abietic acid and decrease competitive adsorption between substrate and solvent, while conversion is not favored by these acid sites.

SUPPORT EFFECT ON CONVERSION OF QUINOLINE OVER ReS2 CATALYST

The conversion of quinoline over ReS2 supported on g-Al2O3, SiO2, ZrO2 and TiO2 catalysts in a batch reactor at 300◦C and 5 MPa of hydrogen pressure was studied. The catalysts were prepared by wet impregnation with a loading of 1.5 atoms of Re per nm2 of support. The catalysts were characterized by N2 adsorption, X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD). The Re(x)/supports catalysts displayed high activities for the conversion of quinoline, although negligible formation of N-free compounds (hydrodenitrogenation) were observed. The intrinsic activities of ReS2 were modified by the support decreased in the order: Re/TiO2 > Re/ZrO2 > Re/SiO2 > Re/g-Al2O3. The highest activity displayed by the Re/TiO2 catalyst was correlated with the Re dispersion and formation of ReS2 species. Meanwhile, the lower conversion of quinoline over the Re/ZrO2, Re/SiO2 and Re/g-Al2O3 catalysts was related to the combined effect of the textural properties of catalysts and the formation of ReS(2-x) species on the supports.