Franklin J. Méndez

Effect of calcination temperature on structural properties and photocatalytic activity of ceria nanoparticles synthesized employing chitosan as template

Ceria nanoparticles were synthesized employing chitosan as template and thermal treatment at different temperatures (350, 650, and 960°C). The effect of calcination temperature on structural properties and photocatalytic activity of ceria nanopowder was also tested. Degradation of an azo dye, Congo Red (CR) as a model aqueous pollutant, was investigated by means of photocatalysis of ceria nanoparticles under visible light irradiation. The influence of catalyst amount, initial CR concentrations, and degradation reaction kinetics were studied. The results were compared with commercial CeO2 at the same degradation conditions.

Preparation of functionalized porous nano-γ-Al2O3 powders employing colophony extract

Graphical abstract

Selective hydrogenation of 1,3-butadiene in presence of 1-butene under liquid phase conditions with NiPd/Al2O3 catalysts

The catalytic performance of Al2O3-supported monometallic and bimetallic catalysts in selective hydrogenation of 1,3-butadiene in the presence of 1-butene under liquid phase conditions was studied. Bimetallic catalysts were prepared by the coimpregnation method with the required amounts of the precursors salts [Ni(NO3)2·6H2O and Pd(NH3)4Cl2·H2O] over pellet-form γ-Al2O3 with a constant content of Pd (0.5 wt%) and varying Ni/Pd atomic ratio (0.25, 0.5, 0.75, and 1) obtaining egg-shell profiles of the active components. The catalysts were characterized by X-ray diffraction, temperature-programmed techniques, such as reduction in hydrogen and desorption of ammonia, N2 physisorption, and transmission electron microscopy. The catalytic test showed that the 1,3-butadiene was selectively hydrogenated when bimetallic catalysts were used. The addition of Ni to the Pd-based catalysts suppressed n-butane formation and increased recovery of 1-butene at medium conversion. Therefore, it was observed an improved catalytic performance of the bimetallic catalysts being highest in the case of the 1NiPd/Al2O3.

NiMo/MCM-41 Catalysts for the Hydrotreatment of Polychlorinated Biphenyls

MCM-41 type mesoporous materials of pure silicon and aluminosilicates (with Si/Al atomic ratios of 20 and 40) were prepared by a facile synthesis method and used to support NiMo catalysts. Characterization by XRD showed typical patterns of this type of mesoporous solids with a partial collapse of the structure on increasing Al content. In addition, signals attributed to the formation of MoO3, NiO and Al2(MoO4)3 in the transition-metal containing catalysts were observed. The 29Si-NMR-MAS spectra showed that local arrangement of the Si–O–Si bonds was regular, independently of the solid being pure or modified with Al, while the 27Al-MAS-NMR spectra of the aluminosilicates showed both structural and non-reticular species. The N2 adsorption–desorption curves showed type IV isotherms, with considerable diminution in the BET areas once the metals were incorporated. The catalytic results in thiophene hydrodesulfurization (HDS) and polychlorinated biphenyl hydrodechlorination (HDCl) revealed a considerable catalytic activity for all prepared catalysts as compared with a commercial NiMo/Al2O3 one, being highest in the case of the NiMo/Al-MCM-41(40) one for HDS, and for NiMo/Al-MCM-41(20) in HDCl. The excellent properties for HDCl can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of the catalysts, namely, to the participation of both coordinatively unsaturated sites of the NiMoS active phase and Brønsted acid sites of the support.Graphical Abstract

Promoting effect of ceria on the performance of NiPd/CeO2–Al2O3 catalysts for the selective hydrogenation of 1,3-butadiene in the presence of 1-butene

The removal of traces of highly unsaturated compounds, such as 1,3-butadiene, from olefin feedstocks via selective hydrogenation is of particular importance because the oligomerization of these impurities produces deactivation and an increased pressure drop across the catalytic beds used in the polymerization processes. The present work focuses on the selective hydrogenation of 1,3-butadiene in the presence of 1-butene using (xCeO2-)Al2O3-supported NiPd catalysts (x = 0, 1, 2, and 3 wt% CeO2) in both liquid and gas conditions. The samples were characterized by XRD, N2 physisorption, Zeta potential, H2-TPR, NH3-TPD, HRTEM and STEM-HAADF. Modifying the catalysts with CeO2 resulted in an increase of 1,3-butadiene conversion, an enhancement of 1-butene selectivity and a decrease of butane production under liquid phase conditions. In contrast, in the gas phase both the Ce-modified and unmodified catalysts behaved similarly: while the fresh catalysts showed similar reactivity to that found in liquid phase conditions, the reacted and thermally pretreated catalysts showed increased reactivity, leading to full hydrogenation up to butane. The improvements observed under liquid phase conditions may be related to modification of the acid strength with increasing CeO2 loading, which would increase the adsorption of 1,3-butadiene and diminish the further hydrogenation of 1-butene. Optimal activity and selectivity were observed for the catalyst with an Ni/Pd atomic ratio of 1, and loadings of 0.5 wt% Pd and 3.0 wt% CeO2.