T.A. Zepeda

Effect of stacking of MoS2 slabs on catalytic performance of supported CoMo-catalysts in hydrodesulfurization of dibenzothiophene

Abstract Hexagonal mesoporous materials with wormhole framework structures, having Si/Ti molar ratios of 80, 40 and 20 (Ti-HMS), were used as supports of sulfided-CoMo HDS catalysts. The catalysts were characterized by N2 adsorption–desorption (SBET), Raman spectroscopy and Highre-solution transmission electron microscopy (HRTEM). The catalysts were tested in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT). The Ti-incorporation into the HMS framework have a beneficial effect in the formation of irregular Mo particles with terminal bonds (Mo=O). The most active catalysts showed the highest amount of irregular Mo particles in their oxide state, as deduced from the highest (Mo=OT)/(Mo–O–Mo) Raman band intensities ratio. The common explanation for the greater activity of catalysts having larger amounts of irregular Mo particles are that those species could be good precursors of irregular stacking of MoS2 slabs, with the molybdenum atoms electronically less saturated. Probably, in this type of sites the adsorption of the reactant molecules will be easier. The presence of the Ti ions has a strong effect on the dispersion of the stacking layers of the MoS2 particles, evidenced by HRTEM results.

Performance and S resistance of novel supported PdPt catalysts on Al2O3–TiO2 material in hydrogenation of biphenyl

Abstract The Al2O3–TiO2 materials were synthesised by sol–gel technique with low and high Ti content (molar ratios of Al/Ti=25 and 2). The samples were used as supports of PdPt catalysts with total loading metals of 1 wt-% (molar ratio of Pd/Pt=4) by incipient wetness impregnation using H2PtCl6 and Pd(NO3)x H2O. The samples were characterised by absorption–desorption of N2, X-ray diffraction, transmission electron microscopy and were tested in the hydrogenation (HYD) of biphenyl model reaction. The PdPt catalysts supported on the mixed Al2O3–TiO2 material with low Ti content exhibited a high HYD activity in comparison with the high content Ti sample. It is proposed that the presence of Ti could modify the catalytic behaviour as a result of changes in the electronic properties of the active phase, interacting with such species. Moreover, Ti increased the sulphur resistance of the metallic particles under HYD conditions.

Formation of Co-Promoted MoS2 Fullerene-Like Nanostructures on SBA-15 as Effective Hydrodesulfurization Catalyst

Cobalt-promoted MoS2 particles were synthesized on mesoporous SBA-15 and on a heteroatom (Al or Ti)-modified SBA-15 materials. The structural features of the materials were analyzed using X-ray diffraction (XRD), N2 adsorption–desorption measurements, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier transform infrared (FTIR) spectroscopy of adsorbed NO, and high-resolution transmission electron microscopy (HRTEM). The formation of very well dispersed MoO3 nanoparticles over the walls of the modified SBA-15 nanostructure leads after sulfidation to MoS2 nano-slabs with a characteristic bent morphology, mostly fullerene-like. Moreover, results show that addition of Ti or even more of Al to the SBA-15 matrix allows stabilizing more dispersed Co-promoted MoS2 particles inside the mesoporous network. Combined, the stabilization effect induced by Ti or Al enhancing dispersion and the formation of curved morphologies lead to superior catalytic properties regarding activity and selectivity during the hydrodesulfurization of dibenzothiophene.Graphical Abstract

CO oxidation over CuO/ZrO2 catalysts: effect of loading and incorporation procedure of CuO

Abstract CuO/ZrO2 catalysts were prepared by in situ sol–gel and impregnation methods, with CuO concentrations of 1 and 3·6 mol.-% calcined at 400°C. The catalysts were characterised by S BET, XRD, diffuse reflectance ultraviolet-visible spectroscopy and temperature programmed reduction (H2). The catalytic activity was performed in the CO oxidation. The XRD, diffuse reflectance ultraviolet-visible spectroscopy and temperature programmed reduction results showed that the dispersion of Cu species depends on the method of preparation and on the copper loading. The CuO/ZrO2 catalysts prepared by impregnation procedure showed higher catalytic activity than those prepared by the in situ sol–gel method. This observation can be explained by the presence of small particles of CuO on the catalyst prepared by impregnation (higher dispersion), which does not occur in the catalysts obtained by the in situ sol–gel method due to an important amount of Cu2+ ions that were incorporated into the support network, which are considered catalytically inactive.

Oxidative dehydrogenation of n-octane over Mg-containing SBA-15 material

Abstract In this study, it is proposed the incorporation of MgO into of SBA-15 via the direct synthesis different atomic ratios of Si/Mg (20, 40 and 80). Although the incorporation of Mg did not affect the mesoporous character of SBA-based materials, it was found dramatic changes in the SBA-15 characteristic honeycomb structure even after the incorporation of small amount of Mg. The creation of more basic sites in SBA-15, because of the addition of Mg, improved ODH conversion of n-octane with respect to SBA-15, used as reference. Sample with a Si/Mg molar ratio of 20 showed the best catalytic performance in the oxidative dehydrogenation of n-octane, while the sample with a Si/Mg molar ratio of 40 achieve the highest productions of olefins.

Study of electronic state of supported gold nanospecies by IR spectroscopy

The nature of different Au species supported on hexagonal mesoporous silica has been studied by infrared spectroscopy of adsorbed CO. Experiments revealed existence of the following states of supported gold: neutral metal particles Au°, ions Au⁺ and a number of partly charged states Au^δ+ with different effective charge. Redox pretreatments (vacuum, O₂ and H₂) of Au/SiO₂ at the different temperatures (100, 300 and 500°C) exert a significant effect on the electronic state of supported Au species. The experiments showed high stability of Au^δ+ states under all treatments; that may prove their active role in catalytic properties of gold.

11th Mexican Congress on Catalysis: Catalysis and Nanotechnology

The ‘‘Mexican Catalysis Academy’’, founded in 1988, has organized 11 biannual conferences, mainly devoted to homogeneous and heterogeneous catalysis. The quality and quantity of the contributions presented in these conferences has increased favorably over the years, as well as the diversity of the research fields. This special issue contains a representative part of the papers presented at the 11th Mexican Congress on Catalysis, in this occasion with the theme ‘‘Catalysis and Nanotechnology’’, which took place in Ensenada B.C., Mexico, from June 2nd to 5th, 2009, with more than 100 contributions. Contributors, in this issue, were invited to submit their original manuscripts which were peer-reviewed according to international procedures. We are most pleased to publish in this issue the Mexican contributions for the scientific community. The main topics in this issue have been related with the synthesis, physico-chemical characterization and catalytic performance of unsupported and supported nano-catalysts, with several nanotechnology catalytic-applications focused on various aspects of the catalysis as follows: • Production of alternative fuels, such as deoxygenation and esterification of fatty acids and hydrogen production. • Hydroprocessing of fraction oils, such as hydrodesulfurization, hydrocracking and oxidative desulfurization of diesel. • Photocatalytic applications for environment protection, such as degradation of alizarin red, phenol, 4-nitrophenol, 4-chlorophenol, etc. • Surface studies of carbon adsorbed species on vanadium versus nickel and platinum single crystals. • Hydrogenation and oxidation reactions.