Aída Gutiérrez-Alejandre

Characterization of alumina–titania mixed oxide supports: Part II: Al2O3-based supports

Abstract Bulk and surface characterization of alumina-rich Al 2 O 3 –TiO 2 mixed oxides with TiO 2 /(Al 2 O 3 +TiO 2 ) molar ratios equal to 0, 0.05 and 0.1, prepared by sol–gel and impregnation procedures have been performed by XRD, DTA, surface area, FTIR, UV–Vis, FT-Raman and TPD of ammonia. The results indicate that in the case of the samples prepared by the sol–gel procedure, an increase in surface area with titania loadings is obtained, in contrast to their impregnation counterparts, where a decrease is observed. The results from XRD, Raman and UV–Vis indicate that better titania dispersions are obtained by the sol–gel procedure and that at the titania loadings used here, no separate titania particles are detected. Additionally, the UV results show that Ti cations are essentially isolated, possibly into an octahedral form and with a lower coordination. In the samples prepared by the sol–gel procedure there is no evidence of titanium oxide species on the surface, suggesting that titania is probably dissolved into the alumina bulk. These results would explain the activity trends observed in alumina-rich Mo/Al 2 O 3 –TiO 2 HDS catalysts.

Redox and acid reactivity of wolframyl centers on oxide carriers: Brønsted, Lewis and redox sites

Abstract Catalysts prepared by impregnating tungsten oxide on alumina, titania and zirconia and their mixed oxides have been characterized by skeletal IR, IR of adsorbed ammonia, Raman and UV–VIS–NIR spectroscopies and by temperature programmed reduction. In all cases catalysts with W loading well below the monolayer have been taken into consideration. Surface mono-oxo wolframyl species with similar low coordination structure have been found to largely predominate in all the supports. However, the WO bond length, the Lewis acidity, the charge transfer transition energies and the reducibility of the WOx species strongly depend on the support nature. In particular, the wolframyls on alumina are most acidic, have higher charge transfer transition energies and are less easily reducible than those on titania. The wolframyls on zirconia show intermediate properties. Evidence is given for the different behavior of wolframyl centers in spite of their similar geometric “molecular” structure. The different properties of wolframyl centers on the supports used here explain the different behavior of these materials for hydrocarbon conversion, in the selective catalytic reduction of NO by ammonia and as precursors of hydrodesulphurization catalysts.

Relationship between hydrodesulfurization activity and morphological and structural changes in NiW hydrotreating catalysts supported on Al2O3–TiO2 mixed oxides

Abstract Characterization and catalytic activity of the NiW-based catalysts supported on Al–Ti( x ) mixed oxides has been obtained. The results from the characterization techniques (Surface area, XRD, DRS, TPR, XPS, FTIR of adsorbed NO and HREM) were used to establish a relationship between the morphological and structural changes of the tungsten phases and catalytic activity. The results indicate that the incorporation of titania to the support enhances the reducibility and sulfidability of the tungsten phases due to mainly a reduced interaction of the tungsten phases with the support. Correlation of the catalytic activity in the thiophene HDS reaction and the number of tungsten atoms in edge and corner positions in the WS 2 crystallites indicates that only the number of tungsten atoms equivalent to those present in one layer of the WS 2 crystallites are active at a given time.

Characterization of alumina-titania mixed oxide supports I. TiO2-based supports

Abstract The bulk and surface properties of a series of titanium-rich Al 2 O 3 -TiO 2 mixed oxides catalytic supports have been determined by different techniques ( S BET , pore size distribution, XRD, DTA, FTIR, FT-Raman, UV-vis diffuse reflectance and FTIR of adsorbed pivalonitrile and pyridine). The analysis of the results indicates that the prepared solids were fairly homogeneous, with titania showing the anatase structure and no segregation of alumina particles. Also, the addition of small amounts of alumina to titania enhances significantly its thermal stability. The UV, FTIR, Raman and XRD results suggest that part of the alumina forms a solid solution with TiO 2 and that two types of aluminum are present, one due to surface monolayer-type species and other due to octahedrally coordinated bulk species. The FT-Raman and the FTIR spectra of adsorbed probe molecules support the idea that the anatase particles are largely covered by surface alumina partial monolayers.

In situ Raman studies during sulfidation, and operando Raman-GC during ammoxidation reaction using nickel-containing catalysts: a valuable tool to identify the transformations of catalytic species

Ni-containing catalysts are investigated under reaction conditions for two different cases, during sulfidation, with Ni-Mo based catalysts, and during ammoxidation reaction, with the Ni-Nb catalysts. It is shown how Raman spectroscopy can follow some of the transformations of these catalysts upon different treatments. For the NiMo/Al(2)O(3)-SiO(2) system it was possible to identify some of the sulfided Mo species formed during the sulfidation of the oxide precursors, while for the bulk Ni-Nb oxide catalysts the simultaneous reaction-Raman results strongly suggest that the incipient interaction between niobium and nickel oxides at low Nb/Ni atomic ratios is directly related to catalytic activity, and that a larger size well-defined NiNb(2)O(6) mixed oxide phase is not active for this reaction. Moreover, the promotion by niobium doping appears to be limited to a moderate niobium loading. It was found that in situ and operando Raman are valuable techniques that allowed the identification of active Mo-S and Ni-Nb species under reaction conditions, and that are not stable under air atmospheres.

Highly reversible sorption of H2S and CO2 by an environmentally friendly Mg-based MOF

Mg-CUK-1, an ecologically friendly material synthesised in water is found to be a high-capacity, highly reversible adsorbent for acidic gases including H2S and CO2. Furthermore, Mg-CUK-1 is demonstrated to retain long-range crystallinity upon sorption cycling; its sorption performance is maintained over multiple cycles, even in the presence of high relative humidity (95%). Reversible H2S adsorption by Mg-CUK-1 is rare among MOFs studied for this purpose to date. The joint experimental and computational studies presented here show that Mg-CUK-1 is an effective solid adsorbent for applications in the field of acid gas capture, an application that is highly relevant for the purification of many industrial gas streams.

Transesterification of Caesalpinia eriostachys seed oil using heterogeneous and homogeneous basic catalysts

ABSTRACT Caesalpinea eriostachys seed oil, as a source of triglycerides with potential application for biodiesel production in Mexico is introduced. Its lipid profile obtained by Gas Chromatography-Mass Spectrometry (GC-MS) revealed saturated and unsaturated glycerol esters as the constituents. Therefore, heterogeneous and homogeneous catalyzed transesterification reactions were assayed employing ZnAl hydrotalcites and KOH, as the catalysts, respectively. The transesterification reactions yielded 59% for Zn/Al(2), 79% for Zn/Al(4), and 90% for KOH, depicting typical behavior, as in biodiesel production data from literature, where Zn-Al hydrotalcites or KOH were assayed. The caloric, density, viscosity values, and fatty acid methyl esters profile from reaction products were concordant to EN 14214, suggesting C. eriostachys as a promising feedstock for biodiesel production.

Molecular Structures of WO3/Al2O3-TiO2 Catalysts Under Controlled Environment

A series of WO3/Al2O3-TiO2 catalysts powders with titania-alumina mixed oxides synthesized by a sol-gel procedure were prepared by the pore volume method. The tungsten content used in the samples was that needed to obtain a coverage of 2.8 W atoms/nm2 calculated on the basis of the support area. The samples were characterized by FT-IR and FT-Raman spectroscopies under controlled atmosphere. The molecular structures of the supported W species at ambient (hydrated) and dehydrated conditions are presented. The insights obtained from these fundamental studies allow a better structural understanding of the surface tungsten oxide species and their transformations under different environments.