A. Infantes-Molina

“Breathing” in Adsorbate-Responsive Metal Tetraphosphonate Hybrid Materials

The structures of various layered calcium tetraphosphonates (CaH6DTMP; H8DTMP=hexamethylenediamine tetrakis(methylenephosphonic acid)), have been determined. Starting from CaH6DTMP.2H2O, thermal treatment and subsequent exposure to NH3 and/or H2O vapors led to four new compounds that showed high storage capacity of guest species between the layers (up to ten H2O/NH3 molecules) and a maximum volume increase of 55 %. The basic building block for these phosphonates consists of an eight-membered ring chelating Ca2+ through two phoshonate groups, and the organic ligand is located within the layers, which are held together by hydrogen bonds. The structural analysis revealed that the uptake/removal of guest species (H2O and NH3) induces significant changes in the framework not only by changing the interlayer distances but also through important conformational changes of the organic ligand. An anisotropic breathing motion could be quantified by the changes of the unit-cell dimensions and ligand arrangements in four crystalline derivatives. Complete characterization revealed the existence of interconversion reactions between the different phases upon gas uptake and release. The observed behavior represents, to the best of our knowledge, the first example of a breathing-like mechanism in metal phosphonates that possess a 2D topology.

Gas phase catalytic hydrodechlorination of chlorobenzene over cobalt phosphide catalysts with different P contents

The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene (CB) at atmospheric pressure was investigated over silica-supported cobalt and cobalt phosphide catalysts containing different P loading and a fixed amount of cobalt (5 wt.%). The effect of the initial P/Co molar ratio on the stoichiometry of the cobalt phosphide phase, the acidity and the hydrogen activation capability were discussed and these properties correlated with the catalytic activity. Catalytic results indicated that the cobalt phosphide phase is much more active than the monometallic cobalt one. The activity raised with the P content present in the sample due to the formation of the CoP phase instead of the Co₂P one, which favored the formation of hydrogen spillover species, increased the amount of weak acid sites and the number of exposed superficial cobalt atoms probably related to a better dispersion of the active phase. All the catalysts gave rise benzene as the main reaction product.

Nickel and cobalt phosphides as effective catalysts for oxygen removal of dibenzofuran: role of contact time, hydrogen pressure and hydrogen/feed molar ratio

The catalytic activity of nickel and cobalt phosphides, with a metal loading of 5 wt.%, supported on silica was investigated in the hydrodeoxygenation reaction (HDO) of dibenzofuran (DBF) as a model oxygenated compound at different contact times, H2 pressures and H2/DBF molar ratios. The aim of the study was to understand the mechanism of the reaction and to study the impact of H2 pressure and H2/DBF molar ratio on the reaction. The catalysts were characterized by N2 adsorption–desorption isotherm measurement at −196 °C, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), CO chemisorption, NH3 Temperature-Programmed Desorption (NH3-TPD), IR spectroscopy and H2 Temperature-Programmed Desorption (H2-TPD). The prepared catalysts were tested in the HDO reaction of DBF in a continuous-flow fixed-bed stainless steel catalytic reactor at pressures ranging from 1–30 bar at 275 °C. The results obtained indicate that the Ni2P catalyst is more active than the CoP catalyst, converting more than 90% of DBF at the highest contact time into oxygen-free products. The activity of both catalysts increases with increased contact time. At low contact times, the intermediates tetrahydrodibenzofuran (THDBF) and hexahydrodibenzofuran (HHDBF) are observed as products, while an increment in the contact time led to the transformation of THDBF and HHDBF into O-free compounds, mainly bicyclohexane (BCH), indicating that the HDO of DBF follows the path: DBF → HHDBF → THDBF → 2-CHP → BCH. Further, both Ni2P and CoP catalysts are active at medium pressures with HDO degrees similar to those obtained at 30 bar. Ni2P is less affected by the changes in H2/DBF ratio than CoP and the catalysts are more active at high H2/DBF molar ratios.

2D corrugated magnesium carboxyphosphonate materials: topotactic transformations and interlayer "decoration" with ammonia.

In this paper we report the synthesis and structural characterization of the 2D layered coordination polymer Mg(BPMGLY)(H(2)O)(2) (BPMGLY = bis-phosphonomethylglycine, (HO(3)PCH(2))(2)N(H)COO(2-)). The Mg ion is found in a slightly distorted octahedral environment formed by four phosphonate oxygens and two water molecules. The carboxylate group is deprotonated but noncoordinated. This compound is a useful starting material for a number of topotactic transformations. Upon heating at 140 °C one (of the two) Mg-coordinated water molecule is lost, with the archetype 2D structure maintaining itself. However, the octahedral Mg in Mg(BPMGLY)(H(2)O)(2) is now converted to trigonal bipyramidal in Mg(BPMGLY)(H(2)O). Upon exposure of the monohydrate Mg(BPMGLY)(H(2)O) compound to ammonia, one molecule of ammonia is inserted into the interlayer space and stabilized by hydrogen bonding. The 2D layered structure of the product Mg(BPMGLY)(H(2)O)(NH(3)) is still maintained, with Mg now acquiring a pseudo-octahedral environment. All of these topotactic transformations are also accompanied by changes in hydrogen bonding between the layers.

Synthesis and Characterization of Metal-Supported Mesoporous Silicas Applied to the Adsorption of Benzothiophene

The present work reports adsorption/desorption studies of benzothiophene (BT) onto SBA-15 loaded with Fe, Pd and Cu employing in situ FT-IR spectroscopy and batch liquid-phase adsorption methods. The adsorbents were prepared by post-synthesis impregnation of metal salts onto pure siliceous SBA-15 by solid mixture and incipient wetness methods. The adsorbents were characterized by nitrogen adsorption isotherms, TEM, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The incorporated metals, in different oxidation states, were dispersed as nanoparticles on the mesoporous channels of SBA-15. The surface area decreased significantly for samples with incorporated metals, especially for those prepared by solid-mixture impregnation (Cu and Pd), although the hexagonal arrangement and the average pore size remained virtually unaltered. As revealed by batch adsorption isotherms, the incorporation of metals effectively increased the retention of the adsorbent towards the sulphur compound in the following order: Pd < Fe > Cu. DRIFT spectra (under in situ adsorption/desorption conditions) of the samples containing Fe and Pd showed that adsorption of BT onto the former is mainly reversible, whereas BT seems to be chemisorbed in the latter and did not desorb readily upon thermal treatment under He flow.

Hydrodechlorination of polychlorinated molecules using transition metal phosphide catalysts

Ni2P and CoP catalysts (5 wt.% of metal) supported on a commercial SiO2 were tested in the gas phase catalytic hydrodechlorination (HDCl) of mono (chlorobenzene-ClB) and polychlorobenzenes (PCBs) (1,2- dichlorobenzene (1,2-DClB), 1,3-dichlorobenzene (1,3-DClB), 1,4-dichlorobenzene (1,4-DClB), and 1,2,4-trichlorobenzene (1,2,4-TClB)) at atmospheric pressure. It was investigated how the number and position of chlorine atoms in the molecule influence the HDCl activity. The prepared catalysts were characterized by X-ray diffraction (XRD), CO chemisorption, N2 adsorption-desorption at -196°C, and X-ray photoelectron spectroscopy (XPS). Characterization results indicated better active phase dispersion and greater amount of P on the Ni2P catalyst surface. Catalytic results showed that the Ni2P was more active and stable in this type of reactions. The hydrodechlorination activity decreased by increasing the number of chlorine atoms in the molecule and chlorine substituents in close proximity. The observed trend in the HDCl activity was: ClB>1,4-DClB>1,3-DClB>1,2-DClB>1,2,4-TClB. The exception was the catalytic response after 24h on stream observed for the Ni2P in the HDCl reaction of 1,2,4-TClB, which was equal to that observed for the 1,4-DClB molecule, and also yielding benzene as the main reaction product.

Transition Metal Sulfide Catalysts for Petroleum Upgrading – Hydrodesulfurization Reactions

© 2012 Rodriguez-Castellon et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Transition Metal Sulfide Catalysts for Petroleum Upgrading – Hydrodesulfurization Reactions

The Effect of Thermal Treatment under Different Atmospheric Conditions on the Catalytic Performance of Nickel Supported on Porous Silica in the Gas-Phase Hydrogenation of Acetonitrile

A series of mesoporous silica-supported nickel catalysts (2.2 wt% Ni) were prepared by impregnation employing the incipient wetness technique using Ni(II) formate as the impregnation salt. Three different atmospheric conditions were employed during the thermal treatment: air, He and H2. The catalysts were characterised by chemical analysis, XRD, N2 adsorption at −196°C, H2-TPR, H2-TPD and XPS. A direct relationship was found between catalytic activity in the gas-phase hydrogenation of acetonitrile and the Ni 2p3/2 binding energy assigned to the Ni0 atoms of the reduced catalysts, where the catalytic activity decreased with increasing binding energy. The best catalyst obtained was that prepared by thermal decomposition in air and subsequent reduction in a hydrogen atmosphere; this catalyst displayed a high metallic surface and a low value for the Ni 2p3/2 binding energy of Ni0.

Au and AuCu nanoparticles supported on SBA-15 ordered mesoporous titania-silica as catalysts for methylene blue photodegradation

The photocatalytic degradation of methylene blue (MB) dye has been performed under UV irradiation in aqueous suspension, employing photocatalysts based on Au (1.5 wt %) and AuCu (Au/Cu = 1, 2.0 wt %), and supported on SBA-15-ordered mesoporous silica, with and without titania (Si/Ti = 3), in order to evaluate the versatility of this mesoporous support in this type of reaction of great impact from the environmental point of view. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption at −196 °C, and X-ray photoelectron spectroscopy (XPS), so as to study their structural, optical, and chemical properties. All the prepared catalysts were found to be active in the test reaction. The bimetallic AuCu-based catalysts attained very high MB degradation values, in particular AuCu/SBA-15 titania-silica sample reached 100% of dye oxidation after the monitored reaction period (120 min).

CoxPy Catalysts in HDO of Phenol and Dibenzofuran: Effect of P content

Cobalt phosphide catalysts supporting on SiO2 presenting different CoxPy stoichiometry were proved in hydrodeoxygenation (HDO) of two different model molecules present in biomass derived bio-oil such as phenol (Ph) and dibenzofuran (DBF). To investigate composition effects a series of cobalt phosphide catalysts presenting different initial P/Co atomic ratio were prepared. The catalysts were characterized by a range of techniques (N2 physisorption, XRD, TEM, NH3-TPD and XPS) and tested for DBF and Ph HDO activity and selectivity. Characterization results evidenced good textural properties, high dispersion of the active phase, as well as the presence of acid sites after P and Co incorporation. The highest activity was observed for catalysts containing an intermediate P/Co content were the CoP phase was the predominat one. Those catalyst containing Co2P or CoP2 phases were less active in these reactions.