T. Blasco

Oxidative dyhydrogenation of short chain alkanes on supported vanadium oxide catalysts

Abstract This paper summarizes the main data appeared in the last years on the oxidative dehydrogenation (ODH) of short chain alkanes on supported vanadium oxide catalysts. The acid-base character of metal oxide support influences the dispersion of vanadium on the surface of the support, as well as the nature of the vanadium species. The reducibility and structure of surface vanadium oxide species and the acid-base character of catalysts, in addition to their catalytic properties in the ODH of C2–C4 alkanes, strongly depend on the metal oxide used as support and the vanadium loading. In this way, it appears that tetrahedral V5+-species are active and selective sites in the ODH of C2–C4 alkanes. The effect of the coordination number and aggregation state of surface vanadium oxide species, and the presence of acid/base sites on the catalytic behavior of supported vanadium oxide catalysts are discussed. It is concluded that these are important factors that must be considered to develop selective catalysts in ODH reactions.

Gold(III) stabilized over ionic liquids grafted on MCM-41 for highly efficient three-component coupling reactions.

Two alkoxysilyl-modified ionic liquids (ILs) have been synthesized and further grafted onto mesoporous silica, MCM-41; these ionic liquids were used for dispersing AuCl3 catalysts that activate C-H bonds as required for the synthesis of propargylamines by coupling alkyne, aldehyde and amine (A(3) coupling) species. (29)Si NMR experiments demonstrate the formation of covalent bonds between alkoxysilyl-modified Bmim IL and the MCM-41 surface through silanol groups. The catalytic activities of Au(III)-supported MCM-41 and Au(III) homogeneous catalysts are lower than those obtained for the IL functionalized Au-MCM-41 solids when the same gold loading is considered. An interaction between Au(III) species and the IL is proposed for explaining the stabilization of gold(III) species. However, successive reaction cycles result in a decrease in the catalytic activity that has been explained on the basis of gold leaching.

Silica supported copper and cerium oxide catalysts for ethyl acetate oxidation

The formation of active sites in the silica supported copper and cerium oxide bi-component catalysts for total oxidation of ethyl acetate was studied by Nitrogen physisorption, XRD, XPS, UV-Vis, Raman, FTIR of adsorbed CO spectroscopies and TPR. It was found that the interaction between the copper oxide nanoparticles and the supported on the silica ceria ones is realized with the formation of interface layer of penetrated into ceria lattice copper ions in different oxidative state. This type of interaction improves the dispersion of copper oxide particles and provides higher accessibility of the reactants to the copper active sites even at low copper amount.

The investigation of beta polymorphs by 19F nuclear magnetic resonance

Abstract ITQ-16 (polymorphs A, B and C of beta zeolite) with different Ge content (Si/Ge=4-30) have been synthesised in fluoride medium using 4-Aza, 1-azoniabicyclo[2,2,2]octane, 1-benzyl (BzD+) as organic structure directing agent (SDA). The X-ray diffraction (XRD) patterns, present the peaks characteristic of polymorph C (zeolite ITQ-17) and (A+B) (zeolite beta) which allows to determine the percentage of the former in every sample. F− anions are incorporated into the [43 54] and double four member ring (D4R) cages of polymorphs A and B, and of polymorph C, respectively, compensating the positively charged SDA. Since the 19F nuclear magnetic resonance (NMR) chemical shift depends on the number of Ge and Si atoms and the geometry of the lodging cage, the spectra of samples ITQ-16 change, with the relative amounts of polymorphs (A+B) and C, and the Si/Ge molar ratio. The percentage of polymorph C calculated from the relative area of the 19F NMR peaks show a good, agreement with those obtained by XRD. Moreover, the detailed analysis of the spectra indicates an enrichment in Ge of the D4R units of polymorph C. The general trend observed is that the relative amount of polymorph, C increases as the Ge content in the sample increases.

29-P-23-Microporous zincophosphates as solid based catalysts

Publisher Summary This chapter discusses microporous zincophosphates as solid base catalysts. Samples of tridimensional microporous zinc phosphates with fully connected framework with structures type FAU and CZP are prepared. The influence of some synthesis parameters on the nature of the crystalline phases obtained, such as crystallization time and temperature, concentration of the different reactives or pH, are also discussed. Physicochemical characterization of the pure samples has been performed by different techniques: X-ray diffraction (XRD), thermogravimetric analysis (TG), in situ thermal XRD analysis, and scanning electron microscopy (SEM). These materials are tested in the Knoevenagel condensation of different esters and benzaldehyde.

Pyrrole as an NMR probe molecule to characterise zeolite basicity

The 1H NMR chemical shift of the N–H group of pyrrole adsorbed on alkali metal ion exchanged FAU-type zeolites depends on the zeolite intrinsic basicity, while, as shown for zeolite LiY, the NMR of alkali metal nuclei reflects the interaction of the aromatic cycle with the cations at sites SII.

1-Benzyl-1-methyl-hexamethylenammonium and some of its fluorine-containing derivatives as structure directing agent for the synthesis of all-silica zeolites

The 1-benzyl-1-methyl-hexamethylenammonium (BMHM) cation under the appropriate synthesis conditions is a good structure directing agent (SDA) for the synthesis of pure silica zeolite beta in fluoride media. The chemical properties of this cation change with the replacement of a fluorine atom by a hydrogen atom in the aromatic ring and the nature and morphology of the crystal phases thus obtained are affected. The 1-orthofluorobenzyl-1-methyl-hexamethylenammonium allows the crystallization of all-silica beta zeolite but the morphology of crystals is very different from that of beta obtained with the all-hydrogen counterpart. The meta-F derivative leads to a mixture of three phases, Beta, nonasil (NON) and a characteristic unidentified phase, whereas by using the para-F cation only, nonasil is obtained.

Structure directing role of cyclic amines containing an aromatic ring in the synthesis of AlPOs and SAPOs

Abstract AlPO and SAPO materials have been synthesised from gels containing N-benzyl cyclic amines as structure directing agents (SDA). The nature of the crystalline phases, their degree of crystallinity, crystal size and morphology and Si incorporation can be modified by tuning the ring size of the cyclic amine.

Characterization of LTA-and CHA-type zeolites by means of solid state NMR

Abstract Pure silica LTA and CHA-type zeolites synthesized in fluoride media have been investigated by l H and 29 Si solid state (MAS) NMR spectroscopy. The l H spectra of the dehydrated samples reveal the presence of different silanol groups (1.5–2.5 ppm), while upon hydration they give a band of water at ca. 3 ppm and a weak peak at 7.5 ppm. The application of l H/ 29 Si cross polarization (CP MAS) two dimensional 2D-heteronuclear correlation technique supports the existence of a variety of Si-OH groups whose relative intensity changes. These groups interact in a different way with water. This type of interaction can be tentatively related with the location of the silanol groups in the crystals.

Nuclear magnetic resonance investigation on the adsorption of pyrrole over alkali-exchanged zeolites X

Abstract The interaction of pyrrole with extraframework cations in zeolites NaX and CsNaX has been studied by 1 H, 23 Na and 133 Cs magic angle spinning (MAS) nuclear magnetic resonance (NMR). 1 H NMR chemical shift of the NH group shifts to low field as the pyrrole loading over zeolite NaX decreases, indicating that the probe molecules selectively adsorb over the more basic sites. The careful analysis of the 23 Na MAS NMR spectra of zeolites NaX and CsNaX containing pyrrole indicates the appearance of a new signal which is attributed to Na + cations, more probably located at the SII sites, strongly interacting with the pyrrole heterocycle. The results obtained for NaX suggests that the stoichiometry of the pyrrole-Na + interaction is 2:1. The 133 Cs MAS NMR spectra indicate that all the supercage Cs + cations in zeolite CsNaX are affected by the presence of pyrrole. Part of them are strongly interacting with the ring of pyrrole as observed for Na + cations. At low loadings, pyrrole molecules prefer being adsorbed over more basic sites, involving Cs + cations.