Adriana Echavarría

Total oxidation of toluene over calcined trimetallic hydrotalcites type catalysts.

Two trimetallic ZnCuAl and MnCuAl hydrotalcites have been successfully synthesized by a co-precipitation method. The manganese based material was identified as a new hydrotalcite phase. Both lamellar precursors were calcined at 450 and 600 degrees C and the resulting catalysts were tested on reaction of total oxidation of toluene. The solids were characterized by X-ray diffraction, thermal analysis, atomic absorption spectroscopy, Fourier transformed infrared spectroscopy, N(2) adsorption and H(2) temperature-programmed reduction. It was found that ZnCuAl materials are composed of copper and zinc oxides supported on alumina; while MnCuAl ones comprise basically spinel phases, which were not completely identified. The catalytic behavior of the calcined samples showed that Mn hydrotalcite calcined at 450 degrees C exhibited the best catalytic performance that corresponds to 100% toluene conversion into CO(2) at about 300 degrees C.

Synthesis and structure of a porous zinc vanadate, Zn3(VO4)2·3H2O

A zinc vanadate with the formula Zn3(VO4)2·3H2O was synthesized by hydrothermal reaction of a gel of composition [(CH3CO2)2Zn·2H2O] : 0.5V2O5: 0.4 [1,3-diaminepropane] : 1.5 NaOH : 114 H2O, held at 170°C for 24 hours. The structure was determined ab initio by means of the EXPO direct methods program and refined with GSAS. The pale yellow solid crystallizes in the hexagonal space group P-6 with a= 6.07877(8), c= 7.1827(2) Å. The structure consists of vanadium tetrahedra bonded to distorted octahedral zinc atoms to create one dimensional columnar passageways for molecules. Though occupied by water in the as synthesized form, the passages could host other small molecules.

Crystal structure a cobalt molybdate type φx: NaCo2OH(H2O)(MoO4)2

A cobalt molybdate with the formula NaCo2OH(H2O)(MoO4)2 was synthesized by hydrothermal reaction at 200°C in 3 days. The structure was determined from powder data by means of the EXPO direct methods program and refined with GSAS. The purple solid crystallizes in the monoclinic space group C2/m with a=9.3789(3), b=6.3330(1), c=7.6280(2) A, and β=115.833(2)a. Octahedral cobalt atoms, centered at 1/4b and 3/4b, share edges to create endless chains running parallel to the b axis. The chains are connected through molybdenum tetrahedra, which share two vertices with consecutive octahedra in one chain and extend the third vertex to an adjacent chain; the fourth vertex protrudes into the interlayer space. This arrangement repeats itself indefinitely in the ab plane to create a layered structure.

Simultaneous tetralin HDA and dibenzothiophene HDS reactions on NiMo bulk sulphide catalysts obtained from mixed oxides

NiMo bulk sulphide catalysts were obtained from mixed-oxides. The mixed-oxides were obtained by calcining the as-synthesized lamellar precursor with the so-called ϕy structure and (NH4)H2xNi3−x(OH)2(MoO4)2 formula. The corresponding mixed-oxides obtained by calcination were characterized by nitrogen adsorption, XRD, and ICP. Mixtures of α-NiMoO4 and β-NiMoO4 were obtained. A batch reactor was used for CS2/n-hexadecane in situ sulphidation of the mixed-oxides. A mixture of dibenzothiophene and tetralin was used for the liquid phase reaction carried out at 613 K and 70 bar. After the catalytic tests, the bulk sulphide catalysts were characterised by nitrogen physical adsorption, synchrotron light XRD, EXAFS and HR-TEM. The EXAFS simulations are consistent with disordered nickel sulphide particles dispersed in the catalysts. HR-TEM images showed randomly oriented, stacked-layer particles typical of Mo sulphide. The bulk catalysts had larger HDS and HDA activities and selectivities for hydrogenation reactions than alumina supported conventional catalysts containing the same Ni : Mo ratio. A pronounced support effect was observed for both HDS and HDA reactions. The use of the support strongly suppressed both cyclohexylbenzene formation in HDS of DBT and cis-decalin formation in HDA of tetralin. This suggests that similar active sites are involved in the formation of these compounds on the one hand, while another type of site is involved in biphenyl and trans-decalin formation on the other.

A zinc phosphate with laminar structure: (ZnPO4)4(H2PO4)2(C4N2H14)2

Abstract A zinc phosphate compound with composition (ZnPO4)4(H2PO4)2(C4N2H14)2 was synthesized by the hydrothermal reaction of zinc oxide and phosphoric acid in the presence of 1,4-diaminebutane. The crystal structure was solved from powder data and exhibits triclinic symmetry with a=8.6590(3) A, b=10.3467(3) A, c=8.3910(3) A, α=102.180(2)°, β=93.676(2)° and γ=88.203(2)°. The new organo-zincophosphate has sheets built from saw-type four member ring ladders, where ZnO4 and PO4 tetrahedrons alternate. Additional phosphate groups project into the interlayer voids where the protonated amine resides.

A zinc chromate of type ΦY : synthesis and structure

Abstract A zinc chromate with the formula (NH 4 OH) 3/2 (ZnCrO 4 ) 2 was synthesized by hydrothermal reaction at 100°C in 24 h. The structure was solved from powder data and refined with GSAS. The yellow solid crystallizes in the hexagonal space group R−3m with a =5.99634(7) A and c =21.5117(3) A. Two types of adjacent rows of zinc octahedra, one of which is full while its neighbor has a vacant site between successive octahedra, are linked through chromate groups which extend two vertices to consecutive edge sharing octahedra in one row and a third vertex which serves as bridge to the contiguous row. The fourth tetrahedral vertex protrudes into the interlayer space. This arrangement repeats itself indefinitely in the ab plane to create a layered structure.

Synthesis and characterisation of the layered zinc phosphate KZn2(PO4)(HPO4)

Abstract A layered potassium zinc phosphate compound with composition KZn 2 (PO 4 )(HPO 4 ) was synthesised by the hydrothermal reaction of zinc chloride and phosphoric acid in the presence of KOH and triethanolamine. The crystal structure of KZn 2 (PO 4 )(HPO 4 ) was reinvestigated and solved from single crystal data in order to complete an early crystallographic work. The material shows a sinusoidal laminar structure based on sheets built from three member ring units, with two vertex-sharing ZnO 4 tetrahedral neighbours and one PO 4 tetrahedron; a three-connected oxygen atom closes the ring. Dangling phosphate groups protrude into the interlayer spaces and neutralize the K + ions. KZn 2 (PO 4 )(HPO 4 ) was also characterized by SEM, TG/DTA, 31 P MAS NMR and chemical analysis.

Structural characterization of a porous zinc vanadate: Zn 3 (VO 4 ) 2 ⋅3H 2 O

A novel porous material of composition Zn 3 (VO 4 ) 2 ⋅3H 2 O was prepared hydrothermally. The solid crystallizes in the hexagonal space group P 6 , with a =6.078 77(8), c =7.1827(2) A, and V =229.857 A 3 .

X-ray powder diffraction data for a new nickel zinc chromate, (NH4OH)3/2NiZn2Cr2O9⋅2H2O

A new nickel zinc chromate with the composition of (NH 4 OH) 3/2 NiZn 2 Cr 2 O 9 ⋅2H 2 O was synthesized by hydrothermal method. The compound was characterized by XRD, TGA, and XRF. X-ray powder diffraction data show that the crystal system of the title compound is hexagonal with space group R -3 m , z =3, and unit-cell parameters: a =5.9794 and c =21.4875 A.

Structural characterization of a new zinc phosphate: (ZnPO4)4(H3PO4)2(C4N2H14)2

A new zinc phosphate was synthesized by the hydrothermal reaction of zinc oxide and phosphoric acid in the presence of 1,4-diaminebutane. The formula of the product is (ZnPO 4 ) 4 (H 3 PO 4 ) 2 (C 4 N 2 H 14 ) 2 and crystallizes in the triclinic system with a =8.6590(3) A, b =10.3467(3) A, c =8.3910(3) A, α=102.180(2)°, β=93.676(2)°, and γ=88.203(2)°.