Carlos E. Scott

Ru/alumina and Ru−Mo/alumina catalysts: an XPS study

RuAl2O3 and RuMoAl2O3 catalysts have been prepared by impregnating respectively γ-Al2O3 and calcined MoAl2O3 with aqueous solutions of ruthenium (III) acetate. XPS spectra of catalysts dried at 393 K, calcined in air at 873 K, and sulfided in H2H2S are reported. Ru and Mo species in the catalysts, according to the respective binding energies, were ruthenium dioxide and oxomolybdenum (VI) in catalysts calcined at 873 K and a ruthenium sulfide and MoS2 in the sulfided catalysts. Unusually low Ru binding energies were found for some catalysts. The properties of the catalysts in thiophene HDS are interpreted with the aid of the XPS results.

Crystal and molecular structure of three oxovanadium(IV) porphyrins: oxovanadium tetraphenylporphyrin(I), oxovanadium(IV) etioporphyrin(II) and the 1:2 adduct of (II) with 1,4-dihydroxybenzene(III) ― Hydrogen bonding involving the VO group ― Relevance to catalytic demetallisation

Abstract The structures of the three title compounds have been determined by X-ray Crystallography. (I) is tetragonal, spacegroup [4/m with Z = 2, a = 13.345(7), c = 9.745(8) A. (II) is triclinic, spacegroup P 1 , Z = 2, a = 10.52(1), b = 11.70(1), c = 12.97(1) A, α = 70.7(1), β = 113.8(1), γ = 108.8(1)°; (III) is orthorhombic, spacegroup Pnaa, Z = 8, a = 17.72(1), b = 18.14(1), c = 18.57(1) A. Data for all three compounds have been collected on a diffractometer and 556 (I), 2316 (II), 1263 (III) above background reflections have been refined to R (0.099, 0.086, 0.082) respectively. (I) has disordered C4h symmetry following a well-known structure type. The features of the oxovanadium(IV) etioporphyrin structures in (II) and (III) are similar. Compound (III), the adduct with 1,4-dihydroxybenzene (quinol, H2Q) [VO(ETP)]2[H2Q], which crystallised from a solution of [VO(ETP)] in tetrahydrofuran stabilized with O.1% quinol, consists of [VO(ETP)] molecules linked by H-bonds through the VO groups to the quinol OH groups. We discuss the general phenomenon of H-bonding to VO groups and its possible relevance to binding of VO porphyrins to OH groups at catalyst surfaces.

Interaction between ruthenium and molybdenum in RuMo/Al2O3 catalysts

Abstract RuMo/Al2O3 catalysts with various molybdenum loadings (0.15–0.6 wt.-%) and 0.6wt.-% ruthenium were prepared and characterized by hydrogen and carbon monoxide chemisorption. n-Hexane hydrogenolysis and cyclohexane dehydrogenation were performed over the reduced catalysts. Cyclohexene dehydrogenation was also carried out over the sulfided catalysts. The results suggest an electron transfer from molybdenum to ruthenium sites.

The interaction of vanadium and nickel porphyrins and metal-free porphyrins with molybdenum-based hydroprocessing catalysts: relevance to catalyst deactivation and catalytic demetallization

Abstract The poisoning of a Co-Mo-alumina hydrodesulphurization (HDS) catalyst by metal-free, vanadium and nickel etio- and tetraphenyl porphyrins and the binding and reactivity of the porphyrins on oxide and sulfide surfaces is described. The surface interactions of porphyrins were studied by adsorption from solution, and UV-visible diffuse-reflectance and ESR spectroscopy. Metalloporphyrins undergo demetallation at acidic sites. The porphyrin ring is oxidized at a meso-carbon by oxomolybdenum(VI) species and adsorbed oxygen to a cation radical and an oxophlorin. During HDS porphyrin bound to the catalyst is hydrogenated at the meso-carbon to phlorin. Interaction of the porphyrins with surfaces is similar to that of polynuclear aromatic hydrocarbons. The relevance of these results to catalyst deactivation and catalytic demetallation is discussed.

Interaction of vanadium and nickel porphyrins with catalysts, relevance to catalytic demetallisation

Abstract The binding of vanadium and nickel porphyrins to γ-Al2O3, SiO2-Al2O3 MoO3/Al2O3, NiO/Al2O3, and to Co- and Ni-Mo/Al2O3 catalysts in their oxide and sulfide forms, and their subsequent decomposition reactions when heated in nitrogen or exposed to hydrogen and thiophene in catalytic hydrodesulfurisation, have been studied by electron spin resonance. We wished to discover which part of the porphyrin molecule became bound to the catalyst and to which surface sites. Our main conclusions are that the porphyrins are bound to the catalyst by a donor-acceptor interaction,, the delocalised π-system of the porphyrin ring being the electron donor, and the Bronsted and/or Lewis acid function of the catalyst being the acceptor. Depending on the conditions, oxidation or hydrogenation of the porphyrin ring at the meso carbons is the initial stage in the decomposition of the bound porphyrins.

Binding and decomposition of oxovanadium(IV) phthalocyanine, tetraphenylporphyrin and etioporphyrin on hydrotreating catalysts studied by X-ray photoelectron and ultraviolet–visible spectroscopies. Relevance to catalytic demetallisation

The interactions of oxovanadium(IV) phthalocyanine, VOPc, oxovanadium(IV) tetraphenylporphyrin, VOTPP, and oxovanadium(IV) etioporphyrin, VOETP, with alumina, silica–alumina, fluorided silica, Co3O4, MoO3, MoS2, MoO3/Al2O3 and Co–Mo/Al2O3 catalysts in the oxide and sulphide forms have been studied by X-ray photoelectron spectroscopy and u.v.–visible diffuse reflectance spectroscopy. Partial demetallisation of VOTPP and VOPc, but not VOETP, occurs on acidic (H+) supports. The VO2+ thereby released is reduced in the X.p.s. spectrometer; porphyrin-bound vanadium is not reduced.Changes of core-electron binding energies of vanadium and nitrogen caused by interaction of the porphyrins with the supports is small, and there is no evidence of a strong interaction with the surface through vanadium or nitrogen. It is therefore suggested that the porphyrins are bound to the surfaces by a donor–acceptor, or charge-transfer, interaction through the π system of the porphyrin ring and Bronsted- and/or Lewis-acid sites of the surfaces.

HDS of Dibenzothiophene and Vanadyl Porphyrin HDP on bulk Fe-Mo mixed sulphides

Abstract Bulk Fe-Mo mixed sulphides were prepared by homogeneous precipitation. The obtained solids were characterised by chemical analysis, X-ray diffraction, X-ray photoelectron spectroscopy, 57 Fe Mossbauer spectroscopy, and nitrogen adsorption (BET) for surface area determinations. HDS of dibenzothophene (in a batch reactor) and HDP of vanadyl octaethyl porphyrin, at high pressure, were used as catalytic tests. It was found that Fe strongly promotes Mo for both reactions, with a more marked synergy for the HDP than for the HDS. 57 Fe Mossbauer spectroscopy suggests that Fe exist in only one phase, for the mixed Fe-Mo sulphides. This phase could be the results of some Fe substitution in the MoS 2 structure. For HDP the activity is maximum at a Fe(Fe+Mo) atomic ratio of 0.68, and increases linearly with the weighted average hyperfine field, which is related to changes in the density of states of d electrons at the Fermi level, clearly suggesting that synergy is related to an electronic effect. For HDS of DBT the activity maximum is located at a Fe/(Fe+Mo) atomic ratio of 0.52.

Effect of the preparation method on the reducibility of molybdena–alumina catalysts

Abstract Two series of molybdena–alumina catalysts were prepared. The first series was prepared by the incipient wetness procedure (1.7–8.8 wt.% Mo) (series IW). A second series was obtained using the equilibrium adsorption (1.3–8.2 wt.% Mo) (series EA) method. X-ray photoelectron spectroscopy (XPS) was used to study the distribution of Mo oxidation states. The average Mo oxidation state estimated from XPS agreed with that obtained by measuring the O 2 consumption on reoxidation, for a given catalyst. The chemisorption of oxygen at −78°C and the isomerization of 1-butene were performed as probes for assaying the number of coordinatively unsaturated sites created by the reduction process. These studies were conducted in order to study possible changes in Mo speciation or distribution, relevant to catalytic reactions, which may occur as a result of the specific features of the preparation method (EA vs. IW). The results showed that for both series of solids, the reducibility of the molybdenum species increases as the metal loading increases, in agreement with the literature. For catalysts with similar loading, the IW series showed a higher degree of reduction with a concomitant increase in the relative abundance of Mo(IV) species attributed to paired double-bonded Mo(IV) entities (as in MoO 2 ). The reducibility data were consistent with the catalytic results and the oxygen chemisorption results. IW preparations (with similar Mo loading) were more active towards the isomerization of 1-butene and chemisorbed larger amounts of oxygen than their EA counterparts. The differences in reducibility can be ascribed to a nonuniform repartition of the molybdenum species between the external and internal surfaces of the alumina, for the IW preparations. Another possible explanation may stem from a decoration effect of the molybdenum species by Al(III) ions. The latter may arise from dissolution of the alumina, which is favored on the EA series due to the long contact time between the solution of the Mo promoter and the support.

SYNTHESIS OF Al-PILC ASSISTED BY ULTRASOUND: REDUCING THE INTERCALATION TIME AND THE AMOUNT OF SYNTHESIS WATER

Of all the known pillared layered clays (PILC), Al-PILC is the most studied. In spite of that, its use on a commercial scale is not yet possible due to the large amount of water required for its synthesis. The aim of the present work was to take advantage of the beneficial effects of ultrasound radiation for reducing intercalation time, and to optimize the synthesis parameters in order to find a viable industrial means of preparing Al-PILC.A comprehensive study of the effect of ultrasonic radiation on the parameters which have a direct effect on the amount of water used in the synthesis was conducted, specifically on the effects of: (1) mmol of Al/g of clay ratio (R) by decreasing the volume of A1 solution and keeping the amount of clay constant, (2) the concentration of clay in the initial suspension (or not suspending the clay at all), and (3) the concentration of the A1 precursor solution. The use of ultrasonic radiation produced the expected reduction in exchange time which was attributed to a decrease of the clay-particle size. This decrease of particle size gave rise to an improvement in the diffusion of the A1 precursor towards the core of the clay grain leading to solids with increased surface areas, basal spacing and X-ray diffraction peak definition. By optimizing the synthesis parameters directly involved in the consumption of water, it was possible to decrease the amount used by >60%.

Hydrotreating on mixed vanadium-nickel sulphides : A study of the synergetic effect

Abstract The preparations of pure and mixed vanadium–nickel sulphides were carried out by the homogeneous precipitation method (under inert atmosphere). Thiophene HDS, pyridine HDN, toluene hydrogenation and vanadyl porphyrin HDP, were carried out as catalytic tests. The catalysts were also characterized by XPS, TPR, BET surface area and XRD. These solids, after sulphidation procedure, exhibit a synergetic effect, the importance of which depends on the hydrotreating reaction. The product distributions obtained in the thiophene hydrodesulphurization and the pyridine hydrodenitrogenation and the activity observed for toluene hydrogenation suggest that the synergy is mainly related to the hydrogenation step. The cause of this synergy could tentatively be assigned to an electronic transfer between the two metallic components in the mixed sulphides.