Tatiana Klimova

Ni and Mo interaction with Al-containing MCM-41 support and its effect on the catalytic behavior in DBT hydrodesulfurization

Abstract A series of Mo and NiMo catalysts supported on Al-containing MCM-41 was prepared and characterized by N2 physisorption, XRD, ammonia TPD, temperature programmed reduction (TPR), UV-Vis diffuse reflectance spectroscopy (DRS) and 27 Al MAS-NMR. It was shown that the incorporation of Al atoms into the siliceous MCM-41 framework causes a deterioration of the textural characteristics and some loss in the periodicity of the MCM-41 pore structure. However, the acidity of the Al-containing MCM-41 is substantially higher. The dispersion of Mo and Ni oxidic species increases with the incorporation of aluminum in the MCM-41 support due to the strong interaction of Mo and Ni oxidic species with aluminum atoms of the support. However, the strong interaction of metal species with the Al-containing MCM-41 supports, up to the formation of Al2(MoO4)3 in the case of unpromoted Mo catalysts, produces an increase in the proportion of Ni and Mo species difficult to reduce. When Ni and Mo are impregnated simultaneously the formation of Al2(MoO4)3 is prevented because of the competitive interaction of both, Ni and Mo species, with Al atoms of the support. For both, Mo and NiMo catalysts, maximum catalytic activity in dibenzothiophene (DBT) hydrodesulfurization is observed for the catalysts supported on Al-MCM-41 with SiO2/Al2O3 molar ratio of 30. When Al-containing MCM-41 is used as a support for NiMo catalyst, some cracking of the main reaction products (biphenyl (BiP), cyclohexylbenzene (CHB) and dicyclohexyl (DCH)) is observed.

New selective Mo and NiMo HDS catalysts supported on Al2O3–MgO(x) mixed oxides

Abstract In the search of selective hydrodesulfurization catalysts with low hydrogenating function, Mo and NiMo catalysts supported on Mg–Al mixed oxides with molar ratios x =MgO/(MgO+Al 2 O 3 )=0.0, 0.05, 0.25, 0.50, 0.75 and 1.0 were prepared by the sol–gel method. The synthesized solids were characterized by surface area, TGA, X-ray diffraction, temperature programmed reduction (TPR), DRS, FTIR and FT-Raman spectroscopy and high resolution electron microscopy (HREM). The catalysts were tested in the thiophene hydrodesulfurization reaction. The results indicate that even with the incorporation of small amounts of magnesia to the alumina support, the hydrogenation function of the catalyst is substantially reduced. The changes in the hydrodesulfurization and hydrogenation functions of the catalysts seem to be due to the formation of magnesium-molybdate and also due to the formation of a NiO–MgO solid solution which takes away the promoting effect of Ni. Therefore, in NiMo catalysts supported on magnesia containing supports, it is necessary to use Ni/(Ni+Mo) atomic ratios greater than 0.3 to recover the promotion effect lost by the interaction of NiO with magnesia. The results also indicate that only the catalysts with low magnesia content ( x

Characterization and catalytic activity of CoMo HDS catalysts supported on alumina-MCM-41

A series of CoMo HDS catalysts supported on alumina with different amounts of aluminum-modified MCM-41 was prepared, characterized by different techniques (SBET, NH3-TPD, TPR, UV–VIS-DRS, HREM and NO adsorption analyzed by FTIR) and tested in the dibenzothiophene hydrodesulfurization reaction. The results show that the incorporation of MCM-41 to the catalyst formulation leads to higher catalytic activity. The TPR results indicate a diminished interaction of the Co and Mo phases with the support, compared to those existing in the alumina-supported catalyst. This decrease in the interaction causes the formation of greater amounts of polymeric Mo species and a decrease in the population of tetrahedral Co as CoAl2O4, as evidenced by the DRS results. The changes in the intensity and position of the NO adsorption IR bands indicate that an interaction between Co and Mo exists and that not all the Co present in the catalysts is completely sulfided, and therefore, may not contribute to the formation of the catalytically active Co–Mo–S mixed phase.

Characterization of Al2O3-ZrO2 mixed oxide catalytic supports prepared by the sol-gel method

Abstract A series of Al 2 O 3 -ZrO 2 mixed oxides was prepared by the sol-gel method with variable amounts of ZrO 2 between pure alumina and pure zirconia. Textural, bulk and surface characterization of the samples was carried out by nitrogen physisorption ( S BET , porosity), surface acidity, zero point charge (ZPC), thermal analysis (DSC, TGA), X-ray diffraction (XRD) and FT-Raman spectroscopy. The textural results show that at low zirconia contents, higher surface areas than those of pure alumina are obtained, and that the mixed oxides samples show a bimodal pore size distribution different from that of a mechanical mixture of the pure oxides. Also, in the zirconia-rich samples, higher surface areas than for pure zirconia are stabilized. The ZPC results indicate the formation of a surface composition equivalent to the bulk composition of the two oxides. The acidity measurements show that, as the density of acid sites in the mixed oxides increases steadily with zirconia content, a sharp increase is observed between the zirconia-rich mixed oxides and the pure ZrO 2 . It appears possible then to tune the acidity of the mixed oxide by changing its composition. The XRD and FT-Raman results show that the incorporation of alumina in the support stabilizes the metastable cubic and tetragonal zirconia phases, possibly by a matrix effect which constrains the size of the ZrO 2 particles below the critical size beyond which the crystallization and transformation process to a more stable zirconia phase occurs.

Synthesis and characterization of hydrotreating Mo catalysts supported on titania-modified MCM-41

Abstract A series of Ti modified MCM-41 supports and their respective Mo catalysts were prepared and characterized to study the effect of support preparation method on the dispersion of titania and on the characteristics of Mo surface species. Two methods of post-synthetic incorporation of titania were tested: chemical grafting and incipient wetness impregnation. The characterization results were compared to those obtained with Ti-MCM-41 supports where Ti was incorporated during the hydrothermal synthesis of MCM-41 (synthetic route). The results show that supports with different TiO 2 content and dispersion, can be obtained. The synthetic route allows to prepare mesoporous supports with ordered structure and high surface area only if the titania content is low (less than 10 wt.%). On the contrary, the post-synthetic methods allow to achieve higher titania loadings without substantial loss of MCM-41 characteristics. The best dispersion of TiO 2 in the MCM-41 channels was obtained by the grafting method. Clear differences in the characteristics of Mo species were observed (Raman and XRD) for catalysts supported on Si-MCM-41, Ti-MCM-41 and Si-MCM-41 covered with titania. The latter materials, prepared via post-synthetic route, show promising features as supports for Mo based hydrotreating catalysts.

Synthesis of Nb-containing mesoporous silica molecular sieves: Analysis of its potential use in HDS catalysts

Abstract In the preparation of mesoporous materials of the MCM-41 type, the synthesis aging time is an important parameter that can alter the structural and chemical properties of the final product. This work analyzes the effect of synthesis aging time on the structural and chemical properties of niobium-containing mesoporous silica with two different Si/Nb atomic ratios, 52 and 31. Samples of Nb-modified mesoporous silica were prepared at aging times of 2, 3, 4 and 8 days. The samples were characterized by N 2 adsorption measurements, XRD, differential thermogravimetric analysis, FT-IR, pyridine adsorption analyzed by FT-IR, HREM, SEM, DRS and Raman spectroscopy. The results show that synthesis aging time has a definitive influence in the textural, structural and chemical properties of niobium-modified mesoporous silica. Short synthesis aging times (2 days) do not allow the proper incorporation of niobium to the silica framework. With synthesis aging times of 3 and 4 days the niobium is well incorporated to the silica framework. Synthesis aging times up to 4 days promotes the formation of hexagonal structures while aging during 8 days induces the formation of cubic structures. Niobium sulfide has been reported to have good hydrodesulfurization (HDS) and hydrogenation (HYD) activities. The results show that niobium incorporated to the framework of Si-MCM-type materials undergoes partial sulfidation, as attested by the TPS experiments and its small catalytic activity in the thiophene hydrodesulfurization reaction. The solids studied here present therefore an interesting potential application as supports for HDS catalysts.

Solvent-free aldol condensations: synthesis of ferrocenyldienones

The aldol condensation of ferrocenecarbaldehyde and acetylferrocene with aldehydes and ketones proceeded more efficiently and stereoselectively in the absence of a solvent than in solution. In all the cases, E-configured enones were obtained, which was confirmed by X-ray crystallographic studies of one of the products.

Regioselectivity of alkylation of the naphthalene fragment in the opening of a small ring in 3-ferrocenyl-3-(1-naphthyl)cyclopropene, Z-2-bromo-1-ferrocenyl-1-(1-naphthyl)cyclopropane, and 1-ferrocenyl-1-(1-naphthyl)cyclopropane

Abstract The opening of a small ring in 3-ferrocenyl-3-(1-naphthyl)cyclopropene (thermolysis, action of HBF4·Et2O or CF3SO3H), Z-2-bromo-1-ferrocenyl-1-(1-naphthyl)cyclopropane (action of AlCl3), and in 1-ferrocenyl-1-(1-naphthyl)cyclopropane (action of Ph3C+BF4−) is accompanied by the alkylation of only the naphthalene fragment giving rise to 1-ferrocenyl-9bH-benzo[e]indene or 1-ferrocenyl-3H-benzo[e]indene. This is connected with a ‘non-bisecting’ position of the naphthalene fragment relative to the three-membered cycle in the starting compounds. The compound 1-ferrocenyl-9bH-benzo[e]indene gives [4+2]-cycloadducts with N-phenyl(azodicarboximide) and N-phenylmaleimide. X-ray structural data are presented for 3-ferrocenyl-3-(1-naphthyl)cyclopropene and its adduct with 1,3-diphenylisobenzofuran, Z-2-bromo-1-ferrocenyl-1-(1-naphthyl)cyclopropane, and 1-ferrocenyl-1-(1-naphthyl)cyclopropane.

Effect of citrate addition in NiMo/SBA-15 catalysts on selectivity of DBT hydrodesulfurization

Abstract NiMo catalysts supported on SBA-15 were prepared by coimpregnation and successive impregnation methods with the addition of citric acid in the impregnation solutions. Addition of citric acid resulted in an increase in both catalysts’ activity in dibenzothiophene HDS and selectivity towards the direct desulfurization route, which was due to an increase in the MoS2 dispersion and in the amount of Ni-Mo-S species.

Synthesis and some chemical properties of 3-ferrocenyl-3-isopropylcyclopropene: 3-ferrocenyl-3-isopropylstructures of cyclopropene and its adducts with 1,3-diphenylisobenzofuran

Abstract X-ray structural analysis allowed the molecular conformation of 3-ferrocenyl-3-isopropylcyclopropene to be established, where the ferrocenyl fragment occupies a bisecting position relative to the three-membered ring. Some heterolytic cleavage of a σ CC bond in cyclopropene was observed. As a result, predominantly linear products are formed: 1,1-dimethyl-2-ferrocenyl-1,3-butadiene, 3-ferrocenyl-4-methyl-2-pentene, 3-ferrocenyl-4-methyl-3-pentenine and also 3-isopropyl-1H-cyclopentaferrocene. Cyclopropene forms a classical Diels–Alder adduct with 1,3-diphenylisobenzofuran and an adduct with the intermediate 3-isopropyl-1,2-(1-propene-1,3-diyl)ferrocene. X-ray structural data of exo -1,5-diphenyl-3- anti -ferrocenyl-3- syn -isopropyl-6,7-benzo-8-oxatricyclo[3.2.1.0 2,4 ]oct-6-ene are presented.