A. Spojakina

Effect of mixed titania-alumina supports on the phase composition of NiMo/TiO2Al2O3 catalysts

NiMo catalysts supported on mixed TiO2Al2O3 oxides containing between 0 and 22 wt.−% TiO2 have been prepared and characterized by temperature-programmed reduction (TPR), infrared (IR) and diffuse reflectance (DR) spectroscopy, BET and ammonia adsorption measurements. The samples have been tested in hydrodesulphurization (HDS) of thiophene. The spectral results show that the proportion of weakly bonded MoO42− groups is higher for NiMo/TiO2Al2O3 catalysts compared to catalysts contained only molybdenum. The increase in TiO2 content in the mixed supports leads to a decrease of inactive NiAl2O4 spinel. An increase of Ni2+ ions in octahedral surroundings, included in a structure analogous to NiTiO3 is observed. Acidity shows the nickel-molybdenum surface interaction to be a result of the formation of a precursor of NiMoO4-like structure. The TPR results demonstrate that addition of titania into the support facilitates the Mo6+ reduction to Mo5+ and Mo4+. The influence of nickel on the molybdenum reducibility is revealed by a decrease of the temperature of reduction of the molybdenum species. The HDS activity of NiMo/TiO2Al2O3 catalysts reaches a maximum at 17 wt.−% TiO2 due to formation of an active phase with an optimal composition of the oxidic precursors.

Effect of phosphorus on the surface state of alumina-supported nickelmolybdenum catalysts for hydrodesulphurization

Abstract The influence of concentration and method of phosphorus introduction in the alumina-supported nickel—molybdenum catalysts on the surface properties and catalytic activity in thiophene hydrodesulphurization (HDS) have been investigated. As a result of a strong interaction between phosphorus and support aluminium phosphates are formed. Molybdenum compounds, among them iso- and heteropoly compounds, are formed on the surface of Al 2 O 3 irrespective of the presence of phosphorus. The promoting effect of phosphorus is expressed in optimization of the phase composition of the catalyst and a decrease in coke formation. A 1 wt.-% ensures the optimum composition of the polymolybdate surface structures and their homogeneous distribution.

Thiophene hydrodesulfurization on P−Mo, Si−Mo and Ti−Mo catalysts

Studies of the catalysts obtained by supporting P−Mo, Si−Mo and Ti−Mo heteropolyacids on anatase in thiophene hydrodesulfurization have revealed that the presence of HPA in the initial catalysts promotes the formation of the molybdenum state ensuring high reaction rates. A possibility for HPA synthesis when supporting paramolybdate on TiO2, accounts for the great effect of the support on the properties of the catalyst.AbstractИсследованы катализаторы, полученные нанесением фосфор-, кремний-, титан-молибденовых гетерополикислот на анатаз, в реакции гидродесульфурирования тиофена. Показано, что стабилизация молибдена в виде гетерополикислоты в исходном катализаторе способствует образованию в условиях реакции состояния модибдена, обеспечивающего протекание реакции с высокой скоростью. Возможность синтеза гетерополикислоты при нанесении парамолибдата на диоксид титана определяет большое влияние носителя на каталитические свойства катализатора.

Synthesis and properties of hydrodesulfurization catalysts. IV. Thiophene hydrodesulfurization on molybdenum catalysts containing heteropoly compounds

Water soluble analogues of aluminium and cobalt heteropolymolybdates have been shown as possible precursors of active sites for thiophene hydrodesulfurization along with other molybdenum compounds. For the characterization of the catalysts Raman spectroscopy has been applied, and the catalytic activity of the samples is discussed.AbstractВодорастворимЫе аналоги гетерополимолибдата алюминия и кобальта оказались возможнЫми Предшественниками активнЫх центров вместе с другими молибденовЫми соединениями в гидродесульфурировании тиофена. БЫла использована спектроскопия Памана и измерение каталитической активности.

NiMo/γ-Al2O3 Catalysts from Ni Heteropolyoxomolybdate and Effect of Alumina Modification by B, Co, or Ni

A hydrotreating NiMo/γ-Al2O3 catalyst (12 wt% Mo and 1.1 wt% Ni) was prepared by impregnation of the support with the Anderson-type heteropolyoxomolybdate (NH4)4Ni(OH)6Mo6O18. Before impregnation of the support, it was modified with an aqueous solution of H3BO3, Co(NO3)2, or Ni(NO3)2. The catalysts were investigated using N2 adsorption, O2 chemisorption, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, temperature-programmed reduction, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The addition of Co, Ni, or B influenced the Al2O3 phase composition and gave increased catalytic activity for 1-benzothiophene hydrodesulfurization (HDS). X-ray photoelectron spectroscopy confirmed that the prior loading of Ni, Co or B increased the degree of sulfidation of the NiMo/γ-Al2O3 catalysts. The highest HDS activity was observed with the NiMo/γ-Al2O3 catalyst with prior loaded Ni.

Thiophene conversion and ethanol oxidation on SiO2-supported 12-PMoV-mixed heteropoly compounds

Abstract Surface properties of supported MoV heteropoly compounds and their activities in hydrodesulfurization of thiophene and oxidation of ethanol were studied. Vanadium incorporated into the phosphomolybdic acid anion increased extent of oxidative dehydrogenation of ethanol to acetaldehyde, whereas the catalyst with (VO)2+ increased complete ethanol oxidation to CO2. The catalysts with (VO)2+ or one V atom in the anion showed an increase in HDS activity. Vanadium in anion of phosphomolybdic acid also increased hydrogenation ability. Acidic sites of medium strength were proved to be the most suitable for ethanol oxidation. Such explicit dependence of thiophene hydrodesulfurization on any type of acidic sites was not confirmed. Activity order of supported MoV heteropoly compounds in HDS of thiophene correlated well with the amount of hydrogen consumed during TPR.

The effect of nickel on the component state and HDS activity of alumina-supported heteropolytungstates

Hydrotreating Ni heteropolytungstate catalysts have been prepared by impregnation of γ-Al2O3-alumina with solutions of H3PW12O40 acid and its Ni salt. The nickel content is varied by adding Ni(NO3)2 salt. The calcined samples are characterized by BET, IR, TPR, and XPS techniques. The catalytic activity is tested for HDS of thiophene. It is shown that the initial heteropolyanion, its lacunary analog, and nickel substituted heteropolyanion are present on the surface as a result of the interaction between the active component and the alumina support. The mixed NiWS phase formed after sulfidation determines the HDS activity of the catalysts.

Study of low-percentage alumina-supported nickel-molybdenum catalysts by ESR spectroscopy and magnetic measurements

Abstract Alumina-supported nickel-molybdenum catalysts (0.7–1.5 wt.-% nickel and 7–15 wt.-% molybdenum) were studied by ESR spectroscopy and magnetic methods. Thiophene hydrodesulphurization (HDS) was used to examine their activity. The effect of sample preparation on the state of nickel and molybdenum under reducing and sulphiding conditions was also investigated. The existence of a definite bond between nickel and molybdenum in the samples is responsible for a higher catalytic activity in HDS owing to the presence of nickel heteropolymolybdate.

Hydrodesulfurization activities of NiMo catalysts supported on mechanochemically prepared Al-Ce mixed oxides

Abstract Al2O3-CeO2 supports containing 1-10 wt% Ce were prepared mechanochemically by milling aluminum and/or cerium nitrates with NH4HCO3. Heteropolymolybdate, (NH4)4NiMo6O24, was used as the precursor of the Ni and Mo to prepare NiMo6/Al2O3-CeO2 components in catalysts by impregnation method. The physicochemical properties of the catalysts were determined using chemical analysis, X-ray diffraction, temperature-programmed H2 reduction, temperature-programmed NH3 desorption, X-ray photoelectron spectroscopy (XPS), and the Brunauer-Emmett-Teller method. The catalyst acidity decreased with increasing Ce concentration in the support. XPS showed that the NiS/MoS ratio decreased two-fold for the Ce-modified alumina support. NiMo6/Al2O3, which had the highest acidity, showed the highest activity in hydrodesulfurization of 1-benzothiophene (normalized per weight of catalyst). The concentration of surface MoOxSy species (which is equal to the concentration of Mo5+) gradually decreased to zero for catalysts with Ce concentrations ( 10 wt%. However, the activities of all the catalysts prepared mechanochemically from Al2O3 and Al2O3-CeO2 supports significantly exceeded that of a reference NiMo6/Al2O3 catalyst prepared by impregnation method using the same precursor and with the same composition.

Catalytic activity of NiMo/TiO2−Al2O3 systems in thiophene hydrodesulfurization

A correlation exists between the number of surface acid sites and the catalytic activity of NiMo/TiO2−Al2O3 systems in thiophene hydrodesulfurization. The catalytic activity for thiophene hydrodesulfurization and surface concentration of Brönsted acid sites increase with the titania content in the TiO2−Al2O3 support.