The state of nickel in the silver modified NiMg/SiO<Subscript>2</Subscript> vegetable oil hydrogenation catalysts

Two series of silver modified Ni-Mg materials were synthesized by precipitation-deposition on SiO₂ support derived from two silica sources: diatomite activated at 800°C (Series a; Mg/Ni = 0.1 and SiO₂/Ni = 1.07) and synthetic water glass (Series b; Mg/Ni = 0.1 and SiO₂/Ni = 1.15). The modification with silver was made at three molar Ag/Ni ratios, namely 0.0025, 0.025, and 0.1. The effects of the source of the silica support and the silver presence and content on the nickel state in the silver modified reduced-passivated NiMg/SiO₂ precursors of the vegetable oil hydrogenation catalyst were established by X-ray diffraction and X-ray photoelectron spectroscopy techniques. The passivation procedure was applied in order to protect the metallic nickel particles from further oxidation. The crystallization of the formed nickel hydrosilicate phases depends on the source of the silica support, more expressed in the diatomite supported samples. It was shown that the silver modification of the NiMg/SiO₂ precursors enhances the reduction of the nickel hydrosilicates accompanied by formation of relatively smaller metallic nickel particles, more pronounced in the water glass supported precursors. The increase of the silver content in the water glass deposited samples is responsible for the metallic nickel dispersion increase. The higher content of the Ni⁰ particles on the surface of the diatomite deposited samples is in accordance with the higher stability of the larger metallic nickel crystallites to oxidation during the passivation step. On contrary, higher dispersed Ni⁰ particles on the surface of the water glass supported samples are more susceptible to the oxida The article is published in the original.     

Surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process: N2 sorption and XPS studies

The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N₂ sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO₂/Ni = 1.0) has been synthesized by precipitation of Ni(NO₃)₂ · 6H₂O solution with Na₂CO₃ solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO₂ causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.     

Influence of the support on the state of nickel in the Ni/SiO2, Ni/ZrO2, and Ni/SO4/ZrO2 oxide systems studied by diffuse-reflectance IR spectroscopy

The Ni/SiO₂, Ni/ZrO₂, and Ni/SO₄/ZrO₂ systems were studied by diffuse-reflectance IR spectroscopy using CO as a probe molecule. The Ni/SiO₂ and Ni/ZrO₂ systems are similar in properties, and the state of nickel in the Ni/ZrO₂ system is determined by the specific surface area. In the Ni/SO₄/ZrO₂ system, the surface sulfur compounds affect substantially the state of nickel: Ni^δ+ species with a partial positive charge are formed due to the strong electron-acceptor properties of the sulfur compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 409–413, March, 1998.     

Furfural Hydrogenation on Nickel‐promoted Cu‐containing Catalysts Prepared from Hydrotalcite‐Like Precursors

The nickel‐promoted Cu‐containing catalysts (Cu_xNi_y‐MgAlO) for furfural (FFR) hydrogenation were prepared from the hydrotalcite‐like precursors, and characterized by X‐ray powder diffraction, inductively‐coupled plasma atomic emission spectroscopy, N₂ adsorption‐desorption, UV‐Vis diffuse reflectance spectra and temperature‐programmed reduction with H₂ in the present work. The obtained catalysts were observed to exhibit a better catalytic property than the corresponding Cu‐MgAlO or Ni‐MgAlO samples in FFR hydrogenation, and the CuNi‐MgAlO catalyst with the actual Cu and Ni loadings of 12.5 wt% and 4.5 wt%, respectively, could give the highest FFR conversion (93.2%) and furfuryl alcohol selectivity (89.2%). At the same time, Cu⁰ species from the reduction of Cu²⁺ ions in spinel phases were deduced to be more active for FFR hydrogenation.     

Propene hydrogenation with PtAg intermetallic phases supported on SiO2 gels

Various intermetallic phases composed of Pt/Ag supported on SiO₂-gel were synthesized by reduction of Pt(allyl)₂ and Ag[cyclooctadiene]₂⁺ precursors anchored on the support surface. This method afforded highly dispersed metallic particles. X-ray analysis was used to ascertain the occurrence of alloy, for structural identification of Pt/Ag phases and degree of dispersion. The catalytic activity of these systems was studied in gas-phase hydrogenation of propene within the temperature range 10–90 °C. Kinetic parameters such as specific reaction rates, reaction orders and apparent activation energies were calculated as functions of the Pt/Ag ratio. Results are compared and discussed in terms of the structural and electronic features of the active metallic phase.     

Liquid Phase Hydrogenation of t,t,c‐1,5,9‐Cyclododecatriene over Ni/MCM‐41 and Ni/SiO2 Catalysts

Ni‐loaded pure siliceous and aluminosilicate MCM‐41 (Ni/MCM‐41) and nickel‐loaded silica (15Ni/SiO₂) were synthesized via wet impregnation and were characterized by various techniques. The H₂ consumption in the TPR analysis was found to be proportional to the Ni amount in the calcined samples. After reduction the average Ni particle sizes of 15Ni/MCM‐41 and 15Ni/SiO₂ were 9–12 and 16 nm, respectively, by means of XRD and TEM measurements. All catalysts owned weak and intermediate Lewis acid sites that increased slightly with increasing the Ni amount and the Al content. In the liquid phase hydrogenation of t,t,c‐1,5,9‐cyclododecatriene over Ni/MCM‐41, the catalytic activity was parallel to the Ni content and enhanced slightly with the acid amount of the catalysts. Consequently, it was proposed that the Ni metallic sites contributed the major effect to the catalytic activity while the Lewis acid sites promoted a small but significant influence on the catalytic performance. It is noteworthy that all 15Ni/MCM‐41 catalysts exhibited remarkably higher activity than that of the conventional 15Ni/SiO₂ catalyst.     

EXAFS investigation of nickel and cobalt precursors of homogeneous ziegler-type hydrogenation catalysts

A preliminary EXAFS study is reported of precursors of homogeneous hydrogenation catalysts obtained by addition of AlEt₃ to nickel or cobalt octoate solutions in benzene. For a given nickel octoate solution studied before reduction, monodentate coordination of the nickel cations to at least four carboxylic anions was established and accurate Ni...O₁, Ni...C₁ distances (i.e. 2.06±0.01 Å, 3.01±0.02 Å) were determined. The spectra of the reduced solutions are however clearly dominated by intense Ni^*...Ni or Co^*...Co signals at distances comparable to the relevant distances of the bulk metal, and thus suggest the presence of rather disordered, amorphous-like metal clusters. Strong evidence is also produced in favour of additional metal...carbon bonds which were often assumed to play an important role in the catalytic activity of these or related solutions.     

Effect of silver modification on structure and catalytic performance of Ni-Mg/diatomite catalysts for edible oil hydrogenation

Silver modified Mg-Ni/diatomite materials with ratios of SiO₂/Ni = 1.07 and Mg/Ni = 0.1, differing in Ag content (Ag/Ni = 0.025 and 0.1) were prepared by the precipitation–deposition method. The effects of silver presence and content on the structure, morphology, texture and H₂-adsorption capacity of the obtained precursors were studied by X-ray diffraction, scanning electron microscopy, Hg-porosimetry and H₂-chemisorption techniques. The catalytic performance of the corresponding catalysts in the soybean oil hydrogenation was investigated. The increase of the silver loading resulted in the development of macroporosity and increase in the total sample porosity. The decrease of both H₂-adsorption capacity and hydrogenation activity are related to the metallic silver covering and blocking effects on the Ni²⁺ species, thus hampering the access of hydrogen. The decrease of hydrogenation activity and favorable limiting of cis–trans isomerization on the silver modified catalyst are explained by Horiuti–Polanyi mechanism based on the assumption that hydrogenation and isomerization proceed at the same active metallic nickel sites via half-hydrogenated intermediates.It was shown that the adjustment of the catalyst composition by changing the content of silver modifier offers the possibility to control the total amount of solid fat content, stearic acid and detrimental trans fatty acids in the hydrogenated derivatives. The catalyst with higher silver content is proposed as a promising candidate for selective edible oil hydrogenation catalyst.     

Synthesis of Ni/SiO<Subscript>2</Subscript> nanoparticles for catalytic benzene hydrogenation

Nickel nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium. The obtained solids were characterized by X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Electron Diffraction (ED), hydrogen chemisorption, and Temperature Programmed Desorption of hydrogen (H₂-TPD). The catalytic properties were evaluated for benzene hydrogenation in the temperature range 75–230 °C. XRD patterns reveal presence of the metallic nickel particles with fcc structure. Metal dispersion and hydrogen storage increase with decreasing metal particle size. The H₂-TPD profiles exhibit two domains, one due to desorption of hydrogen from Ni metal and another due to spillover from metal to the support. The catalytic activity strongly depends on the metal loading. It increases with decreasing metal loading. This is attributed to metal surface area, which also increases with decreasing metal loading. Kinetic studies of benzene hydrogenation on the Ni catalysts showed that the benzene partial order is around −2. This significant negative value is ascribed to a strong adsorption of benzene on the catalyst surface.     

Nickel(II) sorption on hydrous silica: A kinetic and thermodynamic study

Summary Sorption of nickel, Ni²⁺, on SiO₂ ^. xH₂O (silica gel) has been studied as a function of time conditions: amount of silica gel: 0.10-1.00 g, nickel concentration: 5.00 ^. 10^-5-1.20 ^. 10^-3M, ionic strength: 0.20-1.40M NaClO₄, pH 6.50 to 8.50, and temperature 273-318 K. From the kinetic data, the diffusion coefficient of Ni²⁺ ion was calculated to be 1.28(±0.07) ^. 10^-11 m^{2 .} s^-1 under particle diffusion-controlled conditions. The sorption rate was determined as 3.79(±0.35) ^. 10^-3 s^-1 at 298 K, pH 8.40 in 0.20M (NaClO₄). The sorption data were fitted to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. Nickel sorption on 0.20 g silica gel decreased with ionic strength from 77.70±0.70% (0.20M NaClO₄) to 16.12±0.37% (1.40M NaClO₄) at intial pH of 8.50±0.05. A gradual decrease in pH with increasing ionic strength suggests an ion exchange mechanism and the sorption of Ni²⁺ on silica gel increasing with temperature indicates an endothermic enthalpy. The effect of different ligands such as fluoride, carbonate, phosphate and oxalate on Ni²⁺ sorption on silica gel was studied.     

Ni/Fe物质的量的比对Ni-Fe催化剂表面性质和二硝基甲苯加氢活性的影响

采用Fe粉置换氯化镍溶液中的Ni²⁺制备了Ni-Fe催化剂, 并应用于催化二硝基甲苯加氢合成甲苯二胺的反应中。运用XRD、低温氮吸附-脱附、H₂-TPD、XPS和TEM等技术手段对不同Ni/Fe物质的量的比(n_Ni/n_Fe)下催化剂进行了表征。结果表明, n_Ni/n_Fe对Ni-Fe催化剂表面性质影响显著。当n_Ni/n_Fe为1:4时, Fe抑制Ni氧化的作用达到最大, Ni-Fe催化剂化学氢吸附量和活性物种Ni的分散度分别达到了0.16 mmol·g^-1和23%, 催化剂性能得到较大的提升。在优化的催化剂制备条件下, DNT(二硝基甲苯)的转化率和TDA(甲苯二胺)的选择性分别达到了~100%和99%。另外, 对Ni-Zn漆原镍(Urushibara Ni)催化剂和Ni-Fe催化剂催化DNT加氢反应进程进行了研究, 发现它们有相同的加氢中间产物, 但反应不同阶段的催化速率存在差异。     

Gold, palladium and gold–palladium supported on silica catalysts prepared by sol–gel method: synthesis, characterization and catalytic behavior in the ethanol steam reforming

Noble-metal-based catalysts supported on silica (Au/SiO₂, Pd/SiO₂ and Au–Pd/SiO₂) were prepared by the sol–gel method and were evaluated in the steam reforming of ethanol for hydrogen production. The catalysts were characterized by N₂ physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H₂ chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The structural characterization of the Au- and Pd-containing catalysts after calcination showed that the solids are predominantly formed by Au⁰, Pd⁰ and PdO species and was observed that the metallic Pd dispersion diminished in the presence of Au⁰. The results revealed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. The Pd/SiO₂ catalyst showed the best performance among the catalysts tested at the highest reaction temperature (600 °C) due to the more effective action of the metallic active phase, which covers a greater area in this sample. At this same reaction temperature, the Au–Pd/SiO₂ catalyst showed a significant deactivation, probably due to the lower Pd dispersion presented by this catalyst.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XI. Oberflächenchemische Eigenschaften von NiO/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XI. Surface Chemical Properties of NiO/SiO₂ Catalysts NiO/SiO₂ catalysts with different composition prepared by precipitation have been investigated which are characterized by a nickel layersilicate-like structure. The determination of the surface chemical properties was carried out by infrared spectroscopy (before and after pyridine adsorption), ¹H-NMR-measurements, chemisorption of ammonia, and titration with n-butylamine. It has been found three kinds of hydroxid groups which are assigned to Ni? OH and Si? OH groups with respect to investigations on definite nickel layersilicates. Furthermore, coordinatively unsaturated Ni^II surface sites were indicated. The number of the OH groups as well as the centers determined by chemisorption of bases increase with increasing NiO content. The obtained results allow the conclusion that the OH groups and the coordinatively unsaturated Ni^II surface sites are weakly acid.     

Ni/Fe物质的量的比对Ni-Fe催化剂表面性质和二硝基甲苯加氢活性的影响

采用Fe粉置换氯化镍溶液中的Ni²⁺制备了Ni-Fe催化剂,并应用于催化二硝基甲苯加氢合成甲苯二胺的反应中。运用XRD、低温氮吸附-脱附、H₂-TPD、XPS和TEM等技术手段对不同Ni/Fe物质的量的比(n_Ni/n_Fe)下催化剂进行了表征。结果表明,n_Ni/n_Fe对Ni-Fe催化剂表面性质影响显著。当n_Ni/n_Fe为1:4时,Fe抑制Ni氧化的作用达到最大,Ni-Fe催化剂化学氢吸附量和活性物种Ni的分散度分别达到了0.16 mmol·g^-1和23%,催化剂性能得到较大的提升。在优化的催化剂制备条件下,DNT(二硝基甲苯)的转化率和TDA(甲苯二胺)的选择性分别达到了~100%和99%。另外,对Ni-Zn漆原镍(Urushibara Ni)催化剂和Ni-Fe催化剂催化DNT加氢反应进程进行了研究,发现它们有相同的加氢中间产物,但反应不同阶段的催化速率存在差异。     

Nickel catalysis for hydrogenation of <Emphasis Type="Italic">p</Emphasis>-dinitrobenzene to <Emphasis Type="Italic">p</Emphasis>-phenylenediamine

The activity of supported nickel catalysts (5–20% Ni) in the hydrogenation of p-dinitrobenzene to p-phenylenediamine was investigated. The catalysts were obtained by ureainduced precipitation. Activated carbon, alumina, titania, and silica gel were evaluated as supports. The most active catalysts, 5%Ni/TiO₂ and 20%Ni/SiO₂, provided 50–54% yields of p-phenylenediamine at complete dinitrobenzene conversion.     

炭包覆氧化铝负载镍催化剂的制备和表征及其催化加氢性能

以炭包覆A12O3(CCA)为载体,采用等体积浸渍法制备了17%Ni/CCA催化剂,采用热重-差示量热扫描、扫描电镜、X射线光电子能谱、N2物理吸附、H2程序升温还原和X射线衍射等手段对样品进行了表征,并用于粗1,4-丁二醇加氢反应中.结果表明,炭的引入显著改变了Al2O3的表面性质、负载Ni的存在形态以及金属.载体间...     

Effect of the preparation conditions on the physicochemical and catalytic properties of Ni<Subscript>2</Subscript>P/SiO<Subscript>2</Subscript> catalysts

The effect of the reduction conditions on the physicochemical and catalytic properties of Ni₂P/SiO₂ catalysts was studied. The catalysts were prepared by impregnating silica with a solution of nickel acetate and diammonium hydrogen phosphate followed by drying, calcination, and temperature-programmed reduction. The Ni₂P/SiO₂ catalysts were reduced prior to hydrodeoxygenation (HDO) of methyl palmitate in the catalytic reactor (in situ) at temperatures of 550, 600, and 650 °С for 3 h and at 600 °С for 1 and 6 h. The reduction temperature and reduction time were shown to affect the conversion of methyl palmitate, and the optimal reduction conditions of the Ni₂P/SiO₂ catalysts were found. The Ni₂P/SiO₂ catalyst synthesized according to a widely used preparation method, including steps of passivation and rereduction at 450 °С in addition to the reduction step, is inferior in activity to the samples prepared in situ.     

An Effect of a Support Nature and Active Phase Morphology on Catalytic Properties of Ni-Containing Catalysts in Hydrogenation of Biphenyl

Ni/Sup catalysts were prepared, where SBA-15, γ-Al₂O₃, SiO₂ were used as supports (Sup). The synthesized catalysts were investigated by the methods of low-temperature nitrogen adsorption, temperatureprogrammed reduction (TPR), and high-resolution transmission electron microscopy. The catalytic properties of the prepared catalysts were tested in liquid phase hydrogenation of biphenyl under conditions of a flow installation at temperatures of 60–100°C, pressure of 4 MPa, volumetric feed rate of 4–10 h^–1 and H₂: feed ratio of 1500 nM.. A 1 wt % solution of biphenyl in heptane,, as a model mixture, was used. It has been established that the activity of nickel hydrogenation catalysts depends on the nickel content and the type of support. The activity of supported nickel catalysts decreases in the series Ni-12/SBA-15 > Ni-12/SiO₂ >> Ni-12/Al₂O₃. The kinetic characteristics of the biphenyl hydrogenation reaction were determined: the rate constants and activation energy for the hydrogenation of the first and second aromatic rings of the substrate molecule.     

Untersuchungen an oxidischen Katalysatoren. XXXIV. Redoxverhalten des Nickels in NiNaY-Zeolithen 1. Reduzierbarkeit und Reoxydierbarkeit von Nickel in NiNaY-Zeolithen

Studies on Oxide Catalysts. XXXIV. Redoxbehaviour of Nickel in Zeolite NiNaY. 1. Reducibility and Reoxidizability of Nickel in Zeolites NiNaY The properties of metallic nickel in reduced (470–870 K) and reoxidized (470, 670 K) samples were studied by chemical analysis (reaction with K₂Cr₂O₇) and spectroscopic methods (FMR, IR after CO adsorption, UV/VIS). The reduction of Ni²⁺ cations from oxidic clusters proceeds in an onestep reaction. Contrary to this, isolated Ni²⁺ cations are reduced stepwise to Ni⁺ cations and subsequently to metallic nickel. The reduction degree depends in characteristic manner on the reduction temperature. Metallic nickel which was reduced at temperatures < 620 K, can be completely reoxidized at 470 K. Higher temperatures result in metallic aggregations which are not completely reoxidized even at 670 K.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XVI. Reduktionsverhalten amorpher NiO?Al2O3/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al₂O₃/SiO₂ Catalysts The reduction behaviour of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al₂O₃/SiO₂ catalysts is enhanced and the nickel dispersity is decreased at low Al₂O₃ contents. The decrease of the reducibility at Al₂O₃ contents >5 mole% is caused by the formation of nickel spinels and the decrease of the Ni^II ion surface concentration.