Ni-containing Catalysts Research Articles

Green catalytic processing of native and organosolv lignins

Two ways of catalytic depolymerization of native and isolated wood lignins are described: the peroxide delignification of hardwood (aspen, birch) and softwood (abies) in the medium of acetic acid – water over TiO2 catalyst and the thermal dissolution of organosolv lignins (ethanol-lignin and acetone-lignin) in supercritical alcohols (ethanol and butanol) over solid Ni-containing catalysts.The catalyst TiO2 in rutile modification has the higher activity in wood peroxide delignification at 100 °C as compared to TiO2 in anatase modification. The results of kinetic studies and optimization of the processes of peroxide depolymerization of hardwood (aspen, birch) and softwood (abies) lignins in the medium of acetic acid – water over catalyst TiO2 (rutile) at mild conditions (≤100 °C, atmospheric pressure) are compared. The catalyst TiO2 initiates the formation of OH and OOH radicals from H2O2 which promote the oxidative fragmentation of wood lignin. In this case, the peroxide depolymerization of softwood lignin, constructed from phenylpropane units of guaiacyl-type proceeds more difficult than the hardwood lignins, mainly containing syringyl-type units.The solid and soluble products of peroxide catalytic delignification of wood under the optimized conditions were studied by FTIR, XRD, GC–MS and chemical methods. Regardless of the nature of wood the cellulosic products have a structure similar to microcrystalline cellulose. The soluble products mainly consist of monosaccharides and organic acids. Aromatic compounds are present only in a low amount which indicates the oxidative degradation of aromatic rings of lignin phenylpropane units under the used conditions of wood catalytic delignification.The processes of thermal dissolution of acetone-lignin and ethanol-lignin from aspen-wood in supercritical ethanol and butanol over Ni-containing catalyst (NiCu/SiO2, NiCuMo/SiO2) are compared. The composition, structure and thermal properties of organosolv lignins were studied with the use of FTIR, GPC, 1H – 13C HSQC NMR, DTA and elemental analysis.The influence of a composition of Ni-containing catalyst on the thermal conversion in supercritical butanol and ethanol of ethanol-lignin and acetone-lignin was established. The highest conversion of lignins (to 93% wt.) in supercritical alcohols and the highest yield of liquid products (to 90% wt.) were achieved at 300 °C in the presence of catalyst NiCuMo/SiO2.Scheme of green biorefinery of wood based on the use of non-toxic and low-toxic reagents (H2O2, H2O, acetic acid, ethanol, butanol) and solid catalysts (TiO2, NiCuMo/SiO2) is suggested.

Study of Methane Decomposition on Fe/MgO-Based Catalyst Modified by Ni, Co, and Mn Additives

Catalytic decomposition of methane (CDM) generates clean hydrogen and carbon nanomaterials. In this study, methane decomposition to hydrogen and carbon was investigated over Ni-, Co-, or Mn-doped Fe/MgO catalysts. The doping effect of different metals, varying from 3 to 10 wt%, was investigated. The catalytic performance of the obtained materials (noted 15%Fe+x%metal/MgO) revealed that the doping effect of Ni, Co, and Mn significantly improved the activity of Fe/MgO. Among the Ni-doped catalyst series, the 15%Fe+3%Ni/MgO catalyst performed better than the rest of the Ni catalysts. The 6%Co-containing catalyst remained the best in terms of activity in the Co-doped catalyst series and the 15%Fe+6%Mn/MgO solid showed better methane conversion for the Mn-doped series. Overall, 3%Ni-containing catalyst displayed the best catalytic performance among all Ni-, Co-, and Mn-doped catalysts. XRD, N2 sorption, and H2 temperature-programmed reduction (TPR), Laser–Raman spectroscopy, thermogravimetric analysis (TGA) under air, and temperature-programmed oxidation (TPO) were used for catalyst characterization. The results revealed that all the doped catalysts exhibited better metallic active site distribution than 15%Fe/MgO and proved that metal doping played a crucial role in catalytic performance.

Electrocatalytic behaviour towards oxygen reduction reaction of carbon-supported PtxMyAuz (M = Ni, Cu, Co) binary and ternary catalysts

Carbon-supported binary and ternary nanocatalysts based on Pt, Me (Me=Ni, Co, Cu) and Au were synthesized by a “water in oil” microemulsion method and characterized by atomic absorption spectrometry or energy dispersive spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry, transmission electron microscopy, X-ray diffraction, and electrochemical methods. A comparative study of the oxygen reduction reaction on binary and ternary nanocatalysts has been performed. The catalytic activity and the selectivity of the nanocatalysts towards the ORR have been determined in O2-saturated 0.1M HClO4 electrolyte. For binary systems, it was shown that the addition of Ni and Co to Pt led to an improvement of the catalytic activity, whereas the addition of Cu was detrimental for the ORR. The higher activities were achieved for atomic ratios close to that of Pt3Me defined compounds with Pt7Ni3/C displaying the highest activity. The modification of binary catalysts with gold led to increase the activity in the case of systems containing Co and Cu, and led to maintain the activity in the case of Ni-containing catalysts. The order of initial activity is: Pt6Ni2Au2/C>Pt6Co2Au2/C>Pt6Cu2Au2/C. Aging tests have been carried out on ternary catalysts, showing that a part of activity loss was due to gold segregation from the bulk to the surface of nanoparticles. After aging study for 1000 potential cycles between 0.6 and 1.05V vs. RHE in O2-saturated electrolyte, the order of activity was: Pt6Cu2Au2/C>Pt6Co2Au2/C>Pt6Ni2Au2/C.

Kinetics of Mild Steam Reforming of Propane in the Presence of Excess Methane over a Ni-Containing Catalyst

Regularities of the low-temperature steam conversion or mild steam reforming (MSR) of propane in the presence of excess methane over Nicontaining catalyst were thoroughly studied. MSR of the methane-propane mixture was shown to proceed through two stages including the irreversible steam conversion of methane to carbon dioxide and hydrogen and the reversible reaction of methanation of carbon dioxide. The latter reaction is quasi-equilibrium at above ≈250 °C. The first-order rate independent of the concentrations of methane, carbon dioxide and water vapor and the activation energy equal to ca. 120 kJ/mol are characteristic of the propane transformation during MSR of the methanepropane mixture. This is a rather simple macrokinetic scheme that allows the experimental data to be correctly described and temperature and mixture flow rate to be predicted for achieving the maximal propane conversion.

Catalytic Steam Cracking of Heavy Oil in the Presence of Molybdenum- and Nickel-Containing Nanodisperse Catalysts

The process of catalytic steam cracking (CSC) of heavy oil with high contents of sulfur (4.3 wt %) and high-boiling fractions (>500 °C) was studied in the presence of Mo- and Ni-containing nanodisperse catalysts under static conditions (autoclave) at 425 °C. Experimental studies of thermal and steam cracking, as well as of water-free catalytic cracking were carried out for comparison and identification of specific features of CSC. Dependencies of the composition and properties of the liquid and gaseous products on the process conditions, catalyst nature and the presence of water were determined. It was established that the application of Ni-catalysts for CSC causes an increase in the H : C ratio (1.69) in the liquid products against that of the other cracking processes, while the yields of coke and gaseous products increase that results in a decrease in the liquid product yield. With the Mo-catalyst, the produced low-viscous semisynthetic oil is characterized by a higher H : C ratio (1.70 wt %) and the lowest sulfur content (2.8 wt %) in the liquid products. XPS and HRTEM studies of the catalyst-containing solid residue (coke) revealed that in CSC nickel is as well-crystallized nanoparticles Ni 9 S 8 of 15–40 nm in size, and molybdenum as two phases MoO 2 and MoS 2 at the ratio depending on the conditions of heavy oil transformation. The data obtained demonstrate that CSC is a promising process of upgrading heavy oil.

Natural clay-based Ni-catalysts for dry reforming of methane at moderate temperatures

Natural clay based Ni-containing catalysts for dry methane reforming (DRM) were prepared using a Fe and Cu-modified Tunisian clay as support. The catalysts were characterized by means of X-ray diffraction (XRD). H2-temperature programmed reduction (H2-TPR) and CO2-temperature programmed desorption (TPD). The catalysts were either reduced at 800 or at 900°C prior to the DRM tests. Reduction temperature has a determinant influence in Ni crystal size and basicity. The catalysts reduced at 800°C showed better catalytic performance than those reduced at 900°C. The catalysts prepared using the Cu-modified clay yielded the highest CO2 and methane conversions all the time. At 850°C, 72% CO2 conversion was measured, corresponding to a H2/CO ratio near 1, close to the thermodynamically forecasted value.

Investigating the process of heavy crude oil steam cracking in the presence of dispersed catalysts. II: Investigating the effect of Ni-containing catalyst concentration on the yield and properties of products

The process of heavy crude oil (HCO) steam cracking under a batch regime at 425°C in the presence of Ni-containing nanodispersed catalyst (0.3–2.0 wt % with respect to Ni) is investigated. It is established that using this catalyst facilitates the upgrading of semi-synthetic oil produced from HCO: the Н: С ratio rises (in comparison to steam cracking with no catalyst), and the sulfur content and viscosity are reduced. The Н: С ratio in the liquid products grows slightly along with the catalyst content, but the yield of liquid products falls from 81 to 76% during the process with a simultaneous increase in the yield of coke and gaseous products (from 8 to 13 and from 2 to 4 wt %, respectively). Catalyst with coke residue is investigated by means of XRD and TEM. It is shown that nanosized particles of the Ni9S8 phase with sizes of 15–40 nm form from the catalyst precursor (Ni(NO3)2 · 6H2O) under the process conditions. The selection and investigation of catalytic systems for heavy crude oil cracking in the presence of superheated steam, along with optimization of the process conditions, are required to further enhance the efficiency of the upgrading process.

Formation of nanocarbon structures in MgO–C refractories matrix: Influence of Al and Si additives

The in-situ catalytic formation of various nanocarbon structures in the matrix of MgO–C refractories with Ni-containing catalyst and different additives was investigated in the present work. In comparison with the specimens containing Si powder, the addition of metallic Al can be more favorable for the growth of straight and bamboo-like carbon nanotubes in the specimens under the function of the catalyst. Nevertheless, only Ni-encapsulating and hollow carbon onions appeared in the specimens without any additives at all the investigated temperatures. It was suggested that adding metallic Al or Si powder can decrease the partial pressures of oxidizing gases and increase that of hydrocarbon gases in the specimens due to the information of ceramic phases, and the influence of metallic Al was more considerable. Also, the formation mechanisms of these various nanocarbon structures can be determined by the competing processes between the catalyst forward and the carbon shell growth.

CO-Cleanup of Hydrogen-Rich Stream for LT PEM FC Feeding: Catalysts and Their Performance in Selective CO Methanation

In the last two decades, CO preferential oxidation (CO PROX) and CO selective methanation (CO SMET) are assumed as the most feasible reactions for CO removal from H2-rich reformate for low temperature polymer electrolyte membrane fuel cells (LT PEMFC) feeding applications. Despite the existing advantages and disadvantages, both processes provide CO-cleanup to 10 ppm. This brief review illustrates the results obtained during a systematic study of catalysts, their performances and fundamental principles of the selective CO methanation reaction. The most attention is concentrated on Ru and Ni-containing catalysts and their operation in CO SMET reaction.

Direct Au-Ni/Al2O3 catalysed cross-condensation of ethanol with isopropanol into pentanol-2

Ethanol and isopropanol cross-condensation 0.2Au-0.06Ni/γ-Al2O3 catalyst have been developed based on the synergetic effect of gold and nickel in many reactions. A cross-condensation reaction results in the formation of pentanol-2 and pentanon-2 in high yields in the absence of any alkali or sacrificial agents (e.g., hydrogen acceptors or hydrogen donors). In this study, heterogeneous Au-Ni/Al2O3 catalysts were used in this type of reaction for the first time. The catalyst developed in this study is also effective for the self-condensation of ethanol, providing 85% selectivity of linear α-alcohols at 63.5% ethanol conversion. Structural investigations show that the morphological peculiarities and charge state of gold may produce the different activities of mono- and bimetallic Au- and Ni-containing catalysts.

Activation of nickel–chromium hydrogenation catalysts with hydrogen

The kinetics of the reduction of nickel cations in nickel oxide and nickel–chromium catalysts whose oxide precursors have different structures has been investigated by thermal analysis. The reduction of nickel oxide with a hydrogen-containing gas takes place at 250–330°C. The apparent activation energy of this reaction is about 88 kJ/mol. The introduction of up to 30 at % chromium cations into the nickel oxide structure shifts the reduction temperature of nickel in the oxide phase to 300–450°C and increases the apparent activation energy of the reduction of nickel cations to ∼108 kJ/mol. The introduction of 67 at % chromium into nickel oxide results in the formation of an oxide precursor with a spinel structure. The apparent activation energy of the reduction of nickel cations in this spinel is about 163 kJ/mol. The results of this study can be used in optimizing the composition of Ni-containing hydrogenation catalysts and their activation and operation conditions.

Support effect on structure and performance of Co and Ni catalysts for steam reforming of acetic acid

Syngas production from acetic acid steam reforming was demonstrated. For this purpose Co or Ni with different metal loading supported on Al2O3 and ZnO were used as catalysts. The catalytic performance was studied in the 600–800°C temperature range. The best ones were achieved at 800°C over the following catalyst in the order of Ni/Al2O3>Co/ZnO>Ni/ZnO, which provide high acetic acid conversions and high selectivities to the desired products, H2 and CO. As byproducts small amounts of CH4, acetone and ethylene were found, and their selectivity decreased with increasing reaction temperature. The internal morphology and structure of the catalyst was investigated by in-situ X-ray diffraction (XRD), transmission electron microscopy (TEM), and temperature programmed reduction (TPR) analysis. Morphological and structural modifications in the catalysts under reaction conditions, determined by the type of support and active metal, were closely related to the activity of the samples. High catalytic performance of Al2O3 supported samples is observed only over Ni-containing catalysts, due to the good dispersion of the active metal over the support, which promotes the formation of metallic Ni. The best performances of ZnO supported catalysts were achieved at high temperature, when formation of alloy structure was detected together with the complete reduction of the active metals.

SYNTHESIS OF 3D CARBON-GRAPHENE COMPOSITES

The paper describes the preparation and study of carbon-graphene composites on the basis of graphene-like material (GLM) and carbon nanofibers (CNF). CNF/GLM composites were prepared through pyrolysis of ethylene on a Ni-containing catalyst, supported on the surface of the GLM. Ni-containing catalysts were prepared by two methods: (1) hydrothermal treatment of aqueous suspension of graphite oxide and nickel acetate, followed by heating in a hydrogen stream; (2) hydrogen reduction of pre-formed Ni(CH 3 COO) 2 /GO composite. CNF synthesized on the surface of GLM had a diameter of 10 nm and a length from 10 to 300 nm at the synthesis duration from 1 to 60 min. The received material can be used as a carrier of catalysts for organic synthesis, reversible sorption of hydrogen and the electrochemical sources of current.

Acetylene carbonylation over Ni-containing catalysts: role of surface structure and active site distribution

Traditional homogeneous catalyst with heterogeneous Ni catalysts (Ni-ZSM-5, Ni-IM-5 and Ni-MCM-41) for acetylene carbonylation. Using proper parameters to confirm the influence of surface structure and active site distribution on performance.

Investigation of the Process of Catalytic Steam Cracking of Heavy Oil in the Presence of Disperse Catalysts. Part 2. Studies of the Influence Concentration of the Ni-Containing Catalyst on the Product Yield and Properties

The process of steam cracking of heavy oil (HO) was studied under static conditions at 425 °C in the presence of a nanodisperse Ni-containing catalyst (0,3–2,0 wt.% of Ni). This catalyst was established to promote upgrading of the semi synthetic oil produced from HO: the H : O ratio increases (against noncatalytic steam cracking) but the sulfur content and viscosity decreases. An increase in the catalyst loading results only in a minor increase in the H : O ration, while the yield of the liquid products decreases from 81 to 76 % at an increase in the yield of coke and gas products (from 8 to 13 and from 2 to 4 wt.%, respectively). X-ray phase analysis and transmission electron spectroscopic techniques were used for characterization of the catalyst-containing coke residue. The formation of Ni 9 S 8 nanoparticles (15–40 nm in size) from the catalyst precursor (Ni(NO 3 ) 2 ·6H 2 O) under the process conditions was shown. To improve efficiency of the upgrading process needs further choice and studies of catalytic systems for cracking of heavy oil feedstock in the presence of overheated steam and optimization of the process conditions.

Specific features of the electrical properties in partially graphitized porous biocarbons of beech wood

The electrical and galvanomagnetic properties of partially graphitized highly porous bioC(Ni) biocarbon matrices produced by pyrolysis (carbonization) of beech wood at temperatures Tcarb = 850–1600°C in the presence of a Ni-containing catalyst have been studied in comparison with their microstructural features. The temperature dependences of the resistivity, the magnetoresistance, and the Hall coefficient have been measured in the temperature range of 4.2–300 K in magnetic fields to 28 kOe. It has been shown that an additional graphite phase introduction into samples with Tcarb ≥ 1000°C results in an increase in the carrier mobility by a factor of 2–3, whereas the carrier (hole) concentration remains within ~1020 cm−3, as in biocarbons obtained without catalyst. An analysis of experimental data has demonstrated that the features of the conductivity and magnetoresistance of these samples are described by quantum corrections related to their structural features, i.e., the formation of a globular graphite phase of nano- and submicrometer sizes in the amorphous matrix. The quantum corrections to the conductivity decrease with increasing carbonization temperature, which indicates an increase in the degree of structure ordering and is in good agreement with microstructural data.

Reactions of isobutanol over a NASICON-type Ni-containing catalyst activated by plasma treatments

The effect of hydrogen and argon high-frequency (HF) plasma treatment on the catalytic activity of the nickel zirconium phosphate Ni0.5Zr2(PO4)3 in isobutanol dehydration and dehydrogenation has been investigated. The catalyst treated with H2-HF and Ar-HF plasmas shows a ∼2 times higher activity in both reactions. This effect is due to surface restructuring changing the number and accessibility of catalytic sites on the phosphate surface.

Core-shell bifunctional catalyst for steam methane reforming resistant to H2S: Activity and structure evolution

Results of studies on the activity of the Ni-containing catalyst in the steam reforming of methane (SRM) process are presented. It is established that the catalyst shows high activity in SRM, stability to coke formation and resistance to H2S presence in the reaction gas mixture. The catalyst was prepared on the basis of mixed oxides separated from layered vermiculite. The structure and the phase composition of catalytically active components were investigated by XAFS, XRD, EDX, TEM and Moessbauer spectroscopy. It is found that the active components of catalyst are represented by clusters with core-shell configuration where FeNi alloy is a core (∼10 nm) surrounded by superparamagnetic γ-Fe2O3 shell (1–4 nm). These clusters are distributed in the mixed spinel Mg(Fe,Al)2O4 matrix. It is suggested that clusters of FeNi alloy are active in SRM while superparamagnetic γ-Fe2O3 particles are active in the oxidative decomposition of H2S.

Catalytic Decomposition of Natural Gas to CO/CO2-Free Hydrogen Production and Carbon Nanomaterials Using MgO-Supported Monometallic Iron Family Catalysts

Monometallic Fe, Co, and Ni/MgO catalysts with 50 wt.% metal loadings were prepared and examined for natural gas decomposition to nanocarbonaceous materials, particularly multiwalled carbon nanotubes (MWCNTs) and co-valuable hydrogen. The catalytic testing was carried out in a fixed-bed horizontal reactor at 700°C under atmospheric pressure. The fresh and/or used catalysts were characterized using XRD, TPR, HRTEM, SEM, TG/DTA, Raman spectroscopy, and BET surface measurements. The resulting data showed that the 50%Co/MgO catalyst displayed higher catalytic decomposition activity of natural gas to COx-free hydrogen production (∼88%), higher yield of MWCNTs, and excellent stability up to 10 h time-on-stream. On the other hand, the Ni-containing catalyst showed lower catalytic activity toward hydrogen and CNTs production, principally due to the formation of rock-salt MgxNi(1-x)O solid solution as observed from XRD and TPR data. Accordingly, the concentration of Ni particles required for natural gas feed was extremely low. The d orbital of Ni was presumed to be occupied during the formation of the solid solution, which inhibits the solublization or adsorption of hydrocarbons on Ni particles. The MWCNTs obtained over Ni-based catalyst had narrow and homogeneous diameters (∼11–13 nm). However, the Fe/MgO catalyst exhibited intermediate activity between those of Ni and Co˭MgO catalysts toward hydrogen production (∼44%). This catalyst produced mixtures of carbon nanofibers and nanotubes.

Catalytic hydrodeoxygenation of anisole as lignin model compound over supported nickel catalysts

Catalytic hydrodeoxygenation (HDO) of anisole, a methoxy-rich lignin model compound, has been investigated over a series of Ni-containing (10wt% loading) catalysts with activated carbon, SBA-15, SiO2, and γ-Al2O3 supports, in order to understand their ability for removal of OCH3 from anisole. This catalytic reaction had been carried out in an autoclave at 180–220°C and 0.5–3.0MPa H2 pressure. Nickel-catalyzed aromatic ring-hydrogenation compared with the subsequent demethylation and deoxygenation is the fastest step in HDO of anisole under the present reaction conditions. Among these catalysts, the aromatic ring-saturated cyclohexyl methyl ether is mainly obtained over Ni/AC, while the Ni/SiO2 displayed the highest activity in HDO of anisole (selectivity to deoxygenated products >95%). Differences in HDO efficiency among the catalysts are attributed not only to variations in the dispersion of the active phase, but also to the acid sites which may contribute to the cleavage of CO bonds. It has also been shown that the activity toward oxygen-removal strongly depended on reaction temperature and the conversion of anisole favors the production of oxygen-free aromatics by the direct demethoxylation pathway at the relatively low H2 pressure.