Ni-CeO2 Catalyst Research Articles

Three-Dimensional Mesoporous Ni-CeO2 Catalysts with Ni Embedded in the Pore Walls for CO2 Methanation

Mesoporous Ni-based catalysts with Ni confined in nanochannels are widely used in CO2 methanation. However, when Ni loadings are high, the nanochannels are easily blocked by nickel particles, which reduces the catalytic performance. In this work, three-dimensional mesoporous Ni-CeO2-CSC catalysts with high Ni loadings (20−80 wt %) were prepared using a colloidal solution combustion method, and characterized by nitrogen adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and H2 temperature programmed reduction (H2-TPR). Among the catalysts with different Ni loadings, the 50% Ni-CeO2-CSC with 50 wt % Ni loading exhibited the best catalytic performance in CO2 methanation. Furthermore, the 50% Ni-CeO2-CSC catalyst was stable for 50 h at 300° and 350 °C in CO2 methanation. The characterization results illustrate that the 50% Ni-CeO2-CSC catalyst has Ni particles smaller than 5 nm embedded in the pore walls, and the Ni particles interact with CeO2. On the contrary, the 50% Ni-CeO2-CP catalyst, prepared using the traditional coprecipitation method, is less active and selective for CO2 methanation due to the larger size of the Ni and CeO2 particles. The special three-dimensional mesoporous embedded structure in the 50% Ni-CeO2-CSC can provide more metal–oxide interface and stabilize small Ni particles in pore walls, which makes the catalyst more active and stable in CO2 methanation.

Synthesis of Ni-Pd decorated spindle-shape CeO2 for catalytic reduction of nitroarene

Facile single-step hydrothermal approach was developed for the synthesis of Ni and Pd decorated spindle-shape defected CeO2 catalyst for reduction of nitroarene compounds. A Ni-Pd/CeO2 catalyst showed superior activity toward nitroarene reduction than its nickel monometallic counterpart (Ni/CeO2). Addition of very small amount of Pd to Ni-CeO2 catalyst largely changed its morphology, size of active nanoparticles (NPs) as well as its catalytic activity. A synergy between active metals (Pd, Ni) and support (CeO2), strong metal-support interactions, ceria defect sites with high concentrations of Ce+3 and oxygen vacancy sites were suggested to promoting the superior activity of Ni-Pd/CeO2 compared to Ni/CeO2 catalyst.

Ni Nanoparticles on CeO2(111): Energetics, Electron Transfer and Structure by Ni Adsorption Calorimetry, Spectroscopies and DFT

The morphology, interfacial bonding energetics and charge transfer of Ni clusters and nanoparticles on slightly-reduced CeO2-x(111) surfaces at 100 to 300 K have been studied using single crystal adsorption calorimetry (SCAC), low-energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and density functional theory (DFT). The initial heat of adsorption of Ni vapor decreased with the extent of pre-reduction (x) of the CeO2-x(111), showing that stoichiometric ceria adsorbs Ni more strongly than oxygen vacancies. On CeO1.95(111) at 300 K, the heat dropped quickly with coverage in the first 0.1 ML, attributed to nucleation of Ni clusters on stoichiometric steps, followed by the Ni particles spreading onto less favorable terrace sites. At 100 K, the clusters nucleate on terraces due to slower diffusion. Adsorbed Ni monomers are in the +2 oxidation state, and they bind by ~45 kJ/mol more strongly to step sites than terraces. The measured heat of adsorption versus average particle size on terraces is favorably compared to DFT calculations. The Ce 3d XPS lineshape showed an increase in Ce3+/Ce4+ ratio with Ni coverage, providing the number of electrons donated to the ceria per Ni atom. The charge transferred per Ni is initially large but strongly decreases with increasing cluster size for both experiments and DFT, and shows large differences between clusters at steps versus terraces. This charge is localized on the interfacial Ni and Ce atoms in their atomic layers closest to the interface. This knowledge is crucial to understanding the nature of the active sites on the surface of Ni-CeO2 catalysts for which metal-oxide interactions play a very important role in the activation of O-H and C-H bonds. The changes in these interactions with Ni particle size (metal loading) and the extent of reduction of the ceria help to explain how previously reported catalytic activity and selectivity change with these same structural details.

The influence of CO, CO2 and H2O on selective CO methanation over Ni(Cl)/CeO2 catalyst: On the way to formic acid derived CO-free hydrogen

For the first time the influence of CO, CO2 and H2O content on the performance of chlorinated NiCeO2 catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO2 increases with the increasing H2 concentration, is independent of CO2 concentration and decreases with increasing CO and H2O concentrations; the rate of CO2 methanation is weakly sensitive to H2 and CO2 concentrations and decreases with increasing CO and H2O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO2 hydrogenation.For the first time, selective CO methanation over Ni(Cl)/CeO2 was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO2 (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO2-η-Al2O3/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.

Low-temperature trace light-tar reforming in biomass syngas by atmospheric hydrogenation and hydrogenolysis

Nickel-catalyzed atmospheric-pressure hydrogenation and hydrogenolysis of trace light tar in biomass syngas were investigated with two different model biomass syngas compositions and benzene and toluene as model light tars. The optimum methane selectivity was obtained when the reaction temperature was between 623 and 673 K. The reaction rates were influenced by the partial pressures of hydrogen and carbon dioxide. Notably, carbon dioxide retarded the reactions of the aromatic hydrocarbons because of a competitive reaction. A Ni-CeO2 catalyst supported on Al2O3 (Ni-CeO2/Al2O3) enhanced the reactions, and almost all of the carbon atoms in benzene were converted into methane carbon when the hydrogen and carbon dioxide partial pressures were 40 and 30 kPa, respectively, at 673 K in the presence of the Ni-CeO2/Al2O3 catalyst. Furthermore, degradation of the catalysis was not observed for at least 80 min. The composition of this model gas is comparable to that of the syngas obtained by biomass gasification with pure steam. Therefore, trace light aromatic hydrocarbons can be converted into methane through the simple installation of a Ni-CeO2/Al2O3 catalyst bed at the optimum temperature zone downstream of the gasifier, without additional hydrogen, external heating, or secondary air when pure steam is used as a gasifying agent.

Silica–Ceria sandwiched Ni core–shell catalyst for low temperature dry reforming of biogas: Coke resistance and mechanistic insights

In this paper, a novel sandwiched core–shell structured Ni-SiO2@CeO2 catalyst, with nickel nanoparticles encapsulated between silica and ceria, was developed and applied for dry reforming of biogas (CH4 / CO2 = 3/2) under low temperature conditions to test its coke inhibition properties. Ni-phyllosilicate was used as the Ni precursor in order to produce highly dispersed Ni nanoparticles on SiO2. Cerium oxide was chosen as the shell due to its high redox potential and oxygen storage capacity, that can reduce coke formation under severe dry reforming conditions. The core shell Ni-SiO2@CeO2 catalyst showed excellent coke inhibition property under low temperature (600 °C) reforming of biogas, with no coke detected after a 72 h catalytic run. Under the same conditions, Ni-SiO2 catalyst deactivated within 22 h due to heavy coke formation and reactor blockage, while Ni-CeO2 catalyst showed very low activity. The higher activity of the core–shell catalyst is attributed to its higher Ni dispersion and reducibility. TEM and XRD results show that the core–shell catalyst shows higher resistance to Ni particle sintering and agglomeration during the reaction than the Ni-SiO2 and Ni-CeO2 catalysts. In-situ DRIFTS on the Ni-SiO2@CeO2 catalyst indicate a change in the reaction mechanism from a mono-functional pathway on the Ni-SiO2 catalysts to a bi-functional route on the Ni-SiO2@CeO2 catalyst with active participation of oxygen species from CeO2 in carbon gasification. The confinement effect of the sandwich structure and the bifunctional mechanism of dry reforming are the primary reasons for the excellent coke resistance of the Ni-SiO2@CeO2 catalyst.

Fibrous alumina-based Ni-CeO2 catalyst: Synthesis, structure and properties in propane pre-reforming

In the present paper we report the synthesis, structural characterization and catalytic properties of alumina nanofibers supported Ni-CeO2 catalyst (Ni-CeO2/ANF) in pre-reforming of propane as a main component of liquefied petroleum gas. Ni-CeO2/ANF catalyst was prepared via template-assisted wet-combustion synthesis. High dispersion and uniform distribution of nickel and ceria species over nanofibers surface were reached. Ni-CeO2/ANF exhibited sufficient activity, stability and coking-resistance in pre-reforming of propane at low steam to carbon ratio and temperatures of 350–425 °C.

Gasification and Syngas Reforming of City Waste Papers for Solid Oxide Fuel Cells

This study has investigated the thermal processes of three types of Municipal Solid Wastes (MSW) in Taipei. Three key properties of the processes are concerned, the formation of tar, the sulfur content, and the reforming of CH4 as the syngas is used for Solid Oxide Fuel Cells (SOFCs). K2CO3 is used as a catalyst to reduce the amount of tar. One of tar production from MSW is reduced from 37.2 wt% to 13.7 wt%. The raw syngas from gasification is then reformed using a Ni-CeO2 catalyst on a γ-Al2O3 support to optimize the quantity of H2 and reduce the CH4 content. H2S generated by waste paper is in a level of 1.83 ppm, and reduced to 0.04 ppm by CaCO3. Syngas with a composition of 51.3 vol% H2, 44.8 vol% CO and 3.4 vol% CH4 is used for the power generation by a selfassembled SOFC. The best power density is 269 mW.cm-2 at 800°C, which is inferior to the maximum value of 326 mW.cm-2 for a cell that uses H2 as the fuel.

CO and CO2 methanation over supported Ni catalysts

CO and CO2 methanation was investigated over Ni catalysts supported on different supports such as γ-Al2O3, SiO2, TiO2, CeO2, and ZrO2. Among them, Ni/CeO2 was determined to be the most active for CO and CO2 methanation. These catalytic activities increased with increasing surface area of CeO2. To increase the specific catalytic activity for CO and CO2 methanation, various Ni-CeO2 catalysts with different Ni contents were prepared using co-precipitation method. The optimum Ni content was determined for both reactions. The prepared catalysts were characterized with inductively coupled plasma-atomic emission spectroscopy, N2 physisorption, temperature-programmed reduction, temperature-programmed desorption, and X-ray diffraction. The high Ni dispersion and strong CO2 adsorption appeared to be responsible for the high catalytic activity for CO and CO2 methanation. This Ni-CeO2 can be applied to the low-temperature CO and CO2 methanation reactor to achieve high single-pass conversions of CO and CO2.

Effect of metal-support interaction on activity and stability of Ni-CeO2 catalyst for partial oxidation of methane

The objective of the current study was to synthesize a nickel based catalyst with high activity at low temperature for partial oxidation of methane (POM). Ni-nanoparticles supported on CeO2 nanoparticles were synthesized by two step preparation method. First, 30–50nm CeO2 was synthesized by solvo-thermal method and then Ni- nanoparticles were deposited over it following a newly developed procedure, where cetyltrimethylammonium bromide (CTAB) acted as morphology controlling agent and polyvinylpyrrolidone (PVP) as size controlling agent for nickel nanoparticles. The characterizations of synthesized catalysts were done by BET-Surface area, XRD, SEM, TEM, TPR, H2-chemisorpton, TGA and XPS analysis. The catalysts showed excellent coke resisting ability during POM and produces synthesis gas with H2/CO ratio almost 2. The catalyst activated methane at 400°C with 10% methane conversion and converts methane almost completely at 800°C. The catalyst showed above 98% methane conversion at 800°C during 90h of time on stream (TOS) reaction with H2/CO ratio 1.98. Average 5.5nm Ni particles, use of CeO2 as a support played a very crucial role for methane activation at such lower temperature. The synergistic effect between small Ni-nanoparticles and CeO2 nanoparticles of Ni-CeO2 catalyst is the main reason for such activity. Detailed study of other reaction parameters like temperature, Ni loading, weight hourly space velocity (WHSV) was also carried out and reported.

Synthesis of Ni-CeO2 catalyst for the partial oxidation of methane using RF thermal plasma

Ni-CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni-CeO2 catalysts, a precursor containing Ni (∼5-μm diameter) and CeO2 (∼200-nm diameter) powders were heated simultaneously using an RF plasma at a power level of ∼52 kVA and a powder feeding rate of ∼120 g/h. From the X-ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles (<–50-nm diameter) on their surfaces. The catalytic performance was evaluated under atmospheric pressure at > 500 °C and a CH4:O2 molar ratio of 2:1 with Ar diluent. Although the Ni content was high (∼50 mol%), the experimental results reveal a methane conversion rate of > 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on-stream test at 550 °C for 24 h. However, at 750 °C, the on-stream test revealed the formation of filament-like carbons with an increased methane conversion rate over 90%.

Ni/CeO2-thin ceramic layer depositions on ceramic monoliths for syngas production by Oxy Steam Reforming of biogas

Ni-CeO2 catalysts (metals load equal to 7.5wt.%) as thin oxide layers on ceramic monoliths have been obtained by support dip-coating into acid-free stable catalyst dispersion. Ni-based catalysts were prepared by precipitation-dry-impregnation method or solution combustion synthesis and characterized by XRD, BET, CO-Chemisorption, TPR, TEM and SEM-EDX techniques.Coating load (15–20wt.%) was controlled by multiple depositions on the basis of the slurry rheological behavior. Procedure goodness was evaluated in terms of coating load and adhesion performance. Homogeneous and well adherent layers of ca. 10–20μm were found. The performance of final structured systems was evaluated towards biogas oxy-steam reforming (OSR) reaction, highlighting the influence of morphological and structural properties of synthesized Ni-based powders on the catalytic activity. Catalytic tests demonstrated superior performances of solution combustion synthesized Ni/CeO2 catalyst washcoated on monolith, especially at high space velocity.

Carbon nanotube-supported Ni–CeO2 catalysts. Effect of the support on the catalytic performance in the low-temperature WGS reaction

The low temperature water-gas shift (WGS) reaction has been studied over two commercial multiwall carbon nanotubes-supported nickel catalysts promoted by ceria. For comparison purposes, activated carbon-supported catalysts have also been studied. The catalytic performance and the characterization by N2 adsorption analysis, powder X-ray diffraction (XRD), temperature-programmed reduction with H2 (TPR-H2), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis showed that the surface chemistry has an important effect on the dispersion of ceria. As a result, ceria was successfully dispersed over the carbon nanotubes (CNTs) with less graphitic character, and the catalyst afforded better activity in WGS than the catalyst prepared over massive ceria. Moreover, a 20 wt.% CeO2 loading over this support was more active than the analogous catalyst with a 40 wt.% loading. The ceria nanoparticles were smaller when the support was previously oxidized, however this resulted in a decrease of the activity.

Promoter effect of sodium in graphene-supported Ni and Ni–CeO2 catalyst for the low-temperature WGS reaction

The low temperature water–gas shift (WGS) reaction has been studied over Ni–CeO2/Graphene and Ni/Graphene. The catalysts were prepared with 5wt.% Ni and 20wt.% CeO2 loadings, by deposition-precipitation employing sodium hydroxide and urea as precipitating agents. The materials were characterized by TEM, powder X-ray diffraction, Raman spectroscopy, H2-temperature-programmed reduction and X-ray photoelectron spectroscopy (XPS). The characterization and the reaction results indicated that the interaction between the active species and the support is higher than with activated carbon, and this hinders the reducibility of ceria and thus the catalytic performance. On the other hand, the presence of residual sodium in samples prepared by precipitation with NaOH facilitated the reduction of ceria. The catalytic activity was highly improved in the presence of sodium, what can be explained on the basis of an associative reaction mechanism which is favored over NiONa entities.

Ni-CeO2/C Catalysts with Enhanced OSC for the WGS Reaction

In this work, the WGS performance of a conventional Ni/CeO2 bulk catalyst is compared to that of a carbon-supported Ni-CeO2 catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO2/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation.

Synthesis and support composition effects on CH4 partial oxidation over Ni–CeLa oxides

Two series of Ni (6wt%) catalysts supported over CeO2, La2O3 and mixed CeO2–La2O3 were prepared by co-precipitation and by wet-impregnation. The effect of the two Ni loading procedures on the catalyst structural properties was investigated by XRD, TPR and XPS. The catalytic behavior of the catalysts was tested in the methane partial oxidation reaction performed at 1atm in a temperature range of 400–800°C using dilute feed gas mixture with CH4/O2=2 and gas hourly space velocity of 60,000mlg−1h−1. Total methane combustion was observed within the 450°C≤T≤650°C temperature range. Above 650°C partial oxidation of methane started to occur, reaching at 800°C a CO selectivity close to 90%. The lanthanum containing catalysts prepared by wet impregnation exhibited higher CPO activity at lower temperature as compared to the co-precipitated ones. Opposite behavior was observed with the Ni–CeO2 catalysts. During the stability test at high temperature, carbon formed only over the single oxide supported catalysts, Ni–CeO2 and Ni–La2O3. According to the characterization results carbon was not responsible for catalyst deactivation but it prevented the sintering of the nickel particle. The interplay of the crystallite sizes and the formation of various nickel–lanthanum oxide species with different Ni oxidation states were responsible for the differences in the CPO performance.

Biogas as renewable raw material for syngas production by tri-reforming process over NiCeO2 catalysts: Optimal operative condition and effect of nickel content

This study focused on the tri-reforming of simulated biogas over a Ni/ceria based catalysts (nickel content: 1.8wt.%–31.0wt.%) prepared by combustion synthesis to syngas production. The effects of the H2O/CH4, O2/CH4 molar ratios, reaction temperature, and nickel content on the catalysts' performances were studied along with morphological investigations. The chemical–physical analysis reveals a strong interaction between support and well dispersed nickel with some part of nickel incorporated into the CeO2 support, suggesting that the coexistence of different nickel phases, as well as the properties of the CeO2 support, can play an important role in the catalytic activity and stability of Ni/CeO2 catalysts. Among the samples examined, the catalyst with 7.7wt.% Ni loading has showed the highest catalytic activity; under the reaction conditions of the feed gas molar ratios CH4/CO2/O2/H2O=1/0.67/0.1/0.3, GHSV=30,000h−1 and reaction temperature of 800°C, the conversions of CH4 and CO2 were 98.94% and 89.22% respectively producing a syngas with a H2/CO=1.34. Moreover, stable performances of the catalyst are denoted during 150h. It was also observed that the H2/CO molar ratio could be flexibly adjusted by the added amounts of oxygen and steam in order to meet the requirements of downstream processes.

Effect of precipitants on Ni-CeO2 catalysts prepared by a co-precipitation method for the reverse water-gas shift reaction

A series of Ni-CeO2 catalysts were prepared by co-precipitation method with Na2CO3, NaOH, and mixed precipitant (Na2CO3:NaOH; 1:1 ratio) as precipitant, respectively. The effect of the precipitants on the catalytic performance, physical and chemical properties of Ni-CeO2 catalysts was investigated with the aid of X-ray diffraction (XRD), Brumauer-Emmett-Teller method (BET), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetry (TG), and H2-TPR characterizations. The Ni-CeO2 catalysts were examined with respect to their catalytic performance for the reverse water-gas shift reaction, and their catalytic activities were ranked as: Ni-CeO2-CP (Na2CO3:NaOH=1:1)>Ni-CeO2-CP(Na2CO3)>Ni-CeO2-CP(NaOH). Correlating to the characteristic results, it was found that the catalyst prepared by co-precipitation with mixed precipitant (Na2CO3:NaOH; 1:1 ratio) as precipitant had the most amount of oxygen vacancies accompanied with highly dispersed Ni particles, which made the corresponding Ni-CeO2-CP(Na2CO3:NaOH=1:1) catalyst exhibit the highest catalytic activity. While the precipitant of Na2CO3 or NaOH resulted in less or no oxygen vacancies in Ni-CeO2 catalysts. As a result, Ni-CeO2-CP(Na2CO3) and Ni-CeO2-CP(NaOH) catalysts presented poor catalytic performance.

Synthesis of stable Ni-CeO2 catalysts via ball-milling for ethanol steam reforming

This paper describes the fabrication of Ni-CeO2 catalysts for ethanol steam reforming via an easy ball-milling process using skeletal Ni and powder CeO2 as precursors. Hydrogen production from reforming of biomass-derived oxygenates is one of the most promising energy acquisition methods. Although Ni-based catalysts have been intensively employed in reforming reactions, they commonly suffer severe deactivation due to sintering of metal particles and carbon deposition. The prepared Ni-CeO2 catalysts were examined via BET, XRD, TPR, TEM, and compared to a reference Ni/CeO2 catalysts prepared by a conventional method. Due to the nanoconfinement of nickel particles by the support and the strong metal-support interaction, the Ni-CeO2 catalyst has superior ability for anti-sintering and -coke, thus has high reactivity and stability in reforming reactions. This preparation method is facile and favorable from the practical point of view.

Influence of preparation method on performance of Ni-CeO2 catalysts for reverse water-gas shift reaction

This study investigated 1 wt.% Ni-CeO2 catalysts that were prepared using co-precipitation, deposition-precipitation, and impregnation methods for the reverse water-gas shift (RWGS) reaction. Characterizations of the catalyst samples were conducted by Brumauer-Emmett-Teller (BET), atomic absorption spectrophotometer (AAS), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and temperature programmed reduction (TPR). The results showed that the Ni-CeO2 catalyst prepared using the co-precipitation method exhibited the best catalytic performance. In the Ni-CeO2 catalyst prepared using co-precipitation method, a combination of highly dispersed NiO and abundant oxygen vacancies was assumed to play a crucial role in determining the catalytic activity and selectivity of the RWGS reaction.