MgO-supported Ni Catalysts Research Articles

Cost-Effective Single-Step Synthesis of Metal Oxide-Supported Ni Catalyst for H2-Production Through Dry Reforming of Methane

AbstractPreparing catalysts from cheap metal precursors in a single pot are an appealing method for reducing catalytic preparation costs, minimizing chemical waste, and saving time. With regards to the catalytic conversion of dry reforming of methane, it offers the prospect of significantly reducing the cost of H2 production. Herein, NiO-stabilized metal oxides like Ni/TiO2, Ni/MgO, Ni/ZrO2, and Ni/Al2O3 are prepared at two different calcination temperatures (600 °C and 800 °C). Catalysts are characterized by X-ray diffraction, Raman spectroscopy, surface area-porosity analysis, Temperature program experiments, infrared spectroscopy, and thermogravimetry analysis. The MgO-supported Ni catalyst (Ni/MgO-600), ZrO2-supported Ni catalyst (Ni/ZrO2-600), and Al2O3-supported Ni (Ni/Al2O3-600) catalyst calcined at 600 °C show initial equal H2 yields (~ 55%). The population of CH4 decomposition sites over ZrO2-supported Ni catalyst remains highest, but H2-yield drops to 45% against high coke deposition. The catalytic activity remains constant over the Ni/MgO-600 catalyst due to the enrichment of “surface interacted CO2-species”. MgO-supported Ni catalyst calcined at 800 °C undergoes weak interactions of NiO-M′ (M′ = support), serious loss of CH4 decomposition sites and potential consumption of H2 by reverse water gas shift reaction, resulting in inferior H2 yield. H2-yield remains unaffected over an Al2O3-supported Ni catalyst even against the highest coke deposition due to the formation of stable Ni (which exsolves from NiAl2O4) and proper matching between carbon formation and rate of carbon diffusion.

Different supported Ni catalysts for dry reforming of methane: Effect of calcination temperature

Due to the increased environmental consciousness about reducing greenhouse gas emissions of CH4 and CO2, an intriguing study issue is the dry reformation of CH4 (DRM) over a catalyst made of Ni.). Herein in this work, 5.0 wt% NiO was loaded on various supports (S = TiO2-P25, Al2O3, MgO, and ZrO2) through the process of dry impregnation. At 600 °C or 800 °C, the catalysts were then calcined to investigate the impact of calcination temperature on the catalytic performance. The catalysts were characterized by N2 physisorption, Raman spectroscopy, thermalgravimetric analysis, XRD, and TEM. The best catalyst was obtained when the MgO-supported Ni catalyst was operated at 700 °C and was calcined at 600 °C. This catalyst gave average conversions of CH4 and CO2 of 70.04 % and 77.2 %, respectively. However, when the calcination temperature of the same catalyst was increased to 800 °C, the average conversions of CH4 and CO2 dropped to 37.9 % and 48.07 %, respectively. Thus, the calcination pretreatment strongly influenced the catalyst performance, where rising the calcination temperature lowered the activity. The Al2O3-supported sample had the highest surface area, metal-support interaction, and activity. It produced a large amount of carbon nanotubes, whereas the MgO-supported sample presented the least carbon formation, the lowest deactivation factor, and no morphology change due to the reaction in the TEM.

Hydrogen‐rich syngas production from bi‐reforming of greenhouse gases over zirconia modified Ni/ MgO catalyst

Bi-reforming of methane (BRM) is gaining an increase interest due to the critical requirements to mitigate global warming and provide alternative energy resources. However, there has been a serious challenge to the scale-up of the process to commercial production due to the catalyst deactivation. In the present study, the influence of ZrO2 modifications on the activity and stability of MgO-supported Ni catalyst in the BRM reaction was investigated. The ZrO2-MgO mixed oxide support was prepared by co-precipitation method with variation in the ZrO2 composition and subsequently impregnated with Ni. The characterization of the freshly prepared Ni/MgO and Ni/MgO-ZrO2 catalysts using N2 physisorption analysis, X-Ray Diffraction (XRD), FESEM, XPS, H2-TPR, and CO2-TPD techniques revealed suitable physicochemical properties for the BRM reaction. The Ni/MgO-ZrO2 catalysts showed an improved performance in the BRM reaction in terms of activity and stability compared to the Ni/MgO at 800°C and CH4, H2O, CO2 ratio of 3:2:1, respectively. The best performance was obtained using the Ni/15%ZrO2-MgO for the BRM with CO2 and CH4 conversion of 81.5% and 82.5%, respectively. The characterization of the spent Ni/MgO catalyst using Raman spectroscopy, FESEM, and High Resolution Transmission Electron Microscopy (HRTEM) analysis revealed the formation of amorphous carbon that could be responsible for its fast deactivation.

Additive-free vapour-phase hydrogenation of benzonitrile over MgO-supported Ni catalysts

MgO-supported Ni catalysts were selectively catalysed by the hydrogenation of benzonitrile to benzylamine in continuous flow at atmospheric pressure without any additives. Ni/MgO catalysts were synthesized by co-precipitation method with NaOH as the precipitating agent. All the synthesized catalysts were characterized by various physiochemical techniques, namely XRD, H2-TPR, BET surface area, CO2-TPD, SEM, and TEM. Among them, 10% Ni/MgO catalyst showed the best activity with 98% conversion of benzonitrile, 60% selectivity to benzylamine at 473 K. The high dispersion of Ni and strong metal support interactions with MgO are key factors for the catalytic performance. 10Ni/MgO catalyst was found to be consistent throughout the time-on-stream studies of 36 h which clearly explains the excellence of the catalytic system. Ni/MgO catalysts are active in gas phase hydrogenation of benzonitrile to benzylamine at atmospheric pressure.

Identification of active sites in CO2 activation on MgO supported Ni cluster

In this work, initial activation mechanism of CO2 over MgO supported Ni catalysts has been systematically studied through the periodic DFT calculations. In addition, the role of metal cluster, interface and support for CO2 activation is investigated and the active site is identified. CO2 is most favored to be activated on the interface instead of neither Ni cluster nor MgO support. The effective energy for this process is around 0.67 eV, and the dissociation of CO2 (0.62 eV) is the rate-determining step, since it requires much higher energy than that of the CO2 adsorption process (0.05 eV). Thus, the interface between metal cluster and support plays a key role for C=O bond activation. Moreover, CO∗ is preferred to be adsorbed on the Ni cluster, while the O∗ is likely to bind on Mg atom of support. To illustrate the adsorption behavior of CO2 at different sites, the Mulliken atomic charge and electron density difference have been calculated. It was found that the total amount of electron gain for CO2 binding at different sites follows the order of Interface (−0.03 e) < MgO support (−0.05 e) < Ni cluster (−0.07 e), and effective energy barrier rises linearly with the increase of electron gain of CO2 binding at different sites. In addition, electron gain of oxygen atom O1 and oxygen atom O2 of CO2 is the same for Ni cluster and MgO support, however, the electron gain of O1 and O2 is different for Interface. The difference of electron gain for two oxygen atoms shows the electron unbalance of CO2 molecule, which is in favor of C=O activation. This study could shed some light on understanding the active sites of CO2 thermal-catalytic activation over MgO supported Ni catalysts, and is helpful to elucidate the reaction on an atomic level.

Surface titration of supported Ni catalysts by O2-pulse thermal analysis

A new method for determining the Ni0 metal surface area of MgO supported catalysts is proposed. Different series of MgO supported Ni catalysts were prepared and titrated by chemical adsorption of oxygen inside an STA-MS setup. Simultaneous recording of the mass gain upon oxidation, the enthalpy of formation of the oxide and the evolved gas allowed a precise quantification of the metallic Ni surface area. In addition, any uncertainties linked with the complex Ni oxide stoichiometry could be ruled out. A comparison of the newly developed oxygen pulse method with already established techniques using H2 or N2O confirmed the applicability of the method and further revealed its surface sensitivity and accuracy with respect to MgO supported Ni catalysts.

Insight into the influence of addition of a second metal Fe and supports with different morphology on H2 dissociation over Ni/MgO catalysts

The effect of addition of a second metal to activation component and the support with different morphology on H2 dissociation on Ni/MgO catalyst was investigated using density functional theory. The results show that after addition of a second metal Fe, the metal-support interaction is increased in perfect MgO supported Ni catalyst while it is decreased in defective MgO supported Ni catalyst. Although the change is difference between metal-support interaction, the ability of H2 dissociation is increased on the two surfaces. Analyzing those results from addition of Fe, Co and Cu to Ni/MgO, one can conclude that it is neither too strong nor too weak (i.e., medium) interaction between metal and support that favors to improve the catalyst performance.

Catalytic performance of mesoporous MgO supported Ni catalyst in steam reforming of model compounds of biomass fermentation for hydrogen production

Steam reforming (SR) of pure butanol and a specific mixture (butanol/acetone/ethanol = 6/3/1, mass ratio) assumed as a model of bio-butanol raw mixture have been researched over mesoporous MgO supported Ni catalysts with various particle size (3.6–8.8 nm). The catalysts were characterized by N2 adsorption, H2-TPR, XRD, XPS and TEM. The volcano-like curves were observed when the H2 yield and H2 selectivity were plotted as a function of the nickel particle size in butanol steam reforming (BSR) and acetone–butanol–ethanol steam reforming (ABESR) reactions. Prepared mesoporous Ni0.12/MgO catalysts exhibited the highest catalytic performance in two model reaction systems. Surprisingly, the Ni particle size effects in BSR developed difference with counterpart in ABESR. Specifically, the catalytic performance of mesoporous Ni0.20/MgO even outperform that of mesoporous Ni0.08/MgO catalyst with respect to lower by-products selectivity and higher hydrogen yield in ABESR compared to BSR results.

Autothermal reforming of methane over Ni catalysts supported on nanocrystalline MgO with high surface area and plated-like shape

Autothermal reforming of methane (ATRM), combination of partial oxidation and steam reforming was performed over MgO supported Ni catalysts. The preparation of MgO via surfactant-assisted precipitation method led to obtain a nanocrystalline carrier for nickel catalysts. The results demonstrated that methane conversion is significantly increased with increasing the Ni content (5, 7, 10 and 15%Ni) and methane conversion of 15%Ni/MgO was higher than that of other catalysts with lower Ni loading in all operation temperatures. In addition, increasing the system operation temperatures led to decrease in H 2/CO due to the fact that water-gas shift reaction was thermodynamically unfavorable at elevated temperatures. This catalyst also exhibited stable catalytic performance during 50 h time on stream. Furthermore, the influences of varying GHSV and feed ratio on activity of 15%Ni/MgO catalyst were investigated.

Ni catalysts supported on nanocrystalline magnesium oxide for syngas production by CO 2 reforming of CH 4

Abstract CO 2 reforming of methane (CDRM) was carried out over MgO supported Ni catalysts with various Ni loadings. The preparation of MgO supported Ni catalysts via surfactant-assisted precipitation method led to the formation of a nanocrystalline carrier for nickel catalysts. The synthesized samples were characterized by XRD, N 2 adsorption-desorption, H 2 chemisorption, TPR, TPO and SEM techniques. It was found that the high catalytic activity and stability of the prepared catalysts could be attributable to high dispersion of reduced Ni species and basicity of support surface. In addition, the effect of feed ratio, nickel loading and GHSV on the catalytic performance of CDRM over the catalysts were investigated.

Steam reforming of tar from pyrolysis of biomass over Ni/Mg/Al catalysts prepared from hydrotalcite-like precursors

The Ni/Mg/Al catalysts were prepared from the calcination and reduction of hydrotalcite-like compounds containing Ni, Mg and Al, and applied to the steam reforming of tar from pyrolysis of biomass. The dependence of the composition and reduction pretreatment conditions on the catalytic performance was investigated. It is found that the Ni/Mg/Al catalyst with optimized composition of Ni/Mg/Al=9/66/25 exhibited much higher activity, resistance to coke deposition, and stability than Al2O3- and MgO-supported Ni catalysts. The catalyst characterization using XRD, TPR, N2 and H2 adsorption, and TEM indicates that the Ni/Mg/Al catalyst after the reduction has a nanocomposite structure of Ni metal particles (about 8.5nm) and Mg(Ni, Al)O particles (about 11.5nm). Even after the catalytic use, the nanocomposite structure was maintained. High performance of the Ni/Mg/Al catalyst including the suppression of the aggregation of the metal particles can be caused by the nanocomposite structure.

Preparation and characterization of active Ni/MgO in oxidative steam reforming of n-C 4H 10

Oxidative steam reforming of n-C 4H 10 over MgO-supported Ni catalysts is described. The Ni/MgO catalysts were prepared by the impregnation method from aqueous Ni(NO 3) 2 precursor solutions at two pH values. Ni/MgO prepared at pH 7 exhibited considerably higher activity than Ni/MgO prepared from a conventional acidic aqueous precursor solution (pH 3.5). The H 2 formation rate for the modified Ni/MgO was up to 2.3 times that for conventional Ni/MgO under a high space velocity of 1660 L(h g) −1. Furthermore, after reduction at high temperature (1273 K), the modified Ni/MgO showed a higher H 2 formation rate than did Rh/MgO. The superior performance of the modified Ni/MgO was ascribed to stronger resistance to oxidation of Ni 0 due to the formation of relatively large Ni 0 particles.

Narrow diameter distribution of singlewalled carbon nanotubes grown on Ni–MgO by thermal chemical vapor deposition

We have grown singlewalled carbon nanotubes (SWNTs) over MgO-supported Ni catalyst particles at 800 °C with a mixture of acetylene and hydrogen gases. The diameters of SWNTs grown on 3 wt% Ni–MgO particles ranged from 0.7 to 1.0 nm, having a narrow diameter distribution compared to the previous works. This was attributed to the preparation procedure of Ni–MgO templates. Ni catalyst was co-precipitated with MgO, where an appropriate amount of Ni catalyst with uniform grain size remained on MgO surface after forming a solid solution during reaction. This method should be useful for a selective growth that is applicable to future electronic devices.

Formation and characteristic properties of carbonaceous species on nickel-magnesia solid solution catalysts during CH 4[sbnd]CO 2 reforming reaction

Carbonaceous species formed during the reforming of CH 4 with CO 2 over a series of Ni x Mg 1− x O solid solution catalysts and MgO-supported Ni catalysts were characterized by temperature-programmed hydrogenation (TPH) method. Two peaks appeared in the TPH spectra: one between 550 and 700 K (α-carbon) and another above 873 K (β-carbon). It was found that a good relationship exists between the quantity of α-carbon species and the catalytic activity, indicating that α-carbon should be the reaction intermediate. In addition, the amount of β-carbon increased with increasing reaction time, especially on the supported Ni/MgO catalysts which make inactive carbon during the CH 4 CO 2 reforming reaction.