Silica-supported Nickel Catalysts Research Articles

Highly Active and Anticoke Fibrous Silica-Supported Nickel Catalyst for CO2 Methanation

Highly Active and Anticoke Fibrous Silica-Supported Nickel Catalyst for CO₂ Methanation

Effect of various silica-supported nickel catalyst on the production of bio-hydrocarbons from oleic acid

The conversion of fatty acids into bio-hydrocarbons can be carried out through a deoxygenation (DO) reaction. Catalytic deoxygenation of fatty acids can occur through three reaction pathways: decarbonylation, decarboxylation, and hydrodeoxygenation. In this study, three kinds of silica were prepared: (i) silica obtained from the rice husk ash (RHA); (ii) synthetic mesoporous silica SBA-16; and (iii) commercial silica. All prepared silica was used as supported nickel (Ni) catalyst for bio-hydrocarbon production through DO reaction of oleic acid. The objective of this study was to investigate the effect of variations of silica on the reaction pathway and final products composition of DO reaction of oleic acid. The catalysts were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), surface area analysis, and NH3-temperature-programme desorption. Based on XRF and XRD analysis results, it can be concluded that nickel was successfully impregnated into all silica. All samples of catalysts were used in a reaction carried out at temperature of 285 °C under a pressure of 40 bar H2 for 2h. The results showed that all catalysts were able to convert oleic acid to bio-hydrocarbon with differences in products composition. The highest oleic acid conversion of 98.25% was achieved with Ni/RHA catalyst but the obtained liquid products was the lowest among other catalysts. It is found that this phenomenon was closely related to the acidity properties of the catalyst.

Enhanced Methane Dry Reforming with Ni/SiO2 Catalysts Featuring Hierarchical External Nanostructures

Global energy demand escalates the interest in effective and durable catalytic systems for the dry reforming of methane (DRM), a process that converts CO2/CH4 into H2/CO syngas. Porous silica-supported nickel (Ni) catalysts are recognized as a promising candidate due to robust DRM activity associated with the confinement of Ni particles in the mesopores that reduces the catalyst deactivation by carbon byproduct deposits and sintering of active Ni sites. However, the small-sized pore configurations in the mesoporous catalysts hinders the fast mass transfer of reactants and products. A unique combination of the hierarchical nanostructure with macro–mesoporous features of the support is adopted to enhance the catalytic performance via the dual effect of the efficient mass transfer and minimized sintering issue. This study delves into the influence of SiO2 geometry and pore structure on the catalytic performance of Ni-based catalysts. Three types of porous silica supports were synthesized through various methods: (a) hydrothermal-assisted sol–gel for dendritic mesoporous silica (DMS), (b) spray-pyrolysis-assisted sol–gel for spray evaporation-induced self-assembly (EISA) silica, and (c) oven-assisted sol–gel for oven EISA silica. Among the prepared catalysts the hierarchical external nanostructured Ni/DMS showed the superior CH4 and CO2 conversion rates (76.6% and 82.1%), even at high space velocities (GHSV = 360 L∙g−1·h−1). The distinctive macro–mesoporous geometry effectively prevents the sintering of Ni particles and promotes the smooth diffusion of the reactants and products, thus improving catalytic stability over extended reaction periods (24 h). This research highlights the significant impact of macro–mesoporosity revealed in DMS support catalysts on the physicochemical properties of Ni/DMS and their crucial role in enhancing DRM reaction efficiency.

Revealing the anti-sintering phenomenon on silica-supported nickel catalysts during CO2 hydrogenation

The CO2 catalytic hydrogenation represents a promising approach for gas-phase CO2 utilization in a direct manner. Due to its excellent hydrogenation ability, nickel has been widely studied and has shown good activities in CO2 hydrogenation reactions, in addition to its high availability and low price. However, Ni-based catalysts are prone to sintering under elevated temperatures, leading to unstable catalytic performance. In the present study, various characterization techniques were employed to study the structural evolution of Ni/SiO2 during CO2 hydrogenation. An anti-sintering phenomenon is observed for both 9% Ni/SiO2 and 1% Ni/SiO2 during CO2 hydrogenation at 400°C. Results revealed that Ni species were re-dispersed into smaller-sized nanoparticles and formed Ni0 active species. While interestingly, this anti-sintering phenomenon leads to distinct outcomes for two catalysts, with a gradual increase in both reactivity and CH4 selectivity for 9% Ni/SiO2 presumably due to the formation of abundant surface Ni° from redispersion, while an apparent decreasing trend of CH4 selectivity for 1% Ni/SiO2 sample, presumably due to the formation of ultra-small nanoparticles that diffuse and partially filled the mesoporous pores of the silica support over time. Finally, the redispersion phenomenon was found relevant to the H2 gas in the reaction environment and enhanced as the H2 concentration increased. This finding is believed to provide in-depth insights into the structural evolution of Ni-based catalysts and product selectivity control in CO2 hydrogenation reactions.

Photothermal Dry Reforming of Methane over Phyllosilicate-Derived Silica-Supported Nickel Catalysts

Photothermal Dry Reforming of Methane over Phyllosilicate-Derived Silica-Supported Nickel Catalysts

Reforming Methane with CO2 over Hierarchical Porous Silica-Supported Nickel Catalysts Modified with Lanthanum Oxide

Hierarchical porous silica-supported nickel catalysts modified with different amounts of lanthanum (La) were synthesized via “one-pot” method using cetyltrimethylammonium bromide as template, urea as precipitant, and tetraethyl orthosilicate as silica source. Their catalytic performances were evaluated in dry reforming with methane under different conditions (La loading, reaction temperature, and time on stream). The synthesized and spent catalysts were extensively characterized by ICP, physisorption, chemisorption, XRD, TPR, XPS, HAADF-TEM, TPH, Raman’s spectroscopy, and TG analysis. The impact of lanthanum amount on the catalytic performance, sintering, and carbon deposition was discussed. Compared to unmodified catalyst, La promoter induced the nickel nanoparticles with larger crystallite sizes and weakened the metal-support interaction as well as the formation of 1 : 1 nickel-phyllosilicate, leading to the metal sintering increasing in the order Ni1.5La/SiO2 < Ni3.0La/SiO2 < Ni4.5La/SiO2. The modified catalysts exhibited better carbon resistance, which was significantly enhanced with increasing La content. Despite this, the stability increased following the sequence of Ni3.0La/SiO2 < Ni4.5La/SiO2 < Ni1.5La/SiO2. Ni1.5La/SiO2 displayed the best stability at 750°C within 10 h stability test, with CH4 conversion dropping from 61.3 to 58.0%. The deactivation reason for Ni1.5La/SiO2 was mainly the carbon deposition, while that for Ni3.0La/SiO2 and Ni4.5La/SiO2 was the metal sintering. These results emphasized that the activity and stability in the NiLa/SiO2 catalysts for the dry reforming of methane depended on two important factors, the metal-support interaction and the particles size of nickel, providing the necessity and sufficiency to balance two attributes.

Virtuous utilization of carbon dioxide in pyrolysis of polylactic acid

Polylactic acid has been adopted as a strategic alternative to petroplastics because of its biodegradability. The waste generation rate could be proportional to its use, considering the short lifespan of polylactic acid. However, a practical disposal or recycling protocol for polylactic acid waste has not yet been developed. Thus, this study suggests a promising thermochemical platform for valorizing polylactic acid waste into energy resources (syngas). Specifically, carbon dioxide-assisted pyrolysis has been suggested to impart environmental features to polylactic acid disposal. Before the pyrolysis tests, the polylactic acid waste sample was characterized by Fourier transform-infrared spectrometer and thermogravimetric analyses, which showed that polylactic acid contained a substantial amount of additives and impurities (∼13 wt%). The impurity containing polylactic acid was converted into pyrogenic gases and biocrudes through pyrolysis process. The pyrolysis was performed under carbon dioxide condition and led to enhanced carbon monoxide formation from simultaneous homogeneous reactions between CO2 and volatile organic compounds evolved from thermal degradation of polylactic acid. CO2 was reduced and the volatile compounds were oxidized. The evolution of carbon monoxide from pyrolysis under carbon dioxide condition was 2 times higher than that from nitrogen condition. The concentration of carbon monoxide from the pyrolysis of polylactic acid waste with respect to plastics and biomass was considerably higher. This observation indicates that the susceptibility of carbon dioxide to the homogeneous reaction is highly sensitive. To seek a way to hasten the homogeneous reaction, silica supported nickel catalysts were applied. The evolution of carbon monoxide from catalytic pyrolysis under carbon dioxide condition was 4.5 times higher than inert atmosphere.

Photothermal steam reforming of methane over silica-supported nickel catalysts with temperature gradients

The present work demonstrated that the photo-formed temperature gradients changed the product selectivity in the photothermal steam reforming of methane.

Modification of silica supported nickel catalysts with lanthanum for stability improvement in methane reforming with CO2

Dry reforming of methane (DRM) with excessive methane composition at CH4/CO2 = 1.2:1 was studied over lanthanum modified silica supported nickel catalysts (Ni-xLa-SiO2, x: 1, 2, 4, and 6% in the target weight percent of La). The catalysts were prepared by ammonia evaporation method. Nickel phyllosilicate and La2O3 were the main phases in calcined catalysts. The modification of La enhanced the formation of 1:1 and Tran-2:1 nickel-phyllosilicate. There existed an optimum content of La loading at 1.50 wt% in Ni–2La–SiO2 which resulted in its highest reduction degree (95.3%). The catalysts with appropriate amounts of La exhibited higher amount of CO2 adsorption and created more medium and strong base centers. The sufficient number of exposed metallic nickel sites to catalyze the reforming reaction, as well as enough medium and strong basic sites in Ni–La–SiO2 interface to accomplish the carbon removal were two important factors to attenuate catalyst deactivation. The catalyst stability evaluated at 750 °C for 10 h followed the order: Ni–2La–SiO2 > Ni–4La–SiO2 > Ni–1La–SiO2 ≈ Ni–6La–SiO2 > Ni–SiO2. Ni–2La–SiO2 catalyst possessed the lowest deactivation behavior, whose CH4 conversion dropped from 60.2 to 55.9% after 30 h operation at 750 °C, indicating its high resistance against carbon deposition and sintering.

Ceria-modified nickel supported on porous silica as highly active and stable catalyst for dry reforming of methane

Addition of CeO2 was regarded as a promising strategy to enhance the carbon resistance of nickel-based catalysts for dry reforming of methane (DRM) due to the high concentration of reactive oxygen species with excellent oxidation capacity. In this work, ceria-modified porous silica supported nickel catalysts (Ni-CeX-Y/SiO2) were prepared by “one-pot” method and employed to catalyze DRM reaction. Introduction of CeO2 hindered the formation of 1:1 Ni-phyllosilicate species and weakened the interaction between Ni and silica. The surrounding CeO2 on Ni nanoparticle efficiently prevented the nickel sintering. The number of active oxygen species gradually increased with increasing CeO2 loading, which was beneficial to improve the carbon resistance by means of participating in the oxidation of carbon. Therefore, Ni-CeX-Y/SiO2 catalysts exhibited lower carbon deposition and graphitization degree. Ni-Ce5-2/SiO2 and Ni-Ce5-3/SiO2 possessed strong anti-sintering ability and carbon resistance, showing relatively good stability that CH4 conversion decreased from 81.3 to 75.6% and 82.2 to 78.2% over 24 h time on stream. Kinetic study confirmed that introduction of CeO2 decreased the activation energy of CH4 decomposition and CO2 dissociation, hence enhancing the catalytic activity and carbon resistance.

Efficient Ni/SiO2 catalyst derived from nickel phyllosilicate for xylose hydrogenation to xylitol

The lignocellulosic biomass utilization is a feasible way to obtain alternative fuels and chemicals. Xylitol as an ideal sweetener is one of the top twelve value-added chemicals derived from biomass. Xylitol is also used in the pharmaceutical and cosmetics industries. Thus, the production of xylitol from biomass is significantly important. A silica supported nickel catalyst derived from nickel phyllosilicate for efficient aqueous phase xylose hydrogenation to xylitol was developed in this study. Higher xylose conversion was observed over the nickel phyllosilicate derived catalyst compared to nickel oxide derived nickel catalyst prepared by impregnation and commercial Raney Ni catalyst. The excellent xylitol selectivity (approximately 99 %) was also obtained over the nickel phyllosilicate derived catalyst. The differences in structure and property resulted from different preparation methods were investigated by means of XRF, N2 physisorption, XRD, FT-IR, H2-TPR, TEM as well as H2-TPD. The higher nickel dispersion of nickel phyllosilicate derived catalysts, which could be synthesized by ammonia evaporation and deposition-precipitation using Na2CO3 as precipitator, led to higher xylose conversion. In addition, the phyllosilicate derived nickel catalyst demonstrated outstanding stability. Consequently, phyllosilicate derived nickel catalyst is promising for the industrial application for the production of xylitol form xylose aqueous hydrogenation thanks to its higher activity and selectivity as well as good stability.

Impacts of La addition on formation of the reaction intermediates over alumina and silica supported nickel catalysts in methanation of CO2

This study aimed to investigate impacts of Al2O3 and SiO2, the supports of Ni catalysts with distinct properties, and the additive of La on catalytic behaviors and reaction intermediates formed during methanation of CO2. The results showed that the addition of La to either Ni/Al2O3 or Ni/SiO2 led to the reduced size of metallic nickel, the reduced reduction degree of nickel oxide, the increased alkalinity number and the increased activity for methanation of CO2. Furthermore, the addition of La to the Ni/SiO2 catalyst could suppress the formation of CO via the reverse water gas shift (RWGS) reaction. Ni/SiO2 was much more active than the Ni/Al2O3, even though nickel size was much bigger. The in situ Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) studies showed that the addition of La to Ni/Al2O3 interfered with integration of hydroxyl group with *CO2 species and formation of the bicarbonate and carbonate, while favored formation of the formate specie, enhancing the catalytic activity. For Ni/SiO2, instead of formate, CO* became the main reaction intermediate. The strong absorption of CO* favored its further conversion and explained the low selectivity of the silica-based catalysts toward CO. The addition of La to Ni/SiO2 catalyst facilitated further hydrogenation of CO* species to CH4 and promoted the catalytic activity.

Design Synthesis of ITE Zeolite Using Nickel-Amine Complex as an Efficient Structure-Directing Agent.

Modern methodologies for synthesizing zeolites typically involve the employment of costly organic structure-directing agents. Herein, we report the design synthesis of aluminosilicate zeolite with ITE structure using an inexpensive nickel-amine complex (nickel-pentaethylenexamine) as a novel structure-directing agent. Characterizations including X-ray diffraction, scanning electron microscopy, N2 sorption isotherms, and 27Al magic-angle spinning NMR techniques show that the ITE zeolite has high crystallinity, perfect crystals, large surface area, and abundant aluminum species in the framework. More importantly, catalytic tests on the hydrogenation of CO2 into methane show that the Ni-ITE zeolite exhibits better catalytic performance than aluminosilicate-supported and silica-supported nickel catalysts. Obviously, the use of nickel-amine complex offers an alternative and facile way to synthesize aluminosilicate zeolites.

Catalytic performance and characterization of Neodymium-containing mesoporous silica supported nickel catalysts for methane reforming to syngas

Ordered mesoporous silica materials based on nickel and other elements have been extensively studied because controlling the size of metal nanoparticles is an effective method to tune the superficial physicochemical process. Neodymium (Nd)-promoted mesoporous silica xNdMS (x: molar ratio of Nd/Si = 0.01, 0.02, 0.04, 0.06) were prepared through a sol–gel strategy. Nickel-based catalysts with high dispersion by using xNdMS as supports were investigated for methane reforming with carbon dioxide and/or oxygen to produce syngas. xNdMS supports and nickel catalysts were examined by combining textural, structural, local and surface information. The characterization results showed that Nd was successfully incorporated into the mesoporous framework of MS and Nd was beneficial to improve the metal dispersion. All Nd-promoted Ni/MS catalysts were effective for the methane reforming reaction. Ni/0.04NdMS catalyst exhibited the highest initial catalytic activity during 12 h time on stream, which was attributed to its high metal dispersion, more basic sites and the strengthened nickel-support interaction. The readily deactivation and poorest catalytic activity of Ni/MS catalyst were due to the serious oxidation of metallic nickel under reaction medium.

Process Intensification in Ammonia Synthesis Using Novel Coassembled Supported Microporous Catalysts Promoted by Nonthermal Plasma

The Integrated Process Intensification approach is used for the synthesis of ammonia using novel coassembled microporous silica supported nickel catalysts and nonthermal plasma reactors operating at ca. 140 ± 10 °C and ambient pressure. The conversion levels of nitrogen and hydrogen to ammonia are similar to that achieved by the current industrial best practice which is, however, carried out at 100–250 bar and the temperatures 350–550 °C. In order to achieve continuous plasma generation, a novel catalyst, which has a surface area of ca. 200 m2/g in the form of lamellae with ca. 2 nm thick plates of nickel catalyst sandwiched between the silica support, has been used in the presence of plasma catalysis promoters in the form of spheres made from high permittivity material. In addition to process variables (flow rate, feed composition, and plasma power input), the effect of the electrode configuration on conversion was investigated. It is shown that the catalyst activity remained constant over a continuous p...

Orange Peel Oxidative Gasification on Ni Catalysts Promoted with CaO, CeO2 or K2O.

Orange peel can be considered as an attractive raw material to be gasified for hydrogen or syngas production. In this work, the catalytic evaluation of several silica-supported nickel catalysts in the oxidative degradation of waste orange peel is reported. It was found that the catalytic gasification with the K2O-Ni/silica catalyst produces more hydrogen than the non-catalytic route at 600 degrees C. Surprisingly, a significant amount of ethene was obtained with the CeO2-Ni/silica catalyst, which was explained in terms of an oxidative dehydrogenation reaction of ethane formed during biomass or tar decomposition.

Influence of Ni/SiO2 activity on the reaction pathway in sunflower oil hydrogenation

Sunflower oil hydrogenation process was studied on silica supported nickel catalysts. Three texturally different silica gel materials were used as supports for synthesis of Ni/SiO2 catalyst precursors. After precursors’ reduction and paraffin oil impregnation, obtained catalysts were used in sunflower oil hydrogenation reaction. For catalytic test, a new type of catalyst feeder was constructed and presented. The hydrogenation activity of catalysts was monitored through the decrease of refractive index and hydrogen consumption. A correlation between iodine value, refractive index and hydrogen consumption was established. The reaction rate constants were obtained from fatty acid composition of partially hydrogenated oil and further studied for the investigation of possible reaction pathways. Kinetics and mechanisms were evaluated and tested with the aim to reduce the number of reactions participating in the reaction scheme. A set of ordinary differential equations, corresponding to the investigated model, was solved numerically by Gear's algorithm. It was shown that a number of significant reactions in a model depend on the activity of catalysts. More active catalyst results in more reaction pathways and more side chemical reactions.

Kinetic Analysis of Nonisothermal Reduction of Silica-Supported Nickel Catalyst Precursors in a Hydrogen Atmosphere

A series of silica-supported nickel catalyst precursors was synthesized with different SiO2/Ni molar ratios. Reduction of Ni catalyst precursors with different SiO2/Ni molar ratios under a hydrogen atmosphere was investigated at different heating rates. Kinetic parameters were determined using Kissinger–Akahira–Sunose isoconversional and invariant kinetic parameter methods. It was found that for all molar ratios, the apparent activation energy (Ea) is practically constant in the conversion range of 0.20 ≤ α ≤ 0.80. In the considered conversion range, following values of Ea were found: 134.5 kJ mol−1 (SiO2/Ni = 0.20), 139.6 kJ mol−1 (SiO2/Ni = 0.80), and 128.3 kJ mol−1 (SiO2/Ni = 1.15). It was established that the reduction of Ni catalyst precursors with different SiO2/Ni molar ratios is a complex process and can be described by the Šesták–Berggren autocatalytic model. It was found that the reaction is more Langmuir–Hinshelwood type, as hydrogen dissociates rapidly on surface nuclei and the dissociated hydrogen reacts with the Ni–O active system. It was concluded that the reduction process proceeds through bulk nucleation, which is a dominant mechanism, where three-dimensional growth of crystals with polyhedron-like morphology exists. It was found that the Ni/Si ratio decreases after the reduction process. This has been explained by low Ni and higher Si surface concentrations. It has been disclosed that Ni dispersion decreases.

Non-isothermal reduction of silica-supported nickel catalyst precursors in hydrogen atmosphere: a kinetic study and statistical interpretation

A series of silica-supported nickel catalyst precursors was synthesized with different SiO2/Ni mole ratios (0.20, 0.80 and 1.15). Non-isothermal reduction of Ni catalyst precursors was investigated by temperature- programmed reduction at four different heating rates (2, 5, 10 and 20 C min -1 ), in a hydrogen atmosphere. Kinetic parameters (Ea, A) were determined using Friedman iso- conversional method. It was found that for all mole ratios, apparent activation energy is practically constant in con- version range of a = 30-70 %. In considered conversion range, the following values of apparent activation energy were found: Ea = 129.5 kJ mol -1 (SiO2/Ni = 0.20), Ea = 133.8 kJ mol -1 (SiO2/Ni = 0.80) and Ea = 125.0 - kJ mol -1 (SiO2/Ni = 1.15). Using two special functions (y(a) and z(a)), the kinetic model was determined. It was established that reduction of Ni catalyst precursors with different SiO2/Ni mole ratios is a complex process and can be described by two-parameter S y estak-Berggren (SB) autocatalytic model. Based on established values of SB parameters for each mole ratio, the possible mechanism was discussed. It was found that for all investigated ratios, the Weibull distribution function fits very well the exper- imental data, in the wide range of conversions (a = 5-95 %). Based on obtained values of Weibull shape parameter (h), it was found that experimentally evaluated density distribution functions of the apparent activation energies can be approximated by the unbalanced peaked normal distribution.

The difference of roles of alkaline-earth metal oxides on silica-supported nickel catalysts for CO2 methanation

Modification of alkaline-earth oxides to Ni/SiO2 catalyst could affect significantly the reducibility of Ni species under the given reduction conditions.