Smaller Ni Particle Size Research Articles

Catalytic hydrodeoxygenation of lignin-derived phenolic compounds with Ni-based aluminum phosphate catalyst

Lignin-derived products possess high carbon content and offer significant potential to be used as liquid fuels. However, they also contain high oxygen element and unstable functional groups. Hydrodeoxygenation (HDO) is an effective method for upgrading lignin-derived phenolic compounds to produce high-quality liquid biofuels. In this study, a series of Ni-based phosphate catalysts incorporating various metals (Al, Ce, La) were prepared and employed for the HDO of lignin-derived phenolic compounds. The results showed that Ni/AlPO4 had the most efficient HDO performance, with guaiacol conversion of 99.9 % and cyclohexane selectivity of 91.1 % at the reaction temperature of 250 °C. Various catalyst characterization measurements were conducted to assess the impact of metal phosphate species on the crystallography, morphology, physicochemical characteristics and surface properties. Results indicated that Ni/AlPO4 catalyst exhibited stronger acidity, smaller Ni particle sizes and larger specific surface area than other Ni-based phosphate catalysts. Based on the characterization results and experimental data, the corresponding HDO reaction pathways and mechanisms were also proposed. Ni/AlPO4 catalyst was also applied to the HDO of various lignin-derived phenol compounds and achieved a good HDO effect. Moreover, the catalytic upgrading of lignin-oil was also carried out, and a high proportion of hydrocarbon products that increased from 16.0 % to 88.6 % was obtained. This Ni/AlPO4 catalyst provides potential reference for the HDO application of lignin-derived phenolic compounds for the production of hydrocarbon liquid fuels.

Anti-coking Ni encapsulated in SiO2 via one-pot reverse microemulsion method as a versatile catalyst for CO2 methane reforming

This paper reports the varying water-to-surfactant (ω) ratio in reverse microemulsion on the development of Ni encapsulation in bulk SiO2 catalyst for dry reforming of methane. From XRD and TEM analyses, the Ni particle size depends on the water-to-surfactant ratio. It found that an optimized ratio of ω improves the catalytic activity for the dry reforming of methane. The catalyst (Ni-SiO2-ω23) shows 70% CH4 conversion and 78% CO2 conversion at 700 °C and WHSV of 72000 mLgcat−1h−1 operating for 50 h with TOF of 12.6 s−1. It is highly anticipated that the increased fraction of 2:1 nickel phyllosilicate and small Ni particle size contributed to its improved catalytic activity corresponding to the ω ratio. Also, a higher ω value can resist carbon formation in the catalysts, characterized by XRD, TGA, Raman, XPS, and TEM. These results were encouraging that could be applied in similar high-temperature reactions.

Enhanced deoxygenation performance and coke resistance of Ni-based catalysts for jatropha oil conversion by rare earth elements

Herein, three kinds of rare earth elements (Ce, Er and Y) were added to Ni-based catalysts to regulate the deoxygenation ability and coke resistance towards jatropha oil (JO) conversion. Among them, the catalysts with lanthanide metals (Ce and Er) added exhibit positive effects. Conversely, the addition of Y is counterproductive. The one with Er added displays the best catalytic performance, achieving the highest deoxygenation ratio (99.3 %) and product yield (64.7 %), and the resultant biofuel has the highest calorific value (46.02 MJ/kg). The stability of the Ni-Er/50S-Al catalyst is significantly improved due to the enhanced coke resistance compared with the one without Er added. Smaller Ni particle sizes with better dispersion, higher amount of surface Ni0 and surface oxygen vacancies are accomplished by adding Er, which contributes to the enhanced catalytic performance. The addition of Y weakens coke resistance, caused by strong acidity and big Ni particles. This study provides an effective idea for rationally designing catalysts with improved coke resistance and converting vegetable oils into biofuels.

On the influence of the preparation routes of NiMgAl-mixed oxides derived from hydrotalcite on their CO2 methanation catalytic activities

In this work, a series of NiMgAl oxides (NMA) derived from hydrotalcite catalysts were prepared via co-precipitation (NMA-CP), urea hydrolysis (NMA-UH), and impregnation (NMA-IMP) techniques, then subsequently tested for CO2 methanation. The well-defined synthesis of derived hydrotalcite mixed oxides was confirmed by physicochemical characterizations including XRD, SEM, BET, H2-TPR and CO2-TPD. The preparation methods showed a substantial influence on the structure and thermal activity of catalysts. Indeed, the NMA-UH catalyst demonstrated a high and stable catalytic activity in terms of CO2 conversion and CH4 selectivity, with ca. 82.3% and 99.8% (GHSV = 12,000 h−1, H2/CO2 = 4/1) respectively, at 300 °C. This is mainly due to its large specific surface area, small Ni-particle size, and higher basicity.

Glycine-assisted preparation of highly dispersed Ni/SiO2 catalyst for low-temperature dry reforming of methane

Ni-based catalysts have been widely studied in reforming methane with carbon dioxide. However, Ni-based catalysts tends to form carbon deposition at low temperatures (≤600 °C), compared with high temperatures. In this paper, a series of Ni/SiO2-XG catalysts were prepared by the glycine-assisted incipient wetness impregnation method, in which X means the molar ratio of glycine to nitrate. XRD, H2-TPR, TEM and XPS results confirmed that the addition of glycine can increase Ni dispersion and enhance the metal-support interaction. When X ≥ 0.3, these catalysts have strong metal-support interaction and small Ni particle size. The Ni/SiO2-0.7G catalyst has the best catalytic performance in dry reforming of methane (DRM) test at 600 °C, and its CH4 conversion is 3.7 times that of Ni/SiO2-0G catalyst. After 20 h reaction under high GHSV (6 × 105 ml/gcat/h), the carbon deposition of Ni/SiO2-0.7G catalyst is obviously lower than that of Ni/SiO2-0G catalyst. Glycine-assisted impregnation method can enhance the metal-support interaction and decrease the metal particle size，which is a method to prepare highly dispersed and stable Ni-based catalyst.

High-efficiency catalytic hydrodeoxygenation of lignin-derived vanillin with nickel-supported metal phosphate catalysts

Lignin is a natural and renewable aromatic raw material of aromatic chemicals and its depolymerization and downstream products conversion has drawn considerable attention. Herein, a series of Ni loaded metal phosphates (Ni/MP, M = Ti, Zr, Nb, La, or Ce) catalysts were fabricated for the hydrodeoxygenation (HDO) of lignin-derived vanillin (VAN) to produce 2-methoxy-4-methylphenol (MMP). It has been demonstrated that 97.25% VAN conversion could be obtained with a yield of 88.39% of MMP under the mild condition of 220 °C and 0.5 MPa H2 for 30 min with 15 wt% Ni/ZrP. The highest activity of Ni/ZrP was attributed to its small Ni particle size, large specific surface area, strong metal-support interaction, and optimal acidity. It has been proven that Ni, Lewis acid sites (LAS) and Brønsted acid sites (BAS) have a synergistic effect in VAN conversion: Nano-sized Ni catalyze the dissociation of H2 to form active hydrogen species (H). LAS promote the adsorption and activation of VAN and isopropanol. BAS play a vital role in the dehydration reaction. Additionally, H2 was the primary hydrogen donor in the system, while isopropanol was the reaction medium as well as the secondary hydrogen donor, helping to reduce the external H2 supply requirement. By optimizing the reaction conditions and studying the promotion mechanism, we hope to provide an experimental basis for lignin catalytic hydrogenolysis.

Ni-CeO2 Catalyst with High Ni Loading Prepared by Salt-Assisted Solution Combustion for CO2 Methanation

An Ni-CeO2 catalyst with high Ni loading (50 wt.%) prepared by a salt-assisted solution combustion method was characterized by different methods and used for CO2 methanation. The specific surface area of the Ni-CeO2 catalyst prepared by salt-assisted solution combustion is 7 times that of the catalyst prepared by conventional solution combustion. The Ni-CeO2 catalyst prepared by salt-assisted solution combustion has smaller particle sizes of Ni and exhibits excellent activity at low temperatures. The high Ni loading and small Ni particle size can provide more metal Ni site and Ni-CeO2 interface, which help to improve the CO2 methanation performance.

Production of Heterocyclic Primary Amines from Heterocyclic Aldehydes on Ni‐Mo/ZrO2

AbstractNi‐Mo/ZrO2 catalysts with Ni‐Mo loadings of 10 wt % were prepared by a sol‐gel method on a ZrO2 support and subsequently applied in the simple reductive amination of heterocyclic aldehydes. Among the various catalysts prepared, Ni‐Mo/ZrO2 catalysts with Ni:Mo = 2:1 exhibited the highest metal dispersion and the smallest Ni particle size. The results showed that the catalyst has good catalytic performance, in which the yield of furfurylamine can reach 96.6 %. Initially, oximes were synthesized from the corresponding aldehydes and hydroxylamine hydrochloride, and then heterocyclic primary amines were synthesized by simple hydroreductive amination of the oximes with a 12 % methanolic solution of NH3 in the presence of an Ni‐Mo/ZrO2 catalyst. The methanolic solution of NH3 was found to be more effective in inhibiting the formation of secondary and tertiary amines.

Nanoscale Ni enveloped in hydrochar prepared by one-step hydrothermal method for dry reforming of CH4 with CO2

In this work, sugarcane bagasse was used as carbon sources, and nickel particles supported on hydrochar were prepared by one step hydrothermal method for dry reforming of CH4 with CO2. The characterization of the catalysts demonstrated that Ni nanoparticles enveloped in hydrochar were in the rage of 4.23-15.07 nm, and Ni atom dispersion was 8.45-22.93%. The highly dispersion of nanoscale Ni particles were benefit for promoting the catalytic activity of the catalysts, and suppressing the sintering of Ni particles or carbon deposition during DRM. CH4/CO2 conversions of 81.32/93.93% over Ni10/SB-C240 were achieved after 72 h DRM reaction under 850°C and 12000 ml/g•h gas hourly space velocity (GSHV). At the same time, limit carbon deposition on the surface of the used catalyst was observed, and the carbon balance even reached to 99.86%. The influence of Ni particle size on CH4 and CO2 conversions rate was also experimentally investigated, and the results displayed that smaller Ni particle size was beneficial to promote the stability of the catalysts.

Enhancement of hydrothermal synthesis of FDU-12-derived nickel phyllosilicate using double accelerators of ammonium fluoride and urea for CO2 methanation

Nickel phyllosilicate materials were usually prepared by the hydrothermal method under severe conditions with high hydrothermal temperature and long hydrothermal time. In order to obtain Ni-phyllosilicate under mild hydrothermal conditions, a modified hydrothermal method assisted by double accelerators of ammonium fluoride and urea was proposed in this work. The N/F-A100-12 catalyst was prepared by the modified hydrothermal method at 100 °C for 12 h with similar Ni content and morphology as N/F-H220-48 prepared by the conventional hydrothermal method at 220 °C for 48 h. The improvement derived from that ammonium fluoride accelerated the etching of FDU-12 to form the intermediate of H4SiO4, and urea could facilitate the formation of Ni(OH)2, resulting in the quick formation of Ni-phyllosilicate under mild conditions. N/F-A100-12 exhibited high TOFCO2 (220 °C) value of 3.05 × 10−3 s−1 and low activation energy of 96.5 kJ mol−1 for CO2 methanation due to the small Ni particle size and enhanced CO2 and H2 adsorption property. In addition, N/F-A100-12 also displayed high long-term stability and anti-sintering property. In all, the modified hydrothermal method was highly efficient to synthesize Ni-phyllosilicate material under mild hydrothermal conditions.

Decoupling the size and support/metal loadings effect of Ni/SiO2 catalysts for CO2 methanation

CO2 methanation constitutes one of the most promising technologies for highly efficient CO2 utilization while reducing the emission of greenhouse gases. The active Ni-based catalysts show the size-dependent activity for this reaction; however, the Ni size effect was highly coupled with the effect of support or metal loadings. Herein, the effect of nickel particle size in the range of 3.5–7.5 nm on CO2 methanation has been investigated using constant Ni loading of 2 wt.% Ni/SiO2 catalysts based on inert silica support prepared by different methods. The catalyst with small Ni nanoparticle exhibited highly enhanced catalytic performance, illustrating that the performance of CO2 methanation can be improved by tuning the particle size of Ni supported on SiO2. In situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) results indicated that small Ni particle size is beneficial to the formation of initial monodentate carbonate and important intermediates such as monodentate formate and linearly adsorbed CO species which are highly in favor of CO2 methanation reaction. This work provides valuable guidelines for designing an effective CO2 methanation catalyst by tuning the size of Ni nanoparticles.

Hydrogen production by ethanol steam reforming over M-Ni/sepiolite (M = La, Mg or Ca) catalysts

Ethanol steam reforming (ESR) is a technology of great promise for hydrogen production but designing highly efficient, green and inexpensive Ni-based catalysts for inhibiting metal sinter and carbon deposition and increasing catalyst activity and stability is still a key challenge. In this paper, the M-Ni/Sepiolite catalysts (M-Ni/SEP, M = La, Mg or Ca) were synthesized using a hydrothermal-assisted impregnation method. The results from characterizations such as N2 adsorption-desorption, XRD, H2-TPR, XPS, HRTEM and NH3/CO2-TPD showed that La, Mg and Ca promoters can facilitate the dispersion and exposure of Ni0 active sites, enhance the metal-support interaction and modify surface acid/alkaline sites. Furthermore, the results of catalyst activity tests in ESR demonstrated that the Ca–Ni/SEP catalyst exhibited the highest carbon conversion of 95% and hydrogen yield of 65%, attributed to the small mean Ni particle size, strong metal-support interaction, abundant surface Ni0 active sites and modified surface alkaline/acid sites. According to the carbon deposition analyses, it was observed in Ca–Ni/SEP that the carbon deposition amount was evidently decreased, and the graphitic degree of coke was increased due to the increased metal site amount.

Ni-based catalysts supported on MgAl2O4 with different properties for combined steam and CO2 reforming of methane

Three MgAl2O4 spinels were prepared by co-precipitation (cp), sol–gel (sg) and alcoholysis (al) methods, and used as supports for Ni catalysts for combined steam and CO2 reforming of methane (CSCRM). MgAl2O4(cp), MgAl2O4(sg) and MgAl2O4(al) showed different textural, morphological and chemical properties. By comparison of the properties of MgAl2O4 with those of 10Ni/MgAl2O4 (10 wt% Ni loading), it was found that the basicity of MgAl2O4 was a major factor influencing not only the basicity of catalyst but also the Ni particle size and dispersion. MgAl2O4(sg) possessed the highest amount of basic sites leading to 10Ni/MgAl2O4(sg) having the strongest basicity and the smallest Ni particle size. These properties bestowed 10Ni/MgAl2O4(sg) with superior anti-coking and anti-sintering properties as well as the highest activity and stability for CSCRM among all catalysts including 10Ni/MgO and 10Ni/γ-Al2O3. Further investigations on the effect of Ni loading (5–15 wt%) showed that 10Ni/MgAl2O4(sg) was the best catalyst for CSCRM, with stable conversions of CH4 (88.9%) and CO2 (68.6%) over 30 h on stream (CH4:H2O:CO2 = 2.5:2:1 (molar ratio)) at 800 °C, 0.1 MPa and a gas hourly space velocity of 132,000 NmL/(gcat·h).

One-Step Synthesis of Highly Dispersed and Stable Ni Nanoparticles Confined by CeO2 on SiO2 for Dry Reforming of Methane

Sintering and carbon deposition are the two main ways to deactivate Ni-based catalysts during methane reforming. Herein, a stable Ni-CeO2/SiO2(CSC) catalyst was prepared by a one-step colloidal solution combustion method (CSC) and used for dry reforming of methane. In the catalyst, the small Ni particles were confined by CeO2 particles and highly dispersed on the surface of SiO2, forming a spatial confinement structure with a rich Ni-CeO2 interface in the catalyst. The Ni-CeO2/SiO2(CSC) catalyst prepared by the one-step CSC method exhibited superior activity at 700 °C during dry reforming of methane, and the performance of the catalyst was stable after 20 h of reaction with only a small amount of carbon deposition present (1.8%). Due to the spatial confinement effect, Ni was stable and less than 5 nm during reaction. The small Ni particle size and rich Ni-CeO2 interface reduced the rate of carbon deposition. This colloidal combustion method could be applied to prepare stable metal-based catalysts with rich metal–oxide interfaces for high-temperature reactions.

Methane dry reforming over mesoporous La2O3 supported Ni catalyst for syngas production

Abstract In this study, aiming to obtain highly active methane dry reforming (DRM) catalysts with superior coke-resistance. Nanocasting method selecting KIT-6 as hard-template has been employed to synthesize mesoporous La2O3 support, which was applied to support Ni nanoparticles for DRM reaction. N2 adsorption-desorption demonstrates that mesoporous structure is well formed in the La2O3-KIT-6 support with high specific surface area of 81.2 m2 g−1. As support for Ni, much smaller Ni particle size with higher Ni dispersion could be achieved, as evidenced by XRD and H2-TPD results. In addition, XRD and TGA/DSC results indicated that on the 5%Ni/La2O3–S and 5%Ni/La2O3-HT catalysts, the generated La2O2CO3 cannot react timely with the coke due to the poor Ni dispersion, resulting the accumulation of the both on the catalysts surface. However, La2O3-KIT-6 support with high surface area can highly disperse Ni active sites and enlarged the interfaces between La2O2CO3 and Ni, thus facilitate the reaction between the coke and the La2O2CO3 species and keep the surface of Ni sites more clean and active. Therefore, Ni/La2O3-KIT-6 catalyst exhibits excellent catalytic performance as well as the coke-resistance.

Effect of Mg Contents on Catalytic Activity and Coke Formation of Mesoporous Ni/Mg-Aluminate Spinel Catalyst for Steam Methane Reforming

Ni catalysts are most suitable for a steam methane reforming (SMR) reaction considering the activity and the cost, although coke formation remains the main problem. Here, Ni-based spinel catalysts with various Mg contents were developed through the synthesis of mesoporous Mg-aluminate supports by evaporation-induced self-assembly followed by Ni loading via incipient wetness impregnation. The mesoporous Ni/Mg-aluminate spinel catalysts showed high coke resistance under accelerated reaction conditions (0.0014 gcoke/gcat·h for Ni/Mg30, 0.0050 gcoke/gcat·h for a commercial catalyst). The coke resistance of the developed catalyst showed a clear trend: the higher the Mg content, the lower the coke deposition. The Ni catalysts with the lower Mg content showed a higher surface area and smaller Ni particle size, which originated from the difference of the sintering resistance and the exsolution of Ni particles. Despite these advantageous attributes of Ni catalysts, the coke resistance was higher for the catalysts with the higher Mg content while the catalytic activity was dependent on the reaction conditions. This reveals that the enhanced basicity of the catalyst could be the major parameter for the reduction of coke deposition in the SMR reaction.

MoOx‐Doped Ordered Mesoporous Ni/Al2O3 Catalyst for CO Methanation

To address the problems of sintering of Ni particles and poor low‐temperature activity of Ni‐based catalysts for CO methanation, MoOx‐doped (x < 3) ordered mesoporous Ni/Al2O3 catalysts are prepared by two different methods, including the impregnation method and evaporation‐induced self‐assembly (EISA) method. The samples before and after the catalytic reaction are thoroughly characterized by scanning electron microscopy and transmission electron microscopy. The ordered mesoporous structure is retained in all catalysts, whereas the ones prepared by the EISA method demonstrate high specific surface area, small Ni particle size, and high metal dispersion. After reduction in H2 flow, the Mo promoter is in the form of MoOx (x < 3) with the mixed valence of Mo (IV) and Mo (VI), which can increase the density of Ni atomic electron clouds and reduce the Ni particle size. The optimal mesoporous Ni‐Mo/Al2O3 catalyst reaches the maximum CO conversion and CH4 yield of 97.9% and 93.8%, respectively, at 375 °C, 0.1 MPa, and a weight hourly space velocity of 60 000 mL g−1 h−1. In addition, this catalyst demonstrates excellent stability in 100 h‐lifetime test at high space velocity owing to the confinement of the ordered mesoporous structure and the addition of MoOx promoter.

Highly active and stable HF acid modified HZSM-5 supported Ni catalysts for steam reforming of toluene and biomass pyrolysis tar

This paper investigated the performance of HF modified HZSM-5 supported nickel catalysts (Ni/FZ5) in steam reforming of toluene (TSR) and biomass pyrolysis tar (BSR). The mesopores volume of support increased from 0.021 to 0.061 cm3/g with decreasing acid amount from 2.27 to 0.41 mmol/g after HF treatment. Catalysts with different Ni loadings were prepared and characterized. The Ni/FZ5 with Ni loading of 9 wt% possesses relatively large specific surface area (337 m2/g) and average pore size (2.91 nm), as well as small Ni particle size (23 nm) and high dispersion. In the process of TSR, 9Ni/FZ5 was kept above 70% for 7 h. Owing to the calculated lower apparent activation energy (30.76 KJ/mol), 9Ni/FZ5 exhibited the best performance in BSR at 650 °C, achieving the largest H2 yield of 52.8 mmol/g and the highest selectivity of H2 at 72.8%. Additionally, only 1.6 mg/gcatalyst of coke deposition was detected. Moreover, its high activity was still identified with excellent hydrothermal stability even after 7 times of regeneration. All findings suggest that 9Ni/FZ5 is a promising catalyst for biomass tar cracking.

High catalytic activity and stability quasi homogeneous alkali metal promoted Ni/SiO2 aerogel catalysts for catalytic cracking of n-decane

In this study, a series of M-Ni/SiO2 (M = Na, K) aerogel catalysts were synthesized and applied in n-decane cracking in supercritical conditions. Meanwhile the catalytic activity was investigated and compared with conventional wall-coated catalysts, in order to explore the feasibility of Ni/SiO2 aerogel as quasi homogeneous catalyst and find a new method to improve catalytic activity, stability and reduce the coking for hydrocarbons cracking reaction. N2 adsorption–desorption, XRD, SEM-EDS, TEM, H2-TPR and CO2-TPD were used to find the correlation among catalytic activity, stability and catalyst microstructure. The results revealed that the series M-Ni/SiO2 (M = Na, K) aerogel catalysts which are well dispersed in n-decane show better catalytic activity, stability and anti-coking ability compared with wall-coated Ni/SiO2 catalyst, moreover, the catalyst dosage is only a half of wall-coated catalyst. Furthermore, Na and K promoted Ni/SiO2 aerogel catalysts exhibit excellent stability within 50 min at 750 °C and 3.5 MPa. Characterization results indicated that higher surface area, larger pore size, smaller Ni particle sizes, higher Ni dispersion due to stronger active metal-support interaction and proper basicity can be responsible for good catalytic activity, better coke resistance and stability of M-Ni/SiO2 aerogel catalysts.

LaNiO3 as a precursor of Ni/La2O3 for reverse water-gas shift in DBD plasma: Effect of calcination temperature

Reverse water–gas shift (RWGS) is considered as a promising reaction to convert CO2 into CO, which together with H2, can be used for the synthesis of Fisher-Tropsch chemicals. In this study, a hybrid dielectric barrier discharge (DBD) plasma-catalysis system was developed for RWGS at room temperature. LaNiO3 perovskite catalysts calcined at 600, 700, 800 and 900 °C (denoted as LNO-600, LNO-700, LNO-800 and LNO-900) were synthesized and tested for RWGS in DBD plasma reactor. Different methods including XRD, N2 adsorption-desorption, H2-TPR, TEM, CO2-TPD, O2-TPD, XPS, XANES, EXAFS and TG-DTA were employed for the characterization of fresh, reduced and spent catalysts. The results showed that a fully crystallized LaNiO3 perovskite structure could be formed only at temperatures of >800 °C, and lower calcination temperatures resulted in the presence of NiO and amorphous La2O3. Ni was extracted from the LaNiO3 perovskite structure to form Ni supported on La2O3 support (Ni/La2O3) after reduction for all catalysts. The CO2 conversion did not show obvious difference over different catalysts. However, the maximum CO selectivity and the minimum CH4 selectivity were achieved over LNO-600. The higher catalytic activity of LNO-600 should be attributed to its higher Ni dispersion, smaller Ni particle size and stronger metal-support interaction. It should be noted LNO-800 showed the highest coke resistance ability, due to the highest ratio of surface adsorption oxygen and largest oxygen storage capacity evidenced by the XPS and O2-TPD results. In addition, the effect of H2/CO2 ratio on the performance of RWGS was studied and a H2/CO2 ratio of 2:1 was confirmed to be the optimum for the simultaneous achievement of higher CO2 conversion and CO selectivity.