Ni Particle Size Research Articles

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.

SBA-15 and carbon supported nickel, heteropoly acid catalysts for the hydrodeoxygenation of lignin derived trans-anethole to sustainable aviation fuel

Catalyst is the key for the hydrodeoxygenation (HDO) of lignin derivatives to produce alkyl aromatics and alkyl cycloalkanes, key components of 100% sustainable aviation fuels (SAF). Mono and bi-functional catalysts of nickel (Ni) and heterophosphotungstic acid (HPW) supported on SBA-15 and carbons were prepared, characterized and evaluated for the HDO of lignin derived trans-anethole. The SBA-15 structure was intact but its surface area and pore volume decreased with the incorporation of Ni and HPW. UV–Visible DRS and XPS confirmed the presence of Nio and Ni2+ in the bi-functional catalysts. FTIR spectra of pyridine adsorbed Ni(10)-HPW(10)/SBA-15 catalyst showed the presence of both Brønsted and Lewis acid (Ni2+) sites and hence its acidity was higher than mono functional HPW/SBA-15 catalyst as indicated by the ammonia TPD studies. The synergy between them might be the possible reason for the higher and stable conversion, higher HDO selectivity, and more importantly higher selectivity for propyl benzene and propyl cyclohexane over bi-functional catalysts. Among the bi-functional catalysts, the highest conversion and HDO selectivity were observed over Ni(10)-HPW(10)/SBA-15. Its highest selectivity for propyl cyclohexane was due to its mean Ni particle size of 31.02 nm, large enough for the co-adsorption of hydrogen and benzene ring of propyl benzene, thus led to its saturation. Optimum temperature for the maximum conversion and HDO selectivity was found to be 400 °C for the bi-functional catalysts. Comparing carbon and SBA-15 supported Ni-HPW catalysts, later have shown higher HDO selectivity owing to strong metal-support interaction.

H2 produced by catalytic reforming of acetic acid over Ni/char catalyst recycled from the biochar adsorption purification of simulated Ni electroplating wastewater

• Double-green of purifying electroplating Ni wastewater and producing H 2 was realized. • Surface complexation and ions exchange mechanisms of biochar promoted Ni 2+ removal. • The recycled Ni on biochar increased the H 2 yield by 15 times. • Two-step activation of steam and H 2 greatly improved double-green performance. • Steam activation increased surface area, Ni dispersion and surface Ni amount. The new method of using biochar to purify nickel-simulated electroplating wastewater and subsequent preparation of a Ni-based catalyst to produce H 2 in bio-oil reforming reaction is proposed. This process aims to realize the double-green of wastewater treatment and H 2 production. Different types of biochar (rice straw, rice husk and cotton stalk) were used. The results indicated that rice straw char (RSC) performed the highest Ni 2+ removal efficiency due to ash components' high ion exchange capacity and high complexation ability of oxygen-containing functional groups. Then the adsorbed RSC was reduced and recycled to prepare Ni/RSC catalyst. Compared with the unadsorbed RSC, the recycled metal Ni remarkably improved the catalytic activity. The average carbon conversion of acetic acid at 600 °C was increased to 76.26% and H 2 yield was increased by 15 times. To further enhance the double-green performance, a two-step activation process was implemented. The biochar was firstly corroded by steam addition (5%, 15% and 25%) and then the adsorbed biochar was reduced by H 2 . After that, the surface area, oxygen-containing functional groups and exchangeable cations of biochar were remarkably enhanced, which increased the Ni removal efficiency to reach 100%. Besides, the formed metal Ni with the higher metal dispersion and smaller Ni particle size improved the reforming of acetic acid. The activation by adding 25% steam further improved carbon conversion by 13.34% and H 2 yield by 60.47%.

Study on the deactivation of Ni-based catalyst in the hydrotreating process of waste plastic pyrolysis oil

The deactivation mechanism of Ni-based catalyst in the hydrotreating process of waste plastic pyrolysis oil (WPPO) was investigated. The accelerated deactivation experiment of catalyst was performed with model oil containing different impurities, and results indicated that the deactivation of catalyst was related to chlorides, nitrides, and sulfides in WPPO. By changing the concentration of chloride, the interactions between the three impurities were studied. Combined with the characterization results of fresh and spent catalysts, chloride was the direct cause of the deactivation of the catalyst. Chlorine atoms in chlorides were converted into HCl gas in hydrotreating, which reacted with Ni active sites, resulting in the sintering of the average Ni particle size from 52.62 nm to 139.63 nm, and the loss of Ni active components by 3–8 wt%, especially inhibiting the hydrodesulfurization activity of the catalyst. In addition, HCl reacted with NH3 (byproduct of nitride hydrogenation) to generate NH4Cl. The high concentration of HCl in the reaction system increased the crystallization temperature of NH4Cl from 210 °C to 294 °C, which led to the crystallization of ammonium salts in the catalyst bed. NH4Cl crystals adsorbed on the catalyst surface, resulting in a decrease in specific surface area and pore volume, and an increase in the average pore diameter of the catalyst, which was the main reason for the rapid deactivation of the catalyst. Furthermore, based on the deactivation mechanism, several appropriate solutions were proposed.

Effect of reduction degree of Ni-phyllosilicate on the catalytic performance for CO2 methanation: Regulation of catalyst structure and hydroxyl group concentration

In order to reveal the interrelationship among reduction degree and catalyst structure as well as surface hydroxyl group concentration of Ni-phyllosilicate, four different reduction temperatures of 550, 600, 700 and 800 °C were used. The results showed that low-temperature reduction could lead to high catalytic activity for CO2 methanation. In detail, the low-temperature partial reduction catalyst treated at 550 °C (Ni/S-550R) obtained the smallest Ni particle size, the highest specific surface area and the largest pore volume, which were beneficial to the chemisorption and activation of H2. In addition, the unreduced nickel phyllosilicate also provided abundant hydroxyl groups to facilitate the activation of CO2. With the increasing of reduction temperature, the reduction degree increased quickly; however, the TEM and XRD results showed that the Ni sintering was serious reduced at 700 or 800 °C. What's more, the SiO2 support also transferred from amorphous to crystalline at high reduction temperature with the significant collapse of pore structure. In all, a series of characterization results displayed that the low-temperature reduction of Ni-phyllosilicate catalyst exhibited strong H2 and CO2 chemisorption and activation capacity compared with the high-temperature-reduction ones leading to high CO2 methanation activity.

A Hybrid Plasma‐Catalysis System for CO2Hydrogenation over Perovskite‐Type Catalysts: Promoting Effect of A‐Site Substitution

A hybrid dielectric barrier discharge (DBD) plasma‐catalysis system is an effective way to catalyze the conversion of small molecules such as carbon dioxide. Until now, ABO3perovskite catalyst used for CO2hydrogenation to light hydrocarbons reaction has been rarely reported. Herein, the lanthanum nickel perovskite‐type catalysts named as La0.8A'0.2NiO3±δ(A' represents for Ca, Ce, Pr, Sr) are prepared by a modified nitrate citric acid method, and the influence of A‐site substitution on catalytic performance is investigated. The reactivity results show that the substitution of A‐site can improve CO2conversion and C2–4(hydrocarbons containing C2–C4) selectivity in varying degrees. Compared to LaNiO3catalyst, the La0.8Ca0.2NiO3±δcatalyst has CO2conversion increased from 72.6% to 82.3%, and C2–4selectivity from 5.8% to 8.5%. The superior performance can be put down to the formation of smaller Ni particle size on La0.8Ca0.2NiO3±δcatalyst, which promotes the activation of H2. Additionally, the sufficient oxygen vacancies on La0.8Ca0.2NiO3±δprovide more active sites for CO2adsorption and then enhance CO2conversion. The hybrid DBD plasma‐catalysis system is proved effective for CO2hydrogenation, and the idea of using A‐site substitution would serve as a guide for the modification of perovskite‐type ABO3catalysts.

Particle Size Effects of Carbon Supported Nickel Nanoparticles for High Pressure CO2 Methanation

AbstractSupported nickel nanoparticles are promising catalysts for the methanation of CO2. The role of nickel particle size on activity and selectivity in this reaction is a matter of debate. We present a study of metal particle size effects on catalytic stability, activity and selectivity, using nickel on graphitic carbon catalysts. Increasing the Ni particle size from 4 to 8 nm led to a higher catalytic activity, both per gram of nickel and normalized surface area. However, the apparent activation energy remained the same (∼105 kJ mol−1). Comparing experiments at atmospheric to 30 bar pressure demonstrates the importance of testing under industrially relevant pressures; the highest selectivity is obtained at high CO2 conversions and pressures. Finally, the selectivity was particle size‐dependent. The largest particles were not only most active but also most selective to methane. With this work we contribute to the ongoing debate about Ni particle size effects in CO2 methanation.

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.

Design of highly active Ni catalysts supported on carbon nanofibers for the hydrolytic hydrogenation of cellobiose.

The direct transformation of cellulose into sugar alcohols (one-pot conversion) over supported nickel catalysts represents an attractive chemical route for biomass valorization, allowing the use of subcritical water in the hydrolysis step. The effectiveness of this process is substantially conditioned by the hydrogenation ability of the catalyst, determined by design parameters such as the active phase loading and particle size. Herein, mechanistic insights into catalyst design to produce superior activity were outlined using the hydrolytic hydrogenation of cellobiose as a model reaction. Variations in the impregnation technique (precipitation in basic media, incipient wetness impregnation, and the use of colloidal-deposition approaches) endowed carbon-nanofiber-supported catalysts within a wide range of Ni crystal sizes (5.8–20.4 nm) and loadings (5–14 wt%). The link between the properties of these catalysts and their reactivity has been established using characterization techniques such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma-optical emission spectroscopy (ICP-OES). A fair compromise was found between the Ni surface area (3.89 m2/g) and its resistance against oxidation for intermediate crystallite sizes (∼11.3 nm) loaded at 10.7 wt%, affording the hydrogenation of 81.2% cellobiose to sorbitol after 3 h reaction at 190°C and 4.0 MPa H2 (measured at room temperature). The facile oxidation of smaller Ni particle sizes impeded the use of highly dispersed catalysts to reduce the metal content requirements.

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.

The effect of Ni particle size and carbon support on catalytic activity for glucose hydrogenation reaction

Ni nanoparticles supported on carbon black (Ni/CB) with Ni particle sizes 6.9–23.5 nm were found to exhibit a size effect, with a significant impact on catalytic performance in the glucose hydrogenation reaction. A series of Ni nanoparticles with different sizes, as determined by statistical analysis of TEM images, were obtained by varying the synthesis temperature using a sol-gel method. The highest glucose conversion and sorbitol production in glucose hydrogenation was possible with Ni/CB catalysts with Ni particles size around 17 nm obtained at 550 °C. Similarly, graphene nanoplatelets (GNP) supported Ni with different particle sizes synthesized under different temperature conditions have an identical behaviour, that is, GNP-550 exhibits the highest catalytic performance. Therefore, it can be concluded that size effect appeared when the particle size is above 10 nm, which provides a reference for the design of subsequent catalysts for liquid phase hydrogenation reactions pertinent to biomass conversion.

(Digital Presentation) Synthesizing Electrode Microstructures with Predefined Spatial Gradients By Conditional Generative Adversarial Networks

Recent progress of manufacturing techniques in the field of solid oxide fuel cells (SOFCs) enables fabrications of complex multi-sized gradient microstructures with the spatially varied properties. Methods using additive manufacturing, layer-by-layer deposition, tape casting, nano-imprint, pulse laser deposition and laser engraving, etc. provide possibilities to fabricate 3D structures with flexible design. Moreover, the spatially optimized structures can provide better mechanical and thermal properties, enhance diffusion and improve electrochemical reaction kinetics. In particular, multi-layered electrode designs are attracting increasing interest.The layered electrode design and optimization require effective methods to fabricate synthetic microstructures with property gradients. The generative adversarial network (GAN) proves its usabilities in fabricating artificial microstructures belonging to the same class as the training data [1] and reconstructing 3D structures from 2D image [2], etc. The applications primarily focus on the structures with uniform spatial properties identical to the training sample. The Wasserstein GAN was recently applied for the fast inverse design of two-phase homogenous microstructures with user-defined properties [3]. In this study, an approach using conditional GAN (C-GAN) is proposed to flexibly generate multi-phase structures with predefined gradients.The proposed method is tested on the microstructures of porous nickel-gadolinium doped ceria (Ni-GDC) SOFC anodes. The C-GAN training dataset consists of real Ni-GDC microstructures with varied Ni and GDC compositions (GDC share in the range of 30 – 70 vol%) and with varied porosity [4]. In total, 10 different samples were prepared and sintered at 1350 oC in air atmosphere and further reduced in the H2 flow at 800 oC. The fabricated electrodes had significantly different microstructural properties and electrochemical performance. The samples were infiltrated with epoxy resin to enable clear phase recognition, polished to expose cross-section and characterized by the scanning electron microscope (SEM). The SEM images were segmented prior to the C-GAN training.The C-GAN was trained with patches of 256 x 256 pixels which were randomly extracted from SEM images of each sample. The sample with Ni : GDC = 50 : 50 vol% was excluded from the training data and used only for testing. The generator network input consists of 4 variables: random noise vector, Ni share in composite, porosity and particle size (Fig. 1A). The particle size is controlled by the magnification of the training images. The Ni volume fraction and porosity are calculated separately for each patch during the iterative training process.The primary version of the trained C-GAN network generates homogenous artificial microstructures with the patch size of 256 x 256 pixels identical to the training data. The fabricated microstructures (Fig. 1B) show excellent visual and good statistical agreements with the real samples. It is possible to reproduce not only the volumetric fractions, but also the surface area density and triple phase boundary density of the real Ni-GDC electrodes (Fig. 1C). The C-GAN can fabricate not only the microstructures belonging to the training dataset, but also samples with other compositions.Although the C-GAN generator was trained based on patches with 256 × 256 pixels, it can be used for the fabrication of larger structures by increasing the size of the generator input. By adjusting the generator input matrix consisting of the Ni share, porosity and particle size, various microstructure patterns can be fabricated including linear gradients (Fig. 1D) and layered structures (Fig. 1E). Those structures have a significance for the SOFC anodes design as layered designs are conventionally incorporated in SOFC electrodes, e.g. support and active anode layers. In addition, it was shown that the graded structures have superior performance compared with the isotropic anodes [5].The proposed framework provides a convenient tool for generating realistic microstructures with wide range of predefined properties. Further, it can be coupled with the existing simulation tools to evaluate the wide range of graded and layered microstructural designs.[1] A. Gayon-Lombardo, L. Mosser, N. P. Brandon, and S. J. Cooper, npj Comput. Mater., 6, 1–11 (2020).[2] A. Sciazko, Y. Komatsu, and N. Shikazono, ECS Trans., 103, 1363–1373 (2021).[3] X. Lee, et al., Nature Computational Science, 1, 229, (2021).[4] Y. Komatsu, A. Sciazko, and N. Shikazono, J. Power Sources, 485, 229317 (2021).[5] Z. Yan, et al., ECS Trans., 91, 2055, (2019).Fig. 1. A) Schema of C-GAN network, B) synthetic homogenous microstructures fabricated by C-GAN, C) TPB dependence on the Ni and pore volume fractions, D) synthetic structure with predefined gradient and E) synthetic layered structure. Figure 1

Synthesized Ni/MMO catalysts via ultrathin Ni-Al-LDH in a rotating packed bed for hydrogenation of maleic anhydride

Fabricating highly active supported Ni-based catalysts is a fundamental challenge in the industry. Herein, the Ni-Al-LDH with controllable thicknesses from 1 to 19 nm were first synthesized to fabricate Ni/MMO catalysts (MMO: Mixed Metal Oxides) using coprecipitation in a rotating packed bed (RPB), followed by hydrothermal aging. It was found that despite the collapse of the sheet-like structure of the ultrathin Ni-Al-LDH during the thermal treatment, the Ni/MMO (designated as 2-NiAl) catalyst obtained from ultrathin Ni-Al-LDH nanosheets (2 nm) possesses the smallest Ni particle size, highest amount of acid sites and surface ratios of Ni/Al among the prepared catalysts. Thus, 2-NiAl demonstrates the optimal activity for the hydrogenation of maleic anhydride (MA), of which the hydrogenation rate is 9.45 (10-3·molMA·gNi-1·min−1, 80 °C, 2 MPa) with ∼100% selectivity to succinic anhydride, higher than most of previous reported values. Moreover, the turnover frequencies as a function of Ni particle sizes demonstrate a linear correlation, indicating that MA hydrogenation is a structure-sensitive reaction. These results provide a new route to optimize the catalytic performance of Ni-based catalysts and a guidance for designing catalysts derived from LDH for hydrogenation reactions. Furthermore, the prepared 2-NiAl catalyst is a potential catalyst for hydrogenation of MA into SA in the industry.

Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability

The nanorod morphology of the CeO2 support has been recognized as more beneficial than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2 catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1, and temperatures in the range of 545–800 °C. The turnover frequency (TOF) value increased linearly with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier oxidation of the small Ni particles.

2,5-Dimethylfuran Production by Catalytic Hydrogenation of 5-Hydroxymethylfurfural Using Ni Supported on Al2O3-TiO2-ZrO2 Prepared by Sol-Gel Method: The Effect of Hydrogen Donors.

5-Hydroxymethylfurfural (5-HMF) has been described as one of the 12 key platform molecules derived from biomass by the US Department of Energy, and its hydrogenation reaction produces versatile liquid biofuels such as 2,5-dimethylfuran (2,5-DMF). Catalytic hydrogenation from 5-HMF to 2,5-DMF was thoroughly studied on the metal nickel catalysts supported on Al2O3-TiO2-ZrO2 (Ni/ATZ) mixed oxides using isopropanol and formic acid (FA) as hydrogen donors to find the best conditions of the reaction and hydrogen donor. The influence of metal content (wt%), Ni particle size (nm), Nickel Ni0, Ni0/NiO and NiO species, metal active sites and acid-based sites on the catalyst surface, and the effect of the hydrogen donor (isopropanol and formic acid) were systematically studied. The structural characteristics of the materials were studied using different physicochemical methods, including N2 physisorption, XRD, Raman, DRS UV-Vis, FT-IR, SEM, FT-IR Pyad, H2-TPD, CO2-TPD, H2-TPR, TEM and XPS. Second-generation 2,5-DMF biofuel and 5-HMF conversion by-products were analyzed and elucidated using 1H NMR. It was found that the Ni0NiO/ATZ3WI catalyst synthesized by the impregnation method (WI) generated a good synergistic effect between the species, showing the best catalytic hydrogenation of 5-HMF to 2,5-DMF using formic acid as a hydrogen donor for 24 h of reaction and temperature of 210 °C with 20 bar pressure of Argon (Ar).

Tuning Particle Sizes and Active Sites of Ni/CeO2 Catalysts and Their Influence on Maleic Anhydride Hydrogenation.

Supported metal catalysts are widely used in industrial processes, and the particle size of the active metal plays a key role in determining the catalytic activity. Herein, CeO2-supported Ni catalysts with different Ni loading and particle size were prepared by the impregnation method, and the hydrogenation performance of maleic anhydride (MA) over the Ni/CeO2 catalysts was investigated deeply. It was found that changes in Ni loading causes changes in metal particle size and active sites, which significantly affected the conversion and selectivity of MAH reaction. The conversion of MA reached the maximum at about 17.5 Ni loading compared with other contents of Ni loading because of its proper particle size and active sites. In addition, the effects of Ni grain size, surface oxygen vacancy, and Ni–CeO2 interaction on MAH were investigated in detail, and the possible mechanism for MAH over Ni/CeO2 catalysts was deduced. This work greatly deepens the fundamental understanding of Ni loading and size regimes over Ni/CeO2 catalysts for the hydrogenation of MA and provides a theoretical and experimental basis for the preparation of high-activity catalysts for MAH.

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.

Effect of Fe and La on the Performance of NiMgAl HT-Derived Catalysts in the Methanation of CO2 and Biogas

Bulk Ni-based catalysts derived from hydrotalcite-type (HT) compounds show enhanced stability in the hydrogenation of CO2 into CH4, in comparison to their supported counterparts. The composition of the parent hydrotalcite determines the Ni loading and particle size, as well as the basicity of the catalysts. In this work, a comparison between the effect of Fe and La on the performance of NiMgAl HT compounds (Ni/Mg/Al = 25/50/25 atomic ratio) calcined at 600 °C is investigated. After a reduction pretreatment at 750 °C, both promoters enhance the activity in the low-temperature range; however, the La-containing catalyst reaches a better CH4 productivity rate at high oven temperature (i.e., 200 L gNi–1 h–1 at 325 °C). Although the formation of the NiFe alloy improves the activity, lanthanum keeps smaller Ni0 particles and provides a higher basicity to the mixed oxide than Fe. The activity of the NiMgLaAl catalyst can be further tailored by increasing the Ni loading from 25.6 wt % (Ni25Mg50La5Al20) to 44.6 wt % (Ni50Mg25La5Al20). Lastly, the feasibility of HT-derived catalysts in the direct methanation of clean biogas is proved.

Dry (CO2) reforming of methane over zirconium promoted Ni-MgO mixed oxide catalyst: Effect of Zr addition

Dry (CO2) reforming of methane (DRM) for syngas production has gained great attraction since it utilizes two major green house gases (CH4, CO2). However, this process is still far from commercialization due to the catalyst deactivation by coking and metal sintering. In this present work, we have prepared a series of Zr promoted Ni/MgO catalysts using Incipient wetness impregnatiom (IWI) method and applied for (DRM) reaction at temperature range of 500–800 °C. The prepared fresh and spent catalysts were fully characterized with various adsorption and spectroscopic techniques such as XRD, BET-SA, ICP-OES, H2-TPR, CO2-TPD, N2O-pulse chemisorption, SEM, TEM, TGA and O2-TPO. Reduced samples TEM analysis revealed that Zr modified catalysts possessed smaller Ni particles size and N2O-pulse chemisorption results showed that Ni dispersion is improved with Zr addition compared to Ni/MgO. In addition, CO2-TPD analysis confirmed that the basicity gradually increases with the addition of Zr and it enhances the CO2 adsorption capacity. DRM experimental results demonstrated that among all the tested catalysts Ni/3Zr/MgO exhibited remarkable activity and stable conversion with CH4 (78 %), CO2 (91 %) and H2/CO ratio (0.92) over a period of 70 h time on stream without deactivation. Further, CH4-temperature programmed surface reaction (TPSR) proved that Zr promoter significantly decreases the CH4 dissociation energy which could be due to smaller Ni particles, strong metal-support interaction and high Ni metal dispersion.

Ni/CeO2 Catalyst Prepared via Microimpinging Stream Reactor with High Catalytic Performance for CO2 Dry Reforming Methane

Methane reforming with carbon dioxide (DRM) is one promising way to achieve carbon neutrality and convert methane to syngas for high-value chemical production. Catalyst development with better performance is the key to its potential large-scale industrial application due to its deactivation caused by carbon deposition and metal sintering. Hence, a Ni/CeO2 catalyst (Ni/CeO2-M) with higher CO2 conversion and better stability is prepared, supported on CeO2 precipitated via a novel microimpinging stream reactor. A series of ex-situ or in-situ characterizations, such as CO titration measurements, two-step transient surface reaction (two-step TSR), CO2 and CH4 temperature-programmed surface reaction (CO2-TPSR and CH4-TPSR), X-ray absorption fine structure (XAFS), and in-situ Raman spectroscopy study, were used to investigate its structure and mechanism. In contrast to Ni supported on commercial CeO2 (Ni/CeO2-C), the Ni/CeO2-M catalyst with stronger lattice oxygen mobility and higher oxygen storage capacity enhances its CO2 activation ability and carbon deposition. The Ni particle size of the Ni/CeO2-M catalyst decreased, and a higher oxidation state was obtained due to the strong metal–support interaction. Besides the reaction performance improvement of the Ni/CeO2-M catalyst, the novel microimpinging stream reactor could achieve catalyst continuous production with a high preparation efficiency. This work provides a novel method for the high-performance catalyst preparation for DRM reaction and its mechanism study gives a deep insight into high-performance catalyst development via bottom-up study.