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/g_cat/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.     

Hydrogen production by steam reforming of ethanol over Co/CeO2 catalysts: Effect of cobalt content

The Co/CeO₂ catalysts obtained by co-precipitation method were used in the steam reforming of ethanol (SRE). The influence of cobalt active phase content (15–29 wt%), the reaction temperature (420–600 °C) and H₂O/EtOH molar ratio (12/1 and 6/1) were examined. The physicochemical characterization revealed that the cobalt content of the catalyst influences the metal-support interaction which results in catalyst performance in SRE process. The differences between catalytic properties of the Co/CeO₂ catalysts with different metal loading in SRE process decayed at 500 °C for H₂O/EtOH = 12/1. The best performance among the tested catalysts showed the 29Co/CeO₂ catalyst with the highest cobalt content, exhibiting the highest ethanol conversion, selectivity to two most desirable products and the lowest selectivity to by-products in comparison with catalysts containing smaller amount of metal. Its catalytic properties results probably from its unique physicochemical properties, i.e this catalyst contains large amount of cobalt but the metal crystallites are relatively small. Regardless cobalt content, an increase in the water-to-ethanol molar ratio in the feed increased the concentration of hydrogen an carbon dioxide and decreased formation of carbon monoxide, acetone, aldehyde and ethylene.     

Combustion-impregnation preparation of Ni/SiO2 catalyst with improved low-temperature activity for CO2 methanation

Exploiting Ni-based catalysts with excellent low-temperature activity is significant for CO₂ methanation, which is a promising route to CO₂ utilization. In this work, a facile combustion-impregnation method was developed to prepare the SiO₂ supported Ni catalysts. Small Ni particles (around 6 nm) and massive Ni–SiO₂ interface could be obtained due to the “combustion” process. The H₂-temperature programmed desorption (H₂-TPD) revealed the existence of Ni–SiO₂ interface and confirmed the high Ni dispersion obtained by this method, which were vital for the activation of reactant. Moreover, more medium basic sites which were beneficial for the CO₂ activation could also be created. In comparison with the reference Ni/SiO₂ catalyst prepared by the conventional impregnation method, much higher CO₂ conversion (66.9%) and more superior selectivity to CH₄ (94.1%) were achieved with the Ni/SiO₂-Gly catalyst at 350 °C. Additionally, it was also found that glucose, citric acid and glycine were all effective fuels for this combustion-impregnation method, and the as-prepared catalysts all exhibited greatly improved low-temperature activity. Therefore, this work represents an important step toward developing Ni-based catalysts for CO₂ methanation by a promising wide-used method.     

Carbon dioxide reforming of methane to syngas over ordered mesoporous Ni/KIT-6 catalysts

The ordered mesoporous Ni/KIT-6 (KIT-6, an ordered mesoporous SiO₂) catalysts were prepared by impregnation method for carbon dioxide reforming of methane. The physicochemical properties of the prepared catalysts were characterized by H₂-TPR, XRD, BET, and TEM. The research results show that the specific surface area, pore diameter, crystal size of Ni species, and catalytic performance of the Ni/KIT-6 catalysts are obviously affected by the Ni content. Increasing Ni content results in the increment of the crystal size of Ni species, while the dispersion of Ni species shows the opposite trend. The specific surface area and pore size of the Ni/KIT-6 catalyst with the Ni loading of 3 wt% were 493.3 m² g^?1 and 6.22 nm, respectively. Besides, the Ni species are highly dispersed on the surface of KIT-6 support. Thereby, it exhibits the superior catalytic performance of carbon dioxide reforming of methane to syngas (CO and H₂). At atmospheric pressure, the CO₂ and CH₄ conversions for each catalyst following the order: NK3 ≈ NK4 > NK5 > NK2 > NK1 > bulk Ni. When the reaction temperature is 600 °C, the conversions of CH₄ and CO₂ of the NK3 catalyst are 65.1% and 37.0%, respectively. Meanwhile, it also shows excellent stability.     

Hydrogen generation via supercritical water gasification of lignin using Ni‐Co/Mg‐Al catalysts

In this study, a group of Ni‐Co/Mg‐Al catalysts was prepared for hydrogen production via supercritical water gasification of lignin. The effects of different supports and preparation methods were examined. All catalysts were evaluated under the operation conditions of 650 °C, 26 MPa, and water to biomass mass ratio of 5 in a batch reactor. The Cop.2.6Ni‐5.2Co/2.6Mg‐Al catalyst showed the best performance with highest gas yield (12.9 wt%) and hydrogen yield (2.36 mmol·g^?1). The results from catalyst characterization suggest that the properties of this type of catalyst are dependent on multiple factors including support Mg‐Al molar ratio and preparation method, and better coke resistance of the catalyst could be obtained by the preparation method of coprecipitation. Therefore, coprecipitation method should be applied for the preparation of Ni‐Co/Mg‐Al catalysts for hydrogen production via supercritical water gasification of lignin. Copyright © 2017 John Wiley & Sons, Ltd.     

Partial oxidation of methane into syngas (H2 + CO) over effective high-dispersed Ni/SiO2 catalysts synthesized by a sol–gel method

A Ni catalyst supported on mono dispersed silica spheres, Ni/SiO₂-Sph (SG), has been successfully synthesized by a sol–gel method. By comparing it with other Ni catalysts (supported on commercial silica and silica spheres) prepared by an impregnation method, we find that the size of Ni particles and their dispersion are closely related to performances of the catalysts in partial oxidation of methane (POM) into synthesis gas (CO + H₂). Several means such as H₂-TPR, TEM, and XRD are employed to characterize these catalysts. Although the catalyst Ni/SiO₂-Sph (SG) in specific surface area is not large, the Ni particles are the smallest in size (3–5 nm) among the three catalysts, and are uniformly distributed, high dispersed over the silica surfaces, being not much changed as Ni loading. It is notable that the smaller size of the NiO particles is corresponding to the stronger NiO–SiO₂ interactions. The catalyst Ni/SiO₂-Sph (SG) shows the best catalytic performances and the longest lifetime among the three catalysts at the POM conditions.     

Ethanol steam reforming on Ni/CaO catalysts for coproduction of hydrogen and carbon nanotubes

Catalytic steam reforming of ethanol is considered as a promising technology for producing H₂ in the modern world. In this study, using a fixed‐bed reactor, steam reforming of ethanol was performed for production of carbon nanotubes (CNTs) and H₂ simultaneously at 600°C on Ni/CaO catalysts. Commercial CaO and a synthetic CaO prepared using sol‐gel were scrutinized for ethanol's catalytic steam reforming. Analysis results of N₂ isothermal adsorption indicate that the CaO synthesized by sol‐gel has more pore volume and surface area in comparison with the commercial CaO. When Ni was loaded, the Ni/CaO catalyst shows an encouraging catalytic property for H₂ production, and an increase in Ni loading could improve H₂ production. The Ni/CaO catalyst with sol‐gel CaO support has presented a higher hydrogen production and better catalytic stability than the catalysts with the commercial CaO support at low Ni loading. The highest hydrogen yield is 76.8% at Ni loading content of 10% for the Ni/sol‐gel CaO catalyst with WHSV of 3.32/h and S/C ratio of 3. The carbon formed after steam reforming primarily consists of filamentous carbons and amorphous carbons, and CNTs are the predominant type of carbon deposition. The deposited extent of carbon on the used Ni/CaO catalyst lessen upon more Ni loading, and the elongated CNTs are desired to be formed at the surface of the Ni/sol‐gel CaO catalyst. Thus, an efficient process and improved economic value is associated with prompt hydrogen production and CNTs from ethanol steam reforming.     

H2S effect on dry reforming of biogas for syngas production

The effect of hydrogen sulfide (H₂S) on dry reforming of biogas for syngas production was studied both experimentally and theoretically. In the experimental work, the H₂S effect on Ni‐based catalyst activity was examined for reaction temperatures ranging from 600°C to 800°C. It was found that the presence of H₂S deactivated the Ni‐based catalysts significantly because of sulfur poisoning. Although bimetallic Pt‐Ni catalyst has better performance compared with monometallic Ni catalyst, deactivation was still found. The time‐on‐stream measured data also indicated that sulfur‐poisoned catalyst can be regenerated at high reaction temperatures. In the theoretical work, a thermodynamic equilibrium model was used to analyze the H₂S removal effect in dry reforming of H₂S‐contained biogas. Calcium oxide (CaO) and calcium carbonate (CaCO₃) were used as the H₂S sorbent. The results indicated that H₂S removal depends on the initial H₂S concentration and reaction temperature for both sorbents. Although CO₂ was also removed by CaO, the results from equilibrium analysis indicated that the dry reforming reaction in the presence of CaO was feasible similar to the sorption enhanced water‐gas shift and steam‐methane reforming reactions. The simulation results also indicated that CaO was a more preferable H₂S sorbent than CaCO₃ because syngas with an H₂/CO ratio closer to 2 can be produced and requires lower heat duty.     

Deactivation and in-situ regeneration of Dy-doped Ni/SiO2 catalyst in CO2 reforming of methanol

The self-regeneration of Ni-based catalysts has been considered as a promising approach to maintain not only a continuous but also economical process. However, the effect of catalyst nature, operating temperature, amount and types of carbon deposits on the effectiveness of the in-situ regeneration is still not well-investigated. Therefore, in this work, the self-regeneration ability of the undoped and Dy-doped Ni/SiO₂ catalysts, which were prepared by the same impregnation method, were examined in the dry reforming of methanol. The physicochemical properties of the fresh and spent catalysts were analyzed by various techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), oxygen temperature-programmed desorption (O₂-TPD), transmission electron microscopy (TEM), N₂-BET isothermal adsorption. The nature and chemical reactivity of coke deposits formed during dry reforming at various temperatures (550, 600, and 650 °C) and the regeneration possibility of used catalysts through CO₂ gasification at these temperatures were investigated by the in-situ temperature-programmed gasification by CO₂ (TPCO₂). The Dy additive significantly improves the dispersion of the nickel active sites of Ni/SiO₂ catalyst, as demonstrated by the decreased Ni crystal size as well as the increased specific surface area and reduction degree of the catalyst. Furthermore, Dy promotion increases the quantity of oxygen vacancies and the nature of oxygen species, thereby improving the catalyst activity and stability. Specifically, methanol conversion dropped from 93% to 96%–61% and 31% for undoped Ni/SiO₂ at 600 °C and 650 °C, respectively and from about 99% to 87% (at 600 °C) and 52% (at 650 °C) for Dy-doped catalyst.     

Methanation over Ni/SiO2: Effect of the catalyst preparation methodologies

We confirmed here that the catalyst preparation methodologies have a significant effect on the activity and stability of Ni/SiO₂ catalyst for methanation of syngas (CO + H₂). Catalyst characterizations using X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and transmission electron microscope (TEM) were performed to investigate the structure and performance of the catalysts. The activity and stability of catalysts prepared by thermal decomposition and dielectric-barrier discharge (DBD) plasma decomposition of nickel precursor were compared. The plasma decomposition results in a high dispersion, an enhanced interaction between Ni and the SiO₂ support, as well as less defect sites on Ni particles. Enhanced resistance to Ni sintering was also observed. In addition, the plasma prepared catalyst effectively inhibits the formation of inactive carbon species. As a result, the plasma prepared catalyst exhibits significantly improved activity with enhanced stability.     

Steam reforming of ethanol on zinc containing catalysts with spinel structure

Hydrogen production by ethanol steam reforming (SRE) was studied on zinc based catalysts with spinel-like structure. ZnM₂O₄ (M = Al, Co, Fe) mixed oxides were prepared by sol–gel technique with citric acid and characterized by XRD, TPR-H₂, S_BET, TPD-NH₃ and decomposition of cyclohexanol. The XRD patterns confirm presence of well defined spinel-like structure of prepared materials. The highest catalytic activity towards hydrogen production was found for zinc cobaltate: the hydrogen yield on this catalyst is 2.8 mol H₂/mol EtOH. The ZnO promoting the reduction of cobalt cations to Co⁰ that is more active in SRE.     

Optimizing the preparation of Ni-Ce-Pr catalysts for efficient hydrogen production by n-dodecane steam reforming

Nowadays, the development of fuel cell is getting more and more inseparable from the production of hydrogen. Long-chain hydrocarbons steam reforming is a feasible way for hydrogen supply. Herein, various nickel-ceria-praseodymium (Ni-Ce-Pr) catalysts have been prepared by a sol-gel method. Multiple parameters during catalyst preparation, including the amount of Ni, the content of doped Pr and the calcination temperature, were systematically studied for tuning the catalytic performance for n-dodecane steam reforming in a fixed-bed reactor under 15 mL/g_cat·h at 600°C and water-to-carbon molar ratio of 2 at 0.1 MPa. Reaction data showed that both the amount of Ni and the content of doped Pr will greatly affect the n-dodecane conversion and hydrogen production. Additionally, the calcination temperature during catalyst preparation showed a big influence on its performance for n-dodecane steam reforming. After optimization, 10Ni-CePr₂-600 exhibits the highest activity and stability for n-dodecane steam reforming, accompanying with the lowest rate of coke deposition (0.015 g_c/g_cat·h). The structure and oxygen vacancy of the catalyst was characterized by H₂-TPR, Raman, and X-ray photoelectron spectroscopy (XPS). The superior activity and stability of 10Ni-CePr₂-600 are ascribed to the strong interaction between NiO and support along with abundant oxygen vacancies in the Pr-doped ceria.     

The steam reforming of guaiacol for hydrogen via Ni/Al2O3: The influence of dispersion

In this paper, three Ni/Al₂O₃ catalysts with different structure were prepared by different methods. The differences between the catalysts had been compared by H₂ temperature program reduction (H₂-TPR), X-ray diffraction, thermogravimetric analysis, scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The results showed that synthesis method had significant effect on the combination of Ni particle with carrier. The method of coprecipitation could help to improve the combination of Ni and Al₂O₃, and the effect was further enhanced after adding polyethylene glycol (PEG). Due to the enhanced interaction between the active metal and the carrier, the NiO could be easily deoxidized and hard to sinter, which could obtain smaller and more dispersed Ni particles. Moreover, the addition of PEG improved the Ni particle size and its dispersion, and promoted the formation of the unique acicular Al₂O₃. The performance of guaiacol steam catalytic reforming via different catalysts was further analyzed, and the results showed the catalyst obtained by coprecipitation method with PEG exhibited best activity with 73.8% guaiacol conversion and 23.1 wt% H₂ yield.     

Steam reforming of acetic acid for hydrogen production over Ni/CaxFeyO catalysts

Three Ni/Ca_xFe_yO (x/y = 2:1, 1:1, 1:2) catalysts are prepared by impregnation method and applied in steam reforming of acetic acid as the model compound of bio-oil for hydrogen production. The effects of reaction temperature, steam to carbon ratio (S/C), liquid hourly space velocity (LHSV) on gas contents and H₂ yield are carefully investigated and optimized. The fresh and used catalysts are characterized by BET, XRD, H₂-TPR, CO₂-TPD, SEM and TG methods. The experimental and characterization results show that the Ni/CaFe₂O₄ catalyst displays the best activity and stability among the three catalysts, providing 92.1% of H₂ yield under S/C = 5, LHSV = 3.4 h⁻¹ and at 600 °C. The strong interaction between Ni and CaFe₂O₄ support result in the formation of Ni–Fe alloy and Ca₂Fe₂O₅, which shows the synergistic effects on the resistant to carbon deposition and metal sintering, thereby improving the activity and stability of the Ni/CaFe₂O₄ catalyst.     

Combined catalytic partial oxidation and CO2 reforming of methane over ZrO2-modified Ni/SiO2 catalysts using fluidized-bed reactor

Nickel on zirconium-modified silica was prepared and tested as a catalyst for reforming methane with CO₂ and O₂ in a fluidized-bed reactor. A conversion of CH₄ near thermodynamic equilibrium and low H₂/CO ratio (1<H₂/CO<2) were obtained without catalyst deactivation during 10 h, in a most energy efficient and safe manner. A weight loading of 5 wt% zirconium was found to be the optimum. The catalysts were characterized using X-ray diffraction (XRD), H₂-temperature reaction (H₂-TPR), CO₂-temperature desorption (CO₂-TPD) and transmission election microscope (TEM) techniques. Ni sintering was a major reason for the deactivation of pure Ni/SiO₂ catalysts, while Ni dispersed highly on a zirconium-promoted Ni/SiO₂ catalyst. The different kinds of surface Ni species formed on ZrO₂-promoted catalysts might be responsible for its high activity and good resistance to Ni sintering.     

The CO removal performances of Cr-free Fe/Ni catalysts for high temperature WGSR under LNG reformate condition without additional steam

The goal of this study was to investigate Cr-free, Fe/Ni, metal oxide catalysts for the high temperature shift (HTS) reaction of a fuel processor using liquefied natural gas (LNG). As hexavalent chromium (Cr⁶⁺) in commercial HTS catalyst is a hazardous material, we selected Ni as a substitute for chromium in the Fe-based HTS catalyst and investigated the HTS activities of these Cr-free, metal oxide catalysts under the LNG reformate condition. Cr-free, Fe/Ni-based catalysts containing Ni instead of Cr were prepared by coprecipitation and their performance was evaluated under a gas mixture condition (56.7% H₂, 10% CO, 26.7% H₂O, and 6.7% CO₂) that simulated the gas composition from a steam methane reformer (SMR, at H₂O/CH₄ ratio = 3 with 100% CH₄ conversion). Under this condition, the Fe/Ni catalysts showed higher CO removal activities than Fe-only and Cr-containing catalysts, but the methanation was promoted when the Ni content in the catalyst exceeded 50 wt%. Brunner-Emmett-Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS) analyses were performed to explain the HTS activity of the Fe/Ni catalysts based on the catalyst structure.     

Ni/SiO2 core–shell catalysts for catalytic hydrogen production from waste plastics-derived syngas

Ni/SiO₂ core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO₂ core synthesized by the Stöber process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO₂ core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO₂ catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO₂ support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO₂ core–shell catalyst was synthesized in methanol (Ni/SiO₂–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H₂O/h. The Ni/SiO₂–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.     

High-capacity hydrogen generation from hydrazine monohydrate using a noble-metal-free Ni10Mo/Ni–Mo–O nanocatalyst

The development of hydrazine monohydrate (N₂H₄·H₂O) as a viable hydrogen carrier requires high-performance and cost-effective catalysts for selectively promoting its decomposition to generate hydrogen at mild conditions. Herein, we report the synthesis of a non-precious metal nanocatalyst, in both powdery and monolithic forms, using a simple hydrothermal method followed by annealing treatment under H₂ atmosphere. Thus-obtained nanocomposite outperforms the reported non-precious metal catalysts in terms of the overall catalytic properties. More impressively, the system composed of the monolithic Ni₁₀Mo/Ni–Mo–O/Ni foam catalyst, the 85 wt% N₂H₄·H₂O solution and alkali promoter show high hydrogen generation rate, rapid dynamic response and a material-based hydrogen capacity of 6.2 wt%. For the first time, our study demonstrates that the usage of noble-metal-free monolithic catalyst enabled rapid and high-density hydrogen generation from commercial N₂H₄·H₂O solution.     

Synthesis and characterization of Zr-promoted Ni-Co bimetallic catalyst supported OMC and investigation of its catalytic performance in steam reforming of ethanol

This article presents simple method for the OMC-6%Ni-6%Co (ordered mesoporous carbon containing Ni and Co metallic nanoparticles) catalyst synthesis with high surface area and more proper bimetallic nanoparticle dispersion; prepared successfully by soft template hydrothermal method and different zirconium loadings (0.5, 1, 2 wt %) accomplished by impregnation method, which was known as a desired method for the metal dispersion. The catalysts with/without promoter, were characterized by XRD, FTIR and N₂ adsorption-desorption isotherms, FESEM, EDS, EDS mapping, HRTEM and TPR techniques and investigated in steam reforming of ethanol (SRE) at 250–400 °C. XRD and BET results indicated that zirconium addition more than 0.5% wt, decreased the average mesopore diameter of catalysts, total pore volume and particles size. Also, it was stated that Ni²⁺ and Co²⁺ were caught by the RF/F127 network and further reduced into metallic Ni and Co nanoparticles during the carbonization. The Ni and Co nanoparticles were well-dispersed in the OMC walls. FTIR spectroscopy revealed that F127 left the structure and formed the porous structure. TPR analysis of OMC-6%Ni-6%Co/2%Zr sample, indicated that the sample is reduced easily at low temperatures. FESEM and HRTEM images showed that carbon was precipitated in the CNT form on spent catalyst samples surfaces and confirmed the position of Ni and Co bimetallic nanoparticles on the CNTs tip in the OMC-6%Ni-6%Co/2%Zr sample. 2% Zr-promoted bimetallic catalyst revealed appropriate catalytic performance for SRE, such as high activity, hydrogen yield and proper stability due to the synergistic catalysis of cobalt and nickel. Also, effective factors, such as H₂O/EtOH molar ratio and gas hourly space velocity (GHSV) were investigated on the OMC-6%Ni-6%Co/2%Zr catalyst sample.     

Hydrothermal gasification of microalgae over nickel catalysts for production of hydrogen-rich fuel gas: Effect of zeolite supports

A series of Ni catalysts with different zeolites were prepared by wet impregnation method and used to catalyze supercritical water gasification (SCWG) of microalgae for production of hydrogen-rich fuel gas under conditions of 430 °C, 60 min, ρ_H₂O = 0.162 g/cm³, 2 g/g Ni/zeolites. Compared with noncatalytic SCWG, the presence of Ni/zeolite could increase the hydrogen gasification efficiency and carbon gasification efficiency by promoting water–gas shift and steam reforming reactions which are mainly affected by the amount of strong acid sites and Ni, respectively. The highest carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) of 23.61% and 23.55% were achieved with Ni/HY (Na₂O, 0.8%). The gaseous produced mainly consisted of H₂ and CO₂. The H₂ content in the gaseous products varied from 27.15 to 40.51% depending on the Ni/zeolites and increased with increasing the SiO₂/Al₂O₃ molar ratio of HZSM-5, which is 2.3–3.6 times higher than that of produced without catalyst. The H₂ yield varied between 2.57 and 3.61 mmol/g depending on the Ni/zeolites and increased from 2.19 to 5.61 mmol/g with increasing the SiO₂/Al₂O₃ molar ratio from 50:1 to 170:1, which is 3.6–7.8 times higher than that of produced without catalyst. Coke formation, surface area loss, and sintering of Ni could decrease the activity of the Ni/zeolites.