Catalytic conversion of CH4 and CO2 to synthesis gas on Ni/SiO2 catalysts containing Gd2O3 promoter

A series of Ni/SiO₂ catalysts containing different amounts of Gd₂O₃ promoter was prepared, characterized by H₂-adsorption and XRD, and used for carbon dioxide reforming of methane (CRM) and methane autothermal reforming with CO₂ + O₂ (MATR) in a fluidized-bed reactor. The results of pulse surface reactions showed that Ni/SiO₂ catalysts containing Gd₂O₃ promoter could increase the activity for CH₄ decomposition, and Raman analysis confirmed that reactive carbon species mainly formed on the Ni/SiO₂ catalysts containing Gd₂O₃ promoter. In this work, it was found that methane activation and reforming reactions proceeded according to different mechanisms after Gd₂O₃ addition due to the formation of carbonate species. In addition, Ni/SiO₂ catalysts containing Gd₂O₃ promoter demonstrated higher activity and stability in both CRM and MATR reactions in a fluidized bed reactor than Ni/SiO₂ catalysts without Gd₂O₃ even at a higher space velocity.     

Ni-based catalysts for reforming of methane with CO2

Ni catalysts supported on different carriers like δ,θ-Al₂O₃, MgAl₂O₄, SiO₂–Al₂O₃ and ZrO₂–Al₂O₃ were prepared. The solids were characterized by chemical analysis, N₂ adsorption–desorption isotherms, X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, high-resolution transmission electron microscopy and temperature-programmed oxidation. The catalytic properties of the samples were evaluated in the reaction of reforming of methane with CO₂ at 923 K. It was shown that this kind of support greatly affects the structure and catalytic performance of the catalysts. Ni catalyst supported on MgAl₂O₄ showed the highest activity and stability due to the presence of small well dispersed Ni particles with size of 5.1 nm. It was shown that the lowest activity of Ni catalyst supported on SiO₂–Al₂O₃ oxide was caused by the agglomeration of nickel particles and formation of filamentous carbon under reaction conditions detected by the high resolution transmission electron microscopy.     

Effect of Pr addition on the properties of Ni/Al2O3 catalysts with an application in the autothermal reforming of methane

Ni/xPr-Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/γ-Al₂O₃ catalyst; the physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H₂-temperature programmed reduction techniques (TPR). The results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al₂O₃ supports and the promotion of NiO reduction by Pr modification. The CH₄ conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al₂O₃ catalysts maintained the high activity after 48 h while Ni/Al₂O₃ had a significant deactivation.     

Comparative study on the promotion effect of Mn and Zr on the stability of Ni/SiO2 catalyst for CO2 reforming of methane

The stability of Mn-promoted Ni/SiO₂ catalyst for methane CO₂ reforming was investigated comparatively to that of Zr-promoted Ni/SiO₂. The catalysts were prepared by the same impregnation method with the same controlled promoter contents and characterized by TPR, XRD, TG, SEM, XPS and Raman techniques. The addition of Mn to Ni/SiO₂ catalyst promoted the dispersion of Ni species, leading to smaller particle size of NiO on the fresh Ni–Mn/SiO₂ catalyst and the formation of NiMn₂O₄, which enhanced the interaction of the modified support with Ni species. Thus, the Ni–Mn/SiO₂ catalyst showed higher activity and better ability of restraining carbon deposition than Ni/SiO₂ catalyst. Besides, it exhibited stable activity at reaction temperatures over the range from 600 °C to 800 °C. However, the introduction of Zr increased the reducibility of Ni–Zr/SiO₂, and the catalyst deactivated much more dramatically when the reaction temperature decreased due to its poor ability of restraining carbon deposition, and its activity decreased monotonically with time on stream at 800 °C.     

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY₂O₃–Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/γ-Al₂O₃ catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H₂-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH₄ conversion increased with elevating levels of Y₂O₃ from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY₂O₃–Al₂O₃ catalysts maintained high activity after 24 h on stream, while Ni/Al₂O₃ had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke.     

Y2O3-promoted NiO/SBA-15 catalysts highly active for CO2/CH4 reforming

A series of Y₂O₃-promoted NiO/SBA-15 (9 wt% Ni) catalysts (Ni:Y weight ratio = 9:0, 3:1, 3:2, 1:1) were prepared using a sol–gel method. The fresh as well as the catalysts used in CO₂ reforming of methane were characterized using N₂-physisorption, XRD, FT-IR, XPS, UV, HRTEM, H₂-TPR, O₂-TPD and TG techniques. The results indicate that upon Y₂O₃ promotion, the Ni nanoparticles are highly dispersed on the mesoporous walls of SBA-15 via strong interaction between metal ions and the HO–Si-groups of SBA-15. The catalytic performance of the catalysts were evaluated at 700 °C during CH₄/CO₂ reforming at a gas hourly space velocity of 24 L g_cat⁻¹ h⁻¹(at 25 ^°C and 1 atm) and CH₄/CO₂molar ratio of 1. The presence of Y₂O₃ in NiO/SBA-15 results in enhancement of initial catalytic activity. It was observed that the 9 wt% Y–NiO/SBA-15 catalyst performs the best, exhibiting excellent catalytic activity, superior stability and low carbon deposition in a time on stream of 50 h.     

Effect of Ca,Ce or K oxide addition on the activity of Ni/SiO2 catalysts for the methane decomposition reaction

To increase the activity and stability of Ni/SiO₂ catalysts, a series of Ni–Ca, Ni–K and Ni–Ce promoted catalysts were prepared by successive impregnations. The textural properties, reducibility and catalytic performance in the methane decomposition reaction were investigated. The catalyst containing 30 wt.% Ni and 30 wt.% cerium oxide greatly increased the conversion of methane (90% of equilibrium value) and improved the stability, whereas the Ni–K and Ni–Ca were less active and stable than the Ni/SiO₂ catalyst. The results suggest that Ce addition prevents the sintering of nickel particles during reduction process maintaining a random distribution between the silica and cerium oxide improving the distribution and migration of deposited carbon.     

The effect of preparation method on the catalytic performance over superior MgO-promoted Ni–Ce0.8Zr0.2O2 catalyst for CO2 reforming of CH4

The effect of preparation method on MgO-promoted Ni–Ce_0.8Zr_0.2O₂ catalysts was investigated in CO₂ reforming of CH₄. Co-precipitated Ni–MgO–Ce_0.8Zr_0.2O₂ exhibited very high activity as well as stability (X_CH4 > 95% at 800 °C for 200 h) due to high surface area, high dispersion of Ni, small Ni crystallite size, and easier reducibility. Four elements (Ni, Mg, Ce, and Zr) are located at the same position for the co-precipitated catalyst, resulting in easier reducibility.     

The promoting effect of La, Mg, Co and Zn on the activity and stability of Ni/SiO2 catalyst for CO2 reforming of methane

CO₂ reforming of methane into synthesis gas over Ni/SiO₂ catalysts promoted by La, Mg, Co and Zn was investigated. The catalysts were prepared by impregnation method and characterized by XRD, TPR, SEM and TG-DTA techniques. Ni-La/SiO₂ catalyst was found to exhibit high activity and excellent stability with the addition of suitable amount of La promoter, which increased the dispersion of NiO and the interaction between NiO and SiO₂. Two different types of carbon species, namely, easily oxidized carbonaceous species and inert carbon, were observed on the surface of the used catalysts. The inert carbon deposited on Ni-Mg/SiO₂ catalyst may be the main reason for its deactivation, while the principal reason for the deactivation of Ni-Co/SiO₂ catalyst might be the sintering of metallic Ni. The addition of La and Mg decreased the contribution of reverse water-gas shift reaction, leading to higher H₂ yield.     

Catalytic CO2 reforming of CH4 over Cr-promoted Ni/char for H2 production

The objective of the study is to investigate the catalytic performance of Cr-promoted Ni/char in CO₂ reforming of CH₄ at 850 °C. The char obtained from the pyrolysis of a long-flame coal at 1000 °C was used as the support. The catalysts were prepared by incipient wetness impregnation methods with different metal precursor doping sequence. The characterization of the composite catalysts was evaluated by XRD, XPS, SEM-EDS, TEM, H₂-TPR, CO₂-TPD, CH₄-TPSR, and CO₂-TPO. The results indicate that the catalyst prepared by co-impregnation of Ni and Cr possess higher activity than those by sequential impregnation. The optimal loading of Cr on 5 wt% Ni/char is 7.8 wt‰. Moreover, the molar feed ratio of CH₄/CO₂ has a considerable effect on both the stability and the activity of Cr–Ni/char. The main effect of Cr is the great enhance of the adsorption to CO₂. It is interesting that the conversions of CH₄ and CO₂ over Cr-promoted Ni/char and Ni/char decrease initially, following by a steady rise as the reaction proceeds with time-on-stream (TOS). In addition, cyclic tests were conducted and no distinct deterioration in the catalytic performance of the catalysts was observed. On the basis of the obtained results, nickel carbide was speculated to be the active species which was formed during the CO₂ reforming of CH₄ reaction.     

Autothermal reforming of methane over nickel catalysts supported on nanocrystalline MgAl2O4 with high surface area

In this paper autothermal reforming of methane (ATR) was carried out over MgAl₂O₄ supported Ni catalysts with various Ni loadings. MgAl₂O₄ spinel with high specific surface area, as nanocrystalline carrier for nickel catalysts was synthesized by co-precipitation method with the addition of pluronic P123 triblock copolymer as surfactant. The prepared samples were characterized by XRD, BET, TEM, SEM, TPR and TPH techniques. The results demonstrated that methane conversion is significantly increased with increasing the Ni content and methane conversion of 15% Ni/MgAl₂O₄ was higher than that of other catalysts in all operation temperatures. Furthermore the influences of H₂O/CH₄, and O₂/CH₄ molar ratio in feed and GHSV on activity of 5% Ni/MgAl₂O₄ catalyst were investigated.     

Effect of Ce on 5 wt% Ni/ZSM-5 catalysts in the CO2 reforming of CH4 reaction

The aim of this study is to investigate the promotional effect of Ce on Ni/ZSM-5 catalysts in the CO₂ reforming of CH₄ reaction. The evaluation of the catalytic performances of the composite catalysts was conducted in a fixed-bed reactor at atmospheric pressure. The influencing factors, including temperature, Ni and Ce loadings, molar feed ratio of CO₂/CH₄, and time-on-stream (TOS), were investigated. The characteristics of the catalysts were checked with Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The reduction and the basic properties of the composite catalysts were elucidated by temperature-programmed reduction by H₂ (H₂-TPR) and temperature-programmed desorption of CO₂ (CO₂-TPD), respectively. The reactivity of deposited carbon was studied by sequential temperature-programmed surface reaction of CH₄ (CH₄-TPSR) and temperature-programmed oxidation using CO₂ and O₂ (CO₂-TPO and O₂-TPO). Results indicate that higher CH₄ conversion, H₂ selectivity, and desired H₂/CO ratio for 5 wt% Ni & 5 wt% Ce/ZSM-5 could be achieved with CO₂/CH₄ feed ratio close to unity over the temperature range of 500–900 °C. Moreover, the addition of Ce could not only promote CH₄ decomposition for H₂ production but also the gasification of deposited carbon with CO₂. The dispersion of Ni particles could be improved with Ce presence as well. A partial reduction of CeO₂ to CeAlO₃ was observed from XPS spectra over 5 wt% Ni & 5 wt% Ce/ZSM-5 after H₂ reduction and 24 h CO₂–CH₄ reforming reaction. Benefiting from the introduction of 5 wt% Ce, the calculated apparent activation energies of CH₄ and CO₂ over the temperature range of 700–900 °C could be reduced by 30% and 40%, respectively.     

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.     

Steam reforming of methanol over Cu/ZnO/ZrO2/Al2O3 catalyst

Steam reforming of methanol was investigated over Cu–ZnO–ZrO₂–Al₂O₃ catalysts at 473 and 573 K. The Cu:Zn:(Al + Zr) molar ratio was 3:3:4; however, the Zr:Al molar ratio was varied and the catalysts were pretreated at different calcination and reduction temperatures. The synthesized catalysts were characterized by N₂ physisorption, temperature-programmed reduction with H₂ (H₂-TPR), X-ray diffraction, oxidized surface TPR, and infrared spectroscopy after carbon monoxide chemisorption. The crystalline size of Cu decreased on increasing the calcination temperatures from 573 to 623 K and increased on increasing the reduction temperatures from 523 to 573 K. Among the tested catalysts, the Cu–ZnO–ZrO₂ catalyst exhibited the highest and lowest hydrogen-formation rates at 473 and 573 K, respectively. After the reaction at 573 K, all the tested catalysts exhibited an increase in the Cu crystalline size, causing the catalyst deactivation. Among the tested catalysts, the Cu–ZnO–ZrO₂–Al₂O₃ catalyst, where the Cu:Zn:Al:Zr molar ratio was 3:3:2:2, showed the highest and most stable catalytic activity at 573 K. Cu dispersion and catalyst composition affected the catalytic performance for steam reforming of methanol.     

Modifying perovskite-type oxide catalyst LaNiO3 with Ce for carbon dioxide reforming of methane

Perovskite-type oxide catalysts LaNiO₃ and La_1−xCe_xNiO₃ (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H₂ + CO). The gaseous reactants consisted of CO₂ and CH₄ in a molar ratio of 1:1. At a GHSV of 10,000 hr⁻¹, CH₄ conversion over LaNiO₃ catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO₂ conversion increased from 51% to 92%. The achieved selectivities of CO and H₂ were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H₂ to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La₂O₂CO₃ phases after CO₂ reforming. The FE-SEM results reveal carbon whisker of the LaNiO₃ catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H₂-TPR results confirm that Ce metals can store and provide oxygen.     

LaNiO3@SiO2 core–shell nano-particles for the dry reforming of CH4 in the dielectric barrier discharge plasma

LaNiO₃@SiO₂ core–shell nano-particles were prepared by coating LaNiO₃ nano-particles with SiO₂ and then employed to catalyze the dry reforming of CH₄ to produce syngas (CO + H₂) in a coaxial dielectric barrier discharge (DBD) plasma reactor under ambient conditions. Compared to the traditional Ni-based catalysts (Ni/SiO₂, LaNiO₃/SiO₂ and LaNiO₃), LaNiO₃@SiO₂ exhibited better catalytic performance in the dry reforming of CH₄ in DBD plasma reactor, such as higher reactant conversion and product selectivity, and excellent catalytic stability. The conversions of CH₄ and CO₂ reached 88.31% and 77.76%, and selectivities of CO and H₂ were 92.43% and 83.65%, respectively. Results manifested the core–shell structure endowed LaNiO₃@SiO₂ with excellent catalytic performance because the SiO₂ shell was capable of preventing Ni from sintering and mitigating carbon deposition during the reaction.     

Effect of SiO2-ZrO2 supports prepared by a grafting method on hydrogen production by steam reforming of liquefied natural gas over Ni/SiO2-ZrO2 catalysts

SiO₂-ZrO₂ supports with various zirconium contents are prepared by grafting a zirconium precursor onto the surface of commercial Carbosil silica. Ni(20 wt.%)/SiO₂-ZrO₂ catalysts are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of SiO₂-ZrO₂ supports on the performance of the Ni(20 wt.%)/SiO₂-ZrO₂ catalysts is investigated. SiO₂-ZrO₂ prepared by a grafting method serves as an efficient support for the nickel catalyst in the steam reforming of LNG. Zirconia enhances the resistance of silica to steam significantly and increases the interaction between nickel and the support, and furthermore, prevents the growth of nickel oxide species during the calcination process through the formation of a ZrO₂-SiO₂ composite structure. The crystalline structures and catalytic activities of the Ni(20 wt.%)/SiO₂-ZrO₂ catalysts are strongly influenced by the amount of zirconium grafted. The conversion of LNG and the yield of hydrogen show volcano-shaped curves with respect to zirconium content. Among the catalysts tested, the Ni(20 wt.%)/SiO₂-ZrO₂ (Zr/Si = 0.54) sample shows the best catalytic performance in terms of both LNG conversion and hydrogen yield. The well-developed and pure tetragonal phase of ZrO₂-SiO₂ (Zr/Si = 0.54) appears to play an important role in the adsorption of steam and subsequent spillover of steam from the support to the active nickel. The small particle size of the metallic nickel in the Ni(20 wt.%)/SiO₂-ZrO₂ (Zr/Si = 0.54) catalyst is also responsible for its high performance.     

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.     

Preparation and characterization of coke resistant Ni/SiO2 catalyst for carbon dioxide reforming of methane

Silica supported Ni catalyst is highly active for the CO₂ reforming of methane but it has poor stability due to coke formation. In this work, a glow discharge plasma was applied for the decomposition of nickel nitrate on the SiO₂ support, followed by thermal calcination in air. The plasma treatment enhances the interactions between the Ni particles and the silica and significantly improves the Ni dispersion. The plasma-treated Ni/SiO₂ catalyst exhibits comparable activity to the Ni/SiO₂ catalyst prepared by the thermal method without plasma treatment. The coke resistance of the Ni/SiO₂ catalyst is significantly enhanced by the plasma treatment.     

Synthesis of nanocrystalline mesoporous Ni/Al2O3SiO2 catalysts for CO2 methanation reaction

A series of nanocrystalline mesoporous Ni/Al₂O₃SiO₂ catalysts with various SiO₂/Al₂O₃ molar ratios were prepared by the sol-gel method for the carbon dioxide methanation reaction. The synthesized catalysts were evaluated in terms of catalytic performance and stability. The catalysts were studied using XRD, BET, TPR and SEM. The BET results indicated that the specific surface area of the samples with composite oxide support changed from 254 to 163.3 m²/g, and an increase in the nickel crystallite size from 3.53 to 5.14 nm with an increment of Si/Al molar ratio was visible. The TPR results showed a shift towards lower temperatures, indicating a better reducibility and easier reduction of the nickel oxide phase into the nickel metallic phase. Furthermore, the catalyst with SiO₂/Al₂O₃ molar ratio of 0.5 was selected as the optimal catalyst, which showed 82.38% CO₂ conversion and 98.19% CH₄ selectivity at 350 °C, high stability, and resistivity toward sintering. Eventually, the optimal operation conditions were specified by investigating the effect of H₂/CO₂ molar ratio and gas hourly space velocity (GHSV) on the catalytic behavior of the denoted catalyst.