Ni/MgAl2O4 catalyst for low-temperature oxidative dry methane reforming with CO2

Oxidative dry reforming of methane has been performed for 100 h on stream using Ni supported on MgAl₂O₄ spinel at different loadings at 500–700 °C, CO₂/CH₄ molar ratio of 0.76, and variable O₂/CH₄ molar ratio (0.12–0.47). Syngas with an H₂/CO ratio of 1.5–2.1 has been produced by manipulating reforming feed composition and temperature. The developed oxidative dry reforming process allowed high CH₄ conversion at all conditions, while CO₂ conversion decreased significantly with the lowering of the reforming temperature and increasing O₂ concentration. When considering both greenhouse gas conversions and H₂/CO ratio enhancement, the optimal reforming condition should be assigned to 550 °C and O₂/CH₄ molar ratio of 0.47, which delivered syngas with H₂/CO ratio of 1.5. Coke-free operation was also achieved, due to the combustion of surface carbon species by oxygen. The 3.4 wt% Ni/MgAl₂O₄ catalyst with a mean Ni nanoparticle diameter of 9.8 nm showed stable performance during oxidative dry reforming for 100 h on stream without deactivation by sintering or coke deposition. The superior activity and stability of MgAl₂O₄ supported Ni catalyst shown during reaction trials is consistent with characterization results from XRD, TPR, STEM, HR-STEM, XPS, and CHNS analysis.     

A review on ethanol steam reforming for hydrogen production over Ni/Al2O3 and Ni/CeO2 based catalyst powders

Hydrogen is contemplated as an alternative clean fuel for the future. Ethanol steam reforming (ESR) is a carbon-neutral, sustainable, green hydrogen production method. Low cost Ni/Al₂O₃ and Ni/CeO₂ powder catalysts demonstrate high ESR activity. However, acidic nature of Al₂O₃ and instability of CeO₂ lead to deactivation of the catalysts easily. This article examines the research articles published on the modification of Ni by various noble and non-noble metals and on alteration of the supports by different metal oxides in detail and their effect on ESR all through 2000–2021. The ESR reaction mechanisms on Ni/Al₂O₃ and Ni/CeO₂ powder catalysts and basic thermodynamics for different possible reactions and H₂ yield are explored. Manipulation of catalyst morphology (surface area and particle size) via preparation method, selection of active metal promoter and support modifier are found to be significantly important for H₂ production and minimizing carbon deposition on catalysts.     

Promotion effect of different lanthanide doping on Co/Al2O3 catalyst for dry reforming of methane

In this paper, a series of cobalt catalysts modified by different lanthanide metals were synthesized via co-impregnation method using inexpensive industrial-grade alumina as a support for dry reforming of methane. The effect of lanthanide metals as accelerators of cobalt-based catalysts on catalytic performance and anti-coking properties was mainly investigated. The textural relationships between the catalytic performance and physicochemical properties of cobalt-based catalysts doped with different lanthanide metals were further investigated. Different characterization techniques demonstrate the positive effect of lanthanide metals on the physicochemical properties of catalysts. The results show that the electron transfer between cobalt species and lanthanide metal oxides is significantly enhanced due to the introduction of lanthanide elements. The process generates more active sites, which is favorable for the adsorption and activation of methane. In addition, the abundant medium basic sites and oxygen vacancies on the surface of cobalt-based catalysts with the effect of lanthanides promoted the adsorption and activation of carbon dioxide and the gasification of carbon accumulation, which greatly improved the anti-carbon accumulation performance of the catalysts. Therefore, the prepared cobalt-lanthanum-based catalysts showed the best catalytic effect and have great potential for application.     

Hydrogen and/or syngas production by combined steam and dry reforming of methane on nickel catalysts

Two alumina supported Ni catalysts with pore sizes of 5.4 nm and 9 nm were synthetized, characterized and tested in the Combined Steam and Dry Reforming of Methane (CSDRM) for the production of hydrogen rich gases or syngas. The reaction mixture was designed to simulate the composition of real clean biogas, the addition of water being made in order to have molar ratios of H₂O:CO₂ corresponding to 2.5:1, 7.5:1 and 12.5:1. Structural and functional characterization of catalysts revealed that Ni/Al₂O₃ with larger pore size shows better characteristics: higher surface area, lower Ni crystallite sizes, higher proportion of stronger catalytic sites for hydrogen adsorption, and higher capacity to adsorb CO₂. At all studied temperatures, for a CH₄:CO₂:H₂O molar ratio of 1:0.48:1.2, a (H₂+CO) mixture with H₂:CO ratio around 2.5 is obtained. For the production of hydrogen rich gases, the optimum conditions are: CH₄:CO₂:H₂O = 1:0.48:6.1 and 600 °C. No catalyst deactivation was observed after 24 h time on stream for both studied catalysts, and no carbon deposition was revealed on the used catalysts surface regardless the reaction conditions.     

Hydrogen production from glycerol dry reforming over Ag-promoted Ni/Al2O3

In recent times, glycerol has been employed as feedstock for the production of syngas (H₂ and CO) with H₂ as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al₂O₃ catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L g_cat⁻¹ h⁻¹). Ag (3)-Ni/Al₂O₃ gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H₂ production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al₂O₃, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O₂.     

Syngas production from methane dry reforming over Ni/SBA-15 catalyst: Effect of operating parameters

The influence of operating conditions including reactant partial pressure and reaction temperature on the catalytic performance of 10%Ni/SBA-15 catalyst for methane dry reforming (MDR) reaction has been investigated in this study. MDR reaction was carried out under atmospheric pressure at varying CH₄/CO₂ volume ratios of 3:1 to 1:3 and 923–1023 K in a tubular fixed-bed reactor. SBA-15 supported Ni catalyst exhibited high specific surface area of 444.96 m² g^?1 and NiO phase with average crystallite size of 27 nm was detected on catalyst surface by X-ray diffraction and Raman measurements. H₂ temperature-programmed reaction shows that NiO particles were reduced to metallic Ni⁰ phase with degree of reduction of about 90.1% and the reduction temperature depended on the extent of metal-support interaction and confinement effect of mesoporous silica support. Catalytic activity appeared to be stable for 4 h on-stream at 973–1023 K whilst a slight drop in activity was observed at 923 K probably due to deposited carbon formed by thermodynamically favored CH₄ decomposition reaction. Both CH₄ and CO₂ conversions increased with rising reaction temperature and reaching about 91% and 94%, respectively at 1023 K with CO₂ and CH₄ partial pressure of 20 kPa. CH₄ conversion improved with increasing CO₂ partial pressure, ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$ and exhibited an optimum at ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$ of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO₂ conversion was observed with growing ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$. Additionally, CH₄ and CO₂ conversions decreased significantly with rising CH₄ partial pressure because of increasing carbon formation rate via CH₄ cracking in CH₄-rich feed. Post-reaction characterization shows that active Ni metal phase was not re-oxidized to inactive metal oxide during MDR reaction. The heterogeneous nature of deposited carbons including carbon nanofilament and graphite was detected on catalyst surface by Raman measurement.     

Microfibrous entrapment of Ni/Al2O3 for dry reforming of methane: Heat/mass transfer enhancement towards carbon resistance and conversion promotion

An 8-μm-copper microfibrous entrapped Ni/Al₂O₃ (Cu-MFE-Ni/AlO) composite catalyst was developed for demonstrating the process intensification effectiveness of the novel microfibrous entrapment technology on dry reforming of methane (DRM), which is highly regarded for CH₄ utilizing and CO₂ chemical cycling. Computational fluid dynamics (CFD) calculation was employed to illustrate the significant enhancement of the heat transfer of the microfibrous structured bed at steady working state. The results indicated that the average bed temperature of Cu-MFE-Ni/AlO was 1039 K, 75 K higher than that of packed bed with Ni/AlO (PB-Ni/AlO), when the wall temperature was set at 1073 K. As a result, carbon resistance of the catalyst bed was significantly improved by a thermodynamic way along with visible conversion promotion. For instance, at temperature of 1073 K, more than 4-fold reduction of average carbon deposition rate was achieved in the Cu-MFE-Ni/AlO composite bed compared to the PB-Ni/AlO, while the CH₄ conversion was promoted from 84% on the PB-Ni/AlO to 89% on our Cu-MFE-Ni/AlO composite bed with a gas hourly space velocity (GHSV) of 20,000 mL g_cat⁻¹ h⁻¹. Moreover, such microfibrous entrapment technology also provided a unique combination of small catalyst particle size (0.15–0.18 mm) and entirely open structure with large void volume (71.3 vol%) thereby leading to enhanced mass transfer and high permeability (low pressure drop).     

Co and Ni supported on CeO2 as selective bimetallic catalyst for dry reforming of methane

Co/CeO₂ (Co 7.5 wt.%), Ni/CeO₂ (Ni 7.5 wt.%) and Co–Ni/CeO₂ (Co 3.75 wt.%, Ni 3.75 wt.%) catalysts were prepared by surfactant assisted co-precipitation method. Samples were characterized by X-Ray diffraction, BET surface areas measurements, temperature programmed reduction and tested for the dry reforming of methane CH₄ + CO₂ → 2CO + 2H₂ in the temperature range 600–800 °C with a CH₄:CO₂:Ar 20:20:60 vol.% feed mixture and a total flow rate of 50 cm³ min⁻¹ (GHSW = 30,000 mL g⁻¹ h⁻¹). The bimetallic Co–Ni/CeO₂ catalyst showed higher CH₄ conversion in comparison with monometallic systems in the whole temperature range, being 50% at 600 °C and 97% at 800 °C. H₂/CO selectivity decreased in the following order: Co–Ni/CeO₂ > Ni/CeO₂ > Co/CeO₂. Carbon deposition on spent catalysts was analyzed by thermal analysis (TG-DTA). After 20 h under stream at 750 °C, cobalt-containing catalysts, Co/CeO₂ and Co–Ni/CeO₂, showed a stable operation in presence of a deposited amorphous carbon of 6 wt.%, whereas Ni/CeO₂ showed an 8% decrease of catalytic activity due to a massive presence of amorphous and graphitic carbon (25 wt.%).     

Effect of metal additives on the catalytic performance of Ni/Al2O3 catalyst in thermocatalytic decomposition of methane

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO_x-free hydrogen and carbon nanomaterial. In present work, 60 wt% Ni/Al₂O₃ catalysts with different additives (Cu, Mn, Pd, Co, Zn, Fe, Mg) were prepared by co-impregnation method to investigate promotional effects of these metal additives on the activity and stability of 60 wt% Ni/Al₂O₃ and find out a really effective promoter for decomposition of methane. The catalyst was characterized by N₂ adsorption/desorption, X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. While metal additives (5 wt%) were added into 60 wt% Ni/Al₂O₃, the activity stability of 60 wt% Ni/Al₂O₃ was improved and the CH₄ conversion of 60 wt% Ni/Al₂O₃ was also improved except Zn addition. Mn addition was found to improve the catalytic activity of 60 wt% Ni/Al₂O₃ significantly and the CH₄ conversion of 5 wt% Mn-60 wt% Ni/Al₂O₃ was ∼80%. Cu addition was found to remarkably improve the catalytic stability of 60 wt% Ni/Al₂O₃ and the CH₄ conversion of 5 wt% Cu-60 wt% Ni/Al₂O₃ decreased from 61% to 45% after 250 min of reaction time. Carbon nanomaterials formed in the thermocatalytic decomposition process were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon deposits consist of amorphous carbon and carbon nanofibers.     

Production of hydrogen by methane dry reforming over ruthenium-nickel based catalysts deposited on Al2O3, MgAl2O4, and YSZ

In this work, monometallic (1 wt% of Ru or 5 wt% of Ni) and bimetallic catalysts (1 wt% Ru-5 wt.% Ni) deposited on alumina (Al₂O₃), magnesium aluminate spinel (MgAl₂O₄), and yttria-stabilized zirconia (YSZ) were prepared by wet impregnation. The synthesis method of MgAl₂O₄ was optimized and a well crystallized phase with high specific surface area was obtained by using wet impregnation, as a simple and low cost route, at 800 °C for 2 h.The catalytic activity was compared at atmospheric pressure and 750 °C toward methane dry reforming (DRM) reaction with a molar ratio CH₄/CO₂ = 1/1 and a Weight Hourly Space Velocity (WHSV) of 60.000 mL g⁻¹.h⁻¹.Catalytic activity classification was obtained as the following: Ni/MgAl₂O₄ > Ru-Ni/Al₂O₃ > Ru-Ni/MgAl₂O₄ > Ru-Ni/YSZ > Ni/Al₂O₃ > Ni/YSZ > Ru/Al₂O₃ > Ru/YSZ » Ru/MgAl₂O₄. Between the different catalysts, 5 wt% Ni/MgAl₂O₄ catalyst exhibited excellent catalytic activity for DRM. Furthermore, this catalyst was found to be very stable without any deactivation after 50 h under reacting mixture with a low carbon formation rate (3.58 mg_C/g_cat/h). Such superior activity and stability of MgAl₂O₄ supported Ni catalyst is consistent with characterization results from BET, XRD, TPR, CO-pulse chemisorption and CHNS analysis. It can be due to a strong interaction between Ni and MgAl₂O₄ leading to the incorporation of Ni into the spinel lattice and the formation of oxygen vacancies offering a benefit for DRM reaction.Furthermore, it seems that the addition of ruthenium onto Ni/MgAl₂O₄ decreases the interaction between Ni and the spinel leading to a decrease in the catalyst performance. On the other side, the addition of ruthenium on Ni/Al₂O₃ leads to an increase in the catalyst stability and efficiency by inhibiting the formation of poorly active phase NiAl₂O₄ already observed in TPR.     

Hydrogen production from carbon dioxide reforming of methane over Ni-Co/MgO-ZrO2 catalyst: Process optimization

Greenhouse gases, carbon dioxide and methane are utilized in the production of hydrogen through carbon dioxide reforming of methane catalyzed by Ni-Co/MgO-ZrO₂ catalyst. Design of Experiments (DOE) was used to study the effects of process variables such as, carbon dioxide to methane ratios (1-5), gas hourly space velocity (8400-200,000 mL/g/h), oxygen concentration in the feed (3-8 mol%) and reaction temperature (700-800 °C) over methane conversion and yield of hydrogen. The ANOVA analysis indicated that the effect of each process variable was significant to its respective responses in the proposed quadratic model. The response surface methodology (RSM) was used to find the optimum value of the process variables by maximizing the hydrogen yield in the process model. The optimum space velocity as 145,190 mL/g/h at reaction temperature 749 °C with carbon dioxide to methane ratio of 3 and 7 mol% of oxygen in the feed gave 88 mol% of CH₄ conversion and 86 mol% of hydrogen yield, respectively. The experiments were run at the optimum condition gave 87.7 mol% methane conversion and 85.5 mol% of hydrogen yield, which were in good agreement with the simulated values obtained from the model. The catalyst stability and its regeneration characteristics were studied at the optimum condition by monitoring methane conversion and hydrogen yield with time on stream.     

Ni and Ni3C catalysts supported on mesoporous silica for dry reforming of methane

Ni and Ni₃C catalysts supported on nano-sized and mesoporous silica were used to study the dry reforming reaction of biogas. Ni catalysts were deposited over either nano-sized silica or a novel mesoporous silica (450 m²/g), which were the main supports used in this study. Subsequently, a secondary active phase (Pt) and support (MgO) were added. In addition, mesoporous-supported Ni was also subjected to a carburization process with CH₄. Size effects, preparation techniques and chemical nature of co-supports were studied. Catalytical, microstructural, chemical and molecular characterization of fresh and spent materials were carried out using BET, H₂-TPR, XRD, HRTEM, WDXRF, and Raman spectroscopy. The reaction was undertaken at 700 °C and 1 atm. Results evidence that catalyst supported on both mesoporous silica and also nickel carbide catalyst presented high stability and slow deactivation overall in spite the high content of carbon. The addition of Pt did not increase stability of the catalysts.     

Tailored Ce- and Zr-doped Ni/hydrotalcite materials for superior sorption-enhanced steam methane reforming

Multi-functional hybrid materials are attractive for producing high-purity hydrogen (H₂) via catalytic steam reforming coupled with low temperature adsorptive separation of CO₂. In this work, modified Ni/hydrotalcite-like (HTlc) hybrid materials promoted with Ce and Zr species were synthesized and applied for the sorption-enhanced steam methane reforming process (or SESMR). The promotion with Ce and Zr resulted in strongly basic sites for CO₂ adsorption, and hence, improved H₂ production. Especially, the Ce-promoted hybrid material (Ce-HM1) exhibited the highest adsorption capacity (1.41 mol CO₂/kg sorbent), producing 97.1 mol% H₂ at T = 723 K, P = 0.1 MPa, S/C = 4.5 mol/mol and gas hourly space velocity or GHSV = 3600 mL/(g h); the breakthrough time was 1 h. High surface area and basicity of the promoted materials inhibited coke formation and undesired reactions. In addition to the improved catalytic activity and adsorption characteristics, these materials were stable and easily regenerable. Multi-cycle durability tests revealed that both the promoted materials Ce-HM1 and Zr-HM1 remained stable for up to 13 and 17 cycles. In contrast, the unpromoted hybrid material (HM1) was stable for 9 cycles only. Thus, promotion with Ce and Zr was beneficial for producing pure H₂.     

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.     

Syngas production via dry reforming of methane over CeO2 modified Ni/Al2O3 catalysts

Syngas production via dry reforming of methane (DRM) was experimentally investigated using Ni-based catalyst. Ni/Al₂O₃ modification with CeO₂ addition and O₂ addition in the reactant were employed in this study to suppress carbon deposition and to enhance catalyst activity. It was found that DRM performance can be enhanced using CeO₂ modified Ni/Al₂O₃ catalyst due to CeAlO₃ formation. However, an optimum amount of CeO₂ loading exists to obtain the best DRM performance due to the decrease in specific surface area as the CeO₂ loading increases. Without O₂ addition, the reverse water-gas shift reaction plays an important role in DRM. It was found that CH₄ conversion and CO yield were enhanced while CO₂ conversion and H₂ yield are decreased as the CO₂ amount in feedstock increased in DRM. With O₂ addition in the fed reactant, it was found that the methane oxidation reaction plays an important role in DRM. CH₄ conversion can be enhanced by O₂ addition. However, decreases in CO₂ conversion and H₂ and CO yields occurred due to greater H₂O and CO₂ productions from the methane oxidation reaction. The thermogravimetric analysis (TGA) results showed that CeO₂ modified Ni/Al₂O₃ catalyst would have the lowest amount of carbon deposition when O₂ is introduced into the reaction.     

Catalytic performance of a high-cell-density Ni honeycomb catalyst for methane steam reforming

The catalysis of methane steam reforming (MSR) by pure Ni honeycombs with high cell density of 2300 cells per square inch (cpsi) was investigated to develop efficient and inexpensive catalysts for hydrogen production. The Ni honeycomb catalyst was assembled using 30-μm-thick Ni foils, and showed much higher activity than that of a Ni honeycomb catalyst with cell density of 700 cpsi at a steam-to-carbon ratio of 1.36 and a gas hourly space velocity of 6400 h^?1 in a temperature range of 873–1173 K. Notably, the activity increased approximately proportional to the increasing geometric specific surface area of the honeycombs. The turnover rate of the Ni honeycomb catalyst was higher than that of supported Ni catalysts. The changes in chemical state of the Ni catalyst during hydrogen reduction and MSR reaction were analyzed by in situ X-ray absorption fine structure spectroscopy, which revealed that deactivation was mainly due to oxidation of the surface Ni atoms. These results demonstrated that the high-cell-density Ni honeycomb catalyst exhibits good performance for MSR reaction, and easy regeneration of the deactivated Ni honeycomb catalyst is possible only via hydrogen reduction.     

Steam reforming of acetic acid using Ni/Al2O3 catalyst: Influence of crystalline phase of Al2O3 support

Ni-based catalysts supported on various alumina supports with different crystalline phases (γ-, α-, θ- and δ-Al₂O₃) were prepared and the effects of crystalline phases on the catalytic performance towards acetic acid steam reforming (AASR) were investigated. An acetic acid conversion of nearly 100% was observed in all the four catalysts, and their hydrogen selectivities were in the following order: Ni/α-Al₂O₃ (90%) > Ni/γ-Al₂O₃ (79%) > Ni/δ-Al₂O₃ (53%) > Ni/θ-Al₂O₃ (25%). Using different characterization methods, the inner relationship between catalyst crystalline phase and catalytic properties was determined. Through TEM, H₂-TPR and XPS characterization, Compared with α-Al₂O₃, on the surface of other crystalline phases of Al₂O₃ support were formed NiAl₂O₄ which indicated stronger interaction intensity between these supports and Ni., and that would reduce the formation of metallic Ni. It was confirmed that metallic Ni played a core role of catalytic AASR. More metallic Ni content caused better CC bonds and CH bonds breaking capability and eventually enhanced the selectivity towards hydrogen. That would be the key reason for Ni/α-Al₂O₃ showed best hydrogen selectivity among these four catalysts.     

Production of hydrogen by methane dry reforming: A study on the effect of cerium and lanthanum on Ni/MgAl2O4 catalyst performance

Hydrogen production from dry reforming of methane (DRM) was investigated on different Nickel based catalysts deposited on MgAl₂O₄. MgAl₂O₄ spinel was prepared using γ-Alumina supplied from different manufacturers (Sigma Aldrich, Alfa Aesar and Degussa) with low and high specific surface area. Moreover, the influence of different parameters on the catalytic activity on methane dry reforming was studied such as the effect of Ni content, the effect of commercial alumina and the effect of doping nickel with cerium and lanthanum.During this study, the catalytic activity was compared at atmospheric pressure at 750 °C during 4 h then 650 °C during 4 h toward methane dry reforming (DRM) reaction with a molar ratio CH₄/CO₂ = 1/1 and a Weight Hourly Space Velocity (WHSV) of 60.000 mL g⁻¹.h⁻¹. The results showed that among the different catalysts 1.5Ce–Ni5/MgAl₂O₄, synthesized with alumina from Alfa Aesar, exhibited the best catalytic activity for DRM.Furthermore, this catalyst showed the best performance during a stability test at 600 °C for 24 h under reacting mixture with a low carbon formation rate (2.71 mg_C/g_cat/h). Such superior activity is consistent with characterization results from BET, XRD, SEM, TPR and TPO analysis. Furthermore, it seems that the addition of Cerium on Ni/MgAl₂O₄ leads to an increase in catalyst efficiency. It can be due to an effective active oxygen transfer due to the redox properties of CeO_2, leading to the formation of oxygen vacancies offering a benefit for DRM reaction.     

Carbon resistance of xNi/HTASAO5 catalyst for the production of H2 via CO2 reforming of methane

xNi/HTASAO5 catalysts (x = 2.5, 3.3, 4.4, 5.8, 8.2) were prepared for CO₂ reforming of methane. No crystalline nickel species formed on the catalysts with lower nickel content (≤4.4%), and large Ni⁰ crystallite formed on 5.8% (10 nm) and 8.2 wt%Ni/HTASAO5 (17 nm), whereas the surface concentration of Ce³⁺ decreased with Ni loading. The initial conversion of CH₄ increased from 29.5% to 46.9% with Ni loading. The xNi/HTASAO5 (x ≤ 4.4%) performed stably in the reaction due to the presence of dispersed Ni species and high surface Ce³⁺ content without coke formation, however, 5.8% and 8.2 wt%Ni/HTASAO5 exhibited decreased activity with time on stream, because of the formation of large Ni particles with lower surface Ce³⁺, leading to carbon accumulation. Thus, CH₄ conversion stabilized at about 43% and no carbon formed on 4.4 wt%Ni/HTASAO5 with optimum Ni loading.     

Effect of O2 and temperature on the catalytic performance of Ni/Al2O3 and Ni/MgAl2O4 for the dry reforming of methane (DRM)

Al₂O₃ and MgAl₂O₄ supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH₄ and CO₂ conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl₂O₄ than Ni/Al₂O₃. Carbon-whiskers are also detected on both catalysts. O₂ co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl₂O₄ at 600 °C. Furthermore, higher conversions and H₂/CO ratios are achieved. It appears that on spent Ni/MgAl₂O₄ a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O₂, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.