CO2 reforming of methane over NixMg6−xAl2 catalysts: Effect of lanthanum doping on catalytic activity and stability

Ni_xMg_6?xAl₂ and Ni_xMg_6?xAl_1.8La_0.2 (x = 2, 4 or 6) catalysts were prepared via a co-precipitation method and calcined under an air flow at 800 °C. X-ray diffraction (XRD) results showed that the Ni_xMg_6?xAl_1.8La_0.2 catalysts contained different lanthanum oxide species after calcination. Fourier Transform Infrared Spectroscopy (FTIR) spectra demonstrated that the lanthanum doped catalysts adsorbed more CO₂ compared to the lanthanum free solids. This improved basicity was verified in the CO₂-TPD profiles. Temperature programmed reduction (TPR) analyses proved that the addition of lanthanum affected nickel species distribution in the catalysts and strengthened NiO-MgO interactions inside the solid matrix. The CO₂ reforming of methane reaction (Ar/CO₂/CH₄:60/20/20; GHSV 60000 mL g^?1 h^?1) was carried out over the different catalysts in the temperature range of 600 °C–800 °C. Lanthanum addition improved the catalytic activity particularly by favoring the methane dry reforming reaction over all the other secondary reactions in addition to the creation of more basic sites that enhanced CO₂ adsorption and contributed to the removal of carbon deposits. The most active lanthanum containing catalyst kept a constant catalytic performance for 14 h on stream despite the formation of carbon deposits. These carbon deposits can be removed under an oxidative atmosphere at moderate temperature due to the presence of lanthanum oxide species in the catalyst.     

Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on γ-Al₂O₃ with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous γ-Al₂O₃ carrier with the high BET area (186 m²/g) was synthesized by a simple sol–gel method and the Ni, NiMn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127–176 m²/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH₄ conversion in the range of 60–65% at 700 °C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the NiMn/Al₂O₃ catalyst promoted by 4 wt% Mg showed the highest CH₄ conversion in all studied reaction temperatures (550–700 °C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al₂O₃ and 10Ni3Mn4Mg/Al₂O₃ catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al₂O₃ catalyst was stable during the 20 h time on stream without any decline in CH₄ conversion.     

Preparation of Ni/Pt catalysts supported on spinel (MgAl2O4) for methane reforming

MgAl₂O₄ was synthesized through hydrolysis of metallic alkoxides of Mg²⁺ and Al³⁺. The formed spinel precursor phase was calcined at temperatures between 600 and 1100 °C, for 4 h. The spinel was utilized as a Ni/Pt catalyst support. The Ni/MgAl₂O₄ catalysts (15% Ni, w/w) containing small amounts of Pt were tested for methane steam reforming. The solids were analyzed by X-ray diffraction (XRD), temperature programmed reduction (TPR) with H₂ and catalytic tests. The spinel phase was formed at temperatures above 700 °C. The addition of small amounts of Pt to Ni/MgAl₂O₄ promoted an increase in surface area. This probably caused the considerable increase in methane conversion.     

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.     

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.     

Syngas production by the CO2 reforming of CH4 over Ni–Co–Mg–Al catalysts obtained from hydrotalcite precursors

The catalytic performance of the Ni, Co, Mg, and Al mixed-oxide solids, synthesized via hydrotalcite route, was investigated towards the dry reforming of methane for hydrogen production. The hydrotalcite structure was successfully obtained upon the synthesis. After calcination at 800 °C under an air flow, this structure was completely decomposed and the resulting oxides (Co_xNi_yMg_zAl₂800, x and y = 0; 1; 2; 3; 4, z = 2; 4, x + y + z = 6, x, y, and z are the molar ratios) were used as catalysts and were characterized using X-ray diffraction and Temperature-Programmed Reduction. The dry reforming of methane was carried out using a mixture of CH₄:CO₂ (1:1) after 2 h of reduction under an H₂ flow at 800 °C. Co₂Ni₂Mg₂Al₂800 showed the highest catalytic activity in the studied series, ascribable to an interaction between Ni and Co, which is optimal for such Co/Ni ratio. The post-reaction characterization of the catalytic samples by X-ray diffraction and Differential Scanning Calorimetry evidenced a better resistance towards carbon deposition for the catalysts where Co molar ratio is higher than Ni.     

Preparation of high surface area Ni/MgAl2O4 nanocatalysts for CO selective methanation

Methanation of carbon monoxide in the H₂-rich gas stream was performed on a series of the Ni/MgAl₂O₄ catalysts in a fixed bed micro-reactor. The catalysts were synthesized using wetness impregnation method and the prepared samples were characterized by XRD, BET, SEM, TEM, H₂-TPR, CO chemisorption and CO-TPD techniques. The catalyst carrier was prepared by a novel sol-gel method using nitrate salts precursors and propylene oxide as a gelation agent. MgAl₂O₄ as catalyst carrier possessed a high BET area of 340 m² g^?1 with high pore volume (0.563 cc g^?1) and small pore size (6.56 nm). The catalysts also showed high BET area, which decreased with the increase in Ni content. These catalysts exhibited mesoporous structure with average nickel crystal size smaller than 20 nm. The catalyst with Ni content of 25 wt% exhibited the maximum CO conversion and CH₄ selectivity and can be considered as a catalyst with high catalytic potential for the selective methanation of carbon monoxide.     

Biogas reforming for hydrogen enrichment by ceria decorated over nickel catalyst supported on titania and alumina

Catalytic dry reforming of biogas for hydrogen enrichment was studied over cerium oxide promoted nickel catalysts supported on titanium dioxide and aluminium oxide. The catalysts were prepared by wet impregnation method and characterized by H₂-TPR, XRD, BET and FESEM techniques. Their catalytic performance in the biogas dry reforming reaction was studied at temperature ranges from 650 to 850 °C, with a CH₄/CO₂ ratio of 1.5:1. The H₂-TPR results revealed that 11 wt % Ni impregnation on TiO₂ support makes the catalyst with strong metal-support interaction which moderates the metal sintering. Also, the addition of CeO₂ effectively improved the CH₄ and CO₂ conversions as well as H₂ enrichment. At 850 °C, 11 wt % Ni/TiO₂ catalyst leads to 70.5% CH₄ conversion with 32.0% H₂ enrichment, whereas, Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) yielded high CH₄ conversion (84.9%) with 40.6% of H₂ enrichment. No significant change in the activity of the catalyst was observed with 8.8 wt % of carbon deposited on the Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) catalyst, after 7 h of continuous reforming. Moreover, under combined (dry and oxidative) reforming of biogas, the stoichiometric H₂/CO ratio (1.2) was observed at 0.47 O₂/CH₄ ratios with negligible carbon deposition. Thus, Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) catalyst exhibited better activity and selectivity with high catalyst stability at 850 °C.     

Ce promoting effect on the activity and coke formation of Ni catalysts supported on mesoporous nanocrystalline γ-Al2O3 in autothermal reforming of methane

In this study methane autothermal reforming (ATR) was investigated over Ni/Al₂O₃ and Ni/Al₂O₃–CeO₂ catalysts. The catalyst carriers were prepared through a facile one-step method, which produced mesoporous nanocrystalline carriers for Ni catalysts. The samples were characterized by XRD, TPR, BET, TPO and SEM characterization techniques and the catalytic activity and stability were also studied at different conditions (GHSV and feed ratio) in methane ATR. It was found that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ exhibited higher activity compared to the catalysts supported on the Al₂O₃ and promoted Al₂O₃ with 1 and 6 wt.% Ce. The results also showed that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ possessed the highest resistance against carbon deposition in ATR reaction.     

High temperature methanation over Ni catalysts supported on high surface area ZnxMg1-xAl2O4: Influence on Zn loading

A series of 10 wt % Ni based catalysts supported on Zn_xMg_1-xAl₂O₄ were prepared using a co-precipitation and impregnation method for high temperature syngas methanation. The effect of Zn loading on catalysts’ textural property and catalytic performance was investigated by BET, XRD, TEM, H₂-TPR, XPS and CO-TPD analysis. It was found that a modest addition of Zn significantly increased the surface area of the catalysts, which moderated the strong interaction between NiO and the support. This effect enhanced the reduction of the Ni, thereby improving the dispersion of the active metal on the support and intensifying the adsorption of CO. In addition, surface Ni⁰ concentration was improved by the Zn substitution. Among the various catalysts tested, Ni/Zn_0.7Mg_0.3Al exhibited the best catalytic performance at 500 °C, 2.0 MPa and 30, 000 ml g⁻¹·min⁻¹, with a CO conversion, CO₂ conversion and CH₄ selectivity of 99.7, 53.1 and 98.7%, respectively. Furthermore, the Ni/Zn_0.7Mg_0.3Al catalysts also maintained excellent stability during a 120 h life test.     

Preparation and improvement of the mesoporous nanostructured nickel catalysts supported on magnesium aluminate for syngas production by glycerol dry reforming

Dry reforming of glycerol is an interesting method for syngas production due to its H₂/CO ≈ 1 that is suitable for FT synthesis. In this study, the performance of the Ni/MgO.Al₂O₃ catalysts with different nickel contents was investigated in glycerol dry reforming. The MgO.Al₂O₃ carrier was prepared by a simple sol-gel method and the nickel-based catalysts were synthesized by the wet impregnation method. The prepared catalysts possessed high BET surface area and pore volume. The TPR analysis showed a strong interaction between Ni and the catalyst support. The results demonstrated that the glycerol conversion decreased by increasing in CO₂/glycerol (GRR) molar ratio. All the prepared samples showed high stability in glycerol dry reforming during 25 h of reaction, indicating the high resistance of the catalysts against carbon formation. Also, 10 wt%Ni/MgO.Al₂O₃ catalysts possessed the highest catalytic performance (52% of glycerol conversion at 750 °C) due to the high dispersion of nickel on the prepared carrier.     

Carbon dioxide reforming of methane over Ni/Mg0.4Al0.4-La0.1Zr0.1(O) catalyst prepared by recombination sol–gel method

Based on several catalysts preparation methods, we developed a new sol–gel method and produce a series of quaternary catalysts Ni/Mg_xAl_x-La_0.5-xZr_0.5-x(O) (x = 0, 0.13, 0.25, 0.33, 0.4, 0.43, 0.5) using different ratios of binary metallic oxide (MgAl(O) to LaZr(O)). The synthesized samples were employed in the dry reforming of methane (DRM) and mixed reforming of hydrocarbons (CH₄ & C₂H₆) (MRH) to evaluate their performances at 800 °C under atmospheric pressure. The experimental result indicates that the catalytic activity was mainly dependent on the interaction between active component (NiO particle) and support, and Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1(O) exhibited the highest activity (CH₄ 96.1% & CO₂ 95.9%) during DRM. The physicochemical properties of these catalysts were analyzed by N₂ adsorption–desorption, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), H₂ temperature-programmed reduction (H₂-TPR) and thermogravimetric analysis (TGA). The TPR analysis result illustrated that strong interaction between Ni active species and support was observed on catalysis Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1(O), increasing the stability of Ni and thus enhanced both abilities of anti-sintering and anti-coking during the reaction. The XRD characterization of fresh and used Mg_0.4Al_0.4-La_0.1Zr_0.1(O) witnessed that the active component Ni was well dispersed on the support, and the minimal carbon deposition was detected on the used Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1(O) by TGA and SEM compared with other catalysts. The 80 h activity test confirmed that the Mg_0.4Al_0.4-La_0.1Zr_0.1(O) can still perform high conversions (both CH₄ & CO₂ > 95% after 80 h) and stability after a long time DRM reaction. Moreover, the quaternary Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1(O) is also suitable for mixed hydrocarbons reforming to produce syngas, which showed its excellent performance (CH₄ 94%, CO₂ 96% and C₂H₆ 100%) during the reaction and may be widely used in the future.     

Low-temperature CO2 reforming of methane over Ni supported on ZnAl mixed metal oxides

Ni catalysts supported on mixed ZnOAl₂O₃ and on pure ZnO and Al₂O₃ were prepared, characterized by XRD, TPR, and XPS, and tested in long-term methane dry reforming at low temperature (400 °C). Depending on Zn/Al ratio in the supports, the catalysts varied in their physico-chemical properties and exhibited different trends in their on-stream catalytic activity. Catalysts with high alumina content consist of a mixture of alumina and zinc aluminate phases with metallic Ni particles on their surface. These samples show medium activity for reforming and high on-stream stability. The catalysts on mixed Zn-rich supports were more active than those on Al-rich supports and exhibited maxima in their activity after 30–40 h on stream, while Ni on pure ZnO possessed very low activity. Such contrast in performance of Zn-rich catalysts was explained by detected transformation of initially formed NiZn alloy to a mixture of Ni and Ni₃ZnC_0.7 particles that are assumed to have higher activity for reforming. Moreover, the size of Ni-containing particles on Zn-rich supports decreased under reaction conditions resulting in higher Ni dispersion.     

Investigation of Ba doping in A-site deficient perovskite Ni-exsolved catalysts for biogas dry reforming

This work presents the development of an A-site deficient La_0.9−xBa_xAl_0.85Ni_0.15O₃ (x = 0, 0.02, 0.04, and 0.06) perovskite oxide catalyst for dry reforming of model biogas. The catalysts are prepared using a citrate sol-gel method and used for biogas dry reforming at 800 °C for feed ratios (CH₄/CO₂) of 1.5 and 2.0. The fresh and spent catalysts are analyzed using XRD, FTIR, TPD, XPS, FESEM, TEM, TPR, TGA-DTA, and Raman analysis. The XRD analysis exhibits the host perovskite oxide structure and the exsolved Ni phase for all prepared catalysts. The partial doping of Ba improves the metal support interaction and oxygen vacancies that enhance catalytic activity and stability, as revealed by the TPR and XPS analysis. The stability experiment on La_0.9−xBa_xAl_0.85Ni_0.15O₃, for x = 0 catalyst resulted in reduced activity due to the catalyst deactivation by sintering, as confirmed by XRD and FE-SEM. Among all the catalysts studied, La_0.84Ba_0.06Al_0.85Ni_0.15O₃ (LB6AN-15) exhibited the highest catalytic stability with CH₄, and CO₂ conversions are 60% and 93%, respectively, for 40 h time-on-stream due to the strong metal support interactions, high oxygen vacancies, and anti-sintering of exsolved Ni nanoparticles in biogas dry reforming.     

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.     

Carbon dioxide methanation over Ni-M/Al2O3 (M: Fe,CO, Zr,La and Cu) catalysts synthesized using the one-pot sol-gel synthesis method

In this paper, a series of mesoporous supported nickel based catalysts on nanocrystalline alumina carrier promoted with various metals (Fe, CO, Zr, La and Cu) were prepared and employed in carbon dioxide methanation reaction. The samples were characterized by XRD, BET, TPR and SEM techniques. The BET results showed that the incorporation of promoters into nickel based catalysts decreased the surface area. The results showed that among the prepared catalysts, 30 wt.%Ni-5 wt.%La/Al₂O₃ and 30 wt.%Ni-5 wt.%Fe/Al₂O₃ possessed the highest surface area and the largest pore volume, respectively. Likewise, there was a slight decrease in the pore volume and the average pore diameters of the promoted samples. The TPR results depicted that the incorporation of the promoters enhanced the reducibility of the catalysts and shifted the reduction of NiO species to a lower reduction temperature. The CO₂ conversions of all promoted catalysts except Cu-promoted sample were higher peculiarly at low temperatures compared to those attained for the unpromoted catalyst. 30 wt.%Ni-5 wt.%Fe/Al₂O₃ catalyst exhibited the best catalytic performance (70.63% CO₂ conversion and 98.87% CH₄ selectivity at 350 °C), high stability and desirable resistance against sintering.     

Steam reforming and oxidative steam reforming for hydrogen production from bioethanol over Mg2AlNiXHZOY nano-oxyhydride catalysts

Mg₂AlNi_XH_ZO_Y nano-oxyhydrides formation is evidenced during pre-treatment in H₂ at 450 °C of Mg₂AlNi_XO_Y nano-compounds leading to highly performant catalysts in ethanol conversion and H₂ formation, particularly at low temperature, through catalytic steam reforming (SRE) and oxidative steam reforming (OSRE). Total conversion of ethanol is obtained in SRE and OSRE with high stability. A higher production of H₂ (60 L h^?1 g_cat^?1) can be achieved at a reaction temperature of 300 °C in OSRE conditions compared to SRE (10 L h^?1 g_cat^?1) mainly because of a beneficial use of a high concentration of ethanol (14 mol%) in presence of O₂. Moreover, carbon formation is decreased and a much lower input of energy of 50 °C is used to get a temperature of 300 °C when O₂ is added. Different physico-chemical characterizations and in particular in H₂ (TPR, H₂-XRD, INS) and after tests allow to conclude that the presence of Ni²⁺ cations in strong interaction with other cations, anionic vacancies and hydride species on and inside the solid play an important role in the catalytic performance (conversion and selectivity) and stability.     

Selective substitution of Ni by Ti in LaNiO3 perovskites: A parameter governing the oxy-carbon dioxide reforming of methane

A series of LaNi_1?xTi_xO₃ perovskite catalysts varying titanium (x = 0.0, 0.2, 0.4, 0.5, 0.6 and 1.0) are synthesized and investigated using BET, XRD, TPR, TEM, FT-IR and XPS. The catalysts were evaluated for oxy-carbon dioxide reforming of methane at 800 °C under atmospheric pressure maintaining CO₂/CH₄/O₂ ratio 0.8/1.0/0.2. LaNi_0.5Ti_0.5O₃ is showing typical stability with gradual H₂ consumption in TPR. The stability of these catalysts is supported by O 1s binding energies wherein it is clearly evident that incorporation of Ti stabilized LaNiO₃ generating suitable catalysts in the range of x = 0.4–0.6 with high performance.     

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.     

Pellet size dependent steam reforming of polyethylene terephthalate waste for hydrogen production over Ni/La promoted Al2O3 catalyst

The effect of different pellet sizes of nickel (Ni) and lanthanum (La) promoted Al₂O₃ support on the catalytic performance for selective hydrogen production from polyethylene terephthalate (PET) plastic waste via steam reforming process has been investigated. The catalysts were prepared by impregnation method and were characterized using XRD, BET, TPD-CO₂, TPR, SEM, EDX, TEM and TGA. The results showed that NiLa-co-impregnated Al₂O₃ catalyst has excellent activity for the production of hydrogen. Feed conversion of 88.53% was achieved over 10% Ni/Al₂O₃ catalyst which increased to 95.83% in the case of 10% Ni-5% La/Al₂O₃ catalysts with a H₂ selectivity of 70.44%. The catalyst performance in term of gas production and feed conversion was further investigated under various operating parameters, e.g., feed flow-rate, and catalyst pellet size. It was found that at 0.4 ml/min feed flow rate, highest feed conversion and H₂ selectivity were achieved. The Ni particles, which are the noble-based active species are highly effective, thus offered good hydrogen production in the phenol-PET steam reforming process. Incorporation of La as a promoter in Ni/Al₂O₃ catalyst has significantly increased the catalyst reusability with prolonged stability. The NiLa/Al₂O₃ catalyst with larger size showed remarkable activity due to the presence of significant temperature gradients inside the pellet compared to smaller size. Additionally, the catalyst showed only slight decrease in H₂ selectivity and feed conversion even after 24 h, although production of carbon nanotubes was evidenced on its surface.