Ni/Y2B2O7 (BTi,Sn, Zr and Ce) catalysts for methane steam reforming: On the effects of B site replacement

In this study, a series of Y₂B₂O₇ compounds with a fixed Yttrium cation A site but with different B (BTi, Sn, Zr and Ce) sites have been synthesized and used to support Ni for methane reforming for hydrogen production. By replacing the B site with Ti, Sn, Zr and Ce cations in sequence, the r_A/r_B ratios of the resulted Y₂B₂O₇ compounds become smaller. As a consequence, the crystalline structures of the compounds become less ordered with the transformation of the bulk phase from well-ordered pyrochlore (Y₂Ti₂O₇) to less ordered pyrochlore (Y₂Sn₂O₇) and subsequently to defective fluorite (Y₂Zr₂O₇ and Y₂Ce₂O₇). XPS results have revealed that on the surfaces of Ni/Y₂Ti₂O₇ and Ni/Y₂Ce₂O₇, higher O/(Y + B) atomic ratios can be achieved than on the other two catalysts, indicating the presence of more abundant oxygen species, which is beneficial to remove the carbon deposits. In comparison with Y₂Zr₂O₇ and Y₂Ce₂O₇, the supported Ni or Ni₃Sn₂ active sites have stronger interaction with Y₂Ti₂O₇ and Y₂Sn₂O₇ supports, which anchors the active sites tighter on the supports and suppresses its aggregation effectively, thus obtaining catalysts with larger active metallic surface areas and better thermal stability. As a result, the stability and coking resistance of the catalysts can be enhanced. For the reduced Ni/Y₂Sn₂O₇, Ni₃Sn₂ alloy has formed, which improves the coking resistance of the catalyst but degrades its activity significantly. On Ni/Y₂Ti₂O₇ catalyst, which possesses the largest amount of active surface oxygen species, the strongest Ni interaction with the support can also be obtained, therefore, it exhibits the highest activity, stability and strongest coking resistance among all of the catalysts.     

Influence of the preparation method in the metal-support interaction and reducibility of Ni-Mg-Al based catalysts for methane steam reforming

Ni-Mg-Al based catalysts were prepared using different preparation methods (impregnation, impregnation-coprecipitation and coprecipitation) and tested in steam reforming of methane. The differences observed in catalytic activity were directly correlated to the physicochemical properties and the different degree of Ni-Mg-Al interaction. The reducibility results showed that the catalyst prepared by the impregnation-coprecipitation method presented the most optimal metal-support interaction to reduce the NiO preserving the Ni⁰ particles highly dispersed on the support surface. These results demonstrate that the structure and catalytic performance of Ni-Mg-Al based catalysts can be tuned by controlling the metal-support interaction through of the preparation method.     

Design of an annular microchannel reactor (AMR) for hydrogen and/or syngas production via methane steam reforming

A bench-scale annular microchannel reactor (AMR) prototype with microchannel width of 0.3 mm and total catalyst length of 9.53 × 10⁻² m active for the endothermic steam reforming of methane is presented. Experimental results at a steam to methane feed molar ratio of 3.3:1, reactor temperature of 1023 K, and pressure of 11 bar confirm catalyst power densities upwards of 1380 W per cm³ of catalyst at hydrogen yields >98% of thermodynamic equilibrium. A two-dimensional steady-state computational fluid dynamic model of the AMR prototype was validated using experimental data and subsequently employed to identify suitable operating conditions for an envisioned mass-production AMR design with 0.3 mm annular channel width and a single catalyst length of 254 mm. Thermal efficiencies, defined based upon methane and product hydrogen higher heating values (HHVs), of 72.7–57.7% were obtained from simulations for methane capacities of 0.5–2S LPM (space velocities of 195,000–782,000 h⁻¹) at hydrogen yields corresponding to 99%–75% of equilibrium values. Under these conditions, analysis of local composition, temperature and pressure indicated that catalyst deactivation via coke formation or Nickel oxidation is not thermodynamically favorable. Lastly, initial analysis of an envisioned 10 kW autothermal reformer combining 19 parallel AMRs within a single methane-air combustion chamber, based upon existing manufacturing capabilities within Power & Energy, Inc., is presented.     

Combined steam and CO2 reforming of methane over one-pot prepared Ni/La-Si catalysts

The highly dispersed mNi/xLa−Si catalysts with varied weight percentages of Ni and La were synthesized via one-pot sol-gel process and subsequently applied to combined carbon dioxide and steam reforming of methane (CSDRM) for syngas production. The addition of La improved the catalytic activity and stability as well as the coke resistance of the mNi/xLa−Si catalysts. The effects of preparation routes, Ni contents and CO₂/steam (C/S) ratios on the performances of the Ni/LaSi catalysts were studied in detail for the CSDRM. The 17.5Ni/3.0LaSi catalyst synthesized with the assistance of poly (ethylene glycol) and ethylene glycol exhibited the most excellent catalytic activity, stability and coke resistance. In addition, the H₂/CO ratios in the product gas could be tuned by changing the C/S ratios in the feed. When the C/S ratio was 0.5, the H₂/CO ratio of about 2 was achieved for the 17.5Ni/3.0LaSi catalyst.     

An investigation of the simultaneous presence of Cu and Zn in different Ni/Al2O3 catalyst loads using Taguchi design of experiment in steam reforming of methane

Nowadays, increasing environmental pollution as well as restrictions on the use of fossil fuels have shifted the attention toward using hydrogen as a new source of clean and effective energy. Additionally, hydrogen and syngas are employed as feedstock for the production of valuable materials in the petrochemical industry. Methane steam reforming is the main procedure for the hydrogen and syngas production. In this study, Taguchi design of experiment (L9) was used to investigate the effects of simultaneous presence of copper (Cu) and Zinc (Zn) metals on different Ni/Al₂O₃ catalyst loads. It should be noted that some of the catalysts were characterized using XRD, BET, SEM and TGA analyses. According to the Taguchi design, it was concluded that the increment of Cu content enhances the catalyst stability and increases the CO selectivity. Increasing Zn content advocated CH₄ conversion, H₂ yield, and less selectivity toward the CO production. The XRD, BET and SEM test results revealed that the addition of Cu resulted in better distribution of active support phase. The TGA results indicated that the addition of Cu and Zn stabilized the catalyst activity; in this case, Cu was more effective than Zn. The overall results demonstrated that 15% load of Ni on Al₂O₃ support, simultaneous addition of Cu and Zn loads of 1% and 5%, respectively, enhanced the catalyst stability and activity and improved the catalyst performance in the selective hydrogen production as well.     

Plasma assisted preparation of highly active NiAl2O4 catalysts for propane steam reforming

In this study, Ni–Al spinel catalyst prepared with glycine-nitrate combustion method and treated by DBD plasma in different atmospheres have been investigated for propane steam reforming (PSR). It is revealed by H₂-TPR that compared with traditional calcination method, NiO/Ni particles have much stronger interaction with the supports on the plasma-treated Ni–Al spinel catalysts. Therefore, catalysts with smaller NiO/Ni grains sizes, higher metallic Ni active surface areas can be achieved, as evidenced by XRD and H₂ adsorption-desorption measurements. NH₃-TPD results demonstrate that the plasma treatment led to a decrease of the acidity of the Ni–Al spinel catalyst. Furthermore, larger quantities of surface active oxygen sites are also formed after plasma treatment, as testified by the O₂-TPD and XPS results. As a consequence, the plasma-treated catalysts show significantly improved catalytic activities and coke resistance. Plasma treatment in H₂/Ar atmosphere after calcination process is considered to be the best route to prepare NiAl₂O₄ catalysts, which could be employed to obtain PSR catalysts with the highest catalytic activity and best anti-coking performance. It is believed that the higher metallic Ni active surface area and much more surface active oxygen sites induced by plasma treatment are the inherent reasons accounting for the enhanced catalytic performance of the Ni–Al spinel catalysts.     

CO2 reforming of methane over Ni/ZnAl2O4 catalysts: Influence of Ce addition on activity and stability

The catalytic performance of Ni supported on Ce-promoted ZnAl₂O₄ was evaluated in methane dry reforming. The effect of different nominal loadings of cerium (3, 5 and 7 wt%) in the activity, product yield and stability was studied. Ce presented a promote effect in catalytic activity, product yield and especially in stability. However the catalytic performance was considerably influenced by the amount of cerium. SEM images presented smaller particles and TPR profiles revealed stronger active phase/support interaction by Ce addition which led to increasing methane conversion and decreasing coke deposition. Although high amount of Ce was not in favor of its promoting effect due to aggregation of CeO₂ on the catalyst surface. Among the catalysts investigated, the optimal catalytic activity and stability was achieved over the sample with 5 wt% of cerium.     

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.     

Steam reforming of CH4 at low temperature on Ni/ZrO2 catalyst: Effect of H2O/CH4 ratio on carbon deposition

In present work, the H₂O/CH₄ on carbon deposition in SRM reaction over Ni/ZrO₂ was studied. Prepared by impregnation, the catalysts were characterized by TEM, XPS, H₂-TPR, TG-DSC-MS, Raman, and XRD. The results showed that when H₂O/CH₄ = 2 with GHSV of 14460 h⁻¹, the highest CH₄ conversion (46.8%) was achieved on the Ni/ZrO₂ catalyst at 550 °C. This was due to the relatively high surface content of Ni⁰ (27%) species and the formation of easy removal polymer carbon (C₁). When the H₂O/CH₄ was 1, a large amount of difficult to remove fiber carbon (C₂) formed and polymer carbon would wrap around the catalyst to reduce its activity. However, excess water might promote surface reconstruction by converting Ni⁰ to Ni(OH)₂, which reduced the surface Ni⁰ content and then inhibited the catalytic activity, while the amount of carbon deposited, especially C₂, reduced significantly.     

Microkinetic modelling and reaction pathway analysis of the steam reforming of ethanol over Ni/SiO2

Hydrogen production via the steam reforming of biomass-derived ethanol is a promising environmental alternative to the use of fossil fuels and a means of clean power generation. A microkinetic modelling study of ethanol steam reforming (ESR) on Nickel is presented for the first time and validated with minimal parameter fitting against experimental data collected over a Ni/SiO₂ catalyst. The thermodynamically consistent model utilises Transition State Theory and the UBI-QEP method for the determination of kinetic parameters and is able to describe correctly experimental trends across a wide range of conditions. The kinetically controlling reaction steps are predicted to occur in the dehydrogenation pathway of ethanol, with the latter found to proceed primarily via the formation of 1-hydroxyethyl. C-C bond cleavage is predicted to take place at the ketene intermediate leading to the formation of CH₂ and CO surface species. The latter intermediates proceed to react according to methane steam reforming and water-gas shift pathways that are enhanced by the presence of water derived OH species. The experimentally observed negative reaction order for water is explained by the model predictions via surface saturation effects of adsorbed water species. The model results highlight a possible distinction between ethanol decomposition pathways as predicted by DFT calculations on Ni close-packed surfaces and ethanol steam reforming pathways at the broad range of experimental conditions considered.     

Process optimization of DBD plasma dry reforming of methane over Ni/La2O3MgAl2O4 using multiple response surface methodology

In this study, 10% Ni/La₂O₃MgAl₂O₄ nano-flake catalyst was synthesized, characterized and tested in a catalytic dielectric barrier discharge (DBD) plasma for dry reforming of methane (DRM). With design of experiment (DoE), the influence of process parameters namely (1) total feed flow rate (ml min⁻¹), (2) feed ratio (CO₂/CH₄), (3) input power (W) and (4) catalyst loading (g) were examined using multiple response surface methodology (RSM) through a four-factor, five-level central composite design (CCD). Second-order regression models were applied for evaluating the interaction between the process parameters and responses. Input power (X₃) and total feed flow rate (X₁) were the two most influential process parameters followed by catalyst loading (X₄) and feed ratio (X₂). The experimental and predicted results from the optimum conditions fitted-well with less than ±5% margin of error. The possible dynamic interactions between the process variables were elucidated. The optimum values are feed flow rate = 18.8 ml min⁻¹, feed ratio = 1.05, input power = 125.6 W and catalyst loading = 0.6 g. At these conditions, the predicted CH₄ and CO₂ conversions are 79.86% and 84.03%, respectively. The H₂ and CO yields are predicted as 41.37% and 40.47%, respectively while H₂/CO ratio is above unity. The calculated EE from the RSM model is predicted as 0.135 mmol kJ⁻¹. Low carbon deposition observed on the spent catalyst is attributed to the highly basic and oxidative nature of the La₂O₃ co-supported catalyst.     

Effects of Co-substitution on the reactivity of double perovskite oxides LaSrFe2-xCoxO6 for the chemical-looping steam methane reforming

The double perovskite oxides (DPOs) LaSrFe_2-xCo_xO₆ (x = 0, 0.2, 0.4, 0.6, 0.8) were investigated as oxygen carriers for the chemical looping steam methane reforming (CL-SMR). The fresh oxides were prepared by micro-emulsion method and their physical and chemical properties were characterized by X-ray diffraction, H₂-temperature programmed reduction and X-ray photoelectron spectroscopy technologies. Meanwhile, isothermal reactions for methane reforming and steam splitting were carried out in a fixed-bed reactor to determine the influences of Co-substitution on the reactivity of LaSrFe_2-xCo_xO₆. The substitution of metal Co has no obvious effect on the crystal structure of double perovskite, but induces a certain degree of Fe/Co disorder generating oxygen vacancies and/or higher oxidation states of metal cations. Synergistic interaction between surface metal ions, such as (Fe⁴⁺/Fe⁵⁺-O^2--Co²⁺) and (Fe³⁺-O^2--Co³⁺), plays a positive effect for the dissociation of methane. The activity may be more likely to be associated with the active oxygen species in connection with Co species on the DPOs surface and abundant of syngas was generated due to the concordant of methane dissociation with the lattice oxygen diffusion. Comprehensively considered, an optimal range of the degree of Co substitution is x = 0.4–0.6 for LaSrFe_2-xCo_xO₆, probably converting 70% of CH₄ into CO and H₂ with molar ratio around 2:1. At the reduced states, the ability of DPOs for steam splitting is primarily associated with the oxygen vacancies after oxygen consumption. The substitution of metal Co slightly enhances the hydrogen production capacity and resistance to carbon formation, achieving the average hydrogen yields at 2.89–3.33 mmol/g oxygen carrier and 1.46–1.61 wt% of carbon depositions.     

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.     

Dry reforming of methane on Ni/mesoporous-Al2O3 catalysts: Effect of calcination temperature

Catalysts of Ni supported on home-made mesoporous alumina (Ni/M-Al₂O₃) were prepared via facile incipient impregnation method and calcined under different temperature (500–800 °C). Compared with catalysts of Ni supported on commercial alumina, they showed much higher conversion and lower carbon deposition in methane dry reforming (DRM). Among the catalysts, Ni/M-Al₂O₃-700 exhibited the highest DRM activity, with 77.6% CH₄ conversion and 85.4% CO₂ conversion at 700 °C. TPR revealed that almost all the Ni was in the form of NiAl₂O₄ spinel after calcination at 700 °C. Due to the strong metal-support interaction of NiAl₂O₄ structure, the Ni crystal size of Ni/M-Al₂O₃-700 after reduction was around 5 nm. TGA and TEM results showed its carbon deposition after 20 h DRM test was only 3.8% and mainly in the form of amorphous carbon. This work indicates that the formation of NiAl₂O₄ spinel is beneficial to activity and stability towards DRM reaction and controlling calcination temperature is crucial.     

Ni supported on La2O3+ZrO2 for dry reforming of methane: The impact of surface adsorbed oxygen species

This research investigates the effect of doping Ni/La₂O₃+ZrO₂ with nitrates of Ca, Cr, Ga, and Gd on the conversion of the feed and H₂/CO molar ratio. The development of these catalysts is intended to tackle inefficiency of dry reforming of CH₄ which stems from deactivation and sintering of active metal. All promoted catalysts perform better than the un-promoted catalyst. Cr promoted sample gives the best performance with CH₄ and CO₂ conversion averaging 83 and 88% respectively. Also, it maintains good stability. The relative ease of reducing the catalyst plus its porous nature are responsible for its performance. Ca promoted sample has the same area as that of the support indicating the movement of Ni–Ca out of the pores of the support during calcination. According to thermogravimetric analysis, the un-promoted catalyst records the highest amount of carbon while the Ca promoted sample has about 18%.     

Direct electrification of Rh/Al2O3 washcoated SiSiC foams for methane steam reforming: An experimental and modelling study

Electrified methane steam reforming (eMSR) is a promising concept for low-carbon hydrogen production. We investigate an innovative eMSR reactor where SiSiC foams, coated with Rh/Al₂O₃ catalyst, act as electrical resistances to generate the reaction heat via the Joule effect. The novel system was studied at different temperatures, space velocities, operating pressures and catalyst loadings. Thanks to efficient heating, active catalyst and optimal substrate geometry, complete methane conversions were observed even at a high space velocity of 200000 Nl/h/kg_cat. A specific energy demand as low as 1.24 kWh/Nm³_H2, with an unprecedented energy efficiency of 81%, was achieved on a washcoated foam with catalyst density of 86.3 g/L (GHSV = 150000 Nl/h/kg_cat, S/C = 4.1, ambient pressure). A mathematical model was validated against measured performance indicators and used to design an intensified eMSR unit for small scale H₂ production.     

Dry reforming of methane over Ni/dendritic fibrous SBA-15 (Ni/DFSBA-15): Optimization,mechanism, and regeneration studies

Dendritic fibrous type SBA-15 (DFSBA-15) was recently discovered with its outstanding catalytic performance and coke resistance as compared to the conventional SBA-15. The operating conditions for dry reforming of methane (DRM) over 10Ni/DFSAB-15 were optimized by using response surface methodology (RSM), followed by stability and regeneration study. Characterization results (TEM and FESEM) confirmed the homogenous distribution of NiO particles with no morphological change in spherical DFSBA-15 upon Ni addition. Process parameters, such as reaction temperature (X₁, 700 °C–900 °C), gas hourly space velocity (X₂, 15,000 mL/g.h ‒ 35,000 mL/g.h), and CH₄/CO₂ ratio (X₃, 1–3) were studied over CO₂ conversion (Y₁), CH₄ conversion (Y₂), and H₂/CO ratio (Y₃). The optimal reaction conditions were found at X₁ = 794.37 °C, X₂ = 23,815.022 mL/g.h, and X₃ = 1.199, with Y₁ = 95.67%, Y₂ = 93.48%, and Y₃ = 0.983. The in-situ FTIR studies of adsorbed CH₄, CO₂, and CH₄ + CO₂ confirmed the formation of unidentate carbonate, bidentate carbonate, and linear carbonyl species as intermediate species. 10Ni/DFSBA-15 presented good reproducibility by using both regeneration medium (air and CO₂/N₂) with two-fold regeneration by air as compared to CO₂/N₂. It was proven that the synthesized 10Ni/DFSBA-15 was appreciably stable and prone to be regenerated by air for DRM under optimal conditions.     

Synthesis of a new self-supported Mgy(CuxNi0.6-xMn0.4)1-yFe2O4 oxygen carrier for chemical looping steam methane reforming process

Novel self-supported Mg_y(Cu_xNi_0.6-xMn_0.4)_1-yFe₂O₄ with (y = 0, 0.05, 0.1, 0.15, and x = 0, 0.15, 0.3, 0.45, 0.6) oxygen carriers (OCs) are synthesized through the co-precipitation method. The synthesized OCs’ properties are characterized by X-ray powder diffraction (XRD), Raman spectra, transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and Thermogravimetric Analysis (TGA). The synthesized OCs are assessed in Chemical Looping Steam Methane Reforming (CL-SMR) process subject to different mesh sizes, reaction temperatures, Steam/Carbon (S/C) molar ratios, Mg concentrations, and Cu and Ni concentrations. The characterization of the OCs and process results indicate the contributive effect of Mg incorporation on the Cu_xNi_0.6-xMn_0.4Fe₂O₄ support structure. The redox results reveal that Mg_0.1(Cu_0.3Ni_0.3Mn_0.4)_0.9Fe₂O₄ OC is of the highest activity, even at low reduction temperatures. This OC exhibits the highest activity and stability with lowest coke deposition during 24 redox cycles at 650 °C and S/C = 2.5. The highest CH₄ conversion of about 99.4% and H₂ yield of about 84.4% are obtained.     

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al₂O₃ catalytic layer and patterned Pt/Al₂O₃ catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.