Effect of CaO–ZrO2 addition to Ni supported on γ-Al2O3 by sequential impregnation in steam methane reforming

Ni catalysts supported on (CaO–ZrO₂)-modified γ-Al₂O₃ were prepared by sequential impregnation. The effects of varied CaO to ZrO₂ mole ratios at 0, 0.20, 0.35, 0.45, and 0.55 on the activity and stability of the modified Ni catalysts were studied. As a result of using CaO–ZrO₂ as a promoter, each catalyst contained CaO–ZrO₂ at only 5%. γ-Al₂O₃ used as support was modified by CaO–ZrO₂ before the deposition of nickel oxide. The addition of CaO–ZrO₂ at an optimum ratio was expected to improve the stability of Ni catalysts due to the decrease of carbon formation resulting from carbon gasification. All the fresh catalysts were characterized by ICP, XRD, BET surface area, TGA in H₂, and TPR before catalytic testing in steam methane reforming at 600 °C. The spent catalysts were examined by TEM and TGA to observe the catalysts deactivation. The identification of CaO–ZrO₂ phases indicated that CaO and ZrO₂ reacted with each other to be monoclinic solid solution ZrO₂, CaZr₄O₉, CaZrO₃, and CaO corresponding to the phase diagram of CaO–ZrO₂. The existence of CaZrO₃ for 0.55 mol ratio of CaO/ZrO₂ enhanced activity in steam methane reforming because oxygen vacancies in CaZrO₃ greatly preferred the water adsorption creating the favorable conditions for carbon gasification and, then, water gas shift. The prominence and continued existence of these two reactions on the Ni catalysts leads to the particular increase of H₂ yield. Moreover, the increasing amount of CaZrO₃ in the Ni catalysts significantly improved carbon gasification. However, the Ni catalysts with CaZrO₃ showed whisker carbon after catalytic testing; this carbon specie has not been tolerated in steam methane reforming. Therefore, these results significantly differed from the hypothesis.     

Ni/CeO2–MgO catalysts supported on stainless steel plates for ethanol steam reforming

Ni/CeO₂–MgO catalysts on powder form and supported on stainless steel plates were prepared, characterized and tested towards hydrogen generation via the steam reforming reaction of ethanol. The structured catalyst was prepared by the dip-coating technique. The coatings obtained over the stainless steel plates were homogeneous and retained their integrity after the reaction experiences. The samples were characterized by SEM, TEM, XRD, ICP-AES, TPR, OSC and N₂ adsorption–desorption measurements. Catalysts presented very good stability under reaction conditions for 16 h on-stream, without showing a significant variation in the activity or product distribution. The structured catalysts presented similar activities and selectivities respect to those of the powder, whereby the deposition method did not modify the catalytic properties of the particulate material. The presence of the AISI 430 stainless steel substrate also had not a significant influence on the performance of the deposited material.     

Co–Ni bimetal catalyst supported on perovskite-type oxide for steam reforming of ethanol to produce hydrogen

Perovskite-type oxide (PTO) of LaFeO₃ supported Ni–Co bimetallic catalysts were prepared by citric acid complexation-impregnation method and were used for the steam reforming of ethanol (SRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for the reaction have been investigated and compared with the monometal catalysts. The catalysts were characterized by using temperature programmed reduction, X-ray diffraction, transmission electron microscopy and thermal analysis techniques. The results indicate that the catalyst was both highly selective to hydrogen and very stable for SRE reaction. Characterization results indicated that Ni–Co was in the state of solid solution alloy. Comparing with corresponding monometal catalysts, the bimetal catalyst exhibited better anti-sintering ability and similar anti-carbon deposition ability. The valuable information indicated in this work is that based on the special characters of PTO, bimetal nano-particles can be supported on metal oxides, which should be a new and promising method for preparing supported bimetal catalysts.     

Co–Ni alloy supported on CeO2 as a bimetallic catalyst for dry reforming of methane

Dry reforming of methane (DRM) is an effective route to convert two major greenhouse gas (CH₄ and CO₂) to syngas (H₂ and CO). Herein, in this work, monometallic Ni/CeO₂ and a series of bimetallic Co–Ni/CeO₂ catalysts with Co/Ni ratios between 0 and 1.0 have been tested for DRM process at 600–850 °C, atmospheric pressure and a CH₄/CO₂ ratio of 1. The catalysts were characterized by X-ray diffraction, hydrogen-temperature programmed reduction, CO₂-Temperature programmed desorption, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The catalyst with a Co/Ni ratio of 0.8 (labeled as 0.8 Co–Ni/CeO₂) exhibited the highest catalytic activity (CH₄ and CO₂ initial conversion for 80% and 85% at 800 °C, respectively) and the highest stability (less carbon deposition after 600min). This improved activity can be attributed to the Co–Ni alloy, which formed after reduction. Its weak chemisorption with hydrogen results in inhibition of reverse water gas shift reaction. In addition, Co-promoted the adsorption of surface oxygen enhances carbon removal, making it more stable.     

Ce–Fe oxygen carriers for chemical-looping steam methane reforming

Chemical-looping steam methane reforming (CL-SMR) is a novel process for the co-production of pure hydrogen and syngas (synthesis gas) without purification processes. Ce_1−xFe_xO_2−δ oxides (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1) prepared by chemical precipitation were characterized by X-ray powder diffraction, BET, Raman spectra, temperature-programmed reduction technologies and used as oxygen carrier for the CL-SMR process. The methane conversion/water splitting redox properties of samples were evaluated at the different temperatures (800, 850, and 900 °C). With the combination of CeO₂ and Fe₂O₃, Fe₂O₃ particles were well dispersed on ceria surface and a small amount of iron ions was incorporated into the CeO₂ lattice to form a Ce–Fe–O solid solution. It was found that reducibility of CeO₂ was enhanced by the added Fe₂O₃. These results therefore led to the conclusion of the strong Ce–Fe interaction in CeO₂–Fe₂O₃ mixed oxides. As a result, the redox activity of CL-SMR was significantly improved, and increased in desired product yield. The redox performance was also affected by the redox temperatures, and the desired product yield was obviously enhanced at the higher temperatures. It was found that Ce_0.5Fe_0.5O_2−δ oxygen carrier showed the highest performance for the co-production of syngas and hydrogen.     

Insight into Ni/Ce1−xZrxO2−δ support interplay for enhanced methane steam reforming

Nickel catalysts supported in zirconium-doped ceria were optimized for methane steam reforming (MSR) at severe reaction conditions, i.e. low temperature and stoichometric water/methane feed ratio. The solids prepared were characterized by various techniques (BET, XRD, H₂-chemisorption, OSC, H₂-TPR, Raman and XPS), allowing a deeper understanding of the nickel-ceria based support interplay.     

Boosting hydrogen production by ethanol steam reforming on cobalt-modified Ni–Al2O3 catalyst

Ethanol steam reforming (ESR) is one of the most promising reliable and recyclable technologies for hydrogen production. However, the development of robust, efficient Ni-based catalysts that minimize metal sintering and carbon deposition remains a key challenge. The influence of cobalt loading and ESR conditions on H₂ selectivity and catalytic stability is the focus of this study. Ni–Co/Al₂O₃ catalysts with various Co percentages were prepared by the co-impregnation method and complementary characterization tests were performed. Among the catalysts tested, Ni–Co/Al₂O₃ (5 wt% Co) exhibited the smallest metal crystallite size, the highest surface area, and the best catalytic performance. Thereafter, the effects of temperature, LHSV and S:C molar ratio were studied. 100% ethanol conversion and maximum H₂ selectivity (95.14%) were reached at 600 °C, 0.05 L/g_cat.h and S:C molar ratio of 12:1. Furthermore, ethanol turnover frequency (TOF) was computed for each catalyst. TOF results showed that the Ni–Co interaction had an impact on the catalytic activity. Finally, Ni2CoAl was subjected to 50-h stability test and only 6.12 mg_carbon/g_cat.h coke deposition was observed.     

High purity H2 production from sorption enhanced bio-ethanol reforming via sol-gel-derived Ni–CaO–Al2O3 bi-functional materials

Catalytic steam reforming of renewable bio-oxygenates coupled with in-situ CO₂ capture is a promising option for sustainable H₂ production. The current work focuses on high purity H₂ production over Ni–CaO–Al₂O₃ bi-functional materials via sorption enhanced steam reforming of ethanol (SEESR). To ensure the uniform distribution of catalytic sites (Ni), adsorptive sites (CaO) and stabilizer (Al₂O₃) in the bi-functional materials, a citrate sol-gel synthetic route was employed. These materials were characterized by XRD, N₂ physical adsorption, SEM, TG and TPR techniques. It was revealed that the existence of CaO in bi-functional materials could not only in-situ remove CO₂, but also play the role of inhibiting the formation of harmful spinel phase. The stabilizing role of Al component against capacity decay was confirmed, whereas the presence of Ni ions had a negative effect on the cycle CO₂ uptake. The sample of Ni/Al/Ca-85.5 possessed large specific surface area, abundant porosity with fluffy morphology, and thereby, exhibited the best CO₂ sorption capacity during 20 carbonation/calcination cycles. The highest H₂ concentration of 96% was obtained through the SEESR during the pre-breakthrough period when the Ni/Al/Ca-85.5 was employed. Over the optimized bi-functional material, the effect of operating conditions on the SEESR was investigated and the results indicated that temperature of 600 °C, reaction liquid space velocity of 0.05 ml/min and steam/ethanol ratio of 4 were the suitable conditions. After 10 cycles, the bi-functional material of Ni/Al/Ca-85.5 also showed the best performance, with a H₂ purity of about 90% and pre-breakthrough time of 18 min, conforming the high potential of this material for SEESR process.     

Catalytic steam reforming of bio-oil aqueous fraction for hydrogen production over Ni–Mo supported on modified sepiolite catalysts

Hydrogen will be an important energy carrier in the future and hydrogen production has drawn a great deal of attention to its advantages in efficiency and environmental benefit. Catalytic steam reforming in this study was carried out in a fixed bed tubular reactor with sepiolite catalysts. Sepiolite catalysts modified with nickel (Ni) and molybdenum (Mo) were prepared using the precipitation method. Influential parameters such as temperature, catalyst, steam to carbon ratio (S/C), the feeding space velocity (WHSV), reforming length, and activity of catalyst were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. The result of this experiment shows that the acidified sepiolite catalyst with addition of the Ni and Mo greatly improves the activities of catalyst and effectively increases the yield of hydrogen. The favorable reaction condition is as follows: reaction temperature is 700–800 °C; S/C is 16–18; the feeding space velocity is 1.5–2.2 h⁻¹, respectively.     

Biogas dry reforming over Ni–Ce catalyst supported on nanofibered alumina

Four catalysts based on Ni and Ni–Ce supported on two γ-aluminas with different morphology (nanofibers and nanograins) have been prepared and studied in the dry reforming of simulated biogas. Catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma with optical emission spectrometer (ICP-OES), chemisorption of H₂ and elemental analysis (EA) to determine their most relevant physicochemical properties. Characterization results show that metallic Ni particles supported on nanofibered alumina (NFA) presents a higher dispersion and smaller size than that supported on the nanograiny alumina (NGA) probably due to the higher mesoporosity presented by the NFA support. On the other hand, the incorporation of Ce has a similar effect than the fibrous morphology, decreasing also the size of the Ni metallic particles and increasing their dispersion. In the dry reforming of synthetic biogas (CH₄/CO₂ = 1.5) the nanofibered alumina containing 5 wt% Ni and 1.5 wt% Ce (NiCe/NFA) showed the highest catalytic activity at 750 °C (98% CO₂ conversion) and stability (7.7% nickel sinterization level and 2.9 wt% carbon deposition). The stability of this catalyst was also demonstrated at 750 °C during 55 h of reaction time with a loss of activity at the steady state under 2%. In addition, the catalyst was regenerated at 600 °C in oxygen flow, recovering completely its initial catalytic performance. The excellent catalytic behavior of NiCe/NFA material has been related to the fibrous morphology of the alumina support, which promotes a better dispersion of the supported Ni metal particles, decreasing their size and increasing the number of actives sites where dry reforming reaction can take place. In addition, the incorporation of Ce seems to have also an important role by increasing the Ni-support interactions, decreasing sinterization of the metallic Ni particles and coke deposition. The contribution of both effects (morphology and Ce), separately and in combination, have been proved to enhance significantly the catalytic activity and stability of the synthesized catalysts in the dry reforming of simulated biogas.     

Steam reforming of methanol over supported Ni and Ni–Sn nanoparticles

The influence of the synthesis method and Sn addition on Ni/CeO₂–MgO–Al₂O₃ catalyst is correlated to its catalytic behavior in the reaction of methanol steam reforming. The catalysts prepared by impregnation method are compared to samples obtained by deposition of previously obtained nanoparticles by the polyol method. X-ray diffraction (XRD), specific surface area measurements and H₂-temperature programmed reduction (TPR) were used to characterize the catalysts. The differences of the structure, phase transformation and reduction behavior are discussed and related to the catalytic performance of the samples as well as the nature of the carbonaceous deposits formed during the reaction.     

Ni–Re alloy catalysts on Al2O3 for methane dry reforming

Methane reforming with CO₂ is still of great interest due to growing demand creating a continuous need for new hydrogen sources. The main difficulty in this reaction is the deactivation of the catalyst due to the formation of carbon deposits on its surface. Herein, a series of commercial nickel catalysts supported on α-Al₂O₃ and modified with different amounts of rhenium (up to 4 wt%) was investigated. It was revealed that Re addition causes the formation of Ni–Re alloy during high temperature reduction, which was confirmed in deep XRD and STEM studies. The addition of Re positively influences not only the stability of the catalyst, but also increases its activity in the DRM reaction carried out in a Tapered Element Oscillating Microbalance (TEOM). The formation of Ni–Re alloy played a significant role in enhancing the properties of the catalyst.     

Renewable hydrogen production from steam reforming of glycerol by Ni–Cu–Al,Ni–Cu–Mg,Ni–Mg catalysts

H₂ production from glycerol steam reforming by the Ni–Cu–Al, Ni–Cu–Mg, Ni–Mg catalysts was evaluated experimentally in a continuous flow fixed-bed reactor under atmospheric pressure within a temperature range from 450 to 650 °C. The catalysts were synthesized by the co-precipitation methods, and characterized by the elemental analysis, BET, XRD and SEM. The GC and FTIR were applied to analyze the products from steam reforming of glycerol. The coke deposited on the catalysts was measured by TGA experiments during medium temperature oxidation. The results showed that glycerol conversion and H₂ production were increased with increasing temperatures, and glycerol decomposition was favored over its steam reforming at low temperatures. The Ni–Cu–Al catalyst containing NiO of 29.2 wt%, CuO of 31.1 wt%, Al₂O₃ of 39.7 wt% performed high catalytic activity, and the H₂ selectivity was found to be 92.9% and conversion of glycerol was up to 90.9% at 650 °C. The deactivation of catalysts due to the formation and deposition of coke was observed. An improved iterative Coats–Redfern method was used to evaluate the non-isothermal kinetic parameters of coke removal from catalysts, and the results showed the reaction order of n = 1 and 2 in the Fn nth order reaction model predicted accurately the main phase in the coke removal for the regeneration of Ni–Mg and Ni–Cu–Al catalysts, respectively.     

Study on the preparation of Ni–La–Ce oxide catalyst for steam reforming of ethanol

Two schemes for design and preparation of Ni–La–Ce oxide catalysts for steam reforming of ethanol were proposed in this work. The one via citrate complexing method was designed as NiO supported on ceria-lanthanum oxide (CL) solid solution, in which the strong interaction between NiO and CL solid solution was beneficial to inhibit the aggregation of NiO particles, and the abundant of oxygen vacancies existed in CL solid solution was in favor of carbon elimination from catalyst surface. The other was schemed as LaNiO₃ with perovskite structure loaded on CeO₂ support by using impregnation method, in which the particles of metal Ni derived from reduction of LaNiO₃ were highly dispersed, and the formation of La₂O₂CO₃ in the reaction process could act as the carbon scavenger. Both of the catalysts exhibited very good performance for steam reforming of ethanol (SRE), complete C₂H₅OH conversion was obtained with 70.3% of H₂ selectivity at 400 °C over the catalyst obtained from former method and complete C₂H₅OH conversion was achieved at 450 °C with 67% of H₂ selectivity over the catalyst from latter method. The catalyst made according to the citrate complexing method was more active for SRE and more selective for H₂ production. Both of the catalysts displayed very good anti-sintering ability which was tested at 650 °C and at a high space velocity of 180,000 ml g_cat⁻¹ h⁻¹ with reaction mixture of H₂O/C₂H₅OH = 3 in mole ratio. The results indicated that both of oxygen vacancy and La₂O₂CO₃ possessed the ability to remove the deposited carbon, and compared with La₂O₂CO₃ the oxygen vacancy could reduce one third more of the carbon deposited according to TG tests.     

The effect of different atmosphere treatments on the performance of Ni/Nb–Al2O3 catalysts for methane steam reforming

Methane steam reforming is currently the most widely used hydrogen production reaction in industry today. Ni/Nb–Al₂O₃ catalysts were prepared by treatment under H₂, N_2, and air atmosphere prior to reduction and applied for methane steam reforming reaction at low temperature (400–600 °C). The hydrogen-treated catalysts increased catalytic activity, with 55.74% methane conversion at S/C = 2, GSVH of 14400 mL g^?1 h^?1 and 550 °C. The H₂ atmosphere treatment enhanced the Ni–Nb interaction and the formation of stable, tiny, homogeneous Ni particles (6 nm), contributing to good activity and stability. In contrast, the catalysts treated with nitrogen and air showed weaker interactions between Ni and Nb species, whereas the added Nb covered the active sites, which caused the decrease in activity. Meanwhile, carbon accumulation was also observed. This work is informative for preserving small nano-sized nickel particles to enhance catalytic performance.     

Effects of CaO addition on Ni/CeO2–ZrO2–Al2O3 coated monolith catalysts for steam reforming of N-decane

A series of 10 wt%Ni/CeO₂–ZrO₂–Al₂O₃ (10%Ni/CZA) coated monolith catalysts modified by CaO with the addition amount of 1 wt%~7 wt% are prepared by incipient-wetness co-impregnation method. Effects of CaO promoter on the catalytic activity and anti-coking ability of 10%Ni/CZA for steam reforming of n-decane are investigated. The catalysts are characterized by N₂ adsorption-desorption, XRD, SEM-EDS, TEM, NH₃-TPD, XPS, H₂-TPR and Raman. The results show that specific surface area and pore volume of as-prepared catalysts decrease to some extent with the increasing addition of CaO. However, the proper amounts of CaO (≤3 wt%) significantly enhance the catalytic activity in terms of n-decane conversion and H₂ selectivity mainly due to the improved dispersion of NiO particles (precursor of Ni particles). As for anti-coking performance, reducibility of CeO₂ in composite oxide support CZA is promoted by CaO resulting in providing more lattice oxygen, which favors suppressing coke formation. Moreover, the addition of CaO reduces the acidity of 10%Ni/CZA, especially the medium and strong acidity. But far more importantly, a better dispersion of NiO particles obtained by proper amounts of CaO addition is dominant for the lower carbon formation, as well as the higher catalytic activity. For the spent catalysts, amorphous carbon is the main type of coke over 10%Ni–3%CaO/CZA, while abundant filamentous carbon is found over the others.     

Hydrogen production from oxidative steam reforming of ethanol over Ir catalysts supported on Ce–La solid solution

The Ce_1?xLa_xO_2?δ solid solution (CL) supported Ir (nIr/CL, n = 2, 5 and 10 wt.%) catalysts are studied for H₂ production from ethanol oxidative steam reforming (OSR). The Ir dispersion, surface area, oxygen vacancy density and carbon deposition resistance of nIr/CL catalysts are greatly enhanced compared with Ir/CeO₂. Among the tested catalysts, 5%Ir/CL shows the best catalytic performance, exhibiting >99.9% ethanol conversion at 400 °C with H₂ yield rate of 323 μmol·g_cata^?1·s^?1 and no obvious carbon deposition after used. The 5%Ir/CL catalyst contains the highest amount of reducible interface Ce⁴⁺, leading to a strong interaction with surface Ir species at the metal-support interface during the OSR reaction. The strong interaction induces Ir to be well dispersed on the CL support, and is associated with more redox-active sites (interface Ce⁴⁺/Ce³⁺), to guarantee high activity.     

Hydrogen production from oxidative steam reforming of ethanol over rhodium catalysts supported on Ce–La solid solution

The catalytic behaviors of Rh catalysts supported on Ce–La solid solution in H₂ production from the oxidative steam reforming (OSR) of ethanol were studied for the first time. 1%Rh/Ce_0.7La_0.3O_y exhibits 100% ethanol conversion at 573 K with H₂ yield rate 214 μmol g-cat⁻¹ s⁻¹, which is 150 K lower than that required for comparable performance with 1%Rh/CeO₂. La doping also enhanced the stability by accelerating CH₃COCH₃ conversion and gave low CO selectivity due to the high water gas shift activity. X-ray diffraction and Raman spectroscopy characterizations indicate the formation of Ce–La solid solutions and oxygen vacancies. H₂ temperature-programmed reduction and thermo-gravimetric measurement results confirmed that the redox properties of Rh/CeO₂ were greatly enhanced by La doping, which accelerated ethanol conversion, promoted H₂ yield, and maintained good long–term activity for the OSR reaction.     

Hydrogen production through methanol steam reforming: Effect of synthesis parameters on Ni–Cu/CaO–SiO2 catalysts activity

The objectives of this study were to prepare Ni–Cu/CaO–SiO₂ catalysts by a modified polyol process with different preparation conditions and evaluate the feasibility of hydrogen production from methanol steam reforming. CaO–SiO₂ materials possess high specific surface areas and CO₂ absorption capacities which were synthesized through the sol–gel method to serve as supports. The experimental results of the methanol steam reforming indicated that the highest catalytic activity was achieved when the Ni–Cu/CaO–SiO₂ catalyst was prepared under Ar atmosphere at a reduction temperature of 160 °C (160-Ar). The 160-Ar catalyst synthesized by this method has a large pore volume and a high mesoporosity. These physical properties contribute to the effective dispersion of metal particles in the 160-Ar catalyst. Increasing the MeOH/H₂O ratio was found to promote the water–gas shift reaction and direct methanol decomposition to produce more H₂.