Steam reforming of ethanol over Ni-based catalysts: Effect of feed composition on catalyst stability

In this work the effects of steam-to-carbon ratio (S/C), and addition of H₂ or O₂ to the feed on the product yields and carbon deposition in the steam reforming (SR) of ethanol over Ni/MgAl₂O₄, Ni/Ce_0.6Zr_0.4O₂, and Ni/CeO₂ at 600 °C have been investigated. Increasing the S/C-ratio from 1.6 to 8.3 over Ni/MgAl₂O₄ increased conversion of ethanol as well as the yield of H₂, while the carbon deposition and yield of hydrocarbons decreased. Oxygen addition at S/C-ratio of 6 over Ni/MgAl₂O₄, Ni/Ce_0.6Zr_0.4O₂, and Ni/CeO₂ increased conversion, decreased the yield of hydrocarbons, and led to a decrease in the carbon deposition. Carbon deposition was almost eliminated over Ni/MgAl₂O₄ and Ni/Ce_0.6Zr_0.4O₂ at an O/C-ratio of roughly 0.8 or higher. The penalty of adding O₂ was a decrease in the yield of H₂ from 70% at O/C = 0 to 50% at O/C = 0.8–1.     

Support influence on Ni-Cu catalysts behavior under ethanol oxidative reforming reaction

The ethanol oxidative reforming reaction was performed with Ni-Cu catalysts on different supports. The results indicated that Ni-Cu/Nb₂O₅ and Ni-Cu/ZnO were the most appropriate catalysts for the reaction regarding activity, stability, and selectivity for hydrogen production. Ni-Cu/Nb₂O₅ catalysts have strong acidity (at 600 °C), while ZnO has very low acidity. Ni-Cu/Ce_0.6Zr_0.4O₂ catalysts, which only have weak acidity (at 250 °C), presented poor stability and hydrogen selectivity. This shows that acidity has no influence on hydrogen production.     

Nickel zirconia cerate cermet for catalytic partial oxidation of ethanol in a solid oxide fuel cell system

Ni + Ce_xZr_1−xO₂ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) cermets were synthesized and their catalytic performance for partial oxidation of ethanol (POE) reaction was studied. The structure, reducibility properties and carbon deposition behavior of the various catalysts were investigated. Among the various catalysts, Ni + Ce_0.8Zr_0.2O₂ displayed the best catalytic activity in terms of H₂ selectivity and also the highest coking resistance. The fuel cell with Ni + Ce_0.8Zr_0.2O₂ catalyst layer delivered a peak power density of 692 mW cm⁻² at 700 °C when operating on ethanol–O₂ gas mixtures, comparable to that applying hydrogen fuel. The fuel cell also showed an improved operation stability on ethanol–O₂ fuel for 150 h at 700 °C. Ni + Ce_0.8Zr_0.2O₂ is promising as an active and coke-tolerant catalyst layer for solid oxide fuel cells operating on ethanol-O₂ fuel, which makes it highly attractive by applying biofuel in an SOFC system for efficiency electric power generation.     

Ethanol dry reforming over Ni supported on modified ceria-zirconia catalysts– the effect of Ti and Nb dopants

In this work complex metal-oxide catalysts with the general formula 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ were synthesized by the solvothermal method using supercritical alcohols followed by nickel deposition. The catalysts were characterized and studied in ethanol dry reforming reaction (EDR) in the temperature range 600–750 °C. XRD and TEM showed that the synthesis method provides incorporation of doping cations into the ceria-zirconia fluorite structure, leading to mixed oxides formation. The effect of doping cations on structural and surface properties of 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ and activity in the EDR reaction was investigated. Oxygen deficiency δ increases with the introduction of titanium and niobium cations, which contributes to the bifunctional reforming mechanism implementation with rapid oxidation of coke precursors and activation of СО₂ at surface oxygen vacancies. TPO-O₂ analysis after reaction showed no carbon formation above 700 °C, and a few carbon deposits (not exceeding 4%) even after significant catalyst deactivation at 600 °C.     

Deoxygenation of oleic acid over Ce(1–x)Zr(x)O2 catalysts in hydrogen environment

Ce_(1–x)Zr_(x)O₂ catalysts were prepared by co-precipitation method for deoxygenation (DO) of oleic acid. The CeO₂/ZrO₂ ratio was systematically varied to optimize Ce_(1–x)Zr_(x)O₂ catalysts. Ce_0.6Zr_0.4O₂ exhibited the highest oleic acid conversion as well as high selectivity to C₉ ∼ C₁₇ compounds (diesel fuel range) at the reaction temperature of 300 °C. The high activity/selectivity of Ce_0.6Zr_0.4O₂ catalyst was correlated to its reducibility, oxygen storage capacity and crystallite size.     

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

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

Bimetallic catalysts performance during ethanol steam reforming: Influence of support materials

Ni–Cu catalysts supported on different materials were tested in ethanol steam reforming reaction for hydrogen production. These catalysts were evaluated at reaction temperature of 400 °C under atmospheric pressure. The reagents, with a water/ethanol molar ratio equal to 10, were fed at 70 dm³/(h g_cat) (after vaporization). Analysis of the ethanol conversion, as well as evaluation and quantification of the reaction products, indicated the catalyst 10% Ni–1% Cu/Ce_0.6Zr_0.4O₂ as the most appropriate for the ethanol steam reforming under investigated reaction conditions, among the studied catalysts. During 8 h of reaction this catalyst presented an average ethanol conversion of 43%, producing a high amount of H₂ by steam reforming and by ethanol decomposition and dehydrogenation parallel reactions. Steam reforming, among the observed reactions, was quantified by the presence of carbon dioxide. About 60% of the hydrogen was produced from ethanol steam reforming and 40% from parallel reactions.     

High-surface-area Ce0.8Zr0.2O2 solid solutions supported Ni catalysts for ammonia decomposition to hydrogen

Three kinds of Ce_0.8Zr_0.2O₂ solid solutions synthesized via surfactant-assisted route, co-precipitation, and sol–gel method were used as supports of Ni-based catalysts by impregnation. Their catalytic activities in ammonia decomposition to hydrogen were tested, and the structural effect of support and the influence of nickel content on catalytic activity were evaluated. Mesoporous/high-surface-area Ce_0.8Zr_0.2O₂ support synthesized by surfactant-assisted method exhibited better promoting effect than other supports when the same content of Ni was loaded. The interactions between Ni species and Ce_0.8Zr_0.2O₂ supports were found to greatly affect the chemical properties of catalysts, including redox, H₂ adsorption, and catalysis. The promoting effects of Ce in catalysts, plentiful vacancies in the solid solutions due to the doping of Zr⁴⁺, and high surface areas of the supports were discussed on the ammonia decomposition activities of the resultant catalysts, as well as the influence of hydrogen spillover. The ammonia conversion of 95.7% with the H₂ producing rate of 89.3 mL/min·g_cat was achieved at 550 °C over the Ni catalysts supported on the mesoporous/high-surface-area Ce_0.8Zr_0.2O₂.     

H2 and CO production over a stable Ni–MgO–Ce0.8Zr0.2O2 catalyst from CO2 reforming of CH4

Ni–Ce_0.8Zr_0.2O₂ and Ni–MgO–Ce_0.8Zr_0.2O₂ catalysts were investigated for H₂ production from CO₂ reforming of CH₄ reaction at a very high gas hourly space velocity of 480,000 h⁻¹. Ni–MgO–Ce_0.8Zr_0.2O₂ exhibited higher catalytic activity and stability (CH₄ conversion >95% at 800 °C for 200 h). The outstanding catalytic performance is mainly due to the basic nature of MgO and an intimate interaction between Ni and MgO.     

Water–gas shift reaction over Pt and Pt–CeOx supported on CexZr1−xO2

The water–gas shift (WGS) reaction was examined over Pt and Pt–CeO_x catalysts supported on Ce_xZr_1−xO₂ (Ce_0.05Zr_0.95O₂, Ce_0.2Zr_0.8O₂, Ce_0.4Zr_0.6O₂, Ce_0.6Zr_0.4O₂, Ce_0.7Zr_0.3O₂ and Ce_0.8Zr_0.2O₂) under severe reaction conditions, viz. 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. The catalysts were characterized with several techniques, including X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR) with H₂, temperature-programmed oxidation (TPO), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and bright-field transmission electron microscopy (TEM). Among the supported Pt catalysts tested, Pt/Ce_0.4Zr_0.6O₂ showed the highest WGS activity in all temperature ranges. An improvement in the WGS activity was observed when CeO_x was added with Pt on Ce_xZr_1−xO₂ supports (x = 0.05 and 0.2) due to intimate contact between Pt and CeO_x species. Based on CO chemisorptions and TPR profiles, it has been found that the interaction between Pt species and surface ceria-zirconia species is beneficial to the WGS reaction. A gradual decrease in the catalytic activity with time-on-stream was found over Pt and Pt–CeO_x catalysts supported on Ce_xZr_1−xO₂, which can be explained by a decrease in the Pt dispersion. The participation of surface carbonate species on deactivation appeared to be minor because no improvement in the catalytic activity was found after the regeneration step where the aged catalyst was calcined in 10 mol% O₂ in He at 773 K and subsequently reduced in H₂ at 673 K.     

Hydrogen production over Ni/ceria-supported catalysts by partial oxidation of methane

The catalytic performance of Ni dispersed on ceria-doped supports, (Ce_0.88La_0.12) O_2-x, (Ce_0.91Gd_0.09) O_2-x, (Ce_0.71Gd_0.29) O_2-x, (Ce_0.56Zr_0.44) O_2-x and pure ceria, was tested for the catalytic partial oxidation of Methane (CPOX). The catalysts were characterized by Brunauer Emmett Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Ni/ (Ce_0.56Zr_0.44) O_2-x showed higher Hydrogen production than the Ni/Gadolinium-doped catalysts, which may be due to its higher reducibility and surface area. By enhancing the support reducibility in Ni/doped-ceria catalysts, their catalytic activity is promoted because the availability of surface lattice oxygen is increased, which can participate in the formation of CO and H₂. It was also found that Ni/(Ce_0.56Zr_0.44) O_2-x showed higher catalytic performance after redox pretreatments. Similarly, a higher amount of H₂ or O₂ was consumed during hydrogenation and oxidation pretreatments, respectively. This may be correlated to re-dispersion of metallic particles and changes on the metal-support interface. In addition, it was observed that the ionic conductivity of Ni/(Ce_0.56Zr_0.44) O_2-x had an effect on the amount of carbon formed during the CPOX reaction at oxygen concentrations lower than the stoichiometric required, O/C ratios lower than 0.6. Its high oxygen mobility may have accelerated the surface oxidation reactions of carbon by reactive oxygen species, thus, inhibiting carbon growth on the catalyst surface.     

Development of a Ni-Ce0.8Zr0.2O2 catalyst for solid oxide fuel cells operating on ethanol through internal reforming

Inexpensive 20 wt.% Ni-Ce_0.8Zr_0.2O₂ catalysts are synthesized by a glycine nitrate process (GNP) and an impregnation process (IMP). The catalytic activity for ethanol steam reforming (ESR) at 400-650 °C, catalytic stability and carbon deposition properties are investigated. Ni-Ce_0.8Zr_0.2O₂ (GNP) shows a higher catalytic performance than Ni-Ce_0.8Zr_0.2O₂ (IMP), especially at lower temperatures. It also presents a better coking resistance and a lower graphitization degree of the deposited carbon. The superior catalytic activity and coke resistance of Ni-Ce_0.8Zr_0.2O₂ (GNP) is attributed to the small particle size of the active metallic nickel phase and the strong interaction between the nickel and the Ce_0.8Zr_0.2O₂ support, as evidenced by the XRD and H₂-TPR. The Ni-Ce_0.8Zr_0.2O₂ (GNP) is further applied as an anode functional layer in solid oxide fuel cells operating on ethanol steam. The cell yields a peak power density of 536 mW cm⁻² at 700 °C when operating on EtOH-H₂O gas mixtures, which is only slightly lower than that of hydrogen fuel, whereas the cell without the functional layer failed for short-term operations. Ni-Ce_0.8Zr_0.2O₂ (GNP) is promising as an active and highly coking-resistant catalyst layer for solid-oxide fuel cells operating on ethanol steam fuel.     

Synthesis of flowerlike ceria–zirconia solid solution for promoting dry reforming of methane

Using a newly developed two-step hydrothermal process, flowerlike Ce_0.5Zr_0.5O₂ with an oxygen storage capacity (OSC) of 536 μmol O₂ g^?1, almost twice as high as that of pure flowerlike CeO₂ (284 μmol O₂ g^?1), can be synthesized. The synthesized ceria-based oxide supports loaded with Ni are dispersed in a ceramic fiber network to form paper-structured catalysts (PSCs). Among the prepared PSCs, the PSC with the flowerlike Ce_0.5Zr_0.5O₂ exhibits the highest catalytic performance for dry reforming of methane (DRM) at 750 °C with the initial methane conversion of 88.4%, degradation rate of 0.1% h^?1 and amount of deposited carbon of 0.04 g per gram catalyst, whereas for the Ce_0.5Zr_0.5O₂ synthesized by the one-step hydrothermal process, the values are 83.7%, 0.62% h^?1 and 0.07 g per gram catalyst, respectively. This is attributed to the Ni anti-sintering on the petals of the flowerlike structure and the coking tolerance resulting from the high OSC.     

Rh- and Rh–Ni–MgO-based structured catalysts for on-board syngas production via gasoline processing

Rh/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl and Rh/Ni–MgO/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl FeCrAlloy wire mesh supported catalysts were prepared via multistep procedure. They were characterized by XRD, SEM and TEM techniques. A comparative study of autothermal reforming (ATR) of isooctane and simulated gasoline (blends of isooctane, ortho-xylene and naphthalene) over Rh/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl and Rh/Ni–MgO/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl was performed. Both catalysts showed excellent performance in ATR of isooctane at molar ratios of O₂:C = 0.51 and H₂O:C = 2.59, T = 750°С and GHSV = 10000 h⁻¹. In the ATR of isooctane – o-xylene blend in presence of Rh–Ni-containing catalyst carbon formation was observed. Rh-containing catalyst demonstrated rather good activity and stability even in the case of isooctane – o-xylene – naphthalene blend.     

Effect of Co,Fe and Rh addition on coke deposition over Ni/Ce0.5Zr0.5O2 catalysts for steam reforming of ethanol

Ni-based monometallic and bimetallic catalysts (Ni, NiRh, NiCo and NiFe) supported on Ce_0.5Zr_0.5O₂ support were evaluated on the steam reforming of ethanol (SRE) performance. The supports of Ce_0.5Zr_0.5O₂ composite oxide was prepared by co-precipitation method with Na₂CO₃ precipitant and assigned as CeZr(N). The monometallic catalyst was prepared by incipient wetness impregnation method and assigned as Ni/CeZr(N). The bimetallic catalysts were prepared by co-impregnation method to disperse the metals on the CeZr(N) support and assigned as NiM/CeZr(N). All samples were characterized by using XRD, TPR, BET, EA and TEM techniques at various stages of the catalyst. The results indicated that the facile reduction and smaller particle size of Ni/CeZr(N) (T₉₉ = 300 °C) and NiRh/CeZr(N) (T₉₉ = 250 °C) catalysts were preferential than the NiFe/CeZr(N) (T₉₉ = 325 °C) and NiCo/CeZr(N) (T₉₉ = 375 °C) catalysts. Also, both the Ni/CeZr(N) and NiRh/CeZr(N) catalysts displayed better durability among these catalysts over 100 h and 400 h, respectively. Since the serious coke formation for the NiCo/CeZr(N) catalyst, the activity only maintained around 6 h, the durability on the NiFe/CeZr(N) catalyst approached 50 h.     

Ethanol steam reforming over Ni-based spinel oxide

The Ni-based spinel-type oxides, NiB₂O₄ (B = Al, Fe, Mn), were investigated for their catalysis of the ethanol steam reforming reaction. Ethanol conversion over spinel-type oxides without reduction treatment was comparable to that over γ-alumina-supported Ni catalyst with reduction. The spinel oxide of NiAl₂O₄ showed extremely stable performance for 48 h, while the activity of NiFe₂O₄ and NiMn₂O₄ catalysts was reduced by carbon deposition. Catalyst stability for reforming reaction was closely related to the stability of the nickel metal dispersed on the catalyst surface and the spinel structure. Differences in crystallinity and surface area among the catalysts were not crucial factors for determining ethanol conversion for NiAl₂O₄ calcined between 800 °C and 1100 °C. The catalyst calcined at 900 °C exhibited the highest activity for the reforming reaction.     

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

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

High performance Ni exsolved and Cu added La0.8Ce0.2Mn0.6Ni0.4O3-based perovskites for ethanol steam reforming

La_0.8Ce_0.2Mn_0.6Ni_0.4O₃ with (LCMN@CuO) and without (LCMN) CuO addition are prepared by solution methods, followed by reduction in 5% H₂–N₂ stream at 650 °C to form Ni exsolved and CuO reduced catalysts, LCMN@Ni and LCMN@Ni/Cu, for ethanol (EtOH) steam reforming (ESR). The catalysts are characterized by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy etc., and are evaluated for ESR with a steam/carbon ratio of 3 and a weight hourly space velocity (WHSV) of 4 h⁻¹ at temperatures between 500 and 700 °C. Ni exsolution and CuO reduction are confirmed on the substrates in LCMN@Ni and LCMN@Ni/Cu. Both the catalysts demonstrate a complete conversion of EtOH, forming mainly H₂, CO₂, CO and CH₄. And increasing temperature to 700 °C increases the yields of H₂ and CO to the levels about 90% and 40%, respectively, at the cost of CH₄; and such performance remains unchanged for 30 h. These results indicate that both LCMN@Ni and LCMN@Ni/Cu are promising catalysts for ESR, the main difference between them is that the latter is more chemically stable and more resistant to carbon deposition under ESR conditions.     

Enhanced low-temperature activity for CO2 methanation over Ru doped the Ni/CexZr(1−x)O2 catalysts prepared by one-pot hydrolysis method

A series of 30 wt%Ni/Ce_xZr_1?xO₂ catalysts doped with Ru ranging from 0 to 5 wt% were prepared by one-pot hydrolysis of metal nitrates with ammonium carbonate for carbon dioxide methanation at low temperature range of 150–310 °C. The influences of Ce/Zr molar ratios and Ru contents on the physicochemical properties and catalytic activities of prepared catalysts were systematically investigated. The addition Ru can improve the Ni dispersion and the basicity of the yRu-30Ni/Ce_0.9Zr_0.1O₂ catalysts surface. As a result, their low-temperature catalytic activity had been enhanced over these doped Ru promoted catalysts. The optimal catalyst was 3Ru-30Ni/Ce_0.9Zr_0.1O₂ on which the CO₂ conversion reached theoretical equilibrium value as high as 98.2% with the methane selectivity of 100% at a reaction temperature as low as 230 °C. Moreover, there was almost no deactivation for the 3Ru-30Ni/Ce_0.9Zr_0.1O₂ catalyst during 300 h at 230 °C indicating excellent catalytic stability and coke resistence ability. It was also found that the low-temperature activity of 3Ru-30Ni/Ce_0.9Z_r0.1O₂ catalyst prepared by one-pot hydrolysis method was much higher than the one prepared by impregnation method.     

The effect of Cr deposition and poisoning on BaZr0.1Ce0.7Y0.2O3−δ proton conducting electrolyte

With the development of chromium tolerant electrode materials, the evaluation of the chromium deposition and poisoning on electrolyte is critical significance for the commercial and widespread application of solid oxide fuel cell stacks (SOFCs). The Cr deposition and poisoning on BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) proton conducting electrolyte are initially studied, in order to understand and develop the compatibility for proton conducting SOFC (H-SOFCs). The XRD results imply that Cr₂O₃ is not chemically compatible with BZCY and BaCrO₄ is formed at high temperature above 600 °C. To simulate the Cr volatilization from interconnect and poisoning on BZCY surface, the BZCY bar sample is heat-treated in the presence of Cr₂O₃ at 600 °C, 700 °C, and 800 °C for 50 h. It is clear that Cr deposition occurs even at 600 °C by SEM examination. The XPS results indicate the chemical deposition of BaCrO₄ and physical deposition of Cr₂O₃ on BZCY surface at 600 °C but only chemical deposition at 700 °C and 800 °C. The content of Cr deposition increases with the increase of poisoning temperature. Moreover, the proton conductivity of BZCY after Cr deposition reduces after Cr deposition, indicating the Cr poisoning effect of the electrochemical performance of BZCY electrolyte.