Steam reforming of ethanol over Ni/ZrO2 catalysts: Effect of support on product distribution

Ni catalysts supported on ZrO₂ with different crystalline phases and particle sizes were prepared to study the role of zirconia support in ethanol steam reforming for hydrogen production. Catalytic behavior of the catalysts was examined at relatively low temperature of 673 K with different contact times. The decrease in particle size of zirconia results in enhanced metal-support interaction, which accounts for the high activity of the catalyst. Regarding the impact of crystalline phase of zirconia on catalytic performance, tetragonal zirconia yields a higher activity in water gas shift reaction but a lower activity in methane steam reforming than that of monoclinic zirconia. Nevertheless, zirconia plays a secondary role in product distribution, especially at long contact times. Catalytic activity tests performed at elevated temperature demonstrated a high activity and stability of Ni/ZrO₂ catalyst for hydrogen production from steam reforming of ethanol.     

Steam reforming of ethanol over nickel-tungsten catalyst

Ni-W/Al₂O₃ catalysts were synthesized, characterized and tested for the steam reforming of ethanol from 300 to 600 °C. Addition of Ni and W on the alumina, decreased the surface area and increased the pore volume of the mesoporous materials synthesized. The reaction products obtained were: H₂, CO₂, C₂H₄, CH₄, CO₂, CO and CH₃CHO. A promoting effect of Ni-W was observed in the conversion of ethanol to H₂ from 15 to 30 wt.% Ni and 1 wt.% W. The selectivity to H₂ on the alumina with Ni-W, was between 66.53 and 68.53% at 550 °C, appearing some undesirable products, with low ratio of CO/CO₂. Reaction was studied on a fixed bed reactor at atmospheric pressure with an ethanol/water molar ratio of 1:4, from 300 to 600 °C. The catalysts were characterized by the thermal gravimetric analysis (TGA)-Differential thermal analysis (DTA), N₂ physisorption (BET and BJH methods), X-ray diffraction (XRD) and scanning electron microscopy (SEM), these techniques were used for characterization, before and after of the steam reforming.     

Catalytic performance of steam reforming of ethanol at low temperature over LaNiO3 perovskite

A LaNiO₃ perovskite catalyst was prepared using the coprecipitation–oxidation hydrothermal method, followed by calcination at 600 °C for 2 h. The as-prepared sample was composed of La(OH)₃ in nanorod structures and was covered with poorly crystalline Ni(OH)₂. The mixed metal hydroxides were converted into cubic LaNiO₃ perovskite after calcination at 600 °C. A catalytic steam reforming of ethanol (SRE) reaction for hydrogen production was performed in a fixed-bed reactor. The catalyst was reduced in situ in hydrogen at 400 °C prior to the reaction. The ethanol conversion reached 100% at 300 °C with 70% hydrogen selectivity. The highly catalytic activity of the reduced catalyst was due to the well-dispersion of Ni particles on the surface of active catalyst was formed in the in situ reduced catalyst. After a 80 h time-on-stream test at 350 °C, the used catalyst presented a La₂O₂CO₃ component that was formed owing to the reaction of the CO₂ product with La₂O₃. La₂O₂CO₃ acted as a carbon reservoir to eliminate the deposited carbon and further stabilized the Ni particles on the La₂O₃ surface, which resulted in the highly catalytic activity during the entire reaction period. The deposited carbon after the SRE reaction was further examined by TGA, TPR, elemental analysis, and TEM.     

Ceria-promoted Ni@Al2O3 core-shell catalyst for steam reforming of acetic acid with enhanced activity and coke resistance

A series of Ni@Al₂O₃ core-shell catalysts with ceria added to the surface of Ni nanoparticles or inside the alumina shell were prepared, and the effect of ceria addition on the performance of the catalyst in the steam reforming of acetic acid was investigated. The prepared catalysts were characterized by BET, XRD, HRTEM, H₂-TPR and DTG. The addition of ceria to the surface of nickel nanoparticles greatly enhanced the activity of catalyst owing to the presence of the mobile oxygen, which migrated from the ceria lattice. Among the prepared catalysts, the Ni@Al10Ce catalyst showed the highest activity with a conversion of acetic acid up to 97.0% even at a low temperature (650 °C). The molar ratio of CO₂/CO was also improved due to the oxidation of CO by the mobile oxygen into CO₂. The coke formation on the core-shell catalysts was significantly inhibited by the addition of ceria to the surface of nickel nanoparticles due to the oxidation of carbon species by the mobile oxygen in the ceria lattice. However, the Ni@Al10Ce-a catalyst with ceria added to the alumina shell showed a low activity and the formation of a large amount of coke. It is suggested that only the ceria in close to the Ni surface has the promoting effect on the catalytic performance of the Ni@Al₂O₃ catalyst in the steam reforming of acetic acid.     

Pathways of ethanol steam reforming over ceria-supported catalysts

Ceria-supported Pt, Ir and Co catalysts are prepared herein by the deposition–precipitation method and investigated for their suitability in the steam reforming of ethanol (SRE) at a temperature range of 250–500 °C. SRE is tested in a fixed-bed reactor under an H₂O/EtOH molar ratio of 13 and 20,000 h⁻¹ GHSV. Possible pathways are proposed according to the assigned temperature window to understand the different catalysts attributed to specific reaction pathways. The Pt/CeO₂ catalyst shows the best carbon–carbon bond-breaking ability and the lowest complete ethanol conversion temperature of 300 °C. Acetone steam reforming over the Ir/CeO₂ catalyst at 400 °C promotes a hydrogen yield of up to 5.3. Lower reaction temperatures for the water–gas shift and acetone steam reforming are in evidence for the Co/CeO₂ catalyst, whereas the carbon deposition causes its deactivation at temperature over 500 °C.     

Natural gas steam reforming for hydrogen production over metal monolith catalyst with efficient heat-transfer

Heat transfer performance of the natural gas (NG) steam reforming in a reactor bed with metal monolith catalyst has been evaluated in comparison with that in the conventional packed bed with pellet catalysts. 2%Ru/Al₂O₃ catalyst with high intrinsic activity has been wash-coated on metal monolith substrates or used as it was for the packed bed application. The prepared metal monolith catalyst has been applied for NG steam reforming to increase heat-transfer efficiency. Under the same degree of temperature gradient from the furnace wall to the catalyst bed, the heat flux obtained in the monolithic bed reactor was about twice higher than that in the packed bed reactor. Maximum heat transfer coefficient achieved in this study for the former was 0.65 kW/m² K, while that for the latter was 0.3 kW/m² K. This is mainly due to enhanced heat-transfer via metal monolith catalyst.     

Ni catalyst wash-coated on metal monolith with enhanced heat-transfer capability for steam reforming

A commercial Ni-based catalyst is wash-coated on a monolith made of 50 μm-thick fecralloy plates. Compared with the same volume of coarsely powdered Ni catalysts, the monolith wash-coated Ni catalysts give higher methane conversion in the steam reforming reaction, especially at gas hourly space velocities (GHSV) higher than 28,000 h⁻¹, and with no pressure drop. A higher conversion of the monolith catalyst is obtained, even though it contains a lower amount of active catalyst (3 g versus 17 g for a powdered catalyst), which indicates that the heat-transfer capability of the wash-coated Ni catalyst is significantly enhanced by the use of a metal monolith. The efficacy of the monolith catalyst is tested using a shell-and-tube type heat-exchanger reactor with 912 cm³ of the monolith catalyst charged on to the tube side and hot combusted gas supplied to the shell side in a counter-current direction to the reactant flow. A methane conversion greater than 94% is obtained at a GHSV of 7300 h⁻¹ and an average temperature of 640 °C. Nickel catalysts should first be reduced to become active for steam reforming. Doping a small amount (0.12 wt.%) of noble metal (Ru or Pt) in the commercial Ni catalyst renders the wash-coated catalyst as active as a pre-reduced Ni catalyst. Thus, noble metal-doped Ni appears useful for steam reforming without any pre-reduction procedure.     

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.     

Steam reforming of methane over Ni catalyst in micro-channel reactor

A comprehensive study on the catalytic performance of Ni catalyst to implement millisecond steam reforming of methane (SRM) reaction in micro-channel reactors was conducted in this work. A new method to manufacture the metal-ceramics complex substrate as catalyst support was presented, that is, a layer of nano-particles, α-Al₂O₃, was thermally sprayed on a metallic substrate, usually FeCrAlloy. Ni or Rh catalyst was then impregnated on the substrate, forming firm and active catalyst coatings. The fall-off rate of the catalyst can be neglected after the plates experienced the high-temperature SRM reaction, showing the reliability in long-term use and the excellent catalytic performance for SRM reaction in micro-channel reactors. In comparison with the expensive Rh catalyst, Ni also showed wonderful performance to catalyze the SRM reaction in micro-reactors within milliseconds. Using the appropriate reactor design, CH₄ conversion reached above 90% when the residence time was as short as 32 ms for catalyst loading of 6.8 g/m². When the residence time was longer than 100 ms, CH₄ conversion was above 98%. Besides, catalyst deactivation was not detected for 500 h on stream with S/C ratio of 3.0, and for 12 h with S/C of 1.0 as well. Extensive characterizations on these Ni catalyst plates using XRD, SEM, TEM and XPS demonstrated that Ni catalysts prepared in this work did not show any sign of deactivation after being used in the micro-channel system under high-temperature operation.     

Steam reforming of ethanol over bimetallic RhPt/La2O3: Long-term stability under favorable reaction conditions

Recently, the steam reforming of biofuels has been presented as a potential hydrogen source for fuel cells. Because this scenario represents an interesting opportunity for Colombia (South America), which produces large amounts of bioethanol, the steam reforming of ethanol was studied over a bimetallic RhPt/La₂O₃ catalyst under bulk mass transfer conditions. The effect of temperature and the initial concentrations of ethanol and water were evaluated at space velocities above 55,000 h⁻¹ to determine the conditions that maximize the H₂/CO ratio and reduce CH₄ production while maintaining 100% conversion of ethanol. These requirements were accomplished when 21 mol% H₂O and 3 mol% C₂H₅OH (steam/ethanol molar ratio = 7) were reacted at 600 °C. The catalyst stability was assessed under these reaction conditions during 120 h on stream, obtaining ethanol conversions above 99% during the entire test. The effect of both H₂ and air flows as catalyst regeneration treatments were evaluated after 44 and 67 h on stream, respectively. The results showed that H₂ treatment accelerated catalyst deactivation, and air regeneration increased both the catalyst stability and the H₂ selectivity while decreasing CH₄ generation. Fresh and spent catalyst samples were characterized by TEM/EDX, XPS, TPR, and TGA. Although the Rh and Pt in the fresh catalyst were completely reduced, the spent samples showed a partial oxidation of Rh and small amounts of carbonaceous residue. A possible Rh–Pt–Rh₂O₃ structure was proposed as the active site on the catalyst, which was regenerated by air treatment.     

Miniature NH3 cracker based on microfibrous entrapped Ni-CeO2/Al2O3 catalyst monolith for portable fuel cell power supplies

A miniature ammonia cracker, with an overall weight of ≈195 g and volume of ≈50 cm³, has been developed for portable fuel cell power supply. The cracker is composed of a SS-316L tube body, a heating rod and monolithic microfibrous CeO₂-promoted Ni/Al₂O₃ catalysts incorporated within the annular housings between the heating rod and the inner wall of the tubular body. The catalyst monolith is obtained by placing CeO₂ and Ni onto the microfibrous carrier consisting of 3.5 vol% 8 μm diameter nickel fibers and 38 vol% 100–200 μm Al₂O₃ particulates through stepwise incipient wetness impregnation method using cerium and nickel nitrate precursors. This cracker shows pleasing operability for high efficiency H₂ production via ammonia cracking with low pressure drop. Roughly 158 W equivalents of H₂ can be produced with ammonia conversion of >99.9% at 600 °C and 1100 standard cubic centimeter per minute (sccm) ammonia feed gas rate within this cracker through the entire 300 h test. Power density and energy density are estimated to be ≈3160 W/L and ≈2150 Wh/kg, respectively.     

The effect of Ni:Pt ratio on oxidative steam reforming performance of Pt–Ni/Al2O3 catalyst

Oxidative steam reforming of propane was tested over four Pt–Ni/δ-Al₂O₃ bimetallic catalysts aiming to investigate the effect of metal loadings and Ni:Pt loading ratio on catalyst performance. A trimetallic Pt–Ni–Au/δ-Al₂O₃ catalyst was additionally studied aiming to understand the effect of Au presence. Reaction temperature, carbon to oxygen ratio, and residence time were taken as the reaction parameters. The effect of C/O₂ ratio on the hydrogen production and H₂/CO selectivity was found dependent on the Pt and Ni loadings. The results underlined the importance of C/O₂ ratio as an optimization parameter for product distribution. The highest hydrogen production and H₂/CO ratio levels were obtained for the highest C/O₂ ratio tested. An optimum Ni:Pt weight ratio was found around 50 due to suppressed methanation and enhanced hydrogen production activities of these catalysts. The presence of gold in the trimetallic catalyst caused poor activity and selectivity in comparison to bimetallic catalysts.     

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.     

Hydrogen production by auto-thermal reforming of ethanol over Ni catalysts supported on ZrO2: Effect of preparation method of ZrO2 support

Zirconia supports were prepared by a sol–gel method (S-ZrO₂) and by a templating sol–gel method (M-ZrO₂). Nickel catalysts supported on zirconia were then prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. For comparison, a commercial zirconia (C-ZrO₂) was also employed as a support for nickel catalyst. The effect of preparation method of zirconia on the catalytic property and catalytic performance of supported nickel catalysts (Ni/C-ZrO₂, Ni/S-ZrO₂, and Ni/M-ZrO₂) was investigated. The crystalline and physical property of zirconia supports and the catalytic performance of supported nickel catalysts were strongly affected by the preparation method of zirconia. BET surface area and pore volume were decreased in the order of M-ZrO₂ > S-ZrO₂ > C-ZrO₂. Both M-ZrO₂ and S-ZrO₂ supports showed only tetragonal phase of ZrO₂, while C-ZrO₂ support exhibited tetragonal and monoclinic phases of ZrO₂. Crystalline size of nickel species in the Ni/ZrO₂ catalysts decreased with increasing surface area and pore volume of ZrO₂ supports. All the Ni/ZrO₂ catalysts exhibited 100% conversion of ethanol at 500 °C, while product distributions over the Ni/ZrO₂ catalysts were different depending on the preparation method of zirconia. Among the catalysts tested, the Ni/M-ZrO₂ catalyst showed the best catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Well developed mesopore, high surface area, and pure tetragonal phase of ZrO₂ were responsible for fine nickel dispersion and high catalytic performance of Ni/M-ZrO₂. C–C bond cleavage reaction and methane steam reforming reaction were also accelerated over the Ni/M-ZrO₂ catalyst.     

Hydrogen production by steam reforming of ethanol over an Ir/CeO2 catalyst: Reaction mechanism and stability of the catalyst

Steam reforming of ethanol over an Ir/CeO₂ catalyst has been studied with regard to the reaction mechanism and the stability of the catalyst. It was found that ethanol dehydrogenation to acetaldehyde was the primary reaction, and acetaldehyde was then decomposed to methane and CO and/or converted to acetone at low temperatures. Methane was further reformed to H₂ and CO, and acetone was directly converted into H₂ and CO₂. Addition of CO, CO₂, and CH₄ to the water/ethanol mixture proved that steam reforming of methane and the water gas shift were the major reactions at high temperatures. The Ir/CeO₂ catalyst displayed rather stable performance in the steam reforming of ethanol at 650 °C even with a stoichiometric feed composition of water/ethanol, and the effluent gas composition remained constant for 300 h on-stream. The CeO₂ in the catalyst prevented the highly dispersed Ir particles from sintering and facilitated coke gasification through strong Ir–CeO₂ interaction.     

On the dynamics and reversibility of the deactivation of a Rh/CeO2ZrO2 catalyst in raw bio-oil steam reforming

The deactivation mechanism of a commercial Rh/CeO₂ZrO₂ catalyst in raw bio-oil steam reforming has been studied by relating the evolution with time on stream of the bio-oil conversion and products yields and the physicochemical properties of the deactivated catalyst studied by XRD, TPR, SEM, XPS, TPO and TEM. Moreover, the reversibility of the different deactivation causes has been assessed by comparing the behavior and properties of the catalyst fresh and regenerated (by coke combustion with air). The reactions were carried out in an experimental device with two units in series: a thermal treatment unit (at 500 °C, for separation of pyrolytic lignin) and a fluidized bed reactor (at 700 °C, for the reforming reaction). The results evidence that structural changes (support aging involving partial occlusion of Rh species) are irreversible and occur rapidly, being responsible for a first deactivation period, whereas encapsulating coke deposition (with oxygenates as precursors) is reversible and evolves more slowly, thus being the main cause of the second deactivation period. The deactivation selectively affects the reforming of oxygenates, from least to greatest reactivity. Rh sintering is not a significant deactivation cause at the studied temperature.     

Manganese-promoted nickel/alumina catalysts for hydrogen production via auto-thermal reforming of ethanol

The manganese-promoted nickel-based catalysts were prepared via wet-incipient impregnation, and tested in auto-thermal reforming (ATR) of ethanol for hydrogen production. The Ni/Al₂O₃ catalyst, in which Ni existed as NiAl₂O₄, produced a low H₂ yield near 1.85 mol H₂/mol ethanol. The Ni–Mn/Al₂O₃ catalyst showed a better performance in a 30-h test: the conversion of ethanol reached 100%, and a higher H₂ yield remained stable near 3.1–3.2 mol H₂/mol ethanol. This improvement can be attributed to the promotion of Mn: With Mn, the ilmenite-type NiMnO₃ was formed, the reducibility of Ni–Mn/Al₂O₃ was thus improved, and there were more Ni⁰ over the surface of catalysts. Moreover, these Ni⁰ species were stable in the ATR test, as indicated by XRD and XPS.     

Continuous high-purity hydrogen production by sorption enhanced steam reforming of ethanol over modified lithium silicate

Sorption-enhanced steam reforming of ethanol (SE-SRE) with in-situ CO₂ removal is an environmentally friendly and sustainable approach for hydrogen production. Researches on continuous production of high-purity H₂ by SE-SRE over the modified Li₄SiO₄ sorbent were conducted using two parallel reactor in this work. The low cost Li₄SiO₄ derived from rice husk ash (RHA) is a promising high-temperature CO₂ sorbent. However, the poor adsorption kinetics of RHA-Li₄SiO₄ sorbent at low CO₂ concentration is the major challenge. The metallic elements (K, Ca, Al, Mg) were employed to modify the RHA-Li₄SiO₄ for efficient CO₂ capture. The developed sorbents were characterized and tested to study the role of dopants on the crystal, textural, microstructure and CO₂ adsorption kinetics and cyclic stability. Results indicated that K doping effectively inhibited the growth of crystal aggregation and resulted in a fluffy morphology with abundant pores and higher specific surface area, while the addition of Ca, Al and Mg formed a nubby structure with larger particle size. K-doped RHA-Li₄SiO₄ exhibited the best CO₂ uptake properties and the optimal K doping molar content was 0.02 with the maximum capture capacity of 34.16 wt%, which is higher than 27.1 wt% of pure RHA-Li₄SiO₄. Then, the effect of operating conditions on the enhancement behaviors was considered in the SE-SRE system. High-purity H₂ (above 96%) was achieved by coupling K(0.02)/RHA-Li₄SiO₄ sorbent with Ni-based catalyst under the optimum condition (T: 525 °C, liquid hourly space velocity: 0.9 mL/(g·h), sorbent/catalyst: 4 and steam/carbon: 8.0). The adsorption activity of K(0.02)/RHA-Li₄SiO₄ maintained at a high level in ten SE-SRE/regeneration cycles. Finally, a scheme including two parallel fixed-bed reactors was designed and operated periodically for continuous production of high-purity H₂. The reaction switching time was shown to depend strongly on the pre-breakthrough time and operating conditions. As the reaction switching time was 40 min, the products were always only H₂ and CH₄ (no CO and CO₂ appear) and the H₂ purity remained above 90% during 400 min, confirming high purity hydrogen stream can be obtained continuously.     

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.