Steam Reforming Of Propane Research Articles

プロパンの水蒸気改質反応用Ni/γ-Al2O3へのLa2O3添加効果の検討

プロパンの水蒸気改質反応用Ni/γ-Al2O3へのLa2O3添加効果の検討

Steam reforming of liquid hydrocarbons over a nickel–alumina spinel catalyst

Interest in steam reforming of liquid hydrocarbons is growing due to the necessity of developing reliable alternatives for their use in fuel cells. In particular, solid oxide fuel cells, which can operate with mixtures of H 2 and CO, are excellent candidates for being fed with liquid fuels coming from both fossil and renewable sources. Fossil-derived, synthetic diesel is an interesting option. In this work, an Al 2O 3–ZrO 2-supported nickel–alumina spinel was tested in a lab-scale isothermal packed-bed reactor as a catalyst of steam reforming of propane, hexadecane and tetralin as surrogates of constitutive families of all commercially available diesel fuels. The results show that the reaction reaches equilibrium at reaction severities lower than those reported in the literature. When operated at steam excess of 250%, carbon formation is not higher than expected by theoretical thermodynamic equilibrium calculations, and no significant catalyst deactivation is observed over the test durations. Scanning electron microscopy of the fresh and used catalyst surfaces shows no significant quantities of carbon.

A structured catalyst: Noble metal supported on a plate-type zirconia substrate prepared by anodic oxidation for steam reforming of hydrocarbon

A structured catalyst: noble metal supported on a plate-type zirconia substrate was prepared by subjecting a zirconium plate to a process consisting of anodic oxidation in an oxalic acid bath and calcination in the air, followed by rhodium or ruthenium component deposition by the dipping treatment. The catalytic performances of the prepared catalysts were evaluated for steam reforming of n-butane and propane. The substrate surface was significantly corroded by the anodic oxidation and calcination, and a rugged zirconia layer about 100 μm thick was formed. The crystalline state of zirconia was mainly monoclinic and tetragonal. In steam reforming of n-butane, the structured ruthenium catalyst had some activity, while the activity of the rhodium catalyst exceeded that of the commercial catalyst. For the rhodium catalyst, its reforming activity was improved by changing the temperature of dipping bath and the number of dips for adjustment of the rhodium deposition state. The rhodium catalyst prepared by dipping twice at a bath temperature of 25 °C has the largest metal surface area and a higher metal dispersion, which were thought to be the causes for the high performance. In steam reforming of propane, the rhodium catalyst showed a significantly higher activity than the commercial catalyst. The rhodium catalyst was less prone to deterioration of activity due to n-butane and propane reforming.

Simultaneous Coke Reduction with Improved Syngas Production during Propane Steam Reforming using Forced CO2 Cycling

Carbon deposition during hydrocarbon steam reforming is often a major cause of pathological reactor performance and catalyst deactivation. In this paper, we report the effect of forced periodic cycling between propane-steam reforming feed and a carbon gasifying agent (CO2) as a novel reactor strategy to both improve product yield (H2 and CO) and catalyst longevity. Experiments were carried out over Co-Ni/Al2O3 catalyst in a fluidized bed reactor. Cycle period, ?, was varied between 5 to 20 mins at 5 different cycle splits, (0.1 ? s ? 0.9). Both H2 and CO formation rates were higher (up to 5-fold and more than 10-fold, respectively) than that attainable under steady-state operation at all periods investigated. In particular, the time-average H2:CO ratio was lower (< 3.0) than the steady-state equivalent for the pure propane steam reforming (14.0), although it increased monotonically with cycle split. Composition cycling with CO2 also improved catalyst stability and longevity compared to steady-state performance at the cycle periods examined. This strategic reactor operation is therefore a potentially useful key to green process engineering in the overall petrochemical plant design to effect greenhouse gas emission reduction.

Comparison between Ni–Rh/gadolinia doped ceria catalysts in reforming of propane for anode implementations in intermediate solid oxide fuel cells

Steam and autothermal reforming of propane over Ni–Rh/GDC catalysts prepared by coprecipitation and by Pechini method were investigated in the temperature range 873–1073 K. The weight ratio for Ni, Rh and Ce 0.8Gd 0.2O 2 (45:5:50) and the operating temperatures were chosen in order to gain propaedeutical information on fuel reactivity under typical intermediate solid oxide fuel cell (IT-SOFC) operating conditions. The Pechini synthesis allows to obtain catalysts with lower surface area, smaller nickel crystallites and a bimodal distribution of rhodium in comparison to the coprecipitation method. Despite the different methods of synthesis lead to catalysts with different morphological and structural properties, the activity of catalysts is quite similar. At reaction temperature higher than 973 K, under both steam reforming (SR) and autothermal reforming (ATR), the catalysts show high propane conversion and syngas (H 2 + CO) productivity. Deactivation of catalysts was observed at 873 and 973 K under SR conditions due to coke formation. In ATR, coke formation was almost completely depressed and the catalysts resulted to be very stable even at low reaction temperature (873 K). In SR coke formation occurs with higher rate on the catalyst having higher Ni dispersion, probably since propane cracking reaction is the pre-eminent phenomenon in promoting coke formation.

In situ characterizations of Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts for oxidative steam reforming of propane

Catalytic activity results of oxidative steam reforming of propane studied on Pd catalysts are here explained on the basis of different characterization analyses under reaction conditions. XRD in situ was applied to investigate nanostructure features by means of a Rietveld refinement giving additional information about ceria lattice parameter along the reaction. The refinement was applied in all pretreatment steps, after reduction and after reaction. A good correlation was obtained in all conditions. The mean crystallite sizes were calculated for CeO2, Pd0 and PdO at the higher intensity planes. Results of crystallite sizes after reaction during 1, 3, 8 and 20h were determined. One can conclude that CeO2 enhances and maintains the dispersion of Pd on bulk catalyst and prevents Pd from severe aggregation along the reaction because no sintering was detected even after 20h of reaction. The changes in lattice cell parameter determined by Rietveld refinement suggested high oxygen mobility inside the fluoritic structure, facilitating formation of CeO2−x species. DRIFTS were carried out under static and dynamic measurements and compared with TPD of propane in the presence of oxygen. These results showed formation of surface intermediate species (formates/carbonates) and CHz species on surface during the oxidative steam reforming of propane that allows proposing a surface reaction mechanism.

Catalytic coatings on steel for low-temperature propane prereforming to solid oxide fuel cell (SOFC) application

Catalyst layers (4–20 μm) of rhodium (1 wt%) supported on alumina, titania, and ceria–zirconia (Ce 0.5Zr 0.5O 2) were coated on stainless-steel corrugated sheets by dip-coating in very stable colloidal dispersions of nanoparticles in water. Catalytic performances were studied for low-temperature (⩽500 °C) steam reforming of propane at a steam to carbon ratio equal to 3 and low contact time (≈0.01 s). The best catalytic activity for propane steam reforming was observed for titania and ceria–zirconia supports for which propane conversion started at 250 °C and was more than three times better at 350 °C than conversion measured on alumina catalyst. For all catalysts a first-order kinetics was found with respect to propane at 500 °C. Addition of PEG 2000 in titania and ceria–zirconia sols eliminated the film cracking observed without additive with these supports. Besides, the PEG addition strongly expanded the porosity of the layers, so that full catalytic efficiency was maintained when the thickness of the ceria–zirconia and titania films was increased.

Steam reforming of propane in a zirconia membrane reactor with a Rh‐supported Ce0.15Zr0.85O2 catalyst

AbstractThe steam reforming (SR) of propane for hydrogen production at 400–600 °C in a porous yttria‐stabilized zirconia (YSZ) membrane reactor was investigated. The YSZ membrane was used as a hydrogen selective membrane. A Rh‐supported Ce0.15Zr0.85O2 catalyst was packed in the membrane reactor because the catalyst was found to be the most suitable catalyst for the low‐temperature SR of propane on the basis of the results obtained using a packed bed reactor. The conversion of propane in the membrane reactor was higher than that in a packed bed reactor due to the shift of equilibrium toward the hydrogen‐producing side. In spite of relatively low permeation selectivity (ideal H2/CO selectivity = 9 at 100 °C), hydrogen permeation through the membrane caused an increase in the CO2 fraction and a decrease in the CO fraction in reformed gas. This indicates that the water‐gas shift reaction was an important contributor in the product distribution in the membrane reactor. Meanwhile, the methane fraction remained largely unchanged, regardless of selective hydrogen permeation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Influence of ceria and nickel addition to alumina-supported Rh catalyst for propane steam reforming at low temperatures

Kinetic studies reveal that loading ceria and Ni onto alumina-supported Rh dramatically increases the propane reforming rates; adding CeO 2 promotes steam and propane adsorption and activation, while adding Ni mainly enhances C 3 H 8 adsorption and activation. The influence of ceria and nickel addition to alumina-supported Rh catalyst for steam reforming of propane at low temperatures has been studied by preparing and examining 2 wt%Rh/Al 2 O 3 , 2 wt%Rh/20 wt%CeO 2 –Al 2 O 3 , and 2 wt%Rh–5 wt%Ni/20 wt%CeO 2 –Al 2 O 3 . TPR characterization showed that adding ceria makes rhodium oxide easier to reduce and the presence of rhodium also makes ceria easier to reduce through Rh–Ce interaction, whereas the addition of Ni makes Rh 2 O 3 and ceria more difficult to reduce, likely due to Rh–Ni and Ce–Ni interactions. Adding ceria and nickel significantly improved the catalytic activity of Rh catalyst for propane conversion at 475 °C. Kinetic study at different temperatures (450–650 °C) indicated that the addition of ceria and Ni can greatly increase the propane reforming rates by lowering the activation energies from 67.6–68.8 kJ/mol for 2Rh/Al to 50.1–50.4 kJ/mol for 2Rh/20CeAl and to 42.1–42.5 kJ/mol for 2Rh5Ni/20CeAl. The feed steam/carbon molar ratios corresponding to maximum reaction rates at 475 °C increased from 2.0 for 2Rh/Al to 3.0 for 2Rh/20CeAl and 4.5 for 2Rh5Ni/20CeAl catalyst. A kinetic equation based on Langmuir–Hinshelwood model best fitting the experimental data was applied for the propane steam reforming over the Rh-based catalysts. Kinetic results at different partial pressures of propane and steam revealed that the addition of ceria could enhance the steam and propane adsorption, while the addition of Ni could significantly promote the propane adsorption, probably through working with Rh as propane adsorption sites.

High resistance to carbon deposition of silica-coated Ni catalysts in propane stream reforming

Abstract The catalytic performance of Ni metal catalysts uniformly covered with layers of silica for propane steam reforming was compared with the performances of Ni metal catalysts supported on substrates of magnesia (MgO), alumina (Al2O3) and silica (SiO2). The silica-coated Ni catalysts showed high activity for propane steam reforming at 873 K. This catalytic activity is higher than the activity of effective light alkane steam reforming Ni/Al2O3 and Ni/MgO catalysts and we found that the catalytic activity of the silica-supported Ni metal was poor. The coverage of Ni metal particles with silica thus improves their catalytic activity for this reaction. Carbon deposition on silica-coated Ni catalysts during the steam reforming of propane at 873 K was lower than that on Ni/MgO and Ni/Al2O3. Ni K-edge XANES and EXAFS spectra of silica-coated Ni catalyst showed a strong interaction between Ni metal and silica. This interaction prevents the sintering of Ni metal particles during the propane steam reforming, which results in the reduction of carbon deposition on silica-coated Ni catalysts. These properties of silica-coated Ni catalysts result in high catalytic activity and improved catalyst stability.

Effect of preparation method on structural characteristics and propane steam reforming performance of Ni–Al 2O 3 catalysts

Propane steam reforming was studied over Ni–Al 2O 3 catalysts that were prepared by a conventional impregnation (IM) method and a one-step sol–gel (SG) technique. Both Ni–Al 2O 3 catalysts showed similar initial activity. However, IM-Ni–Al 2O 3 deactivated severely with time-on-stream of propane steam reforming. The catalyst prepared using a SG technique demonstrated stable catalytic performance. The two catalysts also showed major differences in product distribution, with SG catalyst giving much higher yields of hydrogen. Catalysts were characterized with temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. It was revealed that, with sol–gel preparation, highly dispersed small Ni crystallites are formed with a strong interaction with the support. This is shown to be important for coke suppression and catalyst stability.

The effect of Ni:Pt ratio on oxidative steam reforming performance of Pt–Ni/Al 2O 3 catalyst

Oxidative steam reforming of propane was tested over four Pt–Ni/δ-Al 2O 3 bimetallic catalysts aiming to investigate the effect of metal loadings and Ni:Pt loading ratio on catalyst performance. A trimetallic Pt–Ni–Au/δ-Al 2O 3 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/O 2 ratio on the hydrogen production and H 2/CO selectivity was found dependent on the Pt and Ni loadings. The results underlined the importance of C/O 2 ratio as an optimization parameter for product distribution. The highest hydrogen production and H 2/CO ratio levels were obtained for the highest C/O 2 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.

Propane reforming on Ni–Ru/GDC catalyst: H2 production for IT-SOFCs under SR and ATR conditions

Abstract Steam and auto-thermal reforming of propane over a Ni–Ru/GDC catalyst prepared by hydrothermal method were investigated under intermediate temperature solid oxide fuel cell (IT-SOFC) operating conditions. Such an approach is propaedeutical for the application of the catalyst in IT-SOFC. At reaction temperature higher than 700 °C, under both steam reforming (SR) and auto-thermal reforming (ATR), high propane conversion and syngas (H 2 + CO) productivity were obtained. In SR significant amount of filamentous carbon was formed mainly at 600 °C, with subsequent catalyst deactivation. In ATR, coke formation was completely depressed and the catalyst resulted to be very stable in all investigated reaction conditions. Notwithstanding the oxygen storage capability and redox properties of ceria in promoting both oxygen activation and carbon residues gasification, without oxygen in gas phase the concentration of oxygen vacancies itself were not able to inhibit carbon deposition. On the other hand, the presence of oxygen in the reaction stream slightly negatively reflects on syngas production, since it promotes CO 2 and H 2 O formation; however, the loss in selectivity is widely compensated by the absence of deactivation phenomena.

Promotion of the long-term stability of reforming Ni catalysts by surface alloying

Carbon-induced catalyst deactivation is one of the main problems associated with the electrocatalytic and catalytic reforming of hydrocarbons over supported Ni catalysts. We have used DFT calculations to study various aspects of carbon chemistry on Ni surfaces. We demonstrate that the carbon tolerance of Ni can be improved by synthesizing Ni-containing surface alloys that, compared to monometallic Ni, preferentially oxidize C atoms rather than form C–C bonds and have a lower thermodynamic driving force, associated with the nucleation of carbon atoms on low-coordinated Ni sites. Using the molecular insights obtained in the DFT calculations, we have identified Sn/Ni surface alloy as a potential carbon-tolerant reforming catalyst. The predictions of the DFT calculations were supported by our reactor and catalyst characterization studies, which showed that Sn/Ni is much more resistant to carbon poisoning than monometallic Ni in the steam reforming of methane, propane, and isooctane at moderate steam-to-carbon ratios.

Ceramic microreactors for on-site hydrogen production from high temperature steam reforming of propane

The steam reforming of hydrocarbon fuels is a promising method for the production of hydrogen for portable electrical power sources. A suitable reactor for this application, however, must be compatible with temperatures above 800 degrees C to avoid coking of the catalytic structures during the reforming process. Here, ceramic microreactors comprising high surface area, tailored macroporous SiC porous monoliths coated with ruthenium (Ru) catalyst and integrated within high-density alumina reactor housings were used for the steam reforming of propane into hydrogen at temperatures between 800 and 1000 degrees C. We characterized these microreactors by studying C3H8 conversion, H2 selectivity, and product stream composition as a function of the total inlet flow rate, steam-to-carbon ratio (S/C), and temperature. As much as 18.2 sccm H2, or 3.3 x 104 sccm H2 per cm3 of monolith volume, was obtained from a 3.5 sccm entering stream of C3H8 at a S/C of 1.095 and temperatures greater than 900 degrees C. Operating at a S/C close to 1 reduces the energy required to heat excess steam to the reaction temperature and improves the overall thermal efficiency of the fuel processor. Kinetic analysis using a power law model showed reaction orders of 0.50 and -0.23 with respect to propane and steam, respectively, indicating that the rate limiting step in the steam reforming reaction is the dissociative adsorption of propane on the Ru catalyst. The performance of the microreactor was not affected after exposure to more than 15 thermal cycles at temperatures as high as 1000 degrees C, and no catalyst deactivation was observed after more than 120 h of continuous operation at 800 degrees C, making these ceramic microreactors promising for efficient on-site hydrogen production from hydrocarbons for use in polymer electrolyte membrane (PEM) fuel cells.

Temperature profiles and residence time effects during catalytic partial oxidation and oxidative steam reforming of propane in metallic microchannel reactors

Microchanneled reactors made from Fecralloy and impregnated with Rh were studied in partial oxidation (POX) and oxidative steam reforming (OSR) reactions for production of hydrogen or synthesis gas. Temperature profiles obtained along the reactor axis confirmed that the metallic microchannel reactor is able to minimize temperature gradients and pointed to gas phase ignition in front of the reactor as the main reason for reduced syngas production and increased hydrocarbon by-product formation at the highest furnace temperatures. Addition of steam to the reactant mixture (OSR) resulted in increased formation of hydrogen relative to propane converted (S*(H 2)), mainly in accordance with the water–gas shift reaction. Reducing the residence time below 10 ms at 800 °C gave increased S*(H 2) and CO selectivity and reduced by-product formation, indicating suppression of the gas phase reactions and possibly also direct formation of H 2 and CO as part of the reaction scheme. The Rh/Al 2O 3/Fecralloy microchannel reactor also shows good stability during more than 70 experiments of both POX and OSR with temperature cycling from 300 to 1000 °C.

Effect of lanthanide promotion on catalytic performance of sol–gel Ni/Al 2O 3 catalysts in steam reforming of propane

The effect of lanthanide elements (La, Ce, and Yb) on the catalytic behavior of sol–gel Ni/Al 2O 3 catalysts in propane steam reforming was investigated. Steady-state reaction experiments show that the addition of small amounts (2 wt.%) of lanthanide elements improves the catalytic activity and stability significantly. The changes in reaction performance are related to catalyst reducibility, nickel surface area and resistance to deactivation. Temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) characterization results reveal that the presence of lanthanide elements enhances the catalyst reducibility; the positive effect is most evident with 20% Ni–2% Ce/Al 2O 3 catalysts. H 2 chemisorption data indicate that 20% Ni–2% Ce/Al 2O 3 catalysts exhibit larger nickel surface area compared to 20% Ni/Al 2O 3 catalysts. Nickel surface area of sol–gel catalysts is also found to be strongly dependent on calcination and reduction temperatures. In situ DRIFTS experiments coupled with TPD and TPReaction suggest that formate and carbonate species are formed upon the reaction of adsorbed propane and water on reduced catalysts.

Deactivation characteristics of lanthanide-promoted sol–gel Ni/Al 2O 3 catalysts in propane steam reforming

Lanthanide-promoted sol–gel nickel catalysts supported on alumina were studied with regard to their activity and stability for propane steam reforming. X-Ray photoelectron spectroscopy, in situ X-ray diffraction, temperature-programmed oxidation, transmission electron microscopy, thermogravimetric analysis coupled with temperature-programmed reaction, and sequential temperature-programmed coking/gasification/hydrogenation were used to investigate the deactivation characteristics of the catalysts prepared. Adding small amounts (2 wt%) of lanthanide elements (i.e., La, Ce, and Yb) significantly improves steam reforming activity and stability. Although the catalysts deactivate more rapidly at higher reaction temperature, the activity loss can be suppressed by increasing the H 2O/C ratio. The catalyst deactivation can be attributed to a combination of nickel sintering and coke formation. In addition, there appears to be partial oxidation of metallic sites after exposure to the reaction medium. Lanthanides cause enhanced sintering resistance, leading to smaller nickel crystallites in Ni/Al 2O 3 catalysts. Cerium promotion effectively inhibits coking by increasing active oxygen species on the nickel surface due to enhanced water adsorption and gasification. Incorporation of cerium also reduces the dissolution and diffusion of carbon through nickel particles, thus preventing the formation of carbon filaments.

Catalytic steam reforming of ethane and propane over CeO 2-doped Ni/Al 2O 3 at SOFC temperature: Improvement of resistance toward carbon formation by the redox property of doping CeO 2

Ni/Al 2O 3 with the doping of CeO 2 was found to have useful activity to reform ethane and propane with steam under Solid Oxide Fuel Cells (SOFCs) conditions, 700–900 °C. CeO 2-doped Ni/Al 2O 3 with 14% ceria doping content showed the best reforming activity among those with the ceria content between 0 and 20%. The amount of carbon formation decreased with increasing Ce content. However, Ni was easily oxidized when more than 16% of ceria was doped. Compared to conventional Ni/Al 2O 3, 14%CeO 2-doped Ni/Al 2O 3 provides significantly higher reforming reactivity and resistance toward carbon deposition. These enhancements are mainly due to the influence of the redox properties of doped ceria. Regarding the temperature programmed reduction experiments (TPR-1), the redox properties and the oxygen storage capacity (OSC) for the catalysts increased with increasing Ce doping content. In addition, it was also proven in the present work that the redox of these catalysts are reversible, according to the temperature programmed oxidation (TPO) and the second time temperature programmed reduction (TPR-2) results. During the reforming process, in addition to the reactions on Ni surface, the gas–solid reactions between the gaseous components presented in the system (C 2H 6, C 3H 8, C 2H 4, CH 4, CO 2, CO, H 2O, and H 2) and the lattice oxygen (O x ) on ceria surface also take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen (O x ) on ceria surface (C n H m +O x → nCO+ m/2(H 2)+O x− n ) can prevent the formation of carbon species on Ni surface from hydrocarbons decomposition reaction (C n H m ⇔ nC+ m/2H 2). Moreover, the formation of carbon via Boudard reaction (2CO⇔CO 2+C) is also reduced by the gas–solid reaction of carbon monoxide (produced from steam reforming) with the lattice oxygen (CO+O x ⇔CO 2+O x−1 ).

Hydrogen production from propane in Rh-impregnated metallic microchannel reactors and alumina foams

Rh-impregnated alumina foams and metallic microchannel reactors have been studied for production of hydrogen-rich syngas through short contact time catalytic partial oxidation (POX) and oxidative steam reforming (OSR) of propane. Effects of temperature and residence time have been compared for the two catalytic systems. Temperature profiles obtained along the central axis were valuable in understanding the different behaviour of the reactor systems. Gas phase ignition occurs in front of the metallic monolith at furnace temperatures above 700 °C, leading to lower hydrogen selectivity. Lowering the residence time below 10 ms for the microchannel monolith increases the syngas selectivity. This probably due to quenching of the gas phase reactions at high linear gas velocity, and suggests that microchannel reactors have potential for isolating kinetic effects and minimising gas phase contributions. The Rh/Al 2O 3 foam systems show higher initial syngas selectivity than the Rh-impregnated microchannel reactors, but deactivate rapidly upon temperature cycling, especially when steam is added as a reactant.