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A study of Ni/La-Al 2 O 3 catalysts: A competitive system for CO 2 methanation
No full textNi/La-γ-Al 2 O 3 samples containing 13.6 wt.% Ni and a variable amount of lanthana (0, 4, 14 and 37 wt.%) were prepared by incipient wetness impregnation, using silica-free γ-Al 2 O 3 support. The materials were characterized, as such or after reaction, with XRD, H 2 -TPR, IR, UV–vis-NIR, XPS and FE-SEM techniques. They were tested as catalysts for CO 2 methanation at atmospheric pressure at GHSV 55000 h −1 . The reaction is under kinetic control at T < 650–673 K, while the product mixture is under thermodynamic control above this temperature range. Lanthanum addition strongly increases the activity of Ni/γ-Al 2 O 3 for CO 2 methanation. Methane selectivity is increased to nearly 100% at low temperatures (T < 650 K). The CO 2 methanation reaction on La-doped Ni/γ-Al 2 O 3 occurs with similar activation energies (80 kJ/mol), and with slightly higher reaction order for hydrogen and lower reaction order for CO 2 than those observed for undoped Ni/γ-Al 2 O 3 . Lanthanum acts as a promoter because of the stronger basicity of the lanthana-alumina support allowing stronger adsorption of CO 2 as surface carbonates that can be act as “reactant reservoirs”. The Ni/La-alumina catalysts studied here are similarly effective as Ru/alumina catalysts for the selective CO 2 methanation at low temperature and atmospheric pressure
Low-Temperature Catalytic Conversion of Ethanol to Acetone on Au/ZrO2 and Au/ZnZrOx Nanostructures
No full textA study of Ni/Al2O3 and Ni–La/Al2O3 catalysts for the steam reforming of ethanol and phenol
No full textLa2O3/gamma-Al2O3, NiO/gamma-Al2O3 and NiO/La2O3/gamma-Al2O3 samples have been prepared by conventional impregnation, using silica-free gamma-Al2O3 support. The materials have been characterized, as such or after reaction, with XRD, skeletal IR, UV-vis-NIR, XPS and FESEM techniques. The catalytic activity has been evaluated in ethanol decomposition through temperature programmed surface reaction (TPSR); and in ethanol steam reforming (ESR); and in mixed ethanol and phenol steam reforming (EPSR as a model reaction for biomass tar steam reforming) in a continuous flow reactor. Ni on alumina exists as a surface NixAl2O3+x spinel, evident by XRD, skeletal IR and vis spectroscopy measurements. La disperses on alumina in a disordered state. In the ternary system, XPS reveals significant Ni-La interactions. The addition of some lanthanum further increases the activity of Ni/Al2O3 for ESR and EPSR. Fresh unreduced catalysts are conditioned in the feed at temperatures above 973 K. Conditioned catalysts give rise to full conversion of reactants in ESR and EPSR at 873 K and higher temperatures, but are severely deactivated by sulfur. The sudden start of the steam reforming activity at 873 K likely corresponds to the temperature onset for the activation of water by metallic nickel
Acido-basicity of lanthana/alumina catalysts and their activity in ethanol conversion
No full textLanthana on alumina samples (0.2, 0.8 and 4.7 theoretical monolayers) were prepared by incipient wetness impregnation using γ-Al2O3 as support. Characterization has been performed by BET, XRD, skeletal FT-IR, DR-UVvis, XPS, HR-TEM, IR spectra of the surface OH, adsorbed pyridine and CO2, and isopropanol TPD. Ethanol conversion was investigated both in temperature-programmed surface reaction (TPSR) dynamic conditions as well as in steady-state flow reactor tests. Lanthanum addition stabilizes alumina with respect to sintering and loss of surface area and La- containing phases are observed only for the high-La loaded catalyst. La-alumina catalysts are less active in ethanol dehydration than alumina but more selective to diethyl ether at partial conversion. 5%La2O3/Al2O3 is also equally or more selective than alumina to ethylene at high conversion, producing less carbonaceous material during reaction. Thus, this catalytic system might be a good candidate for (bio)ethylene production through (bio)ethanol dehydration
Low-Temperature Dehydrogenation of Ethanol on Atomically Dispersed Gold Supported on ZnZrO<sub><i>x</i></sub>
No full textAtomically dispersed gold supported
on nanoscale ZnZrO<sub><i>x</i></sub> composite oxides was
prepared and investigated in
this work as a catalyst for the low-temperature ethanol dehydrogenation
reactions. The composite ZnZrO<sub><i>x</i></sub> support
disperses gold atomically and stabilizes it against growth much better
than either of the neat oxides. Sequential ethanol conversion reactions
to acetaldehyde and acetone take place on the Au/ZnZrO<sub><i>x</i></sub> catalysts within well-separated temperature windows
over the range of tested temperatures (30–400 °C). ZnO
modulates the acidity of the ZrO<sub>2</sub> surface, and the extent
of this was followed by isopropanol temperature-programmed desorption
with online mass spectrometry (IPA-TPD/MS; and by diffuse reflectance
UV−Vis−IR). Catalyst activity and selectivity were tested
by temperature-programmed surface reaction (TPSR) and under steady-state
reaction conditions. The work has demonstrated that ZnZrO<sub><i>x</i></sub> with optimized ZnO distribution preserves the active
Au–O<sub><i>x</i></sub> surface species under reaction
conditions and suppresses undesired dehydration reactions. Addition
of gold on the bare zirconia support passivates the acid sites catalyzing
ethanol dehydration and introduces desired dehydrogenation sites at
low temperatures (∼200 °C)
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Water-Gas Shift With Integrated Hydrogen Separation
Get PDFOptimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membrane, with both processes carried out at high temperature to improve reaction kinetics. Reduced equilibrium conversion of the WGS reaction at high temperatures is overcome by product H{sub 2} removal via the membrane. This project involves fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2}-separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams will be examined in the project. In the first year of the project, we prepared a series of nanostructured Cu- and Fe-containing ceria catalysts by a special gelation/precipitation technique followed by air calcination at 650 C. Each sample was characterized by ICP for elemental composition analysis, BET-N2 desorption for surface area measurement, and by temperature-programmed reduction in H{sub 2} to evaluate catalyst reducibility. Screening WGS tests with catalyst powders were conducted in a flow microreactor at temperatures in the range of 200-550 C. On the basis of both activity and stability of catalysts in simulated coal gas, and in CO{sub 2}-rich gases, a Cu-CeO{sub 2} catalyst formulation was selected for further study in this project. Details from the catalyst development and testing work are given in this report. Also in this report, we present H{sub 2} permeation data collected with unsupported flat membranes of pure Pd and Pd-alloys over a wide temperature window
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Water-Gas Shift With Integrated Hydrogen Separation Process
Get PDFThis project involved fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2} -separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams were examined in the project. Cu-cerium oxide was identified as the most promising high-temperature water-gas shift catalyst for integration with H{sub 2}-selective membranes. Formulations containing iron oxide were found to deactivate in the presence of CO{sub 2}. Cu-containing ceria catalysts, on the other hand, showed high stability in CO{sub 2}-rich gases. This type gas will be present over much of the catalyst, as the membrane removes the hydrogen produced from the shift reaction. The high-temperature shift catalyst composition was optimized by proper selection of dopant type and amount in ceria. The formulation 10at%Cu-Ce(30at%La)O{sub x} showed the best performance, and was selected for further kinetic studies. WGS reaction rates were measured in a simulated coal-gas mixture. The apparent activation energy, measured over aged catalysts, was equal to 70.2 kJ/mol. Reaction orders in CO, H{sub 2}O, CO{sub 2} and H{sub 2} were found to be 0.8, 0.2, -0.3, and -0.3, respectively. This shows that H{sub 2}O has very little effect on the reaction rate, and that both CO{sub 2} and H{sub 2} weakly inhibit the reaction. Good stability of catalyst performance was found in 40-hr long tests. A flat (38 cm{sup 2}) Pd-Cu alloy membrane reactor was used with the catalyst washcoated on oxidized aluminum screens close coupled with the membrane. To achieve higher loadings, catalyst granules were layered on the membrane itself to test the combined HTS activity/ H{sub 2} -separation efficiency of the composite. Simulated coal gas mixtures were used and the effect of membrane on the conversion of CO over the catalyst was evidenced at high space velocities. Equilibrium CO conversion at 400 C was measured at a space velocity of 30,000 h{sup -1} with the 10{micro}m- thick Pd{sub 60}Cu{sub 40} membrane operating under a pressure differential of 100 psi. No carbon deposition took place during operation. The performance of the coupled Cu-ceria catalyst/membrane system at 400 C was stable in {approx} 30 h of continuous operation. The overall conclusion from this project is that Cu-doped ceria catalysts are suitable for use in high-temperature water-gas shift membrane reactors. CO{sub 2}-rich operation does not affect the catalyst activity or stability; neither does it affect hydrogen permeation through the Pd-Cu membrane. Operation in the temperature range of 400-430 C is recommended
High-Temperature Desulfurization of Heavy Fuel-Derived Reformate Gas Streams for SOFC Applications
Get PDFDesulfurization of the hot reformate gas produced by catalytic partial oxidation or autothermal reforming of heavy fuels, such as JP-8 and jet fuels, is required prior to using the gas in a solid oxide fuel cell (SOFC). Development of suitable sorbent materials involves the identification of sorbents with favorable sulfidation equilibria, good kinetics, and high structural stability and regenerability at the SOFC operating temperatures (650 to 800 C). Over the last two decades, a major barrier to the development of regenerable desulfurization sorbents has been the gradual loss of sorbent performance in cyclic sulfidation and regeneration at such high temperatures. Mixed oxide compositions based on ceria were examined in this work as regenerable sorbents in simulated reformate gas mixtures and temperatures greater than 650 C. Regeneration was carried out with dilute oxygen streams. We have shown that under oxidative regeneration conditions, high regeneration space velocities (greater than 80,000 h(sup -1)) can be used to suppress sulfate formation and shorten the total time required for sorbent regeneration. A major finding of this work is that the surface of ceria and lanthanan sorbents can be sulfided and regenerated completely, independent of the underlying bulk sorbent. This is due to reversible adsorption of H2S on the surface of these sorbents even at temperatures as high as 800 C. La-rich cerium oxide formulations are excellent for application to regenerative H2S removal from reformate gas streams at 650 to 800 C. These results create new opportunities for compact sorber/regenerator reactor designs to meet the requirements of solid oxide fuel cell systems at any scale
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Water-Gas Shift With Integrated Hydrogen Separation Process
Get PDFOptimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membrane, with both processes carried out at high temperatures to improve reaction kinetics and permeation. Reduced equilibrium conversion of the WGS reaction at high temperatures is overcome by product H{sub 2} removal via the membrane. This project involves fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2}-separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams will be examined in the project. The first-year screening studies of WGS catalysts identified Cu-ceria as the most promising high-temperature shift catalyst for integration with H{sub 2}-selective membranes. Formulations containing iron oxide were found to deactivate in the presence of CO{sub 2}, and were thus eliminated from further consideration. Cu-containing ceria catalysts, on the other hand, showed high stability in CO{sub 2}-rich gases. This type gas will be present over much of the catalyst, as the membrane removes the hydrogen produced from the shift reaction. Several catalyst formulations were prepared, characterized and tested in the first year of study. Details from the catalyst development and testing work were given in our first annual technical report. Hydrogen permeation through Pd and Pd-alloy foils was investigated in a small membrane reactor constructed during the first year of the project. The effect of temperature on the hydrogen flux through pure Pd, Pd{sub 60}Cu{sub 40} and Pd{sub 75}Ag{sub 25} alloy membranes, each 25 {micro}m thick, was evaluated in the temperature range from 250 C to 500 C at upstream pressure of 4.4 atm and permeate hydrogen pressure of 1 atm. Flux decay was observed for the Pd-Cu membrane above 500 C. From 350-450 C, an average hydrogen flux value of 0.2 mol H{sub 2}/m{sup 2}/s was measured over this Pd-alloy membrane. These results are in good agreement with literature data. In this year's report, we discuss reaction rate measurements, optimization of catalyst kinetics by proper choice of dopant oxide (lanthana) in ceria, long-term stability studies, and H{sub 2} permeation data collected with unsupported flat, 10 {micro}m-thick Pd-Cu membranes over a wide temperature window and in various gas mixtures. The high-temperature shift catalyst composition was further improved, by proper selection of dopant type and amount. The formulation 10 at%Cu-Ce(30 at%La)Ox was the best; this was selected for further kinetic studies. WGS reaction rates were measured in a simulated coal-gas mixture. The stability of catalyst performance was examined in 40-hr long tests. A series of hydrogen permeation tests were conducted in a small flat-membrane reactor using the 10 m{micro}-thick Pd-Cu membranes. Small inhibitory effects of CO and CO{sub 2} were found at temperatures above 350 C, while H{sub 2}O vapor had no effect on hydrogen permeation. No carbon deposition took place during many hours of membrane operation. The reaction extent on the blank (catalyst-free) membrane was also negligible. A larger flat-membrane reactor will be used next year with the catalyst wash coated on screens close coupled with the Pd-Cu membrane
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