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Warm (250–450 °C) cleanup of coal- or biomass-derived syngas requires sorbents and catalysts to protect downstream conversions. We report first a sequential ZnO bed operation in which the capacity is optimized for bulk desulfurization at 450 °C, while subsequent removal of sulfur to parts-per-billion levels can be accomplished at a lower temperature of approximately 300 °C. At this temperature, gaseous sulfur (H2S and COS) could be adsorbed equally well using ZnO, both with and without the presence of H2O in the feed, suggesting direct absorption of COS can occur. Following five sulfidation and regeneration cycles, the bulk desulfurization bed lost about a third of its initial sulfur capacity; however, sorbent capacity stabilized. A bench-scale process consisting of five unit operations is described for the cleanup of a several contaminants in addition to sulfur. Syngas cleanup was demonstrated through successful long-term performance of a poison-sensitive Cu-based water-gas shift catalyst placed downstre...

This study presents an investigation into the steam reforming of hydrocarbons from biomass gasifier-derived syngas over MgAl 2 O 4 -supported transition metals (Ni, Rh, Ir, Ru, Pt, and Pd) and novel bimetallic IrNi catalysts. Using a model syngas consisting of H 2 , CO, CO 2 , CH 4 , C 2 H 4 , and H 2 O, Ir and Rh catalysts were found to be the most stable catalysts (at 850 °C, 1 bar, 114,000 h −1 ). When benzene and naphthalene are added to the feed (as a tar simulant) stability is affected by both tar concentration and type of tar. Catalytic deactivation, caused primarily by coking can be minimized by operating at a high reaction temperature (e.g., 850 °C). In addition, promoting Ni catalyst with Ir significantly enhances stability. By using bimetallic formulations of Ir and Ni (0.5–5.0% Ir, 15%Ni), nickel sintering during the reaction is reduced. Surprisingly, IrNi catalysts also offer more stability than catalysts with Ir particles alone. In agreement with theoretical calculations, small Ir° clusters (∼2–3 atoms) supported on large Ni° particles (≥5 nm) present more resistance to coking than either small Ir° clusters or Ni° particles alone. Hence, superior stability of the bimetallic catalysts results from both resistance to coking and a decrease in nickel sintering. Minimal loss of activity of 12% for TOS = 80 h is demonstrated for a bimetallic catalyst with optimal concentrations of 2.5% Ir and 15% Ni. Both monometallic Ir and Ni catalysts suffer substantial loss of activity (i.e., ≥40% loss, TOS = 80 h) under comparable conditions.

NaNO3 and other alkali nitrate salts, which are present in the molten state during use, have been described as facilitators or catalysts for CO2 absorption by both MgO and MgO-containing double salts. Although MgO exhibits a high capacity (exceeding 70 wt %), its regenerability in multicycle tests shows a significant loss of capacity with cycle number prior to lining out. On the other hand, the MgO–Na2CO3 double salt shows a lower (∼16 wt %) but stable capacity over multiple cycles under pressure swing operation. The purpose of this paper is to elaborate on the concept of molten salts as catalysts for CO2 absorption by MgO, and extend these observations to the MgO-containing double salt oxides. We will show that the phenomena involved with CO2 absorption by MgO and MgO-based double salts are similar and general, but with some important differences. This paper focuses on the following key concepts: (i) identification of conditions that favor or disfavor participation of isolated MgO during double salt abso...

In this paper, we report the fundamental surface properties of Pt/C and Pt–Re/C catalysts and their correlation with catalytic performance in steam reforming of glycerol. We found that the addition of Re increases the catalytic activity, H 2 /CO x ratio, and CO 2 selectivity. N 2 physisorption, CO chemisorption, and attenuated total reflectance infrared (ATR-IR), Raman, and X-ray absorption spectroscopy (XAS) with in situ capabilities were employed to provide insight into the roles of Re. Using ATR-IR, we show that CO adsorption on reduced Pt–Re/C is stronger than on Pt/C. However, CO desorption from Pt–Re/C is much facilitated compared with that from Pt/C after steam pretreatment, which is more representative of the steam reforming conditions. In situ Raman and XAS studies suggest that oxidized rhenium species are formed in steam environments on the Pt–Re/C catalyst surface. The spillover of CO from neighboring Pt to such oxidized rhenium is likely the reason for the facile desorption of CO, which could further react to form CO 2 . Such facile CO desorption leads to enhanced glycerol steam reforming and water-gas shift activities over the Pt–Re/C catalyst.

Syngas, a mixture of CO and H2 (CO/H2), is a key platform for the utilization of nonpetroleum carbon resources such as natural gas or shale gas and coal. Syngas can also be produced from renewable carbon feedstocks such as biomass and even CO2. A variety of products including hydrocarbons and oxygenates, which can be fuels and chemicals, may be produced from syngas. The catalytic transformation of syngas into value-added products is the core of C1 chemistry. This review highlights advances in the past decade in catalytic conversions of syngas into hydrocarbons with an emphasis on selective formations of C5 + hydrocarbons, which are mainly used as liquid fuels, and lower (C2–C4) olefins, key building-block chemicals. Since CO2 is also contained in syngas from some resources, the catalytic hydrogenation of CO2 to hydrocarbons will also be briefly described. Fischer–Tropsch synthesis is a well-established process for syngas to hydrocarbons, but many fundamental aspects remain unclear because of the complexity of the reaction. The products of Fischer–Tropsch synthesis usually follow the Anderson–Schulz–Flory distribution, which is very wide and is nonselective for a target product such as liquid fuels or lower olefins. This article highlights recent advances in understanding the active phase of Fischer–Tropsch catalysts and in designing efficient catalysts using new materials. Furthermore, this article pays particular attention to the breakthrough in the selectivity control, which is the most important challenge for scientific research in syngas chemistry. Besides insights into various factors determining product selectivity as well as activity, we will also discuss emerging methodologies and strategies for the selective conversion of syngas into a specific range of hydrocarbons.

A composite Pd/ZnO/Al2O3-HZSM-5 (Si/Al=40) catalytic system was evaluated for the synthesis of gasoline-range hydrocarbons directly from synthesis gas. Bifunctional catalyst comprising PdZn metal and acid sites present the required catalytically active sites necessary for the methanol synthesis, methanol dehydration, and methanol-to-gasoline reactions. This system provides a unique catalytic pathway for the production of liquid hydrocarbons directly from syngas. However, selectivity control is difficult and poses many challenges. The composite catalytic system was evaluated under various process conditions. Investigated were the effects of temperature (310-375oC), pressure (300-1000 psig), time-on-stream (50 hrs), and gas-hour space velocity (740-2970 hr-1), using a H2/CO molar syngas ratio of 2.0. By operating at the lower end of the temperature range investigated, liquid hydrocarbon formation was favored, as was decreased amounts of undesirable light hydrocarbons. However, lower operating temperatures also facilitated undesirable CO2 formation via the water-gas shift reaction. Higher operating pressures slightly favored liquid synthesis. Operating at relatively low pressures (e.g. 300 psig) was made possible, whereas for methanol synthesis alone higher pressure are usually required to achieve similar conversion levels (e.g. 1000 psig). Thermodynamic constraints on methanol synthesis are eased by pushing the equilibrium through hydrocarbon formation. Catalytic performance was also evaluated by altering Pdmore » and Zn composition of the Pd/ZnO/Al2O3 catalyst. Of the catalysts and conditions tested, selectivity toward liquid hydrocarbon was highest when using a 5% Pd metal loading and Pd/Zn molar ratio of 0.25 and mixed with HZMS-5, operating at 310oC and 300 psig, CO conversion was 43 % and selectivity (carbon weight basis) to hydrocarbons was 49 wt. %. Of the hydrocarbon fraction, 44wt. % was in the C5-C12 liquid product range and consisted primarily of aromatic polymethylbenzenes. However, as syngas conversion increases with increasing temperature, selectivity to liquid product diminished. This is attributed, in large part, to increased saturation of the olefinic intermediates over PdZn metal sites. Under all the conditions and catalysts evaluated in this study, generating liquid product in high yield was challenging (

The CO2 capture properties of M2CO3 (M = Na, K)-promoted and CaCO3-promoted MgO sorbents are investigated by first-principles density functional theory complemented with lattice phonon calculations. The calculated thermodynamic properties indicate that by forming double salts (M2Mg(CO3)2 and CaMg(CO3)2), compared to pure MgO, the maximum allowable CO2 capture temperatures of the M2CO3- and CaCO3- modified MgO sorbents are shifted to higher temperature ranges. Under pre-combustion conditions with PCO2 = 10 bar, the Na2CO3-promoted and CaCO3-promoted MgO sorbents can capture CO2 at temperatures as high as 915 K and 740 K respectively. While under post-combustion conditions with PCO2 = 0.1 bar, their maximum allowable CO2 capture temperatures are 710 K and 600 K respectively. However, when adding K2CO3 into MgO, under both pre- and post-combustion conditions, its maximum CO2 capture temperatures only increased about 10 K relative to pure MgO. These results indicate that by mixing another solid into MgO, it is possible to shift its CO2 capture temperature to fit practical industrial needs.

Systems comprising multiple sorbent and catalytic beds have been developed for the warm cleanup of coal- and biomass-derived syngas. Tailored specifically for biomass application, the process described here consists of six primary unit operations: (1) a Na2CO3 bed for HCl removal, (2) two regenerable ZnO beds in parallel for bulk H2S removal, (3) a ZnO bed for H2S polishing, (4) a NiCu/SBA-16 sorbent for trace metal (e.g., AsH3) removal, (5) a steam reforming catalyst bed for tars and light hydrocarbon reformation and NH3 decomposition, and (6) a Cu-based LT-WGS catalyst bed. Simulated biomass-derived syngas containing possible inorganic contaminants (H2S, AsH3, HCl, and NH3) and hydrocarbons (methane, ethylene, benzene, and naphthalene) was used to demonstrate process effectiveness. The efficiency of the process was demonstrated for a period of 175 h, during which time no signs of deactivation were observed. However, postrun analysis revealed that small levels of sulfur slipped through the sorbent bed tr...

Absorption and desorption of carbon dioxide on Na 2 CO 3 -promoted MgO have been studied at temperatures compatible with warm gas cleanup (300–470 °C) from a pre-combustion syngas. The absorbents are synthesized through the formation and activation of the precipitate resulting from the addition of sodium carbonate to an aqueous solution of magnesium nitrate. The absorbent, which comprises MgO, Na 2 CO 3 and residual NaNO 3 after activation, forms the double salt Na 2 Mg(CO 3 ) 2 on exposure to CO 2 . The thermodynamic properties of the double salt, obtained through computational calculation, predict that the preferred temperature range for absorption of CO 2 with the double salt is significantly higher compared with MgO. Faster CO 2 uptake can be achieved as a result of this higher temperature absorption window. Absorption tests indicate that the double salt absorbent as prepared has a capacity toward CO 2 of 15 wt.% (3.4 mmol CO 2 /g absorbent) and can be easily regenerated through both pressure swing and temperature swing absorption in multiple-cycle tests. Thermodynamic calculations also predict an important effect of CO 2 partial pressure on the absorption capacity in the warm temperature range. The impurity phase, NaNO 3 , is identified as a key component in facilitating CO 2 absorption by these materials. The reason for reported difficulties in reproducing the performance of these materials can be traced to specific details of the synthesis method, which are reviewed in some detail.

In situ X-ray absorption spectroscopy (XAS) results on correlating the Pt local coordination and electronic structure with the Pt/C catalyst activity and selectivity during aqueous reforming of glycerol at different pH are reported. The results show that both low and high pH favor C–O cleavage over that of C–C. However, the selectivity toward C–O bond cleavage was higher under the acidic conditions. XANES measurements under reaction conditions showed that low pH increased the Pt electron density while the effect of basic conditions was minimal. ΔXANES was used to estimate the coverage of adsorbates under reaction conditions and the results suggest a change in the adsorbates coverage by the acidic conditions, resulting in higher electron density on Pt.

The catalytic roles of Co0 and Co2+ during steam reforming of ethanol were investigated over Co/MgO catalysts. Catalysts with different Co0/(Co0+Co2+) fraction were prepared through calcination and/or reduction at different temperatures, and the Co0 fraction was quantified by temperature programmed reduction (TPR) and in situ X-ray photoelectron spectroscopy (XPS). Higher temperature calcination of Co/MgO allowed us to prepare catalysts with more nonreducible Co2+ incorporated in the MgO lattice, while lower calcination temperatures allowed for the preparation of catalysts with higher Co0/(Co0+Co2+) fractions. The catalytic tests on Co0, nonreducible Co2+, and reducible Co2+ indicated that Co0 is much more active than either reducible or nonreducible Co2+ for C−C cleavage and water gas shift reaction. In addition, catalysts with a higher Co0 surface fraction exhibited a lower selectivity to CH4.

Nickel-based catalysts have been widely tested for reforming undesired tar and methane from hot biomass-derived syngas. However, nickel catalysts readily deactivate through the adsorption of sulfur compounds in the syngas. We report a new regeneration process that can effectively regenerate sulfur-poisoned Ni reforming catalysts. This process consists of four sequential treatments: (1) controlled oxidation at 750 °C in 1% O2, (2) decomposition at 900 °C in inert gas, (3) reduction at 900 °C in 2% H2, and (4) reaction at 900 °C under reforming condition. This 4-step regeneration process might have advantages over the conventional steam regeneration process.

It is known that sulfur oxides contribute significantly and deleteriously to the overall performance of lean-burn diesel engine after-treatment systems, especially in the case of NOx traps. A silica-supported silver-based, fast regenerable SO2 absorbent has been developed and will be described. Over a temperature range of 300–550 °C, it absorbs SO2 present in a simulated exhaust gas during the lean cycles, and can be fully regenerated by short rich gas cycles at the same temperature. The preferred silica support is fumed silica. The thermal instability of Ag2O under fuel-lean conditions at 230 °C and above makes it possible to rapidly regenerate the sulfur-loaded absorbent during the fuel-rich cycle due to the lack of a requirement to simultaneously reduce Ag2O to Ag. Ag particles can also effectively oxidize SO2 to SO3, facilitating the formation of Ag2SO4 and requiring no additional oxidation catalysts. This absorbent shows great potential to work under the same lean-rich cycling conditions as those imposed on the NOx traps, and thus can protect the downstream particulate filter and the NOx trap from sulfur poisoning.

Hydrogen production from the aqueous phase reforming of glycerol over several 3%Pt-Re/C catalysts (1-4.5% Re) has been studied in the absence and presence of base, and the results compared with a Re-free 3%Pt/C catalyst. Although the Pt/C catalyst is very selective toward the production of hydrogen, catalytic activity is low. Addition of Re significantly increases the conversion of glycerol, at some loss of hydrogen selectivity to light hydrocarbons and water-soluble oxygenates. Addition of 1%KOH to the feedstock increases the selectivity of the Pt-Re/C catalysts toward hydrogen, but selectivity toward aqueous phase oxygenates also increases except for 3%Pt-3%Re/C, where it remains constant. The increase in hydrogen selectivity with base addition arises primarily from reducing the selectivity toward methane and higher alkanes, products that consume H2. For comparison, KOH addition to the glycerol feed with the Re-free 3%Pt/C catalyst provides an increase in glycerol conversion but results in a decline in both H2 and alkanes relative to aqueous phase oxygenates. This indicates that alternative pathways have been enabled by base addition. The highest hydrogen productivity among the catalysts tested is achieved with a 3%Pt-3%Re/C catalyst with added KOH base, but this hydrogen productivity declines with time on stream. The observed product distributionsmore » as well as deactivation with base can be understood in terms of the different reaction pathways that become emphasized depending on catalyst composition and pH.« less

Rh and Co-based catalyst performance was compared for steam reforming of ethanol under conditions suitable for industrial hydrogen production. The reaction conditions were varied to elucidate the differences in reaction pathways on both catalysts. On Co/ZnO, CH(4) is a secondary product formed through the methanation reaction, while it is produced directly by ethanol decomposition on Rh. The difference in the reaction pathway is shown to favor Co-based catalysts for selective hydrogen production under elevated system pressures (up to 15 bar) of industrial importance. The carbon deposition rate was also studied, and we show that Co is more prone to coking and catalyst failure. However, the Co/ZnO catalyst can be regenerated, by mild oxidation, despite the high carbon deposition rate. We conclude that Co/ZnO is a more suitable catalyst system for steam reforming of ethanol due to the low methane selectivity, low cost and the possibility of regeneration with mild oxidation. (C) 2010 Elsevier B.V. All rights reserved.

With efficient energy recovery, calcium-oxide-based absorbents that operate at elevated temperatures have an advantage over absorbents that operate at lower temperatures for CO2 capture from coal power plants. The major limitation of these absorbents is that the carbonation and decarbonation reactions of CaO and CaCO3 are far from complete or reversible. Rapid loss of CO2 capacity over many carbonation/decarbonation cycles is always observed because of severe absorbent sintering. We have found that this sintering effect can be effectively mitigated by properly mixing calcium oxide precursors with small rod-like MgAl2O4 spinel nanoparticles. A new class of CaO-based absorbents with much improved high-temperature durability was developed by wet physical mixing of calcium acetate with nano MgAl2O4 spinel particles followed by high-temperature calcination. CaO−MgAl2O4 (32 wt % spinel content) material provides 34 wt % CO2 capacity after 65 carbonation−decarbonation cycles (650 and 850 °C, respectively), corre...

Calcium oxide based materials are attractive regenerable absorbents for separating CO{sub 2} from hot gas streams because of their high reactivity, high CO{sub 2} capacity, and low material cost. Their high carbonation temperature makes it possible to recover and use high quality heat released during CO{sub 2} capture, which increases overall process efficiency. However, the performance of all reported CaO-based absorbents deteriorates as the number of carbonation-decarbonation cycles increases. This is caused by absorbent sintering during the highly exothermic carbonation process. We have found that sintering can be effectively mitigated by properly mixing with a modest amount of MgO. A class of CaO-based absorbents with improved durability and CO{sub 2} reactivity were prepared by physical mixing of Ca(CH{sub 3}COO){sub 2} with small MgO particles followed by high temperature calcination. With 26 wt % MgO content, a CaO-MgO mixture prepared by this method gives as high as 53 wt % CO{sub 2} capacity after 50 carbonation-decarbonation cycles at 758{sup o}C. Without MgO addition, the CO{sub 2} capacity of pure CaO obtained from the same source decreases from 66 wt % for the first cycle to 26 wt % for the 50th cycle under the same test conditions.

Concentrating CO2 from the dilute coal combustion or gasification gas stream to a level suitable for sequestration purposes represents a major cost factor to curtail CO2 emissions by capture and sequestration. This paper provides a short review of CO2 capture incentives, current separation processes, and research progress of various new technologies. Scientifically, CO2 can be separated from a gas mixture by all the methods reviewed in this work: distillation, absorption, adsorption, gas/solid reaction, membrane, electrochemical pump, hydrate formation, etc. The challenge lies in practical feasibility and ultimately the cost. Important material issues and their impacts to the process viability will be discussed.

Currently, hydrogen is primarily used in the chemical industry, but in the near future it will become a significant fuel. There are many processes for hydrogen production. This paper reviews the technologies related to hydrogen production from both fossil and renewable biomass resources including reforming (steam, partial oxidation, autothermal, plasma, and aqueous phase) and pyrolysis. In addition, electrolysis and other methods for generating hydrogen from water, hydrogen storage related approaches, and hydrogen purification methods such as desulfurization and water-gas-shift are discussed.

The activity of nickel–yttria stabilized zirconia (Ni–YSZ) solid oxide fuel cell (SOFC) cermet anodes for the steam-reforming of methane has been investigated in the absence of electrochemical effects. The cermet was prepared by co-milling and sintering NiO and 5YSZ powders at 1375 °C in air. During the high-temperature sintering step, NiO dissolved into the YSZ particles to form a solid NiO–YSZ solution. During the subsequent catalyst reduction step, Ni exolved from the YSZ. As a result, many small Ni particles on the order of 10–20 nm formed at the surface of the YSZ. These small particles contributed significantly to the overall reforming activity, along with the large bulk Ni particles within the Ni–YSZ cermet. We observed high initial activity that decreased by as much as an order of magnitude with time on stream, until the anode catalyst reached a stable steady-state activity. The time to reach this stable activity was a function of the pretreatment and reaction conditions. Initial and lined-out activities and average turnover frequencies were obtained for both Ni–YSZ and bulk Ni, based on a rate expression that was first-order in methane and zero-order in steam. Comparative tests at 750 °C showed high initial activity on a per-Ni site basis with both materials, but these turnover rates declined over a period of a few hours. After lineout, there appeared to be a negligible effect of Ni particle size on turnover rate. These results indicate the presence of structure-sensitivity for methane reforming, but only with freshly calcined and reduced catalysts that may contain highly coordinatively unsaturated sites. There was an apparent structure-insensitivity with aged catalysts in which Ni particle sizes were generally ⩾30 nm. Under reaction conditions with high space velocities and low methane conversions, the water–gas shift reaction did not establish thermodynamic equilibrium.

A field-deployable process for generation of clean desulfurized fuel from JP-8 feedstock is described. The process employs a compact hydrodesulfurization unit, operated in the vapor phase using steam reformate provided by an integrated steam reformer, as a replacement for hydrogen co-feed gas. The process includes a microchannel distillation unit upstream of the hydrodesulfurizer unit, which allows use of a lighter feed fraction to be processed in place of the full JP-8. The novel microchannel distillation concept is described and performance data for the unit, operating as a rectifier, are provided. Since the generated light fraction fuel from microchannel distillation contains fewer refractory sulfur components, the subsequent HDS process can readily achieve a significant sulfur reduction. The overall process can generate an ultra-clean JP-8 light fraction fuel with approximately 300 ppb sulfur residual. Hydrodesulfurization of full JP-8 fuel without the microchannel distillation unit was also studied. The effect of various operating parameters on the overall hydrodesulfurization performance, as well as the conversion of some individual sulfur components such as 2,3-dimethyl-benzothiophene, 2,3,5-trimethyl-benzothiophene and 2,3,7-trimethyl-benzothiophene, were investigated. Steam content in reformate at 30 mol% or less was found to improve HDS performance compared with dry reformate, despite a decrease in hydrogen partial pressure. However, at even higher concentrations of steam, hydrodesulfurization performance decreased.

A series of Rh catalysts on various supports (Al2O3, MgAl2O4, ZrO2, and ZrO2–CeO2) have been applied to H2 production from the ethanol steam reforming reaction. In terms of ethanol conversion at low temperatures (below 450 °C) with 1wt% Rh catalysts, the activity decreases in the order: Rh/ZrO2–CeO2 > Rh/Al2O3 > Rh/MgAl2O4 > Rh/ZrO2. Support plays a very important role on product selectivity at low temperatures (below 450 °C). Acidic or basic supports favor ethanol dehydration, while ethanol dehydrogenation is favored over neutral supports at low temperatures. The Rh/ZrO2–CeO2 catalyst exhibits the highest CO2 selectivity up to 550 °C, which is due to the highest water gas shift (WGS) activity at low temperatures. Among the catalysts evaluated in this study, the 2wt% Rh/ZrO2–CeO2 catalyst exhibited the highest H2 yield at 450 °C, which is possibly due to the high oxygen storage capacity of ZrO2–CeO2 resulting in efficient transfer of mobile oxygen species from the H2O molecule to the reaction intermediate.

Rapid deactivation of Rh/Ce0.8Zr0.2O2 catalysts during low temperature ethanol steam reforming was studied. A significant build-up of reaction intermediates, instead of carbon deposit, was observed at low reaction temperatures. This appears to be the cause of rapid catalyst deactivation. Co-feed experiments indicated that possible intermediate products acetone and ethylene caused more severe catalyst deactivation than other oxygenates such as acetic acid and acetaldehyde.

The addition of small quantities of gold to the surface of supported nickel catalysts has been described as a means to retard carbon formation during hydrocarbon steam reforming. Calculations by others have indicated that gold locates at the most catalytically active (step and edge) sites that also serve as nucleation sites for carbon formation. In this paper, we describe experiments to characterize the Ni Au interactions on bimetallic Au Ni/MgAl 2 O 4 catalysts at various Ni and Au loadings. The catalyst structure was investigated using EXAFS/XANES spectroscopy and adsorption–desorption measurements with H 2 and N 2 O. Evidence for surface alloy formation is provided in the Ni K-edge and Au L III -edge EXAFS measurements of Au-promoted 8.8% Ni/MgAl 2 O 4 , especially at Au loadings ⩽ 0.2 wt% . At higher Au concentrations, there is evidence of a combination of alloy and segregated Au species. H 2 chemisorption and N 2 O temperature-programmed desorption (TPD) measurements showed a significant decrease in total surface sites, or surface site reactivity, on Au-modified Ni/MgAl 2 O 4 catalyst. The XANES structure is consistent with perturbation of the electronic structure of both the Ni and Au atoms as a result of alloy formation. TGA studies with steam/ n -butane feed confirmed the ability of Au to retard coke deposition under low S/C reforming conditions, although carbon formation was not fully suppressed. When testing for methane steam reforming, a lower initial activity and deactivation rate resulted from Au promotion of the Ni catalyst. However, both catalysts showed a declining activity with time. The lack of a direct correlation between the surface characterization results and catalytic activity is most likely a result of decreasing effectiveness of the surface alloy with increasing temperature.

Gas-phase hydrodesulfurization of a JP-8 light fraction was investigated over CoMo/Al2O3 and NiMo/Al2O3 catalysts. Use of a light fraction provides a fuel that is more easily desulfurized and allows the process to operate in the vapor phase. This study investigated the utilization of reformate (syngas) from a steam reformer rather than pure H2 as gas feed to HDS unit. This is consistent with what might be available to the military during operation in the field. Dry syngas functions almost as well as pure H2 in the HDS reaction, and sulfur levels below 5 ppmw are readily obtained from a feed initially containing 320 ppmw sulfur. Addition of 40 vol % steam to the syngas has a significant negative impact on HDS performance with CoMo/Al2O3, but only a small effect with NiMo/Al2O3. The impacts of various process conditions on S removal efficiency were examined and will be described.

The desulfurization of Tier 2 gasoline ( + (CuNaY) or H + (CuHY). Capacities on the order of 60 ml gasoline/g adsorbent were obtained with both materials before the sulfur concentration in the effluent exceeded 3 ppmw. Overall, the CuHY zeolite showed somewhat better desulfurization performance. It is proposed that acid sites (H + ) that are present play a role in the desulfurization process, facilitating chemical reactions involving the sulfur-containing molecules. This leads to the generation of sulfur-bearing compounds having molecular weights and sizes greater than those present in the initial feed. Some of these heavier sulfur species are eluted but many do not elute. The net effect is a desulfurization pathway that is the result of entrapment of sulfur-containing molecules in addition to a desulfurization pathway involving direct interaction between the copper and sulfur atoms.

The efficacy of using ZnO as an absorber for the removal of H2S from small fuel processor steam reformate streams was examined. At temperatures below 300 °C, H2S can in principle be reduced to below 100 ppbv, required for safe operation of PEM fuel cells. The ZnO adsorbent performed predictably based on ZnO-H2S-ZnS-H2O equilibria with steam, hydrogen, and CO2 in the feed. However, addition of CO even at levels as low as 1 vol% drastically lowered the sulfur removal capability of the ZnO. This is consistent with the formation of COS by the reaction H2S + CO = H2 + COS. ZnO is not an efficient absorber for COS. Indirect evidence is also provided for the formation of COS via the reaction CO2 + H2S = COS + H2O, which can occur in special cases when CO2 is present but neither H2O nor CO is present in the feed. The potential for COS formation compromises the ability of ZnO to deliver very low sulfur concentration reformate.

Rh/CeO2–ZrO2 catalysts with various CeO2/ZrO2 ratios have been applied to H2 production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O2. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.

Supported Rh catalysts have been developed for selective H2 production at low temperatures. Ethanol dehydration is favorable over either acidic or basic supports such as γ-Al2O3 and MgAl2O4, while ethanol dehydrogenation is more favorable over neutral supports. CeO2–ZrO2-supported Rh catalysts were found to be especially effective for hydrogen production. We focused on a support prepared by a co-precipitation method having composition Ce0.8Zr0.2O2. A 2%Rh/Ce0.8Zr0.2O2 catalyst, prepared via impregnation without pre-calcination of support, exhibited the highest H2 yield at 450 °C among various supported Rh catalysts evaluated in this study. This may be due to both the strong interaction between Rh and Ce0.8Zr0.2O2 and the high oxygen transfer rate favoring reforming of acetaldehyde instead of methane production.

A high-capacity sulfur oxide absorbent, cryptomelane, has been described previously. Its SO2 capacity can be as high as 70 wt %, which is more than 10 times as high as the capacities of standard metal oxide-based SO2 absorbents. In this study, the stability of cryptomelane under oxidizing, inert, reducing, and lean−rich cycling conditions was determined. Cryptomelane is stable in oxidizing and inert atmospheres. However, it is unstable under reducing atmospheres, converting to lower valent manganese oxide compounds. These low-valent oxides have very low capacity toward SO2. Upon reexposing the reduced cryptomelane products to an oxidizing atmosphere, cryptomelane may re-form. Cryptomelane exposed to the types of lean−rich cycles that have been proposed for NOx traps for diesel emission control, over the temperature range 250−550 °C, remains stable and maintains its very high SO2 capacity. It appears possible to use cryptomelane to protect the NOx traps from sulfur oxide degradation during cyclic lean−rich...

Silver hollandite, Ag1.8Mn8O16, has been synthesized by ion exchange of cryptomelane in AgNO3 melt. Compared to the previously described synthesis process, thermal decomposition of AgMnO4 at 970 °C...

High-capacity sulfur dioxide absorbents based on manganese oxide octahedral molecular sieves (OMS) have been identified. These materials are based on MnO6 octahedra sharing faces and edges to form various tunnel structures (2 × 2, 2 × 3, 2 × 4, 3 × 3) differentiated by the number of octahedra on a side. The SO2 capacities of these materials, measured at 325 °C with a feed containing 250 ppmv SO2 in air, are as high as 70 wt % (w/w), remarkably higher than conventional metal oxide based SO2 absorbents. Among the OMS materials, the 2 × 2 member, cryptomelane, exhibits the highest capacity and absorption rate. Its SO2 absorption behavior has been further characterized as a function of temperature, space velocity, and feed composition. The dominant pathway for SO2 absorption is through the oxidation of SO2 to SO3 by Mn4+ followed by SO3 reaction with Mn2+ to form MnSO4. Absorption can occur in the absence of gas-phase oxygen, with a moderate loss in overall capacity. The inclusion of gases NO and CO in the fe...

Upcoming regulations regarding diesel engine emissions require substantial reduction in particulate matter and nitrogen oxides through aftertreatment methods. Since sulfur oxides in the exhaust greatly reduce the performance of the aftertreatment system, a dedicated trap for removal of sulfur oxides has been considered. Most adsorbents are more effective in removing SO{sub 3} than SO{sub 2}; hence oxidation catalysts have been employed to maximize the concentration of SO{sub 3} in the effluent. Although SO{sub 2} concentrations are easily measured, SO3 is less easily quantified. As a result, the only figure of merit for the SOx trap performance has been total capacity, provided by post-characterization. In this paper we describe a chromatographic method for measurement of SO{sub 2} and SO{sub 3} adsorption in real time, which provides adsorbent performance data on breakthrough capacities and sulfur slip, especially important when operating at high space velocities. We also provide experimental measurements of break through capacities for SO{sub 2} and SO{sub 3} adsorption for some common metal oxide adsorbents using this analytical system.

Gasifier-derived syngas from coal has many applications in the area of catalytic transformation to fuels and chemicals. Raw syngas must be treated to remove a number of impurities that would otherwise poison the synthesis catalysts. Inorganic impurities include alkali salts, chloride, sulfur compounds, heavy metals, ammonia, and various P, As, Sb, and Se- containing compounds. Systems comprising multiple sorbent and catalytic beds have been developed for the removal of impurities from gasified coal using a warm cleanup approach. This approach has the potential to be more economic than the currently available acid gas removal (AGR) approaches and improves upon currently available processes that do not provide the level of impurity removal that is required for catalytic synthesis application. Gasification also lends itself much more readily to the capture of CO2, important in the regulation and control of greenhouse gas emissions. CO2 capture material was developed and in this study was demonstrated to assist in methane production from the purified syngas. Simultaneous CO2 sorption enhances the CO methanation reaction through relaxation of thermodynamic constraint, thus providing economic benefit rather than simply consisting of an add-on cost for carbon capture and release. Molten and pre-molten LiNaKCO3 can promote MgO and MgO-based doublemore » salts to capture CO2 with high cycling capacity. A stable cycling CO2 capacity up to 13 mmol/g was demonstrated. This capture material was specifically developed in this study to operate in the same temperature range and therefore integrate effectively with warm gas cleanup and methane synthesis. By combining syngas methanation, water-gas-shift, and CO2 sorption in a single reactor, single pass yield to methane of 99% was demonstrated at 10 bar and 330°C when using a 20 wt% Ni/MgAl2O4 catalyst and a molten-phase promoted MgO-based sorbent. Under model feed conditions both the sorbent and catalyst exhibited favorable stability after multiple test cycles. The cleanup for warm gas cleanup of inorganics was broken down into three major steps: chloride removal, sulfur removal, and the removal for a multitude of trace metal contaminants. Na2CO3 was found to optimally remove chlorides at an operating temperature of 450oC. For sulfur removal two regenerable ZnO beds are used for bulk H2S removal at 450oC (

A pencil lead successfully served as an electrode for the determination of ascorbic acid in commercial orange juice. Cyclic voltammetry was used as an electrochemical probe to measure the current produced from the oxidation of ascorbic acid with a variety of electrodes. The data demonstrate that the less expensive pencil lead electrode gives results that are comparable to those of a more expensive commercial carbon electrode. The level of vitamin C measured was higher than the daily intake recommended by Health Canada and the United States Food and Drug Administration, which is 60 mg/day for a healthy adult. The detection limit of the pencil lead electrode was also determined.

In collaboration with participants of the Coordinating Research Council (CRC) Advanced Vehicle/Fuels/Lubricants (AVFL) Committee, and project AVFL-19, the characteristics of fuels from advanced and renewable sources were compared to commercial diesel fuels. The main objective of this study was to highlight similarities and differences among the fuel types, i.e. ULSD, renewables, and alternative fuels, and among fuels within the different fuel types. This report summarizes the carbon-type analysis from 1H and 13C{1H} nuclear magnetic resonance spectroscopy (NMR) of 14 diesel fuel samples. The diesel fuel samples come from diverse sources and include four commercial ultra-low sulfur diesel fuels (ULSD), one gas-to-liquid diesel fuel (GTL), six renewable diesel fuels (RD), two shale oil-derived diesel fuels, and one oil sands-derived diesel fuel. Overall, the fuels examined fall into two groups. The two shale oil-derived samples and the oil-sand-derived sample closely resemble the four commercial ultra-low sulfur diesels, with SO1 and SO2 most closely matched with ULSD1, ULSD2, and ULSD4, and OS1 most closely matched with ULSD3. As might be expected, the renewable diesel fuels, with the exception of RD3, do not resemble the ULSD fuels because of their very low aromatic content, but more closely resemble the gas-to-liquid sample (GTL) in thismore » respect. RD3 is significantly different from the other renewable diesel fuels in that the aromatic content more closely resembles the ULSD fuels. Fused-ring aromatics are readily observable in the ULSD, SO, and OS samples, as well as RD3, and are noticeably absent in the remaining RD and GTL fuels. Finally, ULSD3 differs from the other ULSD fuels by having a significantly lower aromatic carbon content and higher cycloparaffinic carbon content. In addition to providing important comparative compositional information regarding the various diesel fuels, this report also provides important information about the capabilities of NMR spectroscopy for the detailed characterization and comparison of fuels and fuel blends.« less

The identification of the metabolite demoxepam in human urine establishes that chlordiazepoxide, a common benzodiazepine, has been administered. Like N-oxide metabolites of other drugs, demoxepam cannot be detected by gas chromatography—mass spectrometry (GC-MS), due to thermal decomposition, and the product, nordiazepam, is a metabolite common to many benzodiazepines. Demoxepam can be readily screened using a high-performance liquid chromatography (HPLC) system such as REMEDi HS; at 35°C, no thermal decomposition will occur. Currently, there is no confirmation method available for the detection of demoxepam in urine samples. In this study, we demonstrated that following collection of the HPLC fraction, demoxepam can be confirmed using the technique of direct-probe MS. The mass spectra of demoxepam and nordiazepam differ and are easily distinguishable from each other. Ten urine samples that were analyzed by HPLC and determined to contain demoxepam were evaluated; demoxepam was confirmed in each case by direct-probe MS.

A relatively simple single-photomask process was used to produce high-efficiency large-area solar cells on commercially available heat-exchanger-method (HEM) multicrystalline silicon (mc-Si). Large-area cell efficiencies up to 16.4% were achieved before lamination. These cells were built into two prototype one-sun modules whose performance has set a new standard for mc-Si photovoltaic modules (15% at standard reporting conditions). These results demonstrate that significant performance gains can be achieved in commercial mc-Si modules with currently available substrates through improved processing. Continued evolutionary developments in substrate and cell manufacturing promise to maintain, and likely improve mc-Si's PV market position.

EMCORE's Concentrator Photovoltaic (CPV) systems use large-format Fresnel lenses to achieve 1090X concentration onto high-efficiency multi-junction solar cells. The use of Fresnel lenses is common in CPV systems due to their thin profile and light weight. EMCORE uses silicone-on-glass (SOG) lens technology, which provides a high-reliability, high-durability alternative to acrylic lenses. This paper describes performance variations of these lenses based on the Fresnel groove depth. Both the optical efficiency and temperature dependence of the optical system are evaluated as a function of groove depth.

This report summarizes the carbon-type analysis from 1H and 13C{1H} nuclear magnetic resonance spectroscopy (NMR) of Fuels for Advanced Combustion Engines (FACE) diesel blends, FD-2B, FD 4B, and FD-7B, and makes comparison of the new blends with the original FACE diesel blends, FD 2A, FD 4A, and FD-7A, respectively. Generally, FD-2A and FD-2B are more similar than the A and B blends of FD-4 and FD-7. The aromatic carbon content is roughly equivalent, although the new FACE blends have decreased monoaromatic content and increased di- and tri-cycloaromatic content, as well as a higher overall aromatic content, than the original FACE blends. The aromatic components of the new FACE blends generally have a higher alkyl substitution with longer alkyl substituents. The naphthenic and paraffinic contents remained relatively consistent. Based on aliphatic methyl and methylene carbon ratios, cetane numbers for FD-2A and -2B, and FD-7A and -7B are predicted to be consistent, while the cetane number for FD-4B is predicted to be higher than FD-4A. Overall, the new FACE fuel blends are fairly consistent with the original FACE fuel blends, but there are observable differences. In addition to providing important comparative compositional information on reformulated FACE diesel blends, this report also provides important information about the capabilities of the team at Pacific Northwest National Laboratory in the use of NMR spectroscopy for the detailed characterization and comparison of fuels and fuel blends.

Preface 1. Overview of Feed-to-Liquid (XTL) Conversion David L. King and Arno de Klerk Conversion of Biomass and Coal 2. Experimental and Kinetic Investigation of CO2 and H2O/N2 Gasification of Biomass Fuels Heidi C. Butterman and Marco J. Castaldi 3. Evaluation of Trace Element Partitioning during the Initial Phase of Coal Combustion Using GFAAS Anna A. Raeva, Evguenii I. Kozliak, David T. Pierce, and Wayne S. Seames 4. The Use of S-XANES To Track Thermal Transformations of Metal Sulfides in Argonne Premium Coals Trudy B. Bolin Synthetic Liquids Production 5. On the Preparation of Low Temperature Iron Fischer-Tropsch Catalysts: Strategies That Work and Those That Do Not P. Julius Pretorius 6. Fischer-Tropsch Synthesis: Effect of Pt Promoter on Activity, Selectivities to Hydrocarbons and Oxygenates, and Kinetic Parameters over 15%Co/Al2O3 Wenping Ma, Gary Jacobs, Robert Keogh, Chia H. Yen, Jennifer L. S. Klettlinger, and Burtron H. Davis 7. Evaluation of Promoted Mo Carbide Catalysts for Fischer-Tropsch Synthesis: Synthesis, Characterisation, and Time-on-Stream Behaviour Dai-Viet N. Vo and Adesoji A. Adesina 8. Fischer-Tropsch Synthesis Investigation in a Gas-Inducing Agitated Reactor Using Electrical Capacitance Tomography Bawadi Abdullah, Chirag Dave, Cyrus G. Cooper, Tuan Huy Nguyen, and Adesoji A. Adesina 9. Indirect Liquefaction Carbon Efficiency Arno de Klerk Synthetic Liquids Refining 10. Effect of Feed Distribution on Hydrocracking of Fischer-Tropsch Wax Vincenzo Calemma and Chiara Gambaro 11. Hydrocracking Different Fischer-Tropsch Waxes: Model Simulations Chiara Gambaro and Vincenzo Calemma 12. Hexadecane Hydrotreating as a Surrogate for Fischer-Tropsch Wax Upgrading to Aviation Fuel Using a Co/MoO3/Silica-Alumina Catalyst Heinz J. Robota, Jeremy Jones, Mingsheng Luo, and Amanda Stewart 13. Experimental Investigation of the Oxidation of Methyl Oleate: One of the Major Biodiesel Fuel Components Mingming Lu and Ming Chai Editors' Biographies Indexes Author Index Subject Index

Internal steam reforming of methane within solid oxide fuel cells (SOFC) offers a method of improved thermal management and reduced system complexity. Thermal gradient management is dependent upon controlling the reforming activity along the length of the anode. The inherent activity of Ni-YSZ for the steam reforming of methane is highly dependent upon the pretreatment and reduction procedures employed. During reductive pretreatment of the anode, small Ni crystallites can exolve from the YSZ to provide a significant component to the initial catalytic activity. This activity decreases with time as the small Ni crystallites sinter. Control of this microstructure is key to controlling the thermal gradients along the anode. NiO initially dissolved in 5YSZ increases the amount of undesirable monoclinic phase, and the exolution of Ni crystallites during reduction results in a reduction in the monoclinic phase. With 8YSZ, nickel also dissolves and exolves from the YSZ particles but no monoclinic phase is observed.

Since January 1993, Progress in Photovoltaics has published six-monthly listings of the highest confirmed efficiencies for a range of photovoltaic cell and module technologies. 1–3

A multifactor experimental investigation of silicon surface texturing was conducted using aqueous potassium-hydroxide (KOH) solutions with isopropyl alcohol (IPA) added as a complexing agent. Czochralski, magnetic-Czochralski, and float-zone silicon wafers of different resistivities with both polished and lapped surfaces were included in the experiment. Process variables considered were solution temperature, time in solution, degree of mechanical mixing, KOH concentration, and IPA concentration. Using hemispherical reflectance as the primary gauge of success, process variables that resulted in an effective surface texture with reflectance less than 12% prior to antireflection coating were identified. Of particular interest was a low-temperature (70 degrees C) process with less than 2% concentration of both KOH and IPA and wide process variable tolerances. >

The capabilities of a versatile Nd:YAG pulsed-laser system developed at Sandia National Laboratories for solar cell processing applications is described. The results of statistically based, multifactor experiments used to characterize the influence of laser-system process variables on patterns produced in silicon wafers and silicon-oxide layers are presented, and an initial assessment of laser-grooved solar cell processing conditions is given. >

The successful commercialization of any new photovoltaic technology is difficult. Understanding the product's performance and aging characteristics is a prerequisite for the manufacturer. Amorphous-silicon thin-film modules are now in commercial production, and their market penetration is being limited to some degree by a lack of understanding of environmental influences that impact system design and operation. This paper summarizes our detailed performance characterization of multiple modules from four different manufacturers over several years of continuous outdoor exposure in Albuquerque, NM. Common stabilization characteristics have been observed for both tandem and triple-junction modules, and the influences of solar spectrum and seasonal (thermal) annealing have been clearly identified. Implications for system performance modelling are presented.

The commercialization of multi-junction solar cells for both space and terrestrial applications has increased the need to accurately determine cell performance using typical solar simulators and test equipment. This paper describes specific test methods recently applied in characterizing the performance of both tandem and triple-junction solar cells. Methods applied included: current-voltage measurements in forward and reverse bias using a xenon-arc solar simulator; absolute spectral response measurements of separate junctions using both light and voltage bias; a device simulation model; and a spectral mismatch calculation procedure tailored to multi-junction cells. Procedures are illustrated using measurements for GaInP-GaAs tandem cells, GaInP-GaAs-Ge triple-junction cells, and Ge cells supplied by different manufacturers.

CO2 capture from pre-combustion syngas in the temperature range of 250-400°C is highly desirable from an energy efficiency perspective. Thermodynamically, MgO is a promising material for CO2 capture, but the gas-solid reaction to produce MgCO3 is kinetically slow due to high lattice energy. We report here fast CO2 absorption over a solid MgO-molten nitrate/nitrite aggregate through phase transfer catalysis, in which the molten phase serves as both a catalyst and reaction medium. Reaction with CO2 at the gas-solid-liquid triple phase boundary results in formation of MgCO3 with significant reaction rate and a high conversion of MgO. This methodology is also applicable to other alkaline earth oxides, inspiring the design of absorbents which require activation of the bulk material.

A Pd/ZnO/Al2O3 catalyst was developed for the synthesis of methanol and dimethyl ether (DME) from syngas with temperatures of operation ranging from 250 °C to 380 °C. High temperatures (e.g. 380 °C) are of interest when combining methanol and DME synthesis with a methanol to gasoline (MTG) process in a single reactor bed. A commercial Cu/ZnO/Al2O3 catalyst, utilized industrially for the synthesis of methanol at 220–280 °C, suffers from a rapid deactivation when the reaction is conducted at high temperature (> 320 °C). On the contrary, a Pd/ZnO/Al2O3 catalyst was found to be highly stable for methanol and DME synthesis at 375 °C. The Pd/ZnO/Al2O3 catalyst was thus further investigated for methanol and DME synthesis at P = 34–69 bar, T = 250–380 °C, GHSV = 5000–18 000 h−1, and molar feeds H2/CO = 1, 2, and 3. Selectivity to DME increased with decreasing operating temperature, and increasing operating pressure. Higher space velocity and H2/CO syngas feed ratios also enhanced DME selectivity. Undesirable CH4 formation was observed, however, it could be lessen through choice of process conditions and by catalyst design. By studying the effect of the Pd loading and the Pd : Zn molar ratio the formulation of the Pd/ZnO/Al2O3 catalyst was optimized. A catalyst with 5% Pd and a Pd : Zn molar ratio of 0.25 : 1 has been identified as the preferred catalyst. Results indicate that PdZn particles are more active than Pdo particles for the synthesis of methanol and less active for CH4 formation. A correlation between DME selectivity and concentration of acid sites has been established. Hence, two types of sites are required for the direct conversion of syngas to DME: (1) PdZn particles are active for the synthesis of methanol from syngas, and (2) acid sites which are active for the conversion of methanol to DME. Additionally, CO2 formation was problematic as PdZn was found to be active for the water-gas-shift (WGS) reaction, under all the conditions evaluated.

Understanding the migration of Ni/NiO in Ni-YSZ can potentially help to design a better solid oxide fuel cell (SOFC) anode. We have observed that extensive hydrogen reduction and methane steam reforming of Ni-YSZ caused bulk migration of Ni/NiO to at least ~ 5 µm deeper from the Ni-YSZ surface. No significant bulk migration effects were detected after simple thermal treatments in non-reducing/non-reforming environment. Surface analysis of a single zirconia grain in the first 10-20 nm region from annealed, hydrogen reduced and methane steam reformed Ni-YSZ shows Ni-enriched surface supporting earlier claims of Ni exsolution. 3D-EBSD analysis of thermally treated sample before exposing it to reducing and reforming environment indicated mixed NiO/YSZ phase with some porosity and random grain orientation. The surface analysis and mapping were carried out using ToF-SIMS and AES whereas EDS maps on FIB sliced areas on Ni-YSZ were utilized for the bulk analysis. The results provide additional information related to complex reactions occurring in SOFC during internal reforming conditions.