The effects of CeO2 doped with Na on the dehydration of 1,5-pentanediol were studied by using a fixed-bed reactor at two different temperatures (350 and 400 degrees C) and atmospheric pressure. For characterization, BET surface area, hydrogen temperature-programmed reduction, CO2 temperature-programmed desorption, and diffuse reflectance infrared Fourier transform spectroscopy techniques were utilized. The conversion of the diol on CeO2 was found to depend on Na loading. The selectivity to the desired product (i.e., unsaturated alcohol) increased and the selectivity to undesired products (i.e., tetrahydropyran, tetrahydropyran-2-one, cyclopentanol and cylopentanone) decreased with increasing Na content on CeO2. The basicity of hydroxyl groups or surface oxygen on CeO2 was altered with the addition of Na, and controlled the dehydration reaction pathway.

As a follow-up to a previous alkali chloride poisoning study, the effect of up to 100 ppm KCl on the FischerTropsch synthesis (FTS) performance of representative iron (Fe-Si-Cu doped with Rb as the alkali) and cobalt (PtCo/Al2O3) catalysts was studied at 270 degrees C and 230 degrees C, respectively, by co-feeding KCl in a water/ethylene glycol (EG) solution. The used catalysts were characterized by XANES at the K and Cl K-edges; furthermore, ICP was used to analyze residual K and Cl ions possibly remaining in the FTS products. KCl was found to be a weak poison for the iron and cobalt catalysts. The addition of 20-100 ppm KCl deactivated the catalysts to only a low to moderate extent. For the cobalt catalyst, less than 25 ppm KCl was found to give negligible deactivation. The added KCl and EG-H2O solvent was found to slightly modify the selectivity for both catalysts, such that KCl slightly promoted light hydrocarbon formation as well as olefins and slightly suppressed C5+ and 2-olefin formation, while the EG-H2O solvent was found to have a different effect on the C-1-C-4 and C5+ selectivities. It appears that K and Cl played opposite roles in modifying hydrocarbon selectivities. The ICP results suggested 48-98% K and Cl ions were adsorbed by the iron catalyst. XANES results confirmed the presence of K and Cl ions on the used iron and cobalt catalysts and showed a structure with characteristics that were similar to bulk KCl. Two possible mechanisms, including site blocking by K and Cl ions and electronic modification impacting CO/H-2 adsorption, were proposed to explain the deactivating effect of KCl on the iron and cobalt catalysts.

The hydrogenation of carbon dioxide over K-promoted FeCo bimetallic catalysts prepared by sequential oxalate decomposition and carburization of FeCo with CO was studied in a fixed-bed reactor at 240 degrees C and 1.2MPa. The initial CO2 conversion was found to be dependent on K loading, whereas both unpromoted and K-promoted FeCo catalysts (except 90Fe10Co3.0K) exhibited similar levels of CO2 conversion after a few hours of time on stream. A decarburization study on freshly activated and used FeCo suggests that potassium increases the stability of iron carbides and graphitic carbon under a reducing atmosphere. Also, K addition tends to decrease the hydrogenation function of FeCo bimetallic catalysts and, thus, controls product selectivity. Under similar CO2 conversions, potassium enhanced acetic acid formation while suppressing ethanol production, which indicates that a common intermediate might be responsible for the changes observed with C-2 oxygenates.

The purpose of this investigation was to examine the effect of sulfur impurity on 1%Pt/KL-zeolite catalyst by co-feeding 500 ppbv hydrogen sulfide (H2S) during hexane aromatization under industrially relevant conditions using a plug flow reactor. Product selectivity and hexane conversion were measured with time-on-stream and compared to a clean run carried out under otherwise identical conditions. Sulfur addition to the feed accelerated the rate of deactivation as observed by rapid declines in both hexane conversion and benzene selectivity; hexene selectivity, the product of the less structurally sensitive dehydrogenation reaction, increased significantly. After 20 h, which was enough time to observe sufficient deactivation, the reaction was stopped. For the purpose of catalyst characterization, after cooling to 150 °C, the catalyst was preserved in Polywax 725 to prevent catalyst oxidation. XANES analysis at the potassium K-edge suggests that the local environment for potassium was not significantly altered by sulfur addition, while sulfur K-edge results indicate that sulfur bound to platinum to form platinum sulfide (PtS, not PtS2). Platinum sulfide is likely responsible for accelerating Pt growth, as observed in DRIFTS of adsorbed CO and HR-TEM/STEM micrographs.

Corrosion of A106 carbon steel in anoxic CO2-loaded 30 wt.% monoethanolamine-based solutions (a corrosive solvent for post-combustion CO2 capture) with CO2 loadings ranging from 0.24 to 0.53 mol CO2/mol amine is investigated. The results show that corrosion and formation of a protective layer of corrosion products on the A106 surface are strongly CO2 loading-dependent. That is, initial corrosion is accelerated with increased CO2 loading. However, the formation of chukanovite and subsequently siderite, which dramatically inhibits the corrosion, was promoted with increasing CO2 loading. Chukanovite is a metastable intermediate corrosion product which transforms into siderite. Possible mechanisms are discussed. (C) 2015 Elsevier Ltd. All rights reserved.

The effect of phosphorus addition on silica-supported cobalt catalyst was investigated for Fischer-Tropsch synthesis (FTS). As shown by STEM images and chemisorption, the addition of phosphorus to cobalt of up to 1 wt% increased the dispersion of cobalt. Further addition of phosphorus (e.g., 3 and 5 wt.%), as demonstrated by TPR, pulse reoxidation, and XANES, significantly hindered the reduction of cobalt oxides. The cobalt FTS catalysts containing 0.5 and 1.0 wt% P exhibited greater stability in comparison with undoped and 3.0 wt% P containing cobalt catalysts. Analysis of XANES spectra at the P and Co K-edges, along with DRIFTS results of H-2-activated cobalt catalysts, suggest that cobalt particles interact with PO43- ions, indicating a role played by P in anchoring Co particles to the support, thus hindering the cobalt sintering rate. The initial selectivity to methane was slightly higher for 0.5%P-20%Co/SiO2 and 1.0%P-20%Co/SiO2 catalysts compared to the undoped catalyst, but at longer times differences were small. At higher loadings of P (3 wt.%), FT activity and selectivity were adversely and irreversibly affected. (C) 2016 Elsevier B.V. All rights reserved.

A series of Co–Fe bimetallic catalysts was prepared, characterized, and studied for the hydrogenation of carbon dioxide. The catalyst precursors were prepared via an oxalate coprecipitation method. Monometallic (Co or Fe) and bimetallic (Co–Fe) oxalate precursors were decomposed under a N2 flow at 400 °C and further pretreated under a CO flow at 250 °C. The catalysts (before decomposition of the oxalates or after activation) were characterized by BET, TGA-MS, X-ray diffraction, CO-TPR, SEM, HR-TEM, and Mossbauer spectroscopy techniques. The hydrogenation reaction of CO2 was performed using Co–Fe bimetallic catalysts pretreated in situ in a fixed-bed catalytic microreactor operating in the temperature range of 200–270 °C and a pressure of 0.92 MPa. With increasing Fe fraction, the selectivity to C2–C4 for Co–Fe catalyst increased under all operating conditions. The alcohol selectivity was found to increase with increasing iron content of the Co–Fe catalyst up to 50%, but then it dropped with further additi...

A pH stabilization method was investigated to mitigate corrosion in aqueous 5 M monoethanolamine for post-combustion CO2 capture. The room temperature pH of a naturally aerated CO2-loaded solution (i.e., 9.7) was adjusted with NaHCO3 powders to 9.3 and 9.1, and its effect on corrosion of A106 carbon steel was studied. Lower pH initially accelerated corrosion but promoted protective FeCO3 layer formation and subsequently A106 passivation (i.e., Fe3O4 formation). Dissolved oxygen also played a pivotal role by functioning as an additional oxidizer, retarding FeCO3 formation via preferentially oxidizing Fee* to form rust, and promoting passivation of A106 under the FeCO3 layer. (C) 2016 Published by Elsevier Ltd.

The effect of pretreatment conditions of cobalt on activity and product selectivity for the hydrogenation of carbon dioxide was studied over a 1%Na/20%Co SiO2 catalyst using a fixed-bed catalytic reactor operated at 220 degrees C and 1.89 MPa. The metallic form of cobalt was obtained from the reduction of cobalt oxide (CO3O4) by H-2 at 350 C and produced primarily methane and lower hydrocarbons (C-2-C-4) from CO2. Pretreatments with pure H-2 or syngas (H2 :CO) at 250 degrees C yield a fraction of partially reduced cobalt (COO), which tends to suppress the hydrogenation activity of cobalt somewhat, reducing methane selectivity to a limited degree. After CO activation, partially reduced cobalt oxide (CoO) and cobalt carbide phases formed and produced significantly less methane (i.e., selectivity of 15.3%), and surprisingly, the selectivity for alcohols increased to 73.2%. In the absence of sodium, direct methanation is still a preferred reaction for CO2 for CO pretreated cobalt: the XRD results of used catalysts revealed that the cobalt carbide phase converted to metallic cobalt. The results indicate that Na doping and carbide are important for low methane and high oxygenate selectivities. However, further work is needed to determine whether the role of Na is merely to stabilize the cobalt carbide phase, or whether Na is involved in promoting the catalytic cycle. (C) 2015 Elsevier B.V. All rights reserved.

The effect of ammonia in syngas on the Fischer-Tropsch synthesis (FTS) reaction over 100Fe/5.1Si/2.0Cu/3.0K catalyst was studied at 220-270 degrees C and 1.3 MPa using a 1-L slurry phase reactor. The ammonia added in syngas originated from adding ammonia gas, ammonium hydroxide solution, or ammonium nitrate (AN) solution. A wide range of ammonia concentrations (i.e., 0.1-400 ppm) was examined for several hundred hours. The Fe catalysts withdrawn at different times (i.e., after activation by carburization in CO, before and after co-feeding contaminants, and at the end of run) were characterized by ICP-OES, XRD, Mossbauer spectroscopy, and synchrotron methods (e.g., XANES, EXAFS) in order to explore possible changes in the chemical structure and phases of the Fe catalyst with time; in this way, the deactivation mechanism of the Fe catalyst by poisoning could be assessed. Adding up to 200 ppmw (wt. NH3/av. Wt. feed) ammonia in syngas did not significantly deactivate the Fe catalyst or alter selectivities toward CH4, C5+, CO2, C-4-olefin, and 1-C-4 olefin, but increasing the ammonia level (in the AN form) to 400 ppm rapidly deactivated the Fe catalyst and simultaneously changed the product selectivities. The results of ICP-OES, XRD, and Mossbauer spectroscopy did not display any evidence for the retention of a nitrogen-containing compound on the used catalyst that could explain the deactivation (e.g., adsorption, site blocking). Instead, Mossbauer spectroscopy results revealed that a significant fraction of iron carbides transformed into iron magnetite during co-feeding high concentrations of AN, suggesting that oxidation of iron carbides occurred and served as a major deactivation path in that case. Oxidation of chi-Fe5C2 to magnetite during co-feeding high concentrations of AN was further confirmed by XRD analysis and by the application of synchrotron methods (e.g., XANES, EXAFS). It is postulated that AN oxidized chi-Fe5C2 during FTS via its thermal dissociation product, HNO3. This conclusion is further supported by reaction tests with co-feeding of similar concentrations of HNO3. Additional oxidation routes of iron carbide to magnetite by HNO3 and/or by its thermal decomposition products are also considered: Fe5C2 + NOx (and/or HNO3) -> Fe3O4. In this study, ion chromatography detected that 50-80% HNO3 directly added or dissociated from AN eventually converted to ammonia during or after its oxidation of iron carbide, resulting from the reduction of NOx (NOx + H-2 + CO -> NH3 + CO2 + N-2 + H2O) by H-2 and/or CO. (C) 2015 Elsevier Inc. All rights reserved.

Fischer–Tropsch (FT) synthesis continues to receive widespread attention. Even after 90 years of investigation, the mechanistic route has yet to be fully defined. FT, as a polymerization process, uses CO and H2 as the reactants to produce a broad spectrum of hydrocarbons. Since the conception of the FT synthesis, several different isotopic routes have been employed for mechanistic studies. Various isotopes, such as 13C, 14C, 18O, and 2H, have been utilized through different types of experiments to shed light on the active site(s), the rate-limiting step, and the catalytic pathways. Direct evidence in the FT mechanism has been uncovered by utilizing experiments such as H2/D2 switching trials, as these experiments attempt to shed light on the rate-limiting step of CO hydrogenation. However, before hydrogen participates in the mechanism of CO hydrogenation, it may first dissociatively adsorb on the catalyst surface. The aim of this work is to ascertain to what extent H and D partition on the surface. This is accomplished by passing an equimolar H/D gas mixture over the activated FT catalyst, followed by a TPD method to determine if the active carbide surface displays a partitioning preference toward one of the isotopes. If a preference is observed, then the interpretation of kinetic isotopic effect (KIE) data ascertained in the CO hydrogenation switching experiments could potentially be affected. However, only a very slight isotopic preference toward deuterium was observed, and it is deemed not significant enough to affect an interpretation of the KIE based on H/D switching.

Fly ash was investigated with a variety of chemical, Mineralogical, petrographic, and microbeam:techniques from three coal-fired units, at two Kentucky power plants. Two units burn high sulfur Illinois Basin high volatile bituminous (hvb),coal) and the third unit burns a similar to 70:30 blend of high-sulfur Illinois Basin hvb Coal and law-sulfur, relatively high-CaO Powder Rivet Basin subbituminous coal. With high-S, high-Fe coals in all of the blends, spinel (Magnetite), is an important constituent in the fly ashes. Overall, the fly ashes are dominated by glass. Portlandite was noted in the high-Ca-coal-derived ash: Concentrations of Ba and Sr are highest in the latter fly ash,,a function of the Powder River Basin coal source for a portion of the blend. Rare earth elements do not have a high concentration in any of the fly ashes and do not show any significant partitioning between the electrostatic precipitator (ESP) Or baghouse rows in the individual generating units. In contrast to previously studied fly ashes from plants burning hvb,coals and to other fly ash specimens in this study, the fly ash from the unit burning the Illinois Basin/Powder River Basin coal blend did not have nanoscale carbon on the surface of the spherical inorganic fly ash particles. The absence of carbon may be a function of the nature of the feed coal, with 30% derived from the non-caking sub-bituminous, component in the coal blend, although some contribution of carbon derived-from caking hvb coal would be,expected. The fly ash carbon content is very low, suggesting that the amount of carbon rather than or along with the tank of the coal May be a determining,factor in the absence of nanoscale carbon deposition on the surface of the fly ash particles.

The University of Kentucky Center for Applied Energy Research has conducted a survey of Kentucky\'s utility coal-fired power plants every 5 years since 1992. The survey includes a collection of the feed coal and the coal combustion products (CCPs). The latest collection was in 2012, with the accompanying information survey covering trends in 2011. Overall coal-fired energy production decreased, and the nature of the CCPs changed for a number of reasons, including but not limited to, increased gas production in the Appalachians, a series of warm winters, energy conservation, depletion of Appalachian coal reserves, and utility responses to regulations. From 2011 to 2012, Kentucky\'s coal-fired generation decreased from 91.656 to 82.762 GWh, while gas-fired generation rose from 1.163 to 2.401 GWh. About 10% of the CCPs produced in 2011 were sold compared with 30% in 2006. Some of this can be attributed to an increase in the amount of CCPs in certain categories, primarily flue-gas desulfurization (FGD) gypsum. The latter increase was due to regulations requiring the installation of FGD, while stagnation and decreases in sales were due to multiple factors, including the slowdown in housing construction and to the saturation of the Ohio River Valley market. Overall, comparing 2011 with 2006, all categories of CCPs experienced a decline in sales. The change from low-S to high-S coal with the installation of wet-FGD units has resulted in a shift from low-Fe to high-Fe fly ashes.

Dimethyl Ether (DME) is an alternative liquid fuel developed mainly from coal and natural gas that can be used in compression ignition (CI) engines without major modifications to the diesel configuration. One of the advantages of DME combustion is the low emission levels of nitrous oxides (NOx) and particulate matter (PM) when compared to diesel combustion. Research so far were largely focused on tackling issues due to less viscosity and low heating capacity of DME as compared to diesel and in developing DME specific fuel system to overcome its incompatibility with rubber seals. In this paper, the body of experimental and numerical research on gaseous and PM emissions from DME combustion is reviewed, with the objective being to identify promising methods for emission control in DME engines. Gaseous emissions from DME combustion is a well-researched topic, while PM emissions has not yet been explored in detail. PM emissions, especially ultra-fine particulate matter (UFPM), are expected to become a major concern with the implementation of future emission norms. This review paper critically evaluates some of the novel methods of emission control in CI engines to meet future emission regulations using fuel injection strategies, combustion after-treatment and suggests future direction for DME research.

Low temperature water–gas shift (LT-WGS) was performed over various group I alkali metal (Li, Na, K, Rb, Cs) promoted cobalt carbide (Co2C) catalysts at temperatures ranging from 453 to 573 K and atmospheric pressure. Cobalt carbide (Co2C) was found to be active for the WGS reaction. The stability of the catalyst is related to the stability of the cobalt carbide phases under reaction conditions. Potassium promoted cobalt carbide catalysts exhibited higher activity and stability compared to the other alkali promoted catalysts for LT-WGS. X-ray diffraction analyses of fresh and used catalysts suggest that the origin of deactivation of the catalysts is primarily due to the chemical transition of cobalt from carbide to metal during WGS.

The goal of this work is to explore the ability of the metal-promoted 25%Co/Al2O3 catalyst to maintain good contact between the metal and cobalt and continue facilitating Co oxide reduction after simulated regeneration cycles through oxidation-reduction treatments, an approach designed to simulate the catalyst regeneration process. Unpromoted 25%Co/Al2O3 catalyst was also subjected to treatments and served as a reference. Seven metal promoters were examined in this work, including Pt, Ru, Re, Ag, Au, Rh, and Ir. Fresh and treated catalysts were evaluated by both TPR and XANES spectroscopy, the latter approach utilizing linear combination fittings with appropriate reference compounds. With the unpromoted catalyst, oxidation-reduction cycles tended to have two effects: (1) a fraction of CoO species that lost their interaction with the support emerged and (2) a fraction of more strongly interacting CoO species was formed. A comparison between the freshly calcined sample and samples subjected to simulated regeneration cycles was demonstrated. Pt-, Ru-, Re-, Ag-, and Rh-promoted 25%Co/Al2O3 catalysts maintained their ability to facilitate Co oxide reduction after undergoing oxidation-reduction cycles even up to 3 cycles, while with Ir- and, especially, Au-25%Co/Al2O3 some losses were observed, suggesting some separation between the promoter and cobalt occurred following the treatment cycles. TPR profiles also suggest that some separation of Ru from Co occurs with simulated regeneration cycles, although it does not impact the extent of reduction of Co after three cycles. (C) 2013 Elsevier B.V. All rights reserved.

The sensitivity of 100Fe/5.1Si/2Cu/3K Fischer-Tropsch synthesis (FTS) catalyst to the impurities of KCl, NaCl, KHCO3 and NaHCO3 in syngas (0.1-100 ppm) was studied in a slurry phase reactor at 533.2 or 543.2K, H-2/CO = 0.67-0.77, 1.31 MPa and 10 NL/g-cat/h. The impurities were co-fed with syngas, and the influence of each contaminant concentration on Fe catalyst behavior was examined for 72-144h. The presence of up to 40 ppmw halide compounds (NaCl and KCl) or alkali bicarbonates (NaHCO3 and KHCO3) in syngas at 543.2 K or up to 100 ppm of NaCl and KCl at 533.2 K had little impact on the Fe catalyst activity and selectivities to CH4, C5+ and C-4 olefin and 1-olefin during 400 h (543.2 K) or 1400h testing (533.2 K). CO2 selectivity slightly increased after feeding the impurity-containing solutions, which was due to enhanced water gas shift (WGS). ICP results for the Fe catalysts at the end of the FTS reaction test and of the FTS products (i.e., water, oil or wax phase) indicate that the impurity ions (K+, Na+ or Cl-) introduced were present in all phases of the FTS products, the greater part being retained in the wax. Therefore, the contaminant ions (i.e., Na, K or Cl) in the water solution injected appear to not strongly adsorb on the Fe catalyst surface at typical FTS conditions in the slurry phase reactor. This is assumed to be responsible for the lack of change in FTS behavior for the Fe catalyst using the contaminants studied. (C) 2013 Elsevier B.V. All rights reserved.