Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic fractions of Class... more Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic fractions of Class F fly ashes from Central Appalachian coal sources. Although the enrichment is evident in the inductively coupled plasma–atomic emission spectroscopy (ICP-AES) determinations of the rare earth content, transmission electron microscopy–energy dispersive x-ray spectroscopy (TEM-EDS) examination of the fly ash fails to show the sites of the Gd or Pr. This apparent lack of correlation could be due to the inability of the EDS to detect low concentrations of the rare earth elements definitively; interferences in the analytics, leading to false positives in the chemical analysis; or the overlap of the energies of Gd and/or Pr with more abundant elements, leading to inaccurate negative results.
Four suites of fly ash, all generated at the same power plant, were selected for the study of the... more Four suites of fly ash, all generated at the same power plant, were selected for the study of the distribution of rare earth elements (REE). The fly ashes represented two runs of single‐seam/single‐mine coals and two runs of run‐of‐mine coals representing several coal seams from several mines. Plots of the upper continental crust‐normalized REE, other parameters derived from the normalization, and the principal components analysis of the derived REE parameters (including the sum of the lanthanides plus yttrium and the ratio of the light to heavy REE) all demonstrated that the relatively rare earth‐rich Fire Clay coal‐derived fly ashes have a different REE distribution, with a greater concentration of REE with a relative dominance of the heavy REE, than the other fly ashes. Particularly with the Fire Clay coal‐derived fly ashes, there is a systematic partitioning of the overall amount and distribution of the REE in the passage from the mechanical fly ash collection through to the las...
The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a Ni... more The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a NiMo/Al catalyst was studied at 380 °C and 3.5 MPa using octacosane (C28). The catalyst physical structure and acidity were characterized by BET, XRD, SEM-EDX and FTIR techniques. The N2 activation generated more active nonsulfided NiMo/Al catalyst relative to the H2 or H2S activation (XC28, 70–80% versus 6–10%). For a comparison, a NiMo/Si-Al catalyst was also tested after normal H2 activation and showed higher activity at the same process conditions (XC28, 81–99%). The high activity of the NiMo/Al (N2 activation) and NiMo/Si-Al catalysts was mainly ascribed to a higher number of Brønsted acid sites (BAS) on the catalysts. The hydrocracking of cobalt wax using Pt/Si-Al and Pt/Al catalysts confirmed the superior activity of the Si-Al support. A double-peak product distribution occurred at C4–C6 and C10–C16 on all catalysts, which illustrates secondary hydrocracking and faster hydrocracking...
Abstract Beneficiated fly ash from the combustion of Central Appalachian high volatile bituminous... more Abstract Beneficiated fly ash from the combustion of Central Appalachian high volatile bituminous coals was extracted with HNO3 in a pilot-scale processing plant. Several major oxides (notably CaO and SO3, but also including Fe2O3, MgO, K2O, and P2O5) and minor elements (Mn, As, Sr, Ba, and Pb) are depleted in the post-HNO3-extraction spent ash. The total lanthanides, Y, and Sc concentration is reduced by about 20% in the spent ash, with Gd showing the greatest decrease. Along with Gd, Nd and Dy are also well differentiated between the feed and spent ashes, with La and Sm showing minimal partitioning. The Gd decrease is correlated with the depletion of Fe2O3. The heavy rare earth elements (REE heavier than Eu) and Y are disproportionately concentrated in the HNO3-leachate compared to the light REE. For the ashes studied, Sc did not partition between the feed and spent ashes. Pozzolanicity tests show that the compressive strength and strength activity indices of the spent ash + ordinary Portland cement (OPC) mixes are comparable to 100% OPC, indicating that the spent ashes produced in the pilot-scale runs have the potential to be sold as a Class F fly ash. Ultimately, the beneficiated ash chemistry influences the chemistry of the post-HNO3-extraction spent ash and the HNO3-leachate. A 500-ppm-REE fly ash will presumably be a more economically favorable feedstock than an ash with a significantly lesser concentration.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated... more In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated in a pilot-scale facility in order to produce a product with a relatively consistent concentration of rare earth elements (REE). The <200-mesh final fly ash product was produced by removing the carbon- and Fe-rich particles prior to screening at 200 mesh (75 µm). The Plant D fly ash had high concentrations of CaO and SO3, which were diminished through the two months when the ash was being beneficiated, representing a consequence of the heat, humidity, and excessive rainfall in the Kentucky summer. The high CaO and SO3 concentrations through the early runs likely contributed to the lower REE in the <200-mesh products of those runs. Of the non-REE minor elements, Ba, V, Mn, Zn, and As showed the greatest between-run variations within the runs for each plant. The overall REE concentrations proved to be similar, both on a between-run basis for the individual fly ash sources and on a b...
The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsc... more The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsch synthesis (FTS) performance of a 15% Co/Al2O3 catalyst were investigated. The fresh and spent catalysts were characterized by BET, temperature programmed reduction (TPR), H2-chemisorption, NH3 temperature programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X ray diffraction (XRD). The catalysts were tested in a 1 L continuously stirred tank reactor (CSTR) at 220 °C, 2.2 MPa, H2/CO = 2.1 and 20–55% CO conversion. Addition of 1% of Cd or In enhanced the reduction degree of 15%Co/Al2O3 by ~20%, while addition of 1% Sn slightly hindered it. All three additives adversely impacted Co dispersion by 22–32% by increasing apparent Co cluster size based on the H2-chemisorption measurements. However, the decreased Co active site density resulting from the additives did not result in a corresponding activity loss; instead, the additives decreased the activity of the Co...
Highlights Decomposition of iron oxalate in CO atmosphere yields Hägg and theta carbides. Alk... more Highlights Decomposition of iron oxalate in CO atmosphere yields Hägg and theta carbides. Alkali promoter affects the carburization of iron. Fe with more basic alkali metal have shown higher conversion for CO2. K, Rb, Cs promoters increased olefins and oxygenates selectivity.
The dehydration reaction of 1,5-pentanediol was performed over CeO 2 and modified CeO 2 (CeO 2 ÀM... more The dehydration reaction of 1,5-pentanediol was performed over CeO 2 and modified CeO 2 (CeO 2 ÀMnO x , CeO 2 ÀZnO, CeO 2 ÀMgO, CeO 2 ÀCaO, CeO 2 ÀNa 2 O) catalysts in a fixed-bed tubular reactor at 350 8C and an atmospheric pressure. The undoped CeO 2 produced a mixture of the products containing mainly 4-penten-1-ol, 1-pentanol, cyclopentanol, cyclopentanone and tetrahydropyran-2-one from 1,5-pentanediol, while additions of MgO, MnO x , or ZnO to CeO 2 was found to enhance the overall production rate of unsaturated alcohol. On the other hand, more basic metals like CaO or Na 2 O tend to decline the dehydration activity of CeO 2. The porous structure of CeO 2 did not change appreciably with the addition of metal oxides. Temperature programmed desorption of adsorbed CO 2 on an activated catalyst suggest more CO 2 remain on the catalyst surface, particularly CeO 2 ÀCaO and CeO 2 ÀNa 2 O indicating that fewer defect sites are only available for reaction. The defect sites or oxygen vacancy on CeO 2 controls both activity and selectivity for the dehydration of 1,5-pentanediol.
Phosphorus promotion on Fischer-Tropsch (FT) synthesis was investigated for Co/Al 2 O 3 and Co/Si... more Phosphorus promotion on Fischer-Tropsch (FT) synthesis was investigated for Co/Al 2 O 3 and Co/SiO 2 catalysts having the same Co/P ratio. When P is added to Co/Al 2 O 3 , CO conversion on a per g catalyst basis decreased, while methane selectivity increased. Catalyst stability was higher for the sample containing both P and Pt. The main cause for lower initial conversion is Co site blocking, while the lower extent of cobalt reduction for the P-promoted Co/Al 2 O 3 sample played a lesser role. When SiO 2 is used to support cobalt particles, an initial induction period for the P-promoted catalyst was observed, where CO conversion increased. Higher CO conversion at steady state, as well as improved catalyst stability during FT testing, suggest that P hindered sintering. Over the same period, a decline and leveling off of conversion were observed for the unpromoted catalyst. Completely different effects were observed depending on support type. P only acted as a poison for Co/Al 2 O 3 , whereas beneficial effects on steady state CO conversion and stability occurred with Co/SiO 2. The different effects of P for Al 2 O 3 and SiO 2 supported Co catalysts can be explained by differences in Co-support interactions. With alumina, Co clusters are already stabilized by strong interactions with the support. P has no benefit, as it mainly interacts with alumina instead of Co; pore blocking by P also occurred. In contrast, SiO 2 has weak interactions with Co and less Co cluster stabilization. With P promotion, P anchors Co to the support, improving Co dispersion, stability and steady-state conversion.
Conversion of bio-oil from flash pyrolysis of biomass is a way to produce useful renewable feedst... more Conversion of bio-oil from flash pyrolysis of biomass is a way to produce useful renewable feedstocks for the chemicals industry. Dehydration of pentanediol (1,5-and 2,4-pentanediol) was investigated over CeO 2 , CeO 2-Ga 2 O 3 , and CeO 2-In 2 O 3 catalysts at 250-350 8C. Adding Ga or In (20 mol%) improved the conversion of pentanediol over CeO 2 , but adversely affected selectivity. In the base case, 1,5-pentanediol was converted on CeO 2 to 4-penten-1-ol and 1-pentanol, desired linear alcohols, together with unwanted cyclopentanol and cyclopentanone byproducts. Adding gallium or indium to ceria increased the selectivity towards undesired cyclized products like tetrahydropyran and tetrahydropyran-2-one due to increased acidity. In the base case, 2,4-pentanediol converted on CeO 2 to unsaturated alcohol (e. g., 3-penten-2-ol > 74 % selectivity), but adding Ga or In promoted acid-catalyzed cracking. Tuning the acid-base characteristics of ceria significantly alters the product distribution.
Highlights: Addition of phosphorus to Co/SiO2 up to 1 wt% improved FT activity and stability. ... more Highlights: Addition of phosphorus to Co/SiO2 up to 1 wt% improved FT activity and stability. Higher P loadings on Co/SiO2 were found to hinder the reduction of Co3O4. P anchors Co particles to the support and thus hindering Co sintering rate. FT product selectivity did not change appreciably for 0.5 and 1.0 wt% P.
The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S),... more The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S), and mechanism of sulfur poisoning Fe catalyst were studied using an iron Fischer-Tropsch synthesis (FTS) catalyst (100 Fe/5.1 Si/2.0 Cu/3.0 K). The FTS reaction was carried out at 230-270 o C, 1.3MPa, H 2 /CO = 0.67-0.77 and 30-70% CO conversion using a 1-L slurry phase reactor. The used Fe catalysts were characterized by XRD, Mössbauer spectroscopy and XANES spectroscopy to understand the deactivation mechanism of the Fe based catalyst after adding up to 1 ppm H 2 S in the feed. Co-feeding of 0.1 ppm H 2 S in syngas for 70 h changed very little the activity of the Fe catalyst, but increasing the H 2 S level to 0.2 ppm or above resulted in measurable deactivation of the Fe catalyst over a similar time period. The limit of sulfur level in the syngas feed (sensitivity) was determined to be 50 ppb. Co-feeding of up to 1.0 ppm H 2 S level was found to increase the extents of the secondary reaction of 1-olefins and the water gas shift (WGS) reaction even though the absolute rates were decreased with time. The addition of H 2 S decreased CH 4 selectivity and increased C 5+ selectivities of the Fe catalyst. The Fe/S ratio, which can be used to define the poison ability of sulfur for the iron catalyst, was quantified based on the deactivation data obtained. The Fe/S ratio strongly depended on temperature and decreased
A series of Co-Fe bimetallic catalysts was prepared, characterized and studied for the hydrogenat... more A series of Co-Fe bimetallic catalysts was prepared, characterized and studied for the hydrogenation of carbon dioxide reaction. The catalyst precursors were prepared via an oxalate co-precipitation method. Monometallic (Co or Fe) and bimetallic (Co-Fe) oxalate precursors were decomposed under N 2 flow at 400°C and further pretreated in 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 Mössbauer spectroscopy techniques. The hydrogenation reaction of CO 2 was performed using Co-Fe bimetallic catalysts pretreated in situ in a fixed-bed catalytic micro-reactor operating in the temperature range of 200-270°C and a pressure of 0.92 MPa. With increasing Fe fraction, the selectivity to C 2-C 4 for Co-Fe catalyst increased at 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 addition of iron. Among the three different activation conditions, the CO pretreated Co-Fe (50Co50Fe) catalyst exhibited a much lower selectivity for methane. Addition of 1 wt% Na or 1.7 wt% K to 50Co50Fe catalyst increases its olefinic (C 2-C 4) and oxygenates selectivities.
NOTE: Where it is feasible, a syllabus (headnote) will be released, as is being done in connectio... more NOTE: Where it is feasible, a syllabus (headnote) will be released, as is being done in connection with this case, at the time the opinion is issued. The syllabus constitutes no part of the opinion of the Court but has been prepared by the Reporter of Decisions for the convenience of the reader. See United States v.
Fischer–Tropsch (FT) synthesis continues to receive widespread attention. Even after 90 years of ... more 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.Graphical Abstract
The effect of ammonia in syngas on the Fischer-Tropsch Synthesis (FTS) reaction over 100 Fe/5.1 S... more The effect of ammonia in syngas on the Fischer-Tropsch Synthesis (FTS) reaction over 100 Fe/5.1 Si/2.0 Cu/3.0 K catalyst was studied at 220-270 o 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 cofeeding contaminants, and at the end of run) were characterized by ICP-OES, XRD, Mössbauer 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. NH 3 /av. Wt. feed) ammonia in syngas did not significantly deactivate the Fe catalyst or alter selectivities toward CH 4 , C 5+ , CO 2 , 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 Mössbauer spectroscopy did not display any evidence for the retention of a nitrogen-containing compound
Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic fractions of Class... more Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic fractions of Class F fly ashes from Central Appalachian coal sources. Although the enrichment is evident in the inductively coupled plasma–atomic emission spectroscopy (ICP-AES) determinations of the rare earth content, transmission electron microscopy–energy dispersive x-ray spectroscopy (TEM-EDS) examination of the fly ash fails to show the sites of the Gd or Pr. This apparent lack of correlation could be due to the inability of the EDS to detect low concentrations of the rare earth elements definitively; interferences in the analytics, leading to false positives in the chemical analysis; or the overlap of the energies of Gd and/or Pr with more abundant elements, leading to inaccurate negative results.
Four suites of fly ash, all generated at the same power plant, were selected for the study of the... more Four suites of fly ash, all generated at the same power plant, were selected for the study of the distribution of rare earth elements (REE). The fly ashes represented two runs of single‐seam/single‐mine coals and two runs of run‐of‐mine coals representing several coal seams from several mines. Plots of the upper continental crust‐normalized REE, other parameters derived from the normalization, and the principal components analysis of the derived REE parameters (including the sum of the lanthanides plus yttrium and the ratio of the light to heavy REE) all demonstrated that the relatively rare earth‐rich Fire Clay coal‐derived fly ashes have a different REE distribution, with a greater concentration of REE with a relative dominance of the heavy REE, than the other fly ashes. Particularly with the Fire Clay coal‐derived fly ashes, there is a systematic partitioning of the overall amount and distribution of the REE in the passage from the mechanical fly ash collection through to the las...
The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a Ni... more The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a NiMo/Al catalyst was studied at 380 °C and 3.5 MPa using octacosane (C28). The catalyst physical structure and acidity were characterized by BET, XRD, SEM-EDX and FTIR techniques. The N2 activation generated more active nonsulfided NiMo/Al catalyst relative to the H2 or H2S activation (XC28, 70–80% versus 6–10%). For a comparison, a NiMo/Si-Al catalyst was also tested after normal H2 activation and showed higher activity at the same process conditions (XC28, 81–99%). The high activity of the NiMo/Al (N2 activation) and NiMo/Si-Al catalysts was mainly ascribed to a higher number of Brønsted acid sites (BAS) on the catalysts. The hydrocracking of cobalt wax using Pt/Si-Al and Pt/Al catalysts confirmed the superior activity of the Si-Al support. A double-peak product distribution occurred at C4–C6 and C10–C16 on all catalysts, which illustrates secondary hydrocracking and faster hydrocracking...
Abstract Beneficiated fly ash from the combustion of Central Appalachian high volatile bituminous... more Abstract Beneficiated fly ash from the combustion of Central Appalachian high volatile bituminous coals was extracted with HNO3 in a pilot-scale processing plant. Several major oxides (notably CaO and SO3, but also including Fe2O3, MgO, K2O, and P2O5) and minor elements (Mn, As, Sr, Ba, and Pb) are depleted in the post-HNO3-extraction spent ash. The total lanthanides, Y, and Sc concentration is reduced by about 20% in the spent ash, with Gd showing the greatest decrease. Along with Gd, Nd and Dy are also well differentiated between the feed and spent ashes, with La and Sm showing minimal partitioning. The Gd decrease is correlated with the depletion of Fe2O3. The heavy rare earth elements (REE heavier than Eu) and Y are disproportionately concentrated in the HNO3-leachate compared to the light REE. For the ashes studied, Sc did not partition between the feed and spent ashes. Pozzolanicity tests show that the compressive strength and strength activity indices of the spent ash + ordinary Portland cement (OPC) mixes are comparable to 100% OPC, indicating that the spent ashes produced in the pilot-scale runs have the potential to be sold as a Class F fly ash. Ultimately, the beneficiated ash chemistry influences the chemistry of the post-HNO3-extraction spent ash and the HNO3-leachate. A 500-ppm-REE fly ash will presumably be a more economically favorable feedstock than an ash with a significantly lesser concentration.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated... more In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated in a pilot-scale facility in order to produce a product with a relatively consistent concentration of rare earth elements (REE). The <200-mesh final fly ash product was produced by removing the carbon- and Fe-rich particles prior to screening at 200 mesh (75 µm). The Plant D fly ash had high concentrations of CaO and SO3, which were diminished through the two months when the ash was being beneficiated, representing a consequence of the heat, humidity, and excessive rainfall in the Kentucky summer. The high CaO and SO3 concentrations through the early runs likely contributed to the lower REE in the <200-mesh products of those runs. Of the non-REE minor elements, Ba, V, Mn, Zn, and As showed the greatest between-run variations within the runs for each plant. The overall REE concentrations proved to be similar, both on a between-run basis for the individual fly ash sources and on a b...
The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsc... more The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsch synthesis (FTS) performance of a 15% Co/Al2O3 catalyst were investigated. The fresh and spent catalysts were characterized by BET, temperature programmed reduction (TPR), H2-chemisorption, NH3 temperature programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X ray diffraction (XRD). The catalysts were tested in a 1 L continuously stirred tank reactor (CSTR) at 220 °C, 2.2 MPa, H2/CO = 2.1 and 20–55% CO conversion. Addition of 1% of Cd or In enhanced the reduction degree of 15%Co/Al2O3 by ~20%, while addition of 1% Sn slightly hindered it. All three additives adversely impacted Co dispersion by 22–32% by increasing apparent Co cluster size based on the H2-chemisorption measurements. However, the decreased Co active site density resulting from the additives did not result in a corresponding activity loss; instead, the additives decreased the activity of the Co...
Highlights Decomposition of iron oxalate in CO atmosphere yields Hägg and theta carbides. Alk... more Highlights Decomposition of iron oxalate in CO atmosphere yields Hägg and theta carbides. Alkali promoter affects the carburization of iron. Fe with more basic alkali metal have shown higher conversion for CO2. K, Rb, Cs promoters increased olefins and oxygenates selectivity.
The dehydration reaction of 1,5-pentanediol was performed over CeO 2 and modified CeO 2 (CeO 2 ÀM... more The dehydration reaction of 1,5-pentanediol was performed over CeO 2 and modified CeO 2 (CeO 2 ÀMnO x , CeO 2 ÀZnO, CeO 2 ÀMgO, CeO 2 ÀCaO, CeO 2 ÀNa 2 O) catalysts in a fixed-bed tubular reactor at 350 8C and an atmospheric pressure. The undoped CeO 2 produced a mixture of the products containing mainly 4-penten-1-ol, 1-pentanol, cyclopentanol, cyclopentanone and tetrahydropyran-2-one from 1,5-pentanediol, while additions of MgO, MnO x , or ZnO to CeO 2 was found to enhance the overall production rate of unsaturated alcohol. On the other hand, more basic metals like CaO or Na 2 O tend to decline the dehydration activity of CeO 2. The porous structure of CeO 2 did not change appreciably with the addition of metal oxides. Temperature programmed desorption of adsorbed CO 2 on an activated catalyst suggest more CO 2 remain on the catalyst surface, particularly CeO 2 ÀCaO and CeO 2 ÀNa 2 O indicating that fewer defect sites are only available for reaction. The defect sites or oxygen vacancy on CeO 2 controls both activity and selectivity for the dehydration of 1,5-pentanediol.
Phosphorus promotion on Fischer-Tropsch (FT) synthesis was investigated for Co/Al 2 O 3 and Co/Si... more Phosphorus promotion on Fischer-Tropsch (FT) synthesis was investigated for Co/Al 2 O 3 and Co/SiO 2 catalysts having the same Co/P ratio. When P is added to Co/Al 2 O 3 , CO conversion on a per g catalyst basis decreased, while methane selectivity increased. Catalyst stability was higher for the sample containing both P and Pt. The main cause for lower initial conversion is Co site blocking, while the lower extent of cobalt reduction for the P-promoted Co/Al 2 O 3 sample played a lesser role. When SiO 2 is used to support cobalt particles, an initial induction period for the P-promoted catalyst was observed, where CO conversion increased. Higher CO conversion at steady state, as well as improved catalyst stability during FT testing, suggest that P hindered sintering. Over the same period, a decline and leveling off of conversion were observed for the unpromoted catalyst. Completely different effects were observed depending on support type. P only acted as a poison for Co/Al 2 O 3 , whereas beneficial effects on steady state CO conversion and stability occurred with Co/SiO 2. The different effects of P for Al 2 O 3 and SiO 2 supported Co catalysts can be explained by differences in Co-support interactions. With alumina, Co clusters are already stabilized by strong interactions with the support. P has no benefit, as it mainly interacts with alumina instead of Co; pore blocking by P also occurred. In contrast, SiO 2 has weak interactions with Co and less Co cluster stabilization. With P promotion, P anchors Co to the support, improving Co dispersion, stability and steady-state conversion.
Conversion of bio-oil from flash pyrolysis of biomass is a way to produce useful renewable feedst... more Conversion of bio-oil from flash pyrolysis of biomass is a way to produce useful renewable feedstocks for the chemicals industry. Dehydration of pentanediol (1,5-and 2,4-pentanediol) was investigated over CeO 2 , CeO 2-Ga 2 O 3 , and CeO 2-In 2 O 3 catalysts at 250-350 8C. Adding Ga or In (20 mol%) improved the conversion of pentanediol over CeO 2 , but adversely affected selectivity. In the base case, 1,5-pentanediol was converted on CeO 2 to 4-penten-1-ol and 1-pentanol, desired linear alcohols, together with unwanted cyclopentanol and cyclopentanone byproducts. Adding gallium or indium to ceria increased the selectivity towards undesired cyclized products like tetrahydropyran and tetrahydropyran-2-one due to increased acidity. In the base case, 2,4-pentanediol converted on CeO 2 to unsaturated alcohol (e. g., 3-penten-2-ol > 74 % selectivity), but adding Ga or In promoted acid-catalyzed cracking. Tuning the acid-base characteristics of ceria significantly alters the product distribution.
Highlights: Addition of phosphorus to Co/SiO2 up to 1 wt% improved FT activity and stability. ... more Highlights: Addition of phosphorus to Co/SiO2 up to 1 wt% improved FT activity and stability. Higher P loadings on Co/SiO2 were found to hinder the reduction of Co3O4. P anchors Co particles to the support and thus hindering Co sintering rate. FT product selectivity did not change appreciably for 0.5 and 1.0 wt% P.
The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S),... more The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S), and mechanism of sulfur poisoning Fe catalyst were studied using an iron Fischer-Tropsch synthesis (FTS) catalyst (100 Fe/5.1 Si/2.0 Cu/3.0 K). The FTS reaction was carried out at 230-270 o C, 1.3MPa, H 2 /CO = 0.67-0.77 and 30-70% CO conversion using a 1-L slurry phase reactor. The used Fe catalysts were characterized by XRD, Mössbauer spectroscopy and XANES spectroscopy to understand the deactivation mechanism of the Fe based catalyst after adding up to 1 ppm H 2 S in the feed. Co-feeding of 0.1 ppm H 2 S in syngas for 70 h changed very little the activity of the Fe catalyst, but increasing the H 2 S level to 0.2 ppm or above resulted in measurable deactivation of the Fe catalyst over a similar time period. The limit of sulfur level in the syngas feed (sensitivity) was determined to be 50 ppb. Co-feeding of up to 1.0 ppm H 2 S level was found to increase the extents of the secondary reaction of 1-olefins and the water gas shift (WGS) reaction even though the absolute rates were decreased with time. The addition of H 2 S decreased CH 4 selectivity and increased C 5+ selectivities of the Fe catalyst. The Fe/S ratio, which can be used to define the poison ability of sulfur for the iron catalyst, was quantified based on the deactivation data obtained. The Fe/S ratio strongly depended on temperature and decreased
A series of Co-Fe bimetallic catalysts was prepared, characterized and studied for the hydrogenat... more A series of Co-Fe bimetallic catalysts was prepared, characterized and studied for the hydrogenation of carbon dioxide reaction. The catalyst precursors were prepared via an oxalate co-precipitation method. Monometallic (Co or Fe) and bimetallic (Co-Fe) oxalate precursors were decomposed under N 2 flow at 400°C and further pretreated in 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 Mössbauer spectroscopy techniques. The hydrogenation reaction of CO 2 was performed using Co-Fe bimetallic catalysts pretreated in situ in a fixed-bed catalytic micro-reactor operating in the temperature range of 200-270°C and a pressure of 0.92 MPa. With increasing Fe fraction, the selectivity to C 2-C 4 for Co-Fe catalyst increased at 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 addition of iron. Among the three different activation conditions, the CO pretreated Co-Fe (50Co50Fe) catalyst exhibited a much lower selectivity for methane. Addition of 1 wt% Na or 1.7 wt% K to 50Co50Fe catalyst increases its olefinic (C 2-C 4) and oxygenates selectivities.
NOTE: Where it is feasible, a syllabus (headnote) will be released, as is being done in connectio... more NOTE: Where it is feasible, a syllabus (headnote) will be released, as is being done in connection with this case, at the time the opinion is issued. The syllabus constitutes no part of the opinion of the Court but has been prepared by the Reporter of Decisions for the convenience of the reader. See United States v.
Fischer–Tropsch (FT) synthesis continues to receive widespread attention. Even after 90 years of ... more 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.Graphical Abstract
The effect of ammonia in syngas on the Fischer-Tropsch Synthesis (FTS) reaction over 100 Fe/5.1 S... more The effect of ammonia in syngas on the Fischer-Tropsch Synthesis (FTS) reaction over 100 Fe/5.1 Si/2.0 Cu/3.0 K catalyst was studied at 220-270 o 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 cofeeding contaminants, and at the end of run) were characterized by ICP-OES, XRD, Mössbauer 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. NH 3 /av. Wt. feed) ammonia in syngas did not significantly deactivate the Fe catalyst or alter selectivities toward CH 4 , C 5+ , CO 2 , 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 Mössbauer spectroscopy did not display any evidence for the retention of a nitrogen-containing compound
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