Understanding Noble Metal Addition in Cobalt Fischer Tropsch Catalysts PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Understanding Noble Metal Addition in Cobalt Fischer Tropsch Catalysts PDF full book. Access full book title Understanding Noble Metal Addition in Cobalt Fischer Tropsch Catalysts by Kari Marie Cook. Download full books in PDF and EPUB format.
Author: Kari Marie Cook Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 188
Book Description
The effects of noble metal (NM) promotion and deposition order (co-deposition of NM with the final Co deposition [co-dep] or sequential deposition of NM after Co deposition [seq-dep]) on surface area, pore size, metal retention, crystallite size, noble metal distribution and bonding in Co Fischer Tropsch (FT) catalysts were studied as were the resulting Co reducibility and Fischer Tropsch activity/selectivity properties. Catalysts containing nominally 25wt% Co with either 0.3 wt% Ru, 0.58 wt% Pt, 0.55wt% Re, or no NM on a La-stabilized-Al2O3 support were prepared by wet deposition. The Co, Pt, and Re were uniformly dispersed, but Ru distribution and retention were problematic and deposition-order dependent--85% was lost with co-dep, but it was uniformly distributed while 54% was lost with seq-dep and it was concentrated at the pellet edge. The co-dep catalysts all have smaller reduced Co crystallite size than their corresponding seq-dep catalysts. The average crystallite diameters for all 3 co-dep catalysts are between 4.1 and 4.3nm and ~90% of the crystallites are 6nm. XAFS measurements showed that after reduction at 360oC, Pt is bonded with Co even with mild calcination between the final Co and the Pt deposition. On the other hand, neither Ru nor Re formed direct bonds with Co. Ru remained in a separate metal phase after reduction even at low loadings. Re remained as Re2O7 and still promoted Co reduction well (e.g. 42% reduced to Co metal compared to none for the unpromoted catalyst). By all measures of reducibility (TPR, EOR, H2 uptake), all NM promoted catalysts were more reducible than the unpromoted catalyst. The co-dep catalysts have lower TPR peak temperatures, but lower extents of reduction than their corresponding seq-dep catalysts. The NM type effect on overall extent of reduction trend was Co/Pt-seqCo/Re-seq>Co/Ru-seq=Co/Pt-co>Co/Re-co>Co/Ru-co>Co. The Co/Pt-co catalyst was the most active of all the catalysts both on rate per mass and per site basis. The co-dep catalysts were all more active than the corresponding sequentially deposited catalysts. The co-dep Pt and Re catalyst activity is greater due to higher activity per site, while co-dep Ru activity is greater due to a higher abundance of active sites.
Author: Kari Marie Cook Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 188
Book Description
The effects of noble metal (NM) promotion and deposition order (co-deposition of NM with the final Co deposition [co-dep] or sequential deposition of NM after Co deposition [seq-dep]) on surface area, pore size, metal retention, crystallite size, noble metal distribution and bonding in Co Fischer Tropsch (FT) catalysts were studied as were the resulting Co reducibility and Fischer Tropsch activity/selectivity properties. Catalysts containing nominally 25wt% Co with either 0.3 wt% Ru, 0.58 wt% Pt, 0.55wt% Re, or no NM on a La-stabilized-Al2O3 support were prepared by wet deposition. The Co, Pt, and Re were uniformly dispersed, but Ru distribution and retention were problematic and deposition-order dependent--85% was lost with co-dep, but it was uniformly distributed while 54% was lost with seq-dep and it was concentrated at the pellet edge. The co-dep catalysts all have smaller reduced Co crystallite size than their corresponding seq-dep catalysts. The average crystallite diameters for all 3 co-dep catalysts are between 4.1 and 4.3nm and ~90% of the crystallites are 6nm. XAFS measurements showed that after reduction at 360oC, Pt is bonded with Co even with mild calcination between the final Co and the Pt deposition. On the other hand, neither Ru nor Re formed direct bonds with Co. Ru remained in a separate metal phase after reduction even at low loadings. Re remained as Re2O7 and still promoted Co reduction well (e.g. 42% reduced to Co metal compared to none for the unpromoted catalyst). By all measures of reducibility (TPR, EOR, H2 uptake), all NM promoted catalysts were more reducible than the unpromoted catalyst. The co-dep catalysts have lower TPR peak temperatures, but lower extents of reduction than their corresponding seq-dep catalysts. The NM type effect on overall extent of reduction trend was Co/Pt-seqCo/Re-seq>Co/Ru-seq=Co/Pt-co>Co/Re-co>Co/Ru-co>Co. The Co/Pt-co catalyst was the most active of all the catalysts both on rate per mass and per site basis. The co-dep catalysts were all more active than the corresponding sequentially deposited catalysts. The co-dep Pt and Re catalyst activity is greater due to higher activity per site, while co-dep Ru activity is greater due to a higher abundance of active sites.
Author: Wilson D. Shafer Publisher: MDPI ISBN: 303928388X Category : Science Languages : en Pages : 414
Book Description
Since the turn of the last century when the field of catalysis was born, iron and cobalt have been key players in numerous catalysis processes. These metals, due to their ability to activate CO and CH, haev a major economic impact worldwide. Several industrial processes and synthetic routes use these metals: biomass-to-liquids (BTL), coal-to-liquids (CTL), natural gas-to-liquids (GTL), water-gas-shift, alcohol synthesis, alcohol steam reforming, polymerization processes, cross-coupling reactions, and photocatalyst activated reactions. A vast number of materials are produced from these processes, including oil, lubricants, waxes, diesel and jet fuels, hydrogen (e.g., fuel cell applications), gasoline, rubbers, plastics, alcohols, pharmaceuticals, agrochemicals, feed-stock chemicals, and other alternative materials. However, given the true complexities of the variables involved in these processes, many key mechanistic issues are still not fully defined or understood. This Special Issue of Catalysis will be a collaborative effort to combine current catalysis research on these metals from experimental and theoretical perspectives on both heterogeneous and homogeneous catalysts. We welcome contributions from the catalysis community on catalyst characterization, kinetics, reaction mechanism, reactor development, theoretical modeling, and surface science.
Book Description
Fischer-Tropsch Technology is a unique book for its state-of-the-art approach to Fischer Tropsch (FT) technology. This book provides an explanation of the basic principles and terminology that are required to understand the application of FT technology. It also contains comprehensive references to patents and previous publications. As the first publication to focus on theory and application, it is a contemporary reference source for students studying chemistry and chemical engineering. Researchers and engineers active in the development of FT technology will also find this book an invaluable source of information. * Is the first publication to cover the theory and application for modern Fischer Tropsch technology * Contains comprehensive knowledge on all aspects relevant to the application of Fischer Tropsch technology* No other publication looks at past, present and future applications
Author: B. H. Davis Publisher: CRC Press ISBN: 1420062573 Category : Science Languages : en Pages : 430
Book Description
Rising oil costs have stimulated significant interest in the Fischer-Tropsch synthesis (FTS) as a method for producing a synthetic petroleum substitute. Drawn from the proceedings at a symposium held during the 236th meeting of the American Chemical Society in Philadelphia in August 2008, Advances in Fischer-Tropsch Synthesis, Catalysts, and Cataly
Author: Burtron H. Davis Publisher: CRC Press ISBN: 1466555300 Category : Science Languages : en Pages : 424
Book Description
This book is based on a symposium held during the 248th American Chemical Society meeting that focused on use of the Fischer-Tropsch process in producing synthetic fuels. Its contents reflect the four dominant subjects of the meeting: catalyst preparation and activation, catalyst activity and reaction mechanisms, catalyst characterization and related reactions, and topics concerning commercializing the Fischer-Tropsch process. It covers recent developments related to renewable resources and green energy and provides a glimpse of the commercial potential of the Fischer-Tropsch process in synthetic fuel production.
Author: Gregory Robert Johnson Publisher: ISBN: Category : Languages : en Pages : 196
Book Description
Synthetic fuel production by means of Fischer-Tropsch synthesis (FTS) involves the catalytic hydrogenation of CO over Co-based catalysts. Often, these catalysts incorporate performance-enhancing additives known as promoters. Although not catalytically active for FTS by themselves, promoters can alter the structural and electronic properties of the active Co metal so as to improve catalyst activity, selectivity, or stability. Elements that form metal oxides have been studied for their ability to increase CO consumption rates and shift the product distribution toward higher molecular weight. Despite several decades of study of such elements, there remains limited understanding of the connections between these promotional effects and element properties. Accordingly, this dissertation focuses on clarifying the chemical basis for the effects of metal oxide promotion and making connections to periodic trends. To understand the importance of physical contact between the promoter and the Co, the influence of Co-Mn spatial association on the magnitude of Mn promotional effects was investigated. Elemental maps obtained by STEM-EDS revealed that different catalyst pretreatment methods could control how closely associated the promoter and Co were at the nanoscale. By relating these results to catalytic reaction data, it was determined that higher extents of contact between the two elements were correlated with higher selectivities toward C5+ hydrocarbons. This work was extended to the elements Ce, Gd, La, and Zr, which are among the most commonly studied metal oxide-forming promoters. The presence of the promoter element suppressed methane formation and increased the FTS chain propagation probability, but the sensitivity of these effects toward promoter loading was different for each element. Elements that deposited preferentially onto the Co nanoparticles led to rapid shifts in the product distribution as the promoter loading increased, whereas elements that dispersed over the entire catalyst surface resulted in more gradual changes. For all promoters, the product selectivities became insensitive to loading when the loading reached a quantity nearly equivalent to that which would form a half monolayer of the promoter on the Co nanoparticle surface. These trends are characteristic of the formation of active sites along the interface between the Co and the promoter that exhibit improved product selectivity. Structurally, the oxidation states and local coordination environments of the promoters were consistent with highly dispersed oxides. No evidence for the formation of bimetallic alloys or large promoter-containing crystallites was detected by either X-ray absorption spectroscopy or X-ray diffraction. These data suggest that small promoter oxide moieties decorate the surface of the Co metal nanoparticles so as to form metal-metal oxide interfaces. Under this model, the promotional effects increase in magnitude as the fraction of Co active sites that are adjacent to the promoter increases. When the Co surface is sufficiently covered by the promoter so that the fraction of active sites that are along the perimeter of the promoter moieties is nearly unity, the catalyst performance ceases to improve as a function of promoter loading. Guided by this reasoning, the catalytic properties of the promoted catalysts were investigated using samples in which the fraction of sites that were promoted was near unity. Measurements of reaction kinetics were conducted to assess the impact of metal oxide promotion on the rate parameters governing FTS. The rates of CO consumption for both unpromoted and metal oxide-promoted catalysts followed a Langmuir-Hinshelwood rate law for which H-assisted CO dissociation is assumed to be the rate determining step. Each promoter increased the apparent rate constant and the CO adsorption constant that appear within the rate law. Thus, metal oxide promotion appears both to facilitate the cleavage of the C-O bond and to enhance the extent of CO adsorption onto the catalyst. This finding was reinforced by CO temperature programmed desorption experiments and an evaluation of the effects of Mn promotion on the rate of CO disproportionation. Owing to the appearance of the CO adsorption constant in the numerator and denominator of the rate law, it is possible for promoted catalysts to have both higher and lower turnover frequencies than unpromoted catalysts depending on the chosen operating pressure. As a consequence, an optimal promoter can be found for maximizing the turnover frequency at a given operating pressure. However, product selectivity, which is largely determined by the availability of adsorbed H, is invariably improved by a higher CO adsorption constant because it decreases the ratio of adsorbed H to CO on the Co surface. Strong correlations between catalyst performance and the Lewis acidity of the promoter oxide suggest that Lewis acid-base interactions between the promoter and the adsorbed CO are the cause for the observed metal oxide promotional effects. Much of the experimental data presented in this work favors the hypothesis that CO can interact simultaneously with Co through the C atom and with the promoter cation through the O atom. These chemical interactions, in which the promoter serves as a Lewis acid, weaken the bond between C and O. Experimental evidence for this effect was observed in the lower activation barrier for CO hydrogenation over the ZrO2-promoted catalysts and the appearance of adsorbed carbonyl species on the MnO-promoted catalyst with severely redshifted C-O stretching frequencies measured by in situ infrared spectroscopy. These results provide insight into the chemical mechanism by which metal oxides affect the reaction and identify Lewis acidity of the promoter as the relevant descriptor for quantitatively predicting metal oxide-based promotional effects over Co FTS catalysts.
Author: Kari Marie Cook
Author: Kari Marie Cook
Author: Wilson D. Shafer
Author: André Steynberg
Author: B. H. Davis
Author: Shiro Watanabe
Author: Magdalena Maria Hauman Hauman
Author: Thierry Musanda Mukenz
Author: Burtron H. Davis
Author: Gregory Robert Johnson
Author: D. Kistamurthy