| 1. |
- Lualdi, Matteo, et al.
(författare)
-
Effect of Ti and Al addition via direct synthesis to SBA-15 as support for cobalt based Fischer-Tropsch catalysts
- 2012
-
Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 443-444, s. 76-86
-
Tidskriftsartikel (refereegranskat)abstract
- Different mesoporous SBA-15 supports doped with Ti and Al at 5 and 10 wt% have been synthesized by means of direct synthesis. The supports have been characterized by N 2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), NH 3-temperature programmed desorption (NH 3-TPD), H 2-chemisorption, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM). Titanium doped materials showed to have much shorter channels than the pristine SBA-15, while aluminum addition did not have a significant effect on channel length. After impregnation with 12 wt% Co, the catalysts were further characterized and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483 K, 20 bar, H 2/CO ratio = 2.1, pellet size: 53-90 μm) with and without external water addition. The S C5 + values of the different SBA-supported catalysts were low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitations increased the H 2/CO ratio inside the 1-dimensional (1D) porous network. The selectivity data showed a correlation between the channel length and the extent of CO-diffusion limitations at much shorter diffusion distances than those for conventional 3D porous supports. Water partial pressure showed to increase the syngas diffusion rate (i.e. removal of diffusion limitations on reactants’ arrival), to have a positive kinetic effect on the rate and to favor longer chain hydrocarbons.
|
|
| 2. |
- Lualdi, Matteo, et al.
(författare)
-
Evidence for diffusion-controlled hydrocarbon selectivities in the fischer-tropsch synthesis over cobalt supported on ordered mesoporous silica
- 2011
-
Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 54:16-18, s. 1175-1184
-
Tidskriftsartikel (refereegranskat)abstract
- A series of four cobalt-based catalysts (two of which promoted with ruthenium) supported on SiO2 or SBA-15 were prepared and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483 K, 20 bar, H2/CO ratio = 2.1, pellet size: 53-90 μm). The catalysts were characterized by N2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), H2-chemisorption and transmission electron microscopy (TEM). Ru as promoter enhanced the activity but not the selectivity to long-chain hydrocarbons ({S}-{C}-{ 5+}). The {{S}}-{{C}}-{5+}} values of the SBA-supported catalysts were very low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitation increased the H2/CO ratio inside the 1-dimensional (1-D) porous network. A superimposition of the selectivity results on the correlations found in our recent study, derived for Co-based catalysts supported on γ-Al2O3, α-Al2O3 and TiO2 free from diffusion limitations, was made. While the SiO2-supported catalysts with a 3-D porous structure followed the correlations, the SBA-catalysts deviated significantly at low conversions, giving a further indication that the selectivity results of these catalysts were affected by CO diffusion limitations. Hence, it may be concluded that the kinetically significant diffusion distances (i.e. those long enough to cause an intrapore H 2/CO ratio higher than that of the bulk gas phase) are probably much shorter for 1-D porous networks than for conventional 3-D supports. This is explained by a significantly lower effective diffusivity in 1-D porous networks. The potential of using the correlations between non-ASF distributed hydrocarbons and C5+, to give insight on the occurrence of diffusion limitations, was confirmed by superimposing data from the literature that were anticipated to be influenced by CO diffusion limitations.
|
|
| 3. |
- Lualdi, Matteo, et al.
(författare)
-
Investigation of mixtures of a Co-based catalyst and a Cu-based catalyst for the fischer-tropsch synthesis with Bio-Syngas : The importance of indigenous water
- 2011
-
Ingår i: Topics in catalysis. - : Springer-Verlag New York. - 1022-5528 .- 1572-9028. ; 54:13-15, s. 977-985
-
Tidskriftsartikel (refereegranskat)abstract
- A series of different mechanical mixtures of a narrow-pore Co/γ-Al2O3 catalyst and a Cu-based WGScatalyst has been investigated in the low-temperature Fischer-Tropsch synthesis (483 K, 20 bar) with a model bio-syngas (H2/CO = 1.0) in a fixed-bed reactor. The higher the fraction of WGS-catalyst in the mixture, the lower is the Co-catalyst-time yield to hydrocarbons. This is ascribed to a strong positive kinetic effect of water on the Fischer-Tropsch rate of the Co-catalyst, showing the importance of the indigenously produced water, especially in fixed-bed reactors where the partial pressure of water is zero at the reactor inlet. A preliminary kinetic modeling suggests that the reaction order in PH2O is 0.3 for the Co/γ-Al2O3 catalyst in the range of the studied reactor-average partial pressures of water (i.e., 0.04-1.2 bar).
|
|
| 4. |
- Lualdi, Matteo, et al.
(författare)
-
On the effect of water on the Fischer-Tropsch rate over a Co-based catalyst : The influence of the H2/CO ratio
- 2013
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 214, s. 25-29
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of water partial pressure on the Fischer-Tropsch (FT) rate of a cobalt catalyst supported on narrow-pore γ-Al2O3 was investigated at industrially relevant process conditions (483 K, 30 bar, pellet size: 53-90 μm). Inlet water partial pressure was varied up to 9 bar by external water vapour addition at different H2/CO molar ratios ranging from 1 to 3. The effect of water was found to be positive on FT-rate independently of the H2/CO ratio, but more significantly at H 2-poor condition. Temperature-programmed hydrogenation (TPH) was used to verify the presence of unreactive carbon species on the catalyst after 22 h on stream at the different conditions with and without exposure to about 9 bar water. A higher temperature feature that could be associated to amorphous polymeric carbon was detected at H2-poor conditions but remained unchanged upon 2 h of water exposure which did not result in a change in the amount of amorphous polymeric carbon detectable by TPH.
|
|
| 5. |
- Lögdberg, Sara, et al.
(författare)
-
Effect of water on the space-time yield of different supported cobalt catalysts during Fischer-Tropsch synthesis
- 2011
-
Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 393:1-2, s. 109-121
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of partial pressure of water on the Fischer-Tropsch (FT) rate of six cobalt-based catalysts supported on three different carrier materials (gamma-Al2O3, alpha-Al2O3, TiO2) with varying Co particle sizes was investigated in a fixed-bed reactor by changing space velocity and by external water vapour addition. A typical catalyst pellet size (<100 mu m) for industrial slurry-bed FT reactors was used. Water was found to have a positive kinetic effect, at least up to moderate amounts, on the FT rate of all catalysts in the present study, including the gamma-Al2O3-supported catalyst with pores smaller than similar to 10 nm. The reason for the apparent negative effect on the space-time yield at a direct exposure of Co supported on narrowpore gamma-Al2O3 to high partial pressures of water is due to a rapid and extensive deactivation. This could be ascribed to formation of hard-to-reduce oxidized cobalt species. The choice of support material was found to have a major effect on the response to changes in partial pressure of water, both with respect to deactivation behaviour and kinetics. However, there is a minor Co-particle size effect on the magnitude of the kinetic effect of water, larger Co particles showing a more positive response. Different extents of mass transfer limitations and/or differences in fugacities of H-2, CO and water among the six catalysts could be ruled out as causes for the observed differences.
|
|
| 6. |
- Lögdberg, Sara, et al.
(författare)
-
On the selectivity of cobalt-based Fischer-Tropsch catalysts : Evidence for a common precursor for methane and long-chain hydrocarbons
- 2010
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 274:1, s. 84-98
-
Tidskriftsartikel (refereegranskat)abstract
- A total of 36 cobalt-based supported catalysts were investigated in the Fischer-Tropsch reaction at industrially relevant process conditions: 483 K, 20 bar, molar H-2/CO ratio = 2.1, pellet size: 53-90 mu m. The effect of adding water vapour to the feed was investigated for 20 of the catalysts, and a H-2/CO ratio of 1.0 was used for a few catalysts. The catalysts differed in support material, Co loading, promoters, Cl content, Co particle size (larger than similar to 6 nm), morphology, degree of reduction and preparation technique and showed a large variation in selectivity. For each set of process conditions, a linear relationship seems to exist between the selectivity to methane (and other light products) and C5+ indicating a common precursor, i.e. a common monomer pool, for all hydrocarbon products. A high selectivity to C5+ is mainly an effect of a high intrinsic chain-growth probability and unlikely to be a result of an enhanced cc-olefin readsorption. The universal effect of external water addition on the hydrocarbon selectivities is limited to a decrease in the methane selectivity. A small proportion of the catalysts developed "pure methanation" sites upon exposure to high partial pressures of water.
|
|
