| 1. |
- Arora, Prakhar, 1987
(författare)
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Catalytic Upgrading of Waste Oils to Advanced Biofuels – Deactivation and Kinetic Modelling Study
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for liquid hydrocarbons as transportation fuels is enormous and ever growing. Advanced biofuels is one of the promising solutions to keep pace with the global transition to cleaner energy by reducing greenhouse gas emissions from the transport sector. It is possible to selectively remove oxygen from waste oils like tall oil, used cooking oil etc. via a catalytic hydrodeoxygenation (HDO) process to produce advanced biofuels. These biofuels have similar molecules as in the traditional fossil-based fuels and exhibit improved performance. This thesis focuses on aspects of catalyst deactivation and kinetic modelling of HDO reactions. In the first study, the influence of iron (Fe) as a poison during HDO of a model compound for renewable feeds (Oleic acid) over molybdenum based sulfided catalysts was investigated. Fe is a potential contaminant in renewable feeds due to corrosion during transportation and storage in iron vessels. A series of experiments with varying Fe-oleate concentration in the feed over MoS2/Al2O3 and NiMoS/Al2O3 catalysts. There was a salient drop in the activity of the catalysts. At higher Fe concentration, for the NiMoS catalyst, the selectivity for the direct hydrodeoxygenation product (C18 hydrocarbons) increased. However, it was opposite for the MoS2 catalyst. There was a decrease in the yield of direct hydrodeoxygenation products and an increase in yield of decarbonated products. It was proposed that Fe interacted with these two catalyst systems differently. Fe influenced the critical step of creation of sulfur vacancies in a negative way which resulted in lower activity. Microscopic analysis indicated that Fe was preferentially deposited close or around the nickel promoted phase, which explained why the role of Ni as a promoter for the decarbonation route was subdued for the NiMoS catalyst. In the second study, the kinetics during HDO of stearic acid (SA) over a sulfided NiMo/Al2O3 catalyst were explored to investigate the reaction scheme. Model compounds like octadecanal (C18=O) and octadecanol (C18-OH) were employed to understand the reaction steps and quantify the selectivity. A Langmuir–Hinshelwood-type kinetic model was used to investigate the kinetics. The results from the proposed kinetic model were found to be in good agreement with experimental results. In addition, the model could effectively reproduce the observed experimental profiles of different intermediates like C18=O and C18-OH and illustrate phenomena like inhibiting effects of the fatty acid.
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| 2. |
- Arora, Prakhar, 1987
(författare)
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Deactivation of Catalysts and Reaction Kinetics for Upgrading of Renewable Oils
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transport sector is one of the main contributors of greenhouse gas emissions in the world. Advanced biofuels from renewable oils can play a decisive role in reducing carbon emissions from the transport sector. Advanced biofuels from waste streams like tall oil, used cooking oil etc. can lower the CO2 emissions in a range of up to 90% making our future and society more sustainable. Catalytic hydrodeoxygenation (HDO) is a process in which oxygen is selectively removed from renewable oils to produce advanced biofuels. These biofuels are drop-in hydrocarbons which can substitute fossil-based fuels without infrastructure or vehicle changes. This thesis focuses on aspects of catalyst deactivation and reaction kinetics during the production of such biofuels via HDO reactions. Renewable oils can be sourced from varied streams like tall oil (paper industry residue), animal fats, used cooking oil etc. due to which their composition and innate contaminants can vary significantly. Phosphorus, alkali metals like potassium or sodium, iron, silicon, chlorides etc. are some of the common poisons present in renewable feedstocks which can cause catalyst deactivation during the upgrading process. In the first section of this thesis, the influence of iron (Fe), phosphorus (from phospholipid) and potassium (K) as poisons during HDO of fatty acids over molybdenum based sulfided catalysts was investigated. A range of concentration of poisons was evaluated to show that these poisons severely impacted the activity of catalysts. A change in selectivity was also seen, which is an important parameter to consider during the industrial production of biofuels. Different characterization techniques were employed to study the poison distribution on catalyst samples from lab experiments as well as from a refinery. It was suggested that Fe deposits preferentially near Ni-rich sites which deteriorated the ability of these catalysts to create active sites i.e. via sulfur vacancies. However, phosphorus resulted in irreversible phase transformation of the support to aluminum phosphate (AlPO4) which resulted in catalyst deactivation via pore blockage. In the comparative experiments, with spherical catalyst particles (1.8 mm), the Fe caused the strongest deactivation among P and K, based on the quantity added to feed oil. Although, considering the decrease in surface area per unit of deposited element after the experiment, then P caused the most deactivation. It was concluded that Fe deposited mostly near to the outer surface irrespective of concentration while P and K penetrated deeper in catalyst particles such that the distribution profile was dependent on the concentration. Reaction kinetics of HDO of fatty acids provides critical knowledge which could be applied at the refining scale in process design and optimization. The activity and selectivity of NiMo catalyst during HDO of stearic acid was studied by varying reaction conditions like temperature, pressure, feed concentration and batch-reactor stirring rate and using intermediates like octadecanal and octadecanol. A deeper understanding of the reaction scheme and selectivities was developed based on the experimental results. A Langmuir–Hinshelwood-type mechanism was used to develop a kinetic model which well-predicted the changes in selectivities at varying reaction conditions.
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| 3. |
- Arora, Prakhar, 1987, et al.
(författare)
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Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts
- 2018
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 227, s. 240-251
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Tidskriftsartikel (refereegranskat)abstract
- The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) overmolybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 °C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Nipromoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C18 hydrocarbons)increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C18 hydrocarbons) products and an increase in yield of decarbonated products (C17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.
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| 4. |
- Arora, Prakhar, 1987, et al.
(författare)
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Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.
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| 5. |
- Arora, Prakhar, 1987, et al.
(författare)
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The role of catalyst poisons during hydrodeoxygenation of renewable oils
- 2021
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 367, s. 28-42
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Tidskriftsartikel (refereegranskat)abstract
- Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.
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| 6. |
- Cheah, You Wayne, 1993, et al.
(författare)
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Role of transition metals on MoS 2 -based supported catalysts for hydrodeoxygenation (HDO) of propylguaiacol
- 2021
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Ingår i: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 5:7, s. 2097-2113
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal sulfides (TMSs) are typically used in the traditional petroleum refining industry for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) applications. Bio-oils require an upgrading process like catalytic hydrodeoxygenation (HDO) to produce advanced biofuels and chemicals. Herein, MoS /γ-Al O promoted by transition metals like nickel (Ni), copper (Cu), zinc (Zn), and iron (Fe) was evaluated for the HDO of a bio-oil model compound, 4-propylguaiacol (PG) in a batch reactor at 340 °C under 50 bar H pressure. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a high 94% yield of deoxygenated cycloalkanes, however for the sulfided Cu-promoted catalyst, 42% of phenolics remain in the reaction medium after 5 h. The results also revealed that the sulfided Zn and Fe-promoted catalysts gave a final yield of 16% and 19% at full PG conversion, respectively, for deoxygenated aromatics. A kinetic model considering the main side reactions was developed to elucidate the reaction pathway of demethoxylation and dehydroxylation of PG. The developed kinetic model was able to describe the experimental results well with a coefficient of determination of 97% for the Ni-promoted catalyst system. The absence of intermediates like 4-propylcyclohexanone and 4-propylcyclohexanol during the reaction implies that direct deoxygenation (DDO) is the dominant pathway in the deoxygenation of PG employing sulfided catalysts. The current work also demonstrated that the activity of the transition metal promoters sulfides for HDO of PG could be correlated to the yield of deoxygenated products from the hydrotreatment of Kraft lignin. 2 2 3 2
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| 7. |
- Cheah, You Wayne, 1993, et al.
(författare)
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Slurry co-hydroprocessing of Kraft lignin and pyrolysis oil over unsupported NiMoS catalyst: A strategy for char suppression
- 2023
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 475
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Tidskriftsartikel (refereegranskat)abstract
- Pyrolysis oil (PO) assisted Kraft lignin (KL) liquefaction over an unsupported NiMoS catalyst in a paraffin solvent was explored in this work. A paraffin solvent was used to represent hydrogenated vegetable oil (HVO) which is a biofuel. We have for the first time showed that when co-processing Kraft lignin with pyrolysis oil in a paraffin solvent the char formation could be completely suppressed. The complex composition of PO, containing various compounds with different functional groups, was able to aid the depolymerization pathways of lignin by obstructing the condensation path of reactive lignin derivatives. To further understand the role of different functional groups present in pyrolysis oil during lignin liquefaction, we investigate the co-hydroprocessing of Kraft lignin with various oxygenate monomers using unsupported NiMoS. 4-propylguaiacol (PG) was found to be the most efficient monomer for stabilizing the reactive lignin intermediates, resulting in a low char yield (3.7%), which was 4 times lower than the char production from Kraft lignin hydrotreatment alone. The suppressed rate of lignin fragment repolymerization can be attributed to the synergistic effect of functional groups like hydroxyl (-OH), methoxy (-OCH3), and propyl (-C3H7) groups present in PG. These groups were found to be able to stabilize the lignin depolymerized fragments and blocked the repolymerization routes enabling efficient lignin depolymerization. It was found that the presence of a co-reactant like PG during the heating period of the reactor acted as a blocking agent facilitating further depolymerization routes. Finally, a reaction network is proposed describing multiple routes of lignin hydroconversion to solid char, lignin-derived monomers, dimers, and oligomers, explaining why the co-processing of pyrolysis oil and Kraft lignin completely suppressed the solid char formation.
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| 8. |
- Cheah, You Wayne, 1993, et al.
(författare)
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Upgrading of triglycerides, pyrolysis oil, and lignin over metal sulfide catalysts: A review on the reaction mechanism, kinetics, and catalyst deactivation
- 2023
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:3
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Forskningsöversikt (refereegranskat)abstract
- Human activities such as burning fossil fuels for energy production have contributed to the rising global atmospheric CO2 concentration. The search for alternative renewable and sustainable energy sources to replace fossil fuels is crucial to meet the global energy demand. Bio-feedstocks are abundant, carbon-rich, and renewable bioresources that can be transformed into value-added chemicals, biofuels, and biomaterials. The conversion of solid biomass into liquid fuel and their further hydroprocessing over solid catalysts has gained vast interest in industry and academic research in the last few decades. Metal sulfide catalysts, a common type of catalyst being used in the hydroprocessing of fossil feedstocks, have gained great interest due to their low cost, industrial relevance, and easy implementation into the current refining infrastructures. In this review, we aim to provide a comprehensive overview that covers the hydrotreating of various bio-feedstocks like fatty acids, phenolic compounds, pyrolysis oil, and lignin feed using sulfided catalysts. The main objectives are to highlight the reaction mechanism/networks, types of sulfided catalysts, catalyst deactivation, and reaction kinetics involved in the hydrotreating of various viable renewable feedstocks to biofuels. The computational approaches to understand the application of metal sulfides in deoxygenation are also presented. The challenges and needs for future research related to the valorization of different bio-feedstocks into liquid fuels, employing sulfided catalysts, are also discussed in the current work.
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| 9. |
- Nejadmoghadam, Elham, 1984, et al.
(författare)
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Stabilization of bio-oil from simulated pyrolysis oil using sulfided NiMo/Al 2 O 3 catalyst
- 2023
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Ingår i: Fuel. - 0016-2361. ; 353
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Tidskriftsartikel (refereegranskat)abstract
- Pyrolysis oil comprises compounds with a broad range of functional groups making its thermal/catalytic upgrading challenging due to the formation of undesired char. In this context, the current contribution addresses the thermal and catalytic hydrotreatment of a simulated pyrolysis oil containing all the representative groups of compounds under bio-oil stabilization conditions (180–300 °C, 60 bar, 4 h) using sulfided NiMo/Al2O3. The effect of reaction conditions and different oxygenated organic compounds on the yields and properties of products was compared thoroughly. Interestingly, a correlation between the presence/absence of oxygenated furan and sugar compounds was found to significantly affect the yield of liquid product containing stabilized compounds. The presence of such compound groups significantly enhances the solid formation via oligomerization and polymerization reactions. To gain further insight, the solid products were analyzed/characterized in detail to elucidate their characteristics by extracting them into a dimethyl sulfoxide (DMSO) soluble and insoluble solid fraction. It was found that in the presence of NiMo/Al2O3, increasing temperature from 180 to 300 °C enhances the formation of liquid product due to transformation of some of the soluble solids, while for experiments without the catalyst, the formation of solids was significantly higher. Oppositely, during heating up to 180 °C, no solids were found in the case without the catalyst, however the presence of the catalyst during heating resulted in solid formation due to various catalytic reactions that promoted char formation. Analysis of solids revealed that the structure of soluble solids at lower temperatures (180 °C) using the catalyst was closely related to sugar derivatives, whereas the corresponding insoluble solids with higher molecular weight were not fully char-like developed. However, at higher temperatures, the soluble and insoluble solid compositions were found to contain aliphatic compounds and fully developed char, respectively. Therefore, the stabilization of furan particularly with attached carbonyl groups and sugars derivatives in pyrolysis oil is of great importance to improve upgrading efficiency.
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| 10. |
- Ojagh, Houman, 1976, et al.
(författare)
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Effect of Dimethyl Disulfide on Activity of NiMo Based Catalysts Used in Hydrodeoxygenation of Oleic Acid
- 2017
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 56:19, s. 5547-5557
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Tidskriftsartikel (refereegranskat)abstract
- Alumina supported NiMo catalysts were synthesized. The prepared NiMo catalysts were activated by DMDS in a sulfidation process and characterized. The sulfided NiMo catalysts were next used in hydrodeoxygenation (HDO) of oleic acid in a batch reactor. Afterward, the NiMo catalysts were recovered and used in another set of HDO reactions of oleic acid under the same conditions used in the previous HDO reactions. After the HDO experiments, the active phase and deposited coke on spent catalysts were characterized. The results indicated that higher concentrations of DMDS promoted the production of heptadecane (C-17) but had no effect on the production of octadecane (C-18). Moreover, the XPS results revealed the promotional effect of DMDS concentration on maintenance of the sulfidity of the catalysts. In addition, the results for the experiments with the second run catalyst revealed a clear deactivation due to increased coke depositions. Furthermore, after two repeated experiments with first run and second run catalysts, it was observed that coke formation decreased when the concentration of DMDS was increased. These results dearly indicate a correlation between the concentration of DMDS and coke formation.
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| 11. |
- Olsson Månsson, Emma, 1992, et al.
(författare)
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Removal of Inorganic Impurities in the Fast Pyrolysis Bio-oil Using Sorbents at Ambient Temperature
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:1, s. 414-4254
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Tidskriftsartikel (refereegranskat)abstract
- Fast pyrolysis bio-oil (FPBO) sourced from residual biomass waste (such as sawdust) is a promising feedstock that may be used for biofuel production. Their inorganic elements may, however, vary and cause deactivation of the catalysts in the hydrodeoxygenation (HDO) upgrading biorefinery unit. It was found that the use of zeolite Y and strong acidic ion-exchange resins as adsorbents was almost equally efficient in lowering the concentrations of Ca from <10 to <1 ppm and of Fe, K, and Mg to <0.3 ppm in FPBO at 30 °C, atmospheric pressure, and 4 h adsorption time. The removal efficiency of zeolite and resins exceeded 85–98% (detection limit) of these particular elements. For the first time for the FPBO, phosphorus was reported as being successfully targeted by aluminum oxide, being lowered from 1 ppm to <0.1 ppm, which is a reduction of at least 90%. Characterization of the oil and sorbents suggests that the surface acidity affects the removal efficiency of these elements from FPBO. Organic compounds in the pyrolysis oil, including isopropanol, lactic acid, hydroxy acetone, furfural, guaiacol, and levoglucosan, were semiquantified using two-dimensional gas chromatography coupled with mass spectrometry (GCxGC-MS). Compared to the fresh oil, the compositions and contents of these organic compounds were not impacted significantly by the sorbents under these mild operating conditions. This research indicates that inorganic impurities present in bio-oils can be removed, and thus, they may be considered feedstocks for producing biofuels with less deactivation of HDO catalysts.
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| 12. |
- Salam, Muhammad Abdus, 1983, et al.
(författare)
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Elucidating the role of NiMoS-USY during the hydrotreatment of Kraft lignin
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- Major hurdles in Kraft lignin valorization require selective cleavage of etheric and C–C linkages and subsequent stabilization of the fragments to suppress repolymerization reactions to yield higher monomeric fractions. In this regard, we report the development of efficient NiMo sulfides and ultra-stable Y zeolites for the reductive liquefaction and hydrodeoxygenation of Kraft lignin in a Parr autoclave reactor at 400 °C and 35 bar of H2 (@25 °C). Comparing the activity test without/with catalyst, it is revealed that NiMo sulfides over ultra-stable Y zeolites (silica/alumina = 30) achieved a significant reduction (∼50 %) of the re-polymerized solid residue fraction leading to a detectable liquid product yield of 30.5 wt% with a notable monocyclic and alkylbenzenes selectivity (∼61 wt%). A physical mixture counterpart, consisting of hydrothermally synthesized unsupported NiMoS and Y30, on the other hand, shows lower selectivity for such fractions but higher stabilization of the lignin fragments due to enhanced access to the active sites. Moreover, an extended reaction time with higher catalyst loading of the impregnated NiMoY30 facilitated a remarkable alkylbenzene (72 wt%) selectivity with an increased liquid yield of 38.9 wt% and a reduced solid residue of 16.4 wt%. The reason for the high yield and selectivity over NiMoY30, according to the catalyst characterization (H2-TPR, XPS, TEM) can be ascribed to enhanced stabilization of depolymerized fragments via H2-activation at a lower temperature and high hydrodeoxygenation ability. In addition, the better proximity of the acidic and deoxygenation sites in NiMoY30 was beneficial for suppressing the formation of polycyclic aromatics.
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| 13. |
- Salam, Muhammad Abdus, 1983, et al.
(författare)
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Influence of bio-oil phospholipid on the hydrodeoxygenation activity of NiMoS/Al2O3 catalyst
- 2018
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:10
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Tidskriftsartikel (refereegranskat)abstract
- Hydrodeoxygenation (HDO) activity of a typical hydrotreating catalyst, sulfided NiMo/γ-Al2O3for deoxygenation of a fatty acid has been explored in a batch reactor at 54 bar and 320°C in the presence of contaminants, like phospholipids, which are known to be present in renewable feeds. Oleic acid was used for the investigation. Freshly sulfided catalyst showed a high degree of deoxygenation activity; products were predominantly composed of alkanes (C17 and C18). Experiments with a major phospholipid showed that activity for C17 was greatly reduced while activity to C18 was not altered significantly in the studied conditions. Characterization of the spent catalyst revealed the formation of aluminum phosphate (AlPO4), which affects the active phase dispersion, blocks the active sites, and causes pore blockage. In addition, choline, formed from the decomposition of phospholipid, partially contributes to the observed deactivation. Furthermore, a direct correlation was observed in the accumulation of coke on the catalyst and the amount of phospholipid introduced in the feed. We therefore propose that the reason for the increased deactivation is due to the dual effects of an irreversible change in phase to aluminum phosphate and the formation of choline.
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| 14. |
- Salam, Muhammad Abdus, 1983, et al.
(författare)
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NiMoS on alumina-USY zeolites for hydrotreating lignin dimers: Effect of support acidity and cleavage of C-C bonds
- 2019
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Ingår i: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 4:1, s. 149-163
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Tidskriftsartikel (refereegranskat)abstract
- NiMoS on alumina, USY and mixed alumina-USY supports was studied in a batch reactor to assess the effect of support acidity in valorizing lignin dimers by hydrodeoxygenation (HDO). The reactivity of α-O-4 (benzyl phenyl ether), β-O-4 (2-phenethyl phenyl ether) and 5-5′ (2,2′-dihydroxybiphenyl) linkages was investigated in dodecane at 593 K and a H2 pressure of 5 MPa. A relatively fast rate of hydrogenolysis of the sp3 hybridized etheric bonds was observed for the catalyst supported on the mixed support. With the α-O-4 linkage, the USY supported catalyst selectively yielded deoxygenated aromatics including BTX products with fewer residual C-C dimers. For the β-O-4 linkage, analogous trends have been observed but with more aromatics. Interestingly, with 5-5′ linkages the catalyst on USY and mixed supports can break the C-C linkages without producing other intermediate C-C dimer byproducts. The results show high hydrocracking and isomerization activities of the catalyst supported on USY and mixed supports. This is consistent with XRD, Raman, XPS and TEM measurements, where enhanced dispersion of the active phase was observed. However, hydrogenation activity on the USY support is reduced to a significant degree which results in a large amount of benzene compared to NiMoS-Al2O3 that produces mostly cyclohexane. In addition, elemental analysis revealed that carbon deposition is higher on the USY-based catalyst compared to the alumina-based catalyst owing to its higher acidity. However, the potential for superior C-C bond cleavage on NiMoS-USY opens the possibility to valorize technical lignin in biorefinery processes.
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| 15. |
- Wang, Aiyong, 1989, et al.
(författare)
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Investigation of the robust hydrothermal stability of Cu/LTA for NH3-SCR reaction
- 2019
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 246, s. 242-253
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Tidskriftsartikel (refereegranskat)abstract
- Recently copper ion-exchanged LTA zeolites were proved to be robust for NH3-SCR reaction. In this study, Cu/LTA catalysts with Si/Al = 15 and Cu/Al = 0.4 were synthesized via incipient wetness impregnation (IWI) method, following degreening/hydrothermal aging at different temperatures (750, 800, 850, 900 °C), and used to catalyze standard SCR, fast SCR and NH3/NO oxidation reactions. Catalysts were characterized with surface area/pore volume, powder X-Ray diffraction (XRD), nuclear magnetic resonance (NMR), H2-temperature programmed reduction (H2-TPR) and in situ Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS). Through the BET surface areas, XRD and NMR results, it can be found that the framework structure stability of Cu/LTA catalysts during hydrothermal aging was outstanding, even after harsh aging at 900 °C. Moreover, various Cu species, including Z-Cu2+, Z-[Cu(OH)]+ and CuOx clusters, were quantified for Cu/LTA catalysts hydrothermally aged under various temperatures with H2-TPR and in situ DRIFTS. An imperative finding in this study is the exceptional hydrothermal stability of [Cu(OH)]+ and the gradual conversions of both Cu2+ and CuOx clusters to [Cu(OH)]+ with increasing aging temperature. It is worth noting that this phenomenon is exactly the opposite of Cu/SSZ-13. As it is known from the literature (Song et al., 2017), the formation of CuOx not only decreases the selectivity of NOx conversion, but also can cause deterioration of zeolite structure, since the ion-exchanged copper stabilizes the zeolite. This may also explain why the hydrothermal stability of Cu/LTA samples is outstanding.
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