| 1. |
- Achour, Abdenour, 1980, et al.
(författare)
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Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM
- 2023
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- Selective transformation of BHMF (2,5-bis(hydroxymethyl)furan) to THFDM (tetrahydrofuran-2,5-dimethanol) over a variety of structured Ni/Sx-Z1−x catalysts was investigated. The effects of support, Ni loading, solvent, temperature, pressure, and particle size on the conversion and selectivity were studied. Among them, the 10 wt% Ni catalyst supported on the SiO2:ZrO2 weight ratio of 90:10 (10NiS90Z10) exhibits the best performance in terms of BHMF conversion and THFDM selectivity. Its good performance was attributed to its well-balanced properties, that depend upon the ZrO2 content of the support in combination with SiO2, the active Ni sites-support interaction, and acidity/basicity ratio of each catalyst resulting in different Ni dispersions. Importantly, the 10NiS90Z10 catalyst showed a stable selectivity to THFDM (>94%), with 99.4% conversion of BHMF during 2 h reaction time. Poor catalytic activity resulted from excessive ZrO2 content (>10 wt%). The structural, textural, and acidity properties of NiSi100−y-Zry catalysts, tuned by selectively varying the Ni amount from 5 to 15 wt%, were critically investigated using numerous material characterization techniques. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any measurable loss of catalytic activity.
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| 2. |
- 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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| 3. |
- Chaoquan, Hu, 1981, et al.
(författare)
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Catalytic hydrogenation of C=C and C=O in unsaturated fatty acid methyl esters
- 2014
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 4:8, s. 2427-2444
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Forskningsöversikt (refereegranskat)abstract
- Biodiesel derived from edible and non-edible oils has received much attention as a chemical feedstock or as a raw fuel alternative to the traditional diesel due to its renewability and biodegradability. However, the crude biodiesel containing large amounts of polyunsaturated fatty acid methyl esters (FAMEs) is susceptible to oxidation upon exposure to heat, light, and oxygen. Catalytic hydro-genation of biodiesel has been considered as a feasible and powerful technique to improve the oxidative stability of biodiesel and hence to provide stable raw materials for industrial applications. The catalytic hydrogenation of FAMEs is a complex process but basically consists of hydrogenation of C=C or C=O, depending on the desirable properties of final products. In this review, we summarize recent developments in hydrogenation of C=C and C=O in FAMEs with focus on catalysts, reaction mechanisms, and reactor conditions. The features of hydrogenation of FAMEs are generalized and the opportunities for future research in the field are outlined.
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| 4. |
- Chaoquan, Hu, 1981, et al.
(författare)
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Selectivity and kinetics of methyl crotonate hydrogenation over Pt/Al2O3
- 2015
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 5:3, s. 1716-1730
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogenation of gas-phase methyl crotonate (MC) over Pt/Al2O3 was investigated with the aim to understand C=C hydrogenation in unsaturated methyl esters. Three Pt/Al2O3 catalysts with different Pt dispersions were prepared by varying calcination temperature and evaluated for MC hydrogenation. The main products were found to be methyl butyrate (MB) and methyl 3-butenoate (M3B), resulting from hydrogenation and shift of the C=C bond in MC, respectively. The measured activity for both hydrogenation and shift of the C=C in MC was found to depend on the Pt dispersion where higher Pt dispersion favors the C=C hydrogenation reaction. The effect of reactant concentrations on the activity and selectivity for MC hydrogenation over the Pt/Al2O3 catalyst was examined in detail. Under the investigated conditions, the C=C hydrogenation was found to have a negative reaction order with respect to MC concentration but a positive H2 order. Further understanding of the MC hydrogenation was provided from H2 chemisorption experiments over the catalyst with and without pre-adsorbed MC and from transient experiments using alternating MC and H2 feeds. Based on the present experimental results, a reaction pathway was proposed to describe gas-phase MC hydrogenation over Pt/Al2O3. In order to gain more insight into the reaction, a kinetic analysis of MC hydrogenation was performed by fitting a power-law model to the kinetic data, moreover, dissociative H2 adsorption on the catalyst was found to be the rate-determining step by comparing the power-law model with the overall rate expressions derived from mechanistic considerations.
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| 5. |
- 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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| 6. |
- Ojagh, Houman, 1976, et al.
(författare)
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Effect of DMSO on the catalytical production of 2,5-bis(hydoxymethyl)furan from 5-hydroxymethylfurfural over Ni/SiO2 catalysts
- 2022
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Ingår i: Reaction Chemistry and Engineering. - : Royal Society of Chemistry (RSC). - 2058-9883. ; 7:1, s. 192-200
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Tidskriftsartikel (refereegranskat)abstract
- Hydroconversion of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydoxymethyl)furan (BHMF) was studied over mono- and bimetallic supported catalysts. It was found that monometallic Ni/SiO2 catalysts exhibited superior performance with a total yield of BHMF of up to 99 wt%. This excellent performance may be attributed to higher Ni dispersion and low acidity of the support. Dimethyl sulfoxide (DMSO) is often present in HMF, due to the route used for its synthesis. DMSO adsorption caused a clear reduction of Ni/SiO2 performance for the HMF hydrodeoxygenation reaction. Characterization of the spent catalysts was performed using HAADF-STEM-EDX, Raman, ICP, and XPS spectroscopies, and showed the presence of sulfur and graphitic carbon, which could explain the deactivation.
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| 7. |
- Ojagh, Houman, 1976, et al.
(författare)
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Effect of Thermal Treatment on Hydrogen Uptake and Characteristics of Ni-, Co-, and Mo-Containing Catalysts
- 2015
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:46, s. 11511-11524
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Tidskriftsartikel (refereegranskat)abstract
- Nonsulfided alumina supported Ni, Co, Mo, NiMo, and CoMo hydrotreating catalysts were synthesize. The TEM results indicated low dispersions of the active metals for Mo, NiMo, and CoMo, samples but significantly higher dispersion for the Ni sample. The effect of calcination and reduction on the hydrogen uptake capacity of the samples was investigated. The H-2-chemisorption and XPS results together showed that the precalcination step had a detrimental effect on the hydrogen absorption of the Ni sample formation of stable metal oxides. The XPS results revealed that the metal oxides of all calcined samples reached with the alumina support to form very stable spinels. Futher, the positive effects of a hydrogen atmosphere during the reduction, on the hyderogen uptake of the samples were cinfirmed by H-2-chemisorption measurements. Finally, the heats of adsorption (Delta H) of hydrogen for the Ni and Co samples were calculated to be 140 and 98 kJ mol(-1), respectively.
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| 8. |
- Ojagh, Houman, 1976, et al.
(författare)
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Hydroconversion of abietic acid into value-added fuel components over sulfided NiMo catalysts with varying support acidity
- 2019
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 190, s. 55-55-66
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Tidskriftsartikel (refereegranskat)abstract
- The hydroconversion of abietic-type rosin acids, with a tri-ring structure into mono-ring structure hydrocarbons, was investigated. The reactions were performed at 380 °C under 7500 kPa of H2 pressure over sulfided NiMo catalysts supported on alumina, USY-zeolite and mixed alumina/USY-zeolite. The NiMo supported catalysts were characterized using N2-physisorption, ethylamine-temperature programmed desorption (ethylamine-TPD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and temperature programmedoxidation (TPO). The sulfided NiMo supported on only USY-zeolite showed the highest selectivity towards production of the mono-ring hydrocarbons such as methyl cyclopentane due to the strong Brønsted acid character of USY-zeolite. Whereas, the sulfided NiMo supported on alumina with weaker Brønsted acidity showed strong selectivity towards the di and tri-ring hydrocarbons such as dimethyl tetralins and retene. Moreover, the selectivities towards the mono-ring hydrocarbons over the NiMo catalysts with mixed supports were lower with a higher alumina content. Finally, the results show that the sulfided NiMo catalyst supported on alumina/USY-zeolite support with 50 wt% zeolite achieved a good level of deoxygenation, ring opening and cracking of the rosin acid while avoiding excessive coke formation.
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| 9. |
- Ojagh, Houman, 1976
(författare)
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Hydrodeoxygenation (HDO) catalysts Characterization, reaction and deactivation studies
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Production of biomass derived fuels such as renewable diesel, are primarily intended to reduce the reliance of the conventional engines on petroleum fuels as well as the emission of CO2 from fossil hydrocarbons. Hydrodeoxygenation (HDO) is a powerful technique that has been regularly used in the fuel upgrading processes. Sulfided molybdenum catalysts, supported on alumina and promoted by cobalt or nickel, are frequently used in the HDO processes. Despite the high efficiency of the HDO, catalyst activity and selectivity have raised major concerns from the economic and technological perspectives. The aim of this study was to gain a better understanding of the HDO catalyst structure, and then to assess the effect of different pretreatment and operational conditions on the catalyst activity and selectivity. The effect of preparation and pretreatment conditions on hydrogen uptake capacity and dispersion of the prepared Ni, Co and Mo containing catalysts was evaluated by using several characterization techniques such as BET, ICP-SFMS, SEM, TEM, TPO, ethylamine-TPD, XPS and H2-chemisorption. The H2-chemisorption, XPS and SEM results confirmed the detrimental effect of calcination on hydrogen uptake capacity of catalysts. The effect of pH of the impregnating solutions on the dispersion of the metal phases was also assessed from the TEM experiments. Moreover, HDO reactions of oleic acid and abietic acid over a prepared sulfided NiMo catalyst were studied. The results show that addition of DMDS to an oleic acid feed clearly promoted maintenance of the active sulfided phases on the NiMo catalysts. Higher concentration of DMDS also promoted the decarbonylation/decarboxylation (DCOx) route, and more importantly, decreased the amount of carbon deposition on the NiMo catalyst. On the other hand, addition of abietic acid to an oleic acid feed, is shown to decrease the deoxygenation rate of the oleic acid and increase the amount of carbon deposition on the catalyst. The inhibition effect of abietic acid on the HDO of oleic acid was related to stronger adsorption of the bulkier abietic acid molecules on the active sites compared to oleic acid that may have sterically hindered adsorption of oleic acid on neighboring sites. Furthermore, the poisoning effect of iron on the HDO of oleic acid over sulfided NiMo and Mo catalysts was investigated. It is shown that addition of iron to an oleic acid feed decreased the oxygenate conversion activity of both catalysts and changed their selectivities towards the final products. TEM results of the poisoned spent NiMo catalyst revealed that iron was mainly deposited on and in the vicinity of the Ni particles. This may also indicate that iron has reacted with Ni phase and as a result modified the catalyst activity. Finally, hydroconversion of rosin acids over supported NiMoS catalysts on alumina, USY-zeolite and mixed alumina/USY-zeolite was investigated. Various catalyst properties such as dispersion of the NiMo phases and Brønsted acidity affected the selectivity for the products. The results also indicate that the Brønsted acidity of the support could be optimized by the USY-zeolite content of the catalyst to achieve a satisfactory level of deoxygenation, ring opening and cracking of the rosin acid while avoiding excessive coke formation.
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| 10. |
- Ojagh, Houman, 1976, et al.
(författare)
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The effect of rosin acid on hydrodeoxygenation of fatty acid
- 2019
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Ingår i: Journal of Energy Chemistry. - : Elsevier BV. - 2095-4956. ; 28, s. 85-94
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Tidskriftsartikel (refereegranskat)abstract
- In this study, inhibition of tall oil fatty acid hydrodeoxygenation (HDO) activity due to addition of rosin acid over sulfided NiMo/Al2O3 was investigated. Oleic acid and abietic acid were used as model compounds for fatty acid and rosin acid respectively in tall oil. After completion of each HDO experiment, the NiMo catalysts were recovered and used again under the same conditions. The results showed that the oleic acid HDO activity of sulfided catalysts was inhibited by addition of abietic acid due to competitive adsorption and increased coke deposition. The rate of carbon deposition on the catalysts increased when abietic acid was added to oleic acid feed. Moreover, the coke was in a more advanced form with higher stability for the catalysts exposed to both oleic acid and abietic acid. Furthermore, a clear correlation between the rate of coke formation and concentration of abietic acid was observed.
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