| 1. |
- Bui, Thai Q., et al.
(författare)
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Mesoporous Melamine-Formaldehyde Resins as Efficient Heterogeneous Catalyst for Continuous Synthesis of Cyclic Carbonates from Epoxides and gaseous CO2
- 2020
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 8:34, s. 12852-12869
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Tidskriftsartikel (refereegranskat)abstract
- Herein we report the application of inexpensive mesoporous melamine-formaldehyde resins (MMFR and MMFR250) obtained by a novel template-free and organosolvent-free hydrothermal method as efficient heterogeneous catalysts for direct synthesis of cyclic carbonates from CO2 and epoxides (epichlorohydrin, butylene oxide and styrene oxide). The catalytic activity of the melamine resins was attributed to the abundant Lewis basic N-sites capable of activating CO2 molecules. Based on CO2-Temperature programmed desorption, the concentration of surface basic sites for MMFR and MMFR250 were estimated to be 172 and 56 µmol/g, while the activation energy of CO2 desorption (strength of basic sites) were calculated to be 92.1 and 64.5 kJ/mol. We also observed considerable differences in the catalytic activity and stability of polymeric catalysts in batch and in continuous-flow mode; due to the existence of a synergism between adsorption of CO2 and cyclic carbonates (poison). Our experiments also revealed important role of catalyst surface chemistry and CO2 partial pressure upon catalyst poisoning. Nevertheless, owing to their unique properties (large specific surface area, large mesoporous and CO2 basicity) melamine resins presented excellent activity (turnover frequency 207-2147 h-1), selectivity (>99%) for carbonation of epoxides with CO2 (20 bar initial CO2 or CO2:epoxide mole ratio ~1.5) under solvent-free and co-catalyst-free conditions at 100-120 oC. Most importantly, these low-cost polymeric catalysts were reusable and demonstrated exceptional stability in a flow reactor (tested upto 13 days time on stream, weight hourly space velocity 0.26-1.91 h-1) for continuous cyclic carbonate production from gaseous CO2 with different epoxides (conversion 76-100% and selectivity >99%) under industrially relevant conditions (120 oC, 13 bar, solvent-free/co-catalyst-free) confirming their superiority over the previously reported catalytic materials.
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| 2. |
- Konwar, Lakhya Jyoti, 1987-, et al.
(författare)
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Carbon support effects on metal (Pd, Pt and Ru) catalyzed hydrothermal decarboxylation/deoxygenation of triglycerides
- 2022
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Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 638
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we show that textural properties of carbon supports have limited influence on the activity and stability of carbon supported Pd, Pt and Ru catalysts upon decarboxylation of a model triglyceride (tristearin) in the presence of subcritical water (256–326 °C). In contrast, surface acid-base properties of carbon supports were found to have a marked impact on the performance and stability of these catalysts. More precisely, for Pt group (Pt and Pd) a positive correlation could be observed between the concentration of surface basic sites and catalyst deoxygenation activity and durability while acid sites had the opposite effect. On the other hand, the activity of Ru-based catalysts were not analogously affected by the acid-base properties of carbon supports, even so a positive correlation was found between surface basicity and durability (reusability). Further, the activity of metals in decreasing order of TOF was Ru>Pt>Pd, irrespective of carbon support.
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| 3. |
- Konwar, Lakhya Jyoti, 1987-, et al.
(författare)
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Efficient hydrothermal deoxygenation of tall oil fatty acids into n-paraffinic hydrocarbons and alcohols in the presence of aqueous formic acid
- 2022
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Ingår i: Biomass Conversion and Biorefinery. - : Springer. - 2190-6815 .- 2190-6823. ; 12:1, s. 51-62
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Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal deoxygenation of tall oil fatty acids (TOFA) was investigated in the presence of aqueous formic acid (0.5–7.5 wt%) as a H2 donor in the presence of subcritical H2O pressure (569–599 K). Pd and Ru nanoparticles supported on carbon (5% Pd/CSigma, 5% Ru/CSigma, 10% Pd/CO850_DP, and 5% Ru/COPcomm_DP) were found to be efficient catalysts for deoxygenation of TOFA. The reaction pathway was mainly influenced by the concentration of formic acid and the catalyst. In case of Pd catalysts, in the presence of 0–2.5 wt% formic acid, decarboxylation was the dominant pathway producing n-paraffinic hydrocarbons with one less carbon atom (heptadecane yield up to 94 wt%), while with 5–7.5% formic acid, a hydrodeoxygenation/hydrogenation mechanism was favored producing C18 deoxygenation products octadecanol and octadecane as the main products (yields up to 70 wt%). In contrast, Ru catalysts produced a mixture of C5-C20 (n-and iso-paraffinic) hydrocarbons via decarboxylation, cracking and isomerization (up to 58 wt% C17 yield and total hydrocarbon yield up to 95 wt%) irrespective of formic acid concentration. Kinetic studies showed that the rates of deoxygenation displayed Arrhenius type behavior with apparent activation energies of 134.44 ± 31.36 kJ/mol and 148.92 ± 3.66 kJ/mol, for the 5% Pd/CSigma and 5% Ru/CSigma catalyst, respectively. Furthermore, the experiments with glycerol tristearate, rapeseed oil, sunflower oil, rapeseed biodiesel, and hydrolyzed rapeseed oil produced identical products confirming the versatility of the aforementioned catalytic systems for deoxygenation of C18 feedstocks.
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| 4. |
- Konwar, Lakhya Jyoti, 1987-, et al.
(författare)
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Sidestreams from bioenergy and biorefinery complexes as a resource for circular bioeconomy
- 2018. - 1
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Ingår i: Waste biorefinery. - Amsterdam : Elsevier. - 9780444639929 ; , s. 85-125
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Bokkapitel (refereegranskat)abstract
- One of the main drivers for the establishment of biorefineries and the drive toward bioeconomy is the call for sustainability. However, the modern-day biorefinery must embrace on the concept of whole-crop approach with complete feedstock utilization and zero waste, leading to a portfolio of valuable products in which food, feed, fuels, chemicals, and materials are produced. In this chapter, we address upon the prospective of improving the economics and carbon efficiency of existing bioenergy and biorefinery complexes through a circular bioeconomy-based whole-crop utilization. We emphasize hereupon the possibility to coproduce value-added products (e.g., chemicals, materials, or energy) from the various sidestreams or by-products generated from biorefinery operations such as CO2, glycerol, hemicelluloses, lignin, and extractives together with their potential as a raw material or chemical platform for the production of marketable products using available process technologies.
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| 5. |
- Konwar, Lakhya Jyoti, 1987-, et al.
(författare)
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SO3H-Containing Functional Carbon Materials : Synthesis, Structure, and Acid Catalysis
- 2019
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Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 119:22, s. 11576-11630
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Tidskriftsartikel (refereegranskat)abstract
- The “sulfonated carbons” are a new class of metal-free solid protonic acids characterized by their unique carbon structure and Brønsted acidity (−H0 = 8–11) on par to concentrated H2SO4. These carbon materials covalently functionalized with SO3H groups via C–PhSO3H or C–SO3H linkages can act as versatile water-tolerant solid acids. Due to their low production costs, unique surface chemistry, high chemical and thermal stability, as well as tailorable pore structures they are regarded as potential substitutes to liquid H2SO4. Catalysis, in particular, biomass and large molecule catalysis, is one of the important areas in which acidic carbons have demonstrated exceptional activity and selectivity, outperforming traditional solid acid catalysts (cation-exchange resins, sulfated oxides, and acidic zeolites). In this review we address developments in the different types SO3H- and PhSO3H-functionalized acidic carbon materials, their structure, active sites, and surface properties, applications in catalysis, as well as activation and deactivation characteristics covering important literature since 2004. In particular, we aim to provide a systematic discussion on the specific merits and demerits of such materials obtained from different carbon precursors and functionalization methods which directly influence the structure–stability–acidic properties and catalytic performance.
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| 6. |
- Mikkola, Jyri-Pekka, et al.
(författare)
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Hydrothermal method for producing renewable paraffinichydrocarbons
- 2020
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Patent (populärvet., debatt m.m.)abstract
- The present invention provides a method for producing hydrocarbons having 6 to 20 carbon atoms, comprising the steps of: a) providing a feedstock comprising saturated fatty acids, and/or derivatives thereof; b) deoxygenating the feedstock in the presence of a metal free hydrogenation and decarboxylation catalyst under low-pressure hydrothermal conditions, wherein the temperature is in the range 350-400 °C and the pressure is in the range 10-30 bar; and wherein the catalyst is a heteroatom-doped carbon material. Furthermore, there is provided a system for preforming the method in a single reactor (R) system comprises a bed of a carbon catalyst facilitating simultaneous hydrogenation and decarboxylation.
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| 7. |
- Samikannu, Ajaikumar, et al.
(författare)
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Highly dispersed NbOPO4/SBA-15 as a versatile acid catalyst upon production of renewable jet-fuel from bio-based furanics via hydroxyalkylation-alkylation (HAA) and hydrodeoxygenation (HDO) reactions
- 2020
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Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 272
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report the synthesis of a highly active and mesoporous Brønsted acidic NbOPO4/SBA-15 catalyst. The prepared catalysts were thoroughly characterized by means of analytical techniques such as XRD, FT-IR, XPS, NH3-TPD, SEM-EDS, TEM, TGA, 31P-MAS-NMR and N2-physisorption. The H3PO4 free deposition method was found to be effective for preserving the structure of Silica based carrier. In terms of catalytic performance, these materials demonstrated high activity upon C-C coupling of 2-methyl furan with carbonyl compounds and outperforming bulk NbOPO4, Nb2O5/SBA-15 and traditional solid acid catalysts (Al-MCM-41, Si/Al and H-ZSM-5). The NbOPO4/SBA-15 catalysts were stable and maintained high activity upon reuse and continuous operation (∼65 h). Furthermore, the Pd loaded counterparts (Pd/NbOPO4/SBA-15 and Pd/Nb2O5/SBA-15) also functioned as bifunctional catalysts and exhibited excellent activity upon subsequent hydrodeoxygenation of C-C coupling products. Most importantly, in terms of jet-fuel range hydrocarbons selectivity, these catalysts outperformed monofunctional Pd/carbon and aluminosilicate based bifunctional catalysts.
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