| 1. |
- De Gracia Triviño, Juan Angel, et al.
(författare)
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The Role of Counterions in Intermolecular Radical Coupling of Ru-bda Catalysts
- 2022
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Ingår i: Topics in catalysis. - : Springer Nature. - 1022-5528 .- 1572-9028. ; 65:1-4, s. 383-391
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular radical coupling (also interaction of two metal centers I2M) is one of the main mechanisms for O-O bond formation in water oxidation catalysts. For Ru(bda)L-2 (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylate, L = pyridine or similar nitrogen containing heterocyclic ligands) catalysts a significant driving force in water solution is the hydrophobic effects driven by the solvent. The same catalyst has been successfully employed to generate -N2 from ammonia, also via I2M, but here the solvent was acetonitrile where hydrophobic effects are absent. We used a classical force field for the key intermediate [(RuN)-N-VI(bda)(py)(2)](+) to simulate the dimerization free energy by calculation of the potential mean force, in both water and acetonitrile to understand the differences and similarities. In both solvents the complex dimerizes with similar free energy profiles. In water the complexes are essentially free cations with limited ion paring, while in acetonitrile the ion-pairing is much more significant. This ion-pairing leads to significant screening of the charges, making dimerization possible despite lower solvent polarity that could lead to repulsion between the charged complexes. In water the lower ion pairing is compensated by the hydrophobic effect leading to favorable dimerization despite repulsion of the charges. A hypothetical doubly charged [(RuIN)-I-VI(bda)py(2)](2+) was also studied for deeper understanding of the charge effect. Despite the double charge the complexes only dimerized favorably in the lower dielectric solvent acetonitrile, while in water the separated state is more stable. In the doubly charged catalyst the effect of ion-pairing is even more pronounced in acetonitrile where it is fully paired similar to the 1+ complex, while in water the separation of the ions leads to greater repulsion between the two catalysts, which prevents dimerization.
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| 2. |
- Farah, Elise, et al.
(författare)
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Controlling the Activity and Selectivity of HZSM-5 Catalysts in the Conversion of Biomass-Derived Oxygenates Using Hierarchical Structures : The Effect of Crystalline Size and Intracrystalline Pore Dimensions on Olefins Selectivity and Catalyst Deactivation
- 2023
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Ingår i: Topics in catalysis. - : Springer Nature. - 1022-5528 .- 1572-9028. ; 66:17-18, s. 1310-1328
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of biomass-derived oxygenates over zeolite catalysts constitutes a challenge for the efficient production of bio-based chemicals and fuels due to difficulty in controlling the selectivity and high coke formation of such reactions. This is partly attributed to the microstructure of zeolite catalyst which affects the conversion and selectivity of products derived from biomass-derived oxygenates. In this study, the conversion and deactivation characteristics of three different model oxygenates found in biomass bio-oil (namely, acetol, furfural and guaiacol) over ZSM-5 zeolites of varying acidity, pore and crystal size prepared with bottom-up and top-down approaches were evaluated using a fixed bed microreactor at atmospheric pressure and a space velocity of 5 h−1 at a temperature range of 450–650 °C. Analysis of the experimental results indicates that the optimum temperature for such conversions is in the vicinity of 600 °C allowing for complete conversion of the compounds and high resistance to coking. The mechanisms of those conversions are discussed based on the obtained results. In general, crystal size and mesoporosity induce easier access to active sites improving mass transfer but also alter the location type, and strength of acid sites allowing for higher yields of primary and intermediate products such as olefins.
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| 3. |
- Feng, Yingxin, 1994, et al.
(författare)
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Simplified Kinetic Model for NH3‑SCR Over Cu‑CHA Based on First‑Principles Calculations
- 2023
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 66:13-14, s. 743-749
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Tidskriftsartikel (refereegranskat)abstract
- Selective catalytic reduction with ammonia as reducing agent (NH3-SCR) is an efficient technology to control NOx emission during oxygen excess. Catalysts based on Cu-chabazite (Cu-CHA) have shown good performance for NH3-SCR with high activity and selectivity at low temperature and good hydrothermal stability. Here, we explore a first-principles based kinetic model to analyze in detail which reaction steps that control the selectivity for N2 and the light-off temperature. Moreover, a simplified kinetic model is developed by fitting lumped kinetic parameters to the full model. The simplified model describes the reaction with high accuracy using only five reaction steps. The present work provides insight into the governing reaction mechanism and stimulates design of knowledge-based Cu-CHA catalysts for NH3-SCR.
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| 4. |
- Gajdek, Dorotea, et al.
(författare)
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Sulfidation of Supported Ni, Mo and NiMo Catalysts Studied by In Situ XAFS
- 2023
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 66:17-18, s. 1287-1295
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Tidskriftsartikel (refereegranskat)abstract
- Active sites in Mo-based hydrotreating catalysts are produced by sulfidation. To achieve insights that may enable optimization of the catalysts, this process should be studied in situ. Herein we present a comparative XAFS study where the in situ sulfidation of Mo/δ-Al2O3 and Ni/δ-Al2O3 is compared to that of δ-Al2O3 supported NiMo catalysts with different NiMo ratios. The study also covers the comparison of sulfidation of Ni and Mo using different oxide supports as well as the sulfidation conditions applied in the reactor. The XAFS spectra confirms the oxide phase for all catalysts at the beginning of the sulfidation reaction and their conversion to a sulfidized phase is followed with in situ measurements. Furthermore, it is found that the monometallic catalysts are less readily sulfidized than bimetallic ones, indicating the importance of Ni-Mo interactions for catalyst activation. Mo K-edge XAFS spectra did not show any difference related to the support of the catalyst or the pressure applied during the reaction. Ni K-edge XAFS spectra, however, show a more complete sulfidation of the Ni species in the catalyst when SiO2 is used as a support as compared to the Al2O3. Nevertheless, it is believed that stronger interactions with Al2O3 support prevent sintering of the catalyst which leads to its stabilization. The results contribute to a better understanding of how different parameters affect the formation of the active phase of the NiMo catalysts used in the production of biofuel.
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| 5. |
- Kauppinen, Minttu Maria, 1991, et al.
(författare)
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Hydrogen Adsorption on Pd–In Intermetallic Surfaces
- 2023
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 66:17-18, s. 1457-1464
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been shown that CO 2 hydrogenation to methanol over PdIn and In 2O 3 depends critically on the adsorption energy of hydrogen. Here we use density functional theory calculations to investigate hydrogen adsorption over Pd–In intermetallic compound surfaces with different Pd:In ratios. The electronic structure and properties of hydrogen adsorption are investigated for a range of surface facets and compared to the corresponding results for the pure parent metals and Cu. Increased In content is found to shift the Pd(d) density of states away from the Fermi level, making the intermetallic Pd–In compounds to appear “Cu-like”. We find a linear correlation between the hydrogen binding energy and the d-band center of surface Pd atoms. Understanding of how the hydrogen adsorption energy depends on composition and structure provides a possibility to enhance the performance of CO 2 hydrogenation catalysts to methanol.
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| 6. |
- Kristensen, Tove, et al.
(författare)
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Parametric Analysis and Optimization of Vanillin Hydrodeoxygenation Over a Sulfided Ni-Mo/δ-Al2O3 Catalyst Under Continuous-Flow Conditions
- 2023
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 66:17-18, s. 1341-1352
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental understanding of the process parameters affecting the catalytic hydrodeoxygenation (HDO) of bio-oils is of significance for enabling further progression and improvement of industrial biofuel upgrading methods. Herein, a novel demonstration and evaluation of the effect of temperature, pressure, and weight hourly space velocity in the continuous HDO of vanillin to cresol over a Ni-Mo/δ-Al2O3 catalyst are presented. Response surface methodology was used as a statistical experimental design method, and the application of central composite design enabled the generation of a statistically significant simulation model and a true optimization parametric study. The distribution of Ni and Mo on δ-Al2O3 was confirmed using scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX). No gradients with EDX mapping could be identified, and the elemental analysis showed well-dispersion of the metals. The mesoporous character of the catalyst-support system was unraveled using N2 physisorption. Experiments were conducted within the parametric range of 250–350 °C, 3–9 bar, and 15–35 h−1. Both temperature and pressure were found to have statistically significant linear and quadratic effects on the selectivity for cresol. The parametric interaction of temperature with pressure and space velocity also had a significant effect on the resulting response. The optimal temperature range becomes more critical at lower space velocities. Optimal selectivity for cresol was established at 314 °C, 5 bar, and 35 h−1. The fitting quality of the generated regression model was statistically confirmed and experimentally validated to describe the specified HDO process within the 95% two-sided confidence interval.
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| 7. |
- Matsuzawa, Akinobu, et al.
(författare)
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On the Importance of Considering Multinuclear Metal Sites in Homogeneous Catalysis Modeling
- 2022
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Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 65:1-4, s. 96-104
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Tidskriftsartikel (refereegranskat)abstract
- In this short review, we provide an account of a number of computational studies of catalytic reaction mechanisms carried out in our groups. We focus in particular on studies in which we came to realize during the course of the investigation that the active catalytic species was a bimetallic complex, rather a monometallic one as previously assumed. In some cases, this realization was in part prompted by experimental observations, but careful exploration based on computation of the speciation of the metal precursor also provided a powerful guide: it is often possible to predict that bimetallic species (intermediates or transition states) lie lower in free energy than a priori competitive monometallic species. In this sense, we argue that in organometallic catalysis, the rule whereby two is better than one turns out to be relevant much more often than one might expect.
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| 8. |
- Sauer, Christopher, 1993, et al.
(författare)
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Isomorphous Substitution of Gallium into MFI-Framework Zeolite Increases 2,5-Dimethylfuran to Aromatics Selectivity and Suppresses Catalyst Deactivation
- 2023
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 66, s. 1329-1340
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Tidskriftsartikel (refereegranskat)abstract
- The valorization of biomass-derived molecules into commodity chemicals is important for the transition to renewable feedstocks. The model platform molecule 2,5-dimethylfuran (2,5-dmf) can be converted into value-added aromatics such as benzene, toluene, and xylenes (BTX) over zeolite catalysts. To explore the role of the zeolite acid site(s) in BTX selectivity, gallium has been isomorphously substituted into the framework, resulting in a Ga-silicate. Compared to the ZSM-5 counterpart, this modification shows enhanced benzene selectivity as well as resistance to deactivation by coke in continuous catalytic performance tests. Guido J. L. de Reijer and Christopher Sauer have contributed equally to this work.
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| 9. |
- Trunschke, Annette, et al.
(författare)
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Towards Experimental Handbooks in Catalysis
- 2020
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 63:19-20, s. 1683-1699
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Tidskriftsartikel (refereegranskat)abstract
- The “Seven Pillars” of oxidation catalysis proposed by Robert K. Grasselli represent an early example of phenomenological descriptors in the field of heterogeneous catalysis. Major advances in the theoretical description of catalytic reactions have been achieved in recent years and new catalysts are predicted today by using computational methods. To tackle the immense complexity of high-performance systems in reactions where selectivity is a major issue, analysis of scientific data by artificial intelligence and data science provides new opportunities for achieving improved understanding. Modern data analytics require data of highest quality and sufficient diversity. Existing data, however, frequently do not comply with these constraints. Therefore, new concepts of data generation and management are needed. Herein we present a basic approach in defining best practice procedures of measuring consistent data sets in heterogeneous catalysis using “handbooks”. Selective oxidation of short-chain alkanes over mixed metal oxide catalysts was selected as an example.
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| 10. |
- Abdelaziz, Omar Y., et al.
(författare)
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Oxidative Depolymerization of Kraft Lignin to Aromatics Over Bimetallic V–Cu/ZrO2 Catalysts
- 2023
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Ingår i: Topics in Catalysis. - 1022-5528. ; 66:17-18, s. 1369-1380
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Tidskriftsartikel (refereegranskat)abstract
- Zirconia-supported vanadium–copper catalysts (VCux:yZr) were used for the oxidative depolymerization of softwood LignoBoost Kraft lignin (LB). Various VCux:yZr catalysts were prepared (x:y = 0:1, 1:4, 1:2, 3:4, 1:1, and 1:0) by incipient wetness impregnation, and reactions were performed in alkaline water at 150 °C under an O2 pressure of 5 bar for 10 min. 1H–13C HSQC NMR spectroscopy was used for product identification and quantification. The most promising catalyst was VCu1:2Zr, giving a total monomer yield of 9 wt% and the highest selectivity for vanillin (59%). This catalyst was characterized before and after use by N2 physisorption, XRD, TGA, SEM-EDS, and XPS. Cleavage of the main interunit linkages in LB, including the β-O-4 bonds and recalcitrant C–C bonds, was also observed. The findings of this study demonstrate the potential of the V–Cu/ZrO2 catalyst system in the production of value-added aromatics from technical lignin under relatively mild conditions. This would contribute to the more sustainable use of an underutilized side-stream in forest-based industries, provided catalyst reuse can be successfully demonstrated.
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