| 1. |
- Bjerregaard, Joachim, 1996, et al.
(författare)
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Interpretation of H 2 -TPR from Cu-CHA Using First-Principles Calculations
- 2024
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:11, s. 4525-4534
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-programmed reduction and oxidation are used to obtain information on the presence and abundance of different species in complex catalytic materials. The interpretation of the temperature-programmed reaction profiles is, however, often challenging. One example is H2 temperature-programmed reduction (H2-TPR) of Cu-chabazite (Cu-CHA), which is a material used for ammonia assisted selective catalytic reduction of NOx (NH3-SCR). The TPR profiles of Cu-CHA consist generally of three main peaks. A peak at 220 °C is commonly assigned to ZCuOH, whereas peaks at 360 and 500 °C generally are assigned to Z2Cu, where Z represents an Al site. Here, we analyze H2-TPR over Cu-CHA by density functional theory calculations, microkinetic modeling, and TPR measurements of samples pretreated to have a dominant Cu species. We find that H2 can react with Cu ions in oxidation state +2, whereas adsorption on Cu ions in +1 is endothermic. Kinetic modeling of the TPR profiles suggests that the 220 °C peak can be assigned to Z2CuOCu and ZCuOH, whereas the peaks at higher temperatures can be assigned to paired Z2Cu and Z2CuHOOHCu species (360 °C) or paired Z2Cu and Z2CuOOCu (500 °C). The results are in good agreement with the experiments and facilitate the interpretation of future TPR experiments.
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| 2. |
- Han, Joonsoo, 1990, et al.
(författare)
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Effect of SO 2 and SO 3 Exposure to Cu-CHA on Surface Nitrate and N 2 O Formation for NH 3 -SCR
- 2024
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Ingår i: ACS ENGINEERING AU. - 2694-2488. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- We report effects of SO2 and SO3 exposure on ammonium nitrate (AN) and N2O formation in Cu-CHA used for NH3-SCR. First-principles calculations and several characterizations (ICP, BET, XRD, UV-vis-DRS) were applied to characterize the Cu-CHA material and speciation of sulfur species. The first-principles calculations demonstrate that the SO2 exposure results in both (bi)sulfite and (bi)sulfate whereas the SO3 exposure yields only (bi)sulfate. Furthermore, SOx adsorption on framework-bound dicopper species is shown to be favored with respect to adsorption onto framework-bound monocopper species. Temperature-programmed reduction with H-2 shows two clear reduction states and larger sulfur uptake for the SO3-exposed Cu-CHA compared to the SO2-exposed counterpart. Temperature-programmed desorption of formed ammonium nitrate (AN) highlights a significant decrease in nitrate storage due to sulfur species interacting with copper sites in the form of ammonium/copper (bi)bisulfite/sulfate. Especially, highly stable sulfur species from SO3 exposure influence the NO2-SCR chemistry by decreasing the N2O selectivity during NH3-SCR whereas an increased N2O selectivity was observed for the SO2-exposed Cu-CHA sample. This study provides fundamental insights into how SO2 and SO3 affect the N2O formation during ammonium nitrate decomposition in NH3-SCR applications, which is a very important topic for practical applications.
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| 3. |
- Ho, Hoang Phuoc, 1983, et al.
(författare)
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Effect of the Preparation Methods on the Physicochemical Properties of Indium-Based Catalysts and Their Catalytic Performance for CO 2 Hydrogenation to Methanol
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:6, s. 5407-5420
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Tidskriftsartikel (refereegranskat)abstract
- Indium oxides (In2O3) and indium oxides supported zirconia (ZrO2) have been known possible alternatives for conventional copper-based catalysts in the CO2-hydrogenation to methanol. This study aims to investigate the effect of preparation techniques on the physicochemical properties of indium-based materials and their catalytic performance for the hydrogenation of CO2 to methanol. Two series of both single oxide In2O3 and binary In2O3-ZrO2 have been synthesized by combustion, urea hydrolysis, and precipitation with different precipitating agents (sodium carbonate and ammonia/ethanol solution). Physicochemical properties of materials are characterized by elemental analysis, XRD, N2 physisorption, SEM/EDX, micro-Raman, XPS, H2-TPR, and CO2-TPD. Cubic In2O3 was the common phase generated by all four synthesis methods, except for urea hydrolysis, where rhombohedral In2O3 was additionally present. The combustion method produced the materials with the lowest specific surface areas while the precipitation using ammonia/ethanol aided in creating more oxygen defects. The synthesis methods strongly influenced the degree of interaction between the oxides and resulted in improvements in properties that boosted the catalytic performance of the binary oxides compared to their single-oxide counterparts.
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| 4. |
- Nejadmoghadam, Elham, 1984, et al.
(författare)
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Stabilization of fresh and aged simulated pyrolysis oil through mild hydrotreatment using noble metal catalysts
- 2024
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Ingår i: Energy Conversion and Management. - 0196-8904. ; 313
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Tidskriftsartikel (refereegranskat)abstract
- The nature and reactivity of the oxygenates, containing different functional chemical groups, and especially carbonyl compounds, render pyrolysis oil unstable. Alterations in physical and chemical properties of pyrolysis oil during storage and the catalytic stabilization of this oil is therefore critical and is the objective of the current work. In this study, Pd/Al2O3, Pt/Al2O3, Rh/Al2O3, Re/Al2O3 and sulphided NiMo/Al2O3 catalysts were employed in the hydrotreatment (180 °C, 60 bar H2, 4 h) of simulated pyrolysis oil to examine their effect on stabilization and potential polymerization routes. Of all the catalysts used, Pd/Al2O3 with well-dispersed metal particles, and a high char-suppressing potential was the most effective catalyst. It had the highest bio-liquid yield and the highest selectivity to low molecular weight stabilized oxygenates and deoxygenated products. In addition, the acidity in the light fraction was low and a very low solid product formation was found that consisted mainly of soluble polymers composed predominantly of aliphatic compounds and sugars, whereas insoluble polymers were not fully developed char. The solid yield increased in the following order: Pd (3.3 wt%) < Rh (13.3 wt%) < NiMo (13.6 wt%) < Pt (21.5 wt%) < Re (25.8 wt%) < Blank (27.4 wt%). This trend was also accompanied by an enhanced yield of heavy oligomers in the corresponding liquid phase abundant in phenolic compounds compared to carboxylic acids and aliphatic compounds based on GPC and P-NMR analyses. The Pd loading necessary to obtain a high-quality product was also assessed, and the lower carbon loss when using catalysts with smaller contents of metal was revealed. Based on the results a detailed reaction network was proposed regarding the reactions during stabilization of sugars, aldehydes, ketones, furans, acids and phenols present in pyrolysis oil. To delve deeper into the simulated pyrolysis oil properties, it was subjected to accelerated aging. Interestingly as much as 79 % of the feed was converted during aging. According to GC/MS analysis only large oligomers were formed that could not be detected. When removing the most reactive components from the feed, i.e. the sugar and furan, the conversion was lowered to 53 %. Catalytic stabilization was conducted on the aged oil and compared with stabilization followed by aging. The results showed that the solid formation increased from 5.1 to 9.1 % when the pyrolysis oil was first aged, followed by stabilization. A suggested reason for this is the large amount of oligomers that were formed during the aging. Thus, aging before stabilization is very negative for an industrial process.
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| 5. |
- Salam, Muhammad Abdus, 1983, et al.
(författare)
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One-pot reductive liquefaction of sawdust to renewables over MoO x -Al 2 O 3 variants: insight into structure-activity relationships
- 2024
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Ingår i: Sustainable Energy and Fuels. - 2398-4902. ; 8:12, s. 2668-2681
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Tidskriftsartikel (refereegranskat)abstract
- Valorization of forest residual products can offer a vital pathway to derive bio-based chemicals and fuel components. Herein, we report the effective and direct conversion of sawdust biomass over a supported Mo-oxide catalyst that results in a dominant fraction of aliphatic/cyclic alkanes and alkylbenzenes with low residual solids. The reductive liquefaction was conducted in an autoclave reactor using a series of MoOx-Al2O3 variants in the range of 340-400 °C with an initial H2 pressure of 35 bar for 4 h. At 340 °C, a correlation between Mo-loadings and reactivity for depolymerization and hydrodeoxygenation was found optimal for a surface density of 3.2 Mo-atoms per nm2 corresponding to 8 wt% Mo-loading. The liquefied fraction showed high selectivity (∼38%) for the formation of cycloalkanes and alkylbenzenes. At higher temperatures (400 °C) enhanced reactivity over the optimal catalyst showed higher cycloalkane and alkylbenzenes formation (∼57%) at a low biomass-to-catalyst feed mass ratio (3 : 1). At a higher ratio (10 : 1), alkylphenols (∼41%) are the leading product fraction followed by cycloalkanes and alkylbenzenes (∼34%) with a high liquefied monomer bio-oil product yield of 39.4 wt%. Catalyst characterization via XRD, Raman, H2-TPR, and XPS analysis revealed that the origin for this reactivity arises from the Mo species formed and stabilized over the support surface. A well dispersed, octahedral, higher fraction of easily reducible Mo-species (Mo5+) was evident over the optimal catalyst which enables enhanced C-O cleavage facilitating the hydrodeoxygenation reaction. Moreover, the solid residue yield could be reduced to below 5 wt% by optimizing the reaction conditions and particle size of the sawdust.
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| 6. |
- Shao, Jieling, 1993, et al.
(författare)
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Pt-based catalysts for NOx reduction from H2 combustion engines
- 2024
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 14:11, s. 3219-3234
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Tidskriftsartikel (refereegranskat)abstract
- Platinum supported on SSZ-13 zeolite has been found to be a potential catalyst for the selective catalytic reduction of NO by H-2. This work has studied the effects of the H-2/NO molar feed ratios (0/4.4/8.8/13.2) and the impact of water on the performance of the H-2-SCR of NO on the Pt/SSZ-13 catalyst. A higher H-2/NO ratio promoted the start of the reaction at lower temperatures and favoured the production of N-2. The effect of Pt loadings was also studied with three loadings of 0.5/1.0/2.0 wt%. It was found that the 0.5 wt% Pt sample displayed the highest N-2 selectivity of 75%. In addition, an inhibiting effect of water for H-2-SCR at low temperatures was proved. Pt/SSZ-13 has shown good hydrothermal durability after 6 h in total ageing pretreatment at 800 degrees C and interestingly the nitrogen formation even increased. The support effect of SSZ-13, BETA and Al2O3 on H-2-SCR was evaluated in terms of catalytic performance and their catalytic durabilities by hydrothermal ageing experiments, showing that zeolites are significantly better for H-2 SCR. In situ DRIFT measurements helped to explore the mechanism of H-2-SCR on the Pt catalyst. A careful design of the measurements was used to distinguish the overlapping peaks of the water on the DRIFT spectrum. NH4+ ions are formed and it was shown that they play a role as intermediates during the reaction to assist the NO reduction.
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| 7. |
- Yao, Dawei, 1991, et al.
(författare)
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Deciphering SO2 poisoning mechanisms for passive NOx adsorption: A kinetic modeling approach and development of a high-resistance catalyst
- 2024
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 487
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Tidskriftsartikel (refereegranskat)abstract
- Passive NOx adsorption (PNA) is a promising technology aimed at reducing NOx emissions from vehicles during the cold start phase of the engine. This work investigated the SO2 poisoning mechanism of PNA through a combination of experimental research and kinetic modeling, leading to the development of a novel PNA sample with high resistance to SO2 poisoning. Pd/SSZ-13 samples were synthesized using different drying conditions, revealing that samples dried at room temperature showed lower degradation (10 %) compared to those dried at 80 °C (26 %). Investigation into the degradation revealed that ion-exchanged Pd sites with a hydroxyl group were more resistant to SO2 poisoning than other Pd sites. It is also found that SO2 aids in NOx storage on Pd sites, enhancing the PNA performance. A kinetic model was developed to describe the SO2 poisoning behavior and its influence on NOx storage. The model, which was verified under various conditions, effectively simulated the PNA behavior and SO2 poisoning of Pd/SSZ-13.
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