| 1. |
- Chen, X. X., et al.
(author)
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Traditional earth-abundant coal as new energy materials to catalyze the oxygen reduction reaction in alkaline solution
- 2016
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In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 211, s. 568-575
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Journal article (peer-reviewed)abstract
- Coal is an earth-abundant energy resource, however, its direct combustion results in serious environmental pollution. Therefore, it becomes important to design value-added products from coal and to maximize its value chain. Herein, brown coal was used to develop non-precious metal catalysts for the oxygen reduction reaction (ORR) in fuel cells as green energy conversion systems. The brown coal was first pretreated with different acids, followed by N-doping at 800 degrees C in a stream of NH3. A trace amount of Fe was further added to improve the electrocatalytic performance of the prepared catalyst towards ORR. The prepared coal-derived N-doped carbon further modified with 0.5% Fe exhibited onset potential of 0.92 V vs. RHE at a current density of -0.1 mA cm(-2) and a predominantly 4-electron transfer pathway of oxygen to water in 0.1 M NaOH, which was evaluated by RDE and RRDE. The prepared electrocatalysts were further characterized by elemental analysis, XRD, Raman and XPS. The results suggest that the coal-derived ORR catalyst have convoluted graphitic and amorphous carbon structures. The N-content increased after acid-pretreatment and subsequent functionalization with nitrogen, while it slightly decreased after Fe incorporation apparently due to coordination of Fe with N. ORR activity enhancement after the incorporation of Fe is expected to mainly arise from a synergetic effect involving the interaction of Fe with N groups distributed in the carbon matrix. (C) 2016 Elsevier Ltd. All rights reserved.
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| 2. |
- Englund, Johanna, 1988, et al.
(author)
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Deactivation of a Pd/Pt Bimetallic Oxidation Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation
- 2019
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In: Catalysts. - : MDPI. - 2073-4344. ; 9:12
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Journal article (peer-reviewed)abstract
- The reduction of anthropogenic greenhouse gas emissions is crucial to avoid further warming of the planet. We investigated how effluent gases from a biogas powered Euro VI heavy-duty engine impact the performance of a bimetallic (palladium and platinum) oxidation catalyst. Using synthetic gas mixtures, the oxidation of NO, CO, and CH4 before and after exposure to biogas exhaust for 900 h was studied. The catalyst lost most of its activity for methane oxidation, and the activity loss was most severe for the inlet part of the aged catalyst. Here, a clear sintering of Pt and Pd was observed, and higher concentrations of catalyst poisons such as sulfur and phosphorus were detected. The sintering and poisoning resulted in less available active sites and hence lower activity for methane oxidation.
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| 3. |
- Leistner, Kirsten, 1984, et al.
(author)
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Ammonia Desorption Peaks Can Be Assigned to Different Copper Sites in Cu/SSZ-13
- 2017
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 147:8, s. 1882-1890
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Journal article (peer-reviewed)abstract
- The purpose of this study is to attribute NH 3 -TPD peaks observed over Cu/SSZ-13 catalysts to different catalytic sites. This is done by comparing a large number of copper loadings, especially below 40% ion exchange, to be able to see effects relevant to sites in both 6-membered and 8-membered rings. We found that intermediate (200–300 °C) and high (400–500 °C) temperature NH 3 -TPD peaks followed similar trends to the copper species in 6-membered and 8-membered rings respectively, as seen by H 2 -TPR and NO-DRIFTS. Thus we propose that these two TPD peaks represent ammonia stored on H and Cu sites in 6 and 8-membered rings, respectively. This assignment is further supported by the finding that the intermediate and high temperature NH 3 -TPD peaks of samples with different Si/Al ratios also follow the same trend. Moreover, we observe that the activation energy for ammonia oxidation is significantly lower for Cu in 6MR compared to Cu in 8MR rings. Graphical Abstract: [Figure not available: see fulltext.].
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| 4. |
- Pan, Haoran, et al.
(author)
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Microwave-Assisted Synthesis of Co/CoOx Supported on Earth-Abundant Coal-Derived Carbon for Electrocatalysis of Oxygen Evolution
- 2019
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In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 166:8, s. F479-F486
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Journal article (peer-reviewed)abstract
- The evident demand for hydrogen as the ultimate energy fuel for posterity calls for the development of low-cost, efficient and stable electrocatalysts for water splitting. Herein, we report the synthesis of Co/CoOx supported on coal-derived N-doped carbon via a simple microwave-assisted method and demonstrate its application as an efficient catalyst for the oxygen evolution reaction (OER). With the optimal amount of cobalt introduced into the N-doped coal-derived, the developed catalyst achieved overpotentials of 0.370 and 0.429 V during water oxidation at current densities of 1 mA cm(-2) and 10 mA cm(-2), respectively. There was no noticeable loss in the activity of the catalyst during continuous galvanostatic polarization at a current density of 10 mA cm(-2) for a test period of 66 h. The synergistic interaction of the Co/CoOx moieties with the pyridinic and pyrollic nitrogen functional groups in the N-doped carbon, as well with the other heteroatoms species in the pristine coal favored enhancement of the OER electrocatalytic performance. (C) The Author(s) 2019. Published by ECS.
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| 5. |
- Safo, Isaac Adjei, et al.
(author)
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Oxidation and stability of multi-walled carbon nanotubes in hydrogen peroxide solution
- 2018
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In: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584. ; 214, s. 472-481
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Journal article (peer-reviewed)abstract
- The oxidation and stability of multi-walled carbon nanotubes (CNTs) have been investigated by exposing CNTs in 30% w/v H2O2 solution at room temperature (RT) for up to 8 weeks and at 80 degrees C for up to 8 h. H2O2 oxidation not only generated surface oxygen-containing groups, but also created surface defects, as disclosed by results of temperature-programmed desorption and X-ray Photoelectron Spectroscopy. The total surface oxygen content was found to be correlated to the final H2O2 concentration. The higher the total surface oxygen content on CNTs, the lower the final H2O2 concentration. Meanwhile, the carbon oxidation and simultaneous H2O2 decomposition were observed and confirmed by an online analysis of evolved gases during the oxidation stepwise heated from room temperature to 80 degrees C. Raman study showed that the DIG and D'/G ratios of the CNTs oxidized at RT first decreased with an oxidation time of 4 weeks and then increased when prolonging the oxidation time up to 8 weeks. Similar trend was also observed on the CNTs oxidized at 80 degrees C. The size of CNTs was gradually reduced with increasing oxidation time as shown by SEM studies. Our work reveals the critical changes in the surface oxygen groups as well as the changes in morphology at two distinct stages of hydrogen peroxide treatment, purification and then functionalization. CNTs can withstand 30% w/v H2O2 oxidation for only a certain time, while they may be damaged or consumed eventually in long-term applications. Our study contributes to filling in the knowledge gap about CNT surface oxidation and structural changes with H2O2 treatment under industrial conditions.
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| 6. |
- Wang, Aiyong, 1989, et al.
(author)
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A deactivation mechanism study of phosphorus-poisoned diesel oxidation catalysts: Model and supplier catalysts
- 2020
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In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 10:16, s. 5602-5617
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Journal article (peer-reviewed)abstract
- The effect of phosphorus poisoning on the catalytic behavior of diesel oxidation catalysts was investigated over model and supplier monolith catalysts, i.e., Pd-Pt/Al2O3. The results of ICP and XPS from the vapor-phase poisoning over model catalysts suggested that the temperature of phosphorus poisoning affects both the overall content of phosphorus and the dispersion of phosphorus (i.e., inlet/outlet and surface/bulk). Phosphorus oxide (P2O5), metaphosphate (PO3-), and phosphate (PO43-) were identified in the poisoned model and supplier catalysts. The distribution of these species on poisoned model catalysts was highly dependent on the poisoning temperature, i.e., a higher temperature resulted in a higher concentration of PO43-. The outlets of the monoliths contained more PO43- and less P2O5 than the inlets. Both active sites and surface OH groups on model and supplier catalysts were contaminated upon phosphorus poisoning. It is found that PO43- had a stronger influence on the active sites than P2O5. One significant finding in this study is that the vapor-phase phosphorus poisoning could be a practical and cost efficient approach to simulate an accelerated aging/poisoning process.
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| 7. |
- Wang, Aiyong, 1989, et al.
(author)
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Deactivation mechanism of Cu active sites in Cu/SSZ-13 — Phosphorus poisoning and the effect of hydrothermal aging
- 2020
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 269
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Journal article (peer-reviewed)abstract
- Non-poisoned and P-poisoned Cu/SSZ-13 catalysts with different types of Cu sites, i.e., [Cu(OH)]+ and Cu2+, were investigated for NH3-SCR. Phosphorus was found to interact more with [Cu(OH)]+ than Cu2+. Moreover, less phosphorus was required per Cu for poisoning in the samples with a high content of [Cu(OH)]+. We propose a phosphorus poisoning mechanism based on H2-TPR and XPS: poisoning of one Cu2+ involved two P atoms, i.e., P2O5, but for [Cu(OH)]+ contamination, only one P atom (PO3− or PO43−) is needed. Furthermore, phosphorus poisoning resulted in a decline in NH3/NO oxidation and an improvement in SCR activity at high temperatures. Upon hydrothermal aging, [Cu(OH)]+−phosphate/metaphosphate complexes were likely easier detached from the framework than the Cu2+−P2O5 species. This resulted in that the P-poisoned catalyst with high content [Cu(OH)]+ experienced more severe deactivation and dealumination than the non-poisoned catalyst. Additionally, 27Al-NMR suggested that the formation of AlPO4 has a linear relationship with [Cu(OH)]+/Cu2+ ratios.
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| 8. |
- Wang, Aiyong, 1989, et al.
(author)
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Insight into the effect of phosphorus poisoning of Cu/zeolites with different framework towards NH 3 -SCR
- 2023
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 454
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Journal article (peer-reviewed)abstract
- Cu/zeolites were prepared to elucidate the effect of phosphorus poisoning on different zeolite framework structures for NH3-SCR. The results show that there are significant differences in phosphorus poisoning depending on the zeolite framework structure. The PO3−/PO43− species gradually decreased along with an increase in P2O5 in the following order: Cu/SSZ-13, Cu/ZSM-5, and Cu/BEA. One possible reason could be the increased pore size of these zeolites, which results in less steric hindrance for larger P2O5 species. P2O5 is suggested to enhance the redox ability of Cu ions, which results in an increase in low-temperature activity in NH3-SCR, whereas Cu ions were significantly poisoned by PO3−/PO43−, resulting in low-temperature deactivation. Furthermore, the effect of phosphorus poisoning on the structure of Cu/ZSM-5 was found to be much greater than that of Cu/BEA and Cu/SSZ-13, possibly due to phosphorus attacked the surface defects of the zeolite, causing local expansion and cracking.
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| 9. |
- Wang, Aiyong, 1989, et al.
(author)
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Layered Pd/SSZ-13 with Cu/SSZ-13 as PNA − SCR dual-layer monolith catalyst for NOx abatement
- 2021
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In: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 360, s. 356-366
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Journal article (peer-reviewed)abstract
- A concept of a layered Pd/SSZ-13 with Cu/SSZ-13 as PNA-SCR dual-layer monolith catalyst for NOx abatement is demonstrated. NO-TPD was employed for determining the NOx storage, and the samples are characterized in detail using SEM-EDX, CO/NO-DRIFTS, XPS and H2-TPR. 750 °C hydrothermal treatment greatly promotes the NOx storage capacity and the addition of CO promotes NOx storage capacity and also shifts the NOx desorption temperature. The dual-layer sample (Pd/SSZ-13+Cu/SSZ-13) maintains most of the NOx storage capacity while the NOx desorption temperature is modified due to Cu/SSZ-13 as the top layer. The layered sample work well for NH3-SCR reaction. Notably, for Pd/SSZ-13+Cu/SSZ-13, more than 80 % of the NOx trapped at low temperature (i.e., 80 °C) can desorb in the suitable SCR temperature region where NOx conversion higher than 80 % is found. However, some loss of NO storage is found after SCR experiments. Overall, the dual-layer concept shows interesting potential for NOx abatement, but requires further developments on the PNA material to ensure stable storage capacity.
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| 10. |
- Wijayanti, Kurnia, 1979, et al.
(author)
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Effect of gas compositions on SO2 poisoning over Cu/SSZ-13 used for NH3-SCR
- 2017
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 219, s. 142-154
-
Journal article (peer-reviewed)abstract
- This study focuses on the effect of gas composition during SO2 poisoning over Cu/SSZ-13 for NH3-SCR application and was performed by conducting SO2-TPD experiments in a variety of lean gas compositions. In addition, the poisoned monoliths were characterized in detail using ICP-SFMS, UV–vis and XPS. During SO2 poisoning under dry and lean conditions, two different sulfur species were found, which were assigned to weakly bound SO2 and copper sulfate like species. Moreover, a significantly larger amount of copper sulfates was present in humid environment. The presence of NH3 during the poisoning resulted in the formation of ammonium sulfate species which were decomposed at the same temperature independently if the poisoning with SO2 was conducted in ammonia oxidation conditions or under standard or fast SCR conditions. Moreover, if the temperature ramp was conducted with O2 and H2O compared to Ar alone, more stable sulfate species were formed. In addition, SO2 poisoning under standard SCR conditions resulted in mostly ammonium sulfate formation at 200 °C, whereas copper sulfates were predominant after poisoning at 400 °C. After hydrothermal aging at 800 °C, more reducible copper species were noticeable and UV–vis showed that copper oxides had been formed. Sulfur poisoning of the hydrothermally aged sample resulted in the additional formation of copper sulfates during poisoning at 200 °C, which was not the case for poisoning of the fresh catalyst. Thus, the copper oxide species enhanced the copper sulfate formation.
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