| 1. |
- Han, Joonsoo, 1990, et al.
(författare)
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N 2 O Formation during NH 3 -SCR over Different Zeolite Frameworks: Effect of Framework Structure, Copper Species, and Water
- 2021
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 60:49, s. 17826-17839
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Tidskriftsartikel (refereegranskat)abstract
- The formation characteristics of N2O were investigated with respect to copper-functionalized zeolites, i.e., Cu/SSZ-13 (CHA), Cu/ZSM-5 (MFI), and Cu/BEA (BEA) and compared with the corresponding zeolites in the H form as references to elucidate the effect of the framework structure, copper addition, and water. Temperature-programmed reduction with hydrogen showed that the CHA framework has a higher concentration of Cu2+ (Z2Cu) compared to MFI and BEA. The characterizations and catalyst activity results highlight that CHA has a framework structure that favors high formation of ammonium nitrate (AN) in comparison with MFI and BEA. Moreover, AN formation and decomposition were found to be promoted in the presence of Cu species. On the contrary, lower N2O formation was observed from Cu/CHA during standard and fast SCR reactions, which is proposed to be due to highly stabilized AN inside the zeolite cages. On the other hand, significant amounts of N2O were released during heating due to decomposition of AN, implying pros and cons of AN stability for Cu/CHA with possible uncontrolled N2O formation during transient conditions. Additionally, important effects of water were found, where water hinders AN formation and increases the selectivity for decomposition to NO2 instead of N2O. Thus, less available AN forming N2O was observed in the presence of water. This was also observed in fast SCR conditions where all Cu/zeolites exhibited lower continuous N2O formation in the presence of water.
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| 2. |
- Isapour Toutizad, Ghodsieh, 1986, et al.
(författare)
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In situ DRIFT studies on N2O formation over Cu-functionalized zeolites during ammonia-SCR
- 2022
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 12:12, s. 3921-3936
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the zeolite framework structure on the formation of N2O during ammonia-SCR of NOx was studied for three different copper-functionalized zeolite samples, namely Cu-SSZ-13 (CHA), Cu-ZSM-5 (MFI), and Cu-BEA (BEA). The evolution of surface species during the SCR reaction at different temperatures was monitored with step-response experiments using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different reaction conditions. Also, density functional theory (DFT) calculations were performed to assist the interpretation of the experimental results. The DRIFTS results indicate that NO+ and nitrate species are the main products formed during NO oxidation, and NO appears to adsorb on both Cu-Lewis and Al-Lewis acid sites. The DFT calculations for NO adsorption on the SSZ-13 sample reveal adsorption at Bronsted acid sites with similar adsorption energies but with a slight difference in NO+ stretching vibrations in the DRIFT spectra. Within the standard SCR reaction, in the O-H stretching region, the number of NH3 molecules adsorbed on the Bronsted acid sites is higher for the small-pore size sample compared to the medium- and large-pore zeolites. The obtained DRIFTS results for nitrate species are supported by DFT calculations by simulating the IR spectra of mobile and framework bound nitrate species, which both have a signature at 1604 cm(-1) associated with the O-N bond on NO3-. It is revealed that N2O is produced in a higher amount at lower temperatures for all three samples irrespective of the NO/NO2 ratio. Furthermore, the obtained results from both DRIFTS studies and flow reactor experiments show the higher formation of N2O for the large-pore zeolite compared to the medium- and small-pore zeolite.
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| 3. |
- Isapour Toutizad, Ghodsieh, 1986
(författare)
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Nitrous Oxide Formation over Zeolite-based Catalysts during Ammonia-SCR: The Effect of Framework Structure, Acidity, and Copper Content
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emission control of anthropogenic nitrous oxide (N2O), a by-product formed through fossil- and renewable fuel combustion, agricultural activities, and industrial chemical processes, has attracted large considerations due to its substantial contribution in global warming and ozone layer depletion. Selective catalytic reduction with ammonia (NH3-SCR) is the most prevailing technology for the abatement of nitrogen oxides (NOx) in the exhaust gases from lean-burn processes, with the possible formation of N2O. Therefore, the development of catalysts for efficient NOx reduction with no or minor N2O formation is of major importance. Hence, zeolite-based catalysts exchanged with copper have shown to be efficient catalysts for NOx reduction owing to their high catalytic performance under practical reaction conditions. This work aims to increase the understanding of the N2O formation during NH3-SCR, in particular studying the effect of different parameters, from zeolite framework structure, ammonia storage capacity of the zeolites, to Si/Al and Cu/Al molar ratios. Three different zeolites with varying pore sizes, from small to medium and large pore zeolites (SSZ-13, ZSM-5 and beta), were chosen to investigate their performance as SCR catalysts. A range of SSZ-13 samples with Si/Al molar ratios of 6, 12, and 24 were prepared by hydrothermal crystallization, and exchanged with copper, Cu/Al= 0-0.4 molar ratios, to investigate the effect of the Si/Al and Cu/Al molar ratios on the ammonia storage capacity and the SCR performance of the samples. Furthermore, the role of the sample pretreatment on the SCR performance was investigated for the SSZ-13 sample with Si/Al= 12 molar ratio. The prepared samples were studied by flow reactor experiments and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to evaluate the catalytic activity and selectivity, and to monitor the evolution of surface species during reaction. Copper ions as active sites in the zeolite catalyzing the SCR reaction by NO activation and formation of NO+ and/or surface nitrate species. During SCR, the nitrate species can subsequently react with NH3 and form ammonium nitrate (AN) as an intermediate, which partially contributes to N2O formation upon decomposition. In order to understand the system in more detail, we have investigated important factors such as Si/Al and Cu/Al molar ratio and temperature on the NH3 storage capacity of the samples based on SSZ-13. Temperature programmed desorption by NH3 (NH3-TPD) carried out to characterize the nature of the different acid sites in the zeolite. It is revealed that the samples with low Si/Al molar ratio provide higher NH3 storage capacity, which increases with increasing Cu loading. After NH3-TPD, SCR experiments were subsequently performed resulting in higher NOx conversion and N2O formation by increasing the Cu content for all samples. Results from DRIFTS showing vibrational peaks associated with N2O in accordance with the flow reactor findings. Moreover, the role of pretreatment for the NH3-SCR performance was evaluated for the sample with Si/Al= 12, and the results show that the pretreatment in NH3 and NO, in the absence of O2, reveals higher low-temperature activity for standard SCR compared to the pretreatment including O2.
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| 4. |
- Isapour Toutizad, Ghodsieh, 1986
(författare)
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The effect of framework structure on N2O formation over Cu-based zeolites during NH3-SCR reactions
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Anthropogenic nitrous oxide (N2O), which is generally formed as a byproduct of industrial chemical processes and fossil fuel combustion, has attracted significant attention in recent years due to its destructive role in global warming and ozone layer depletion. Among different developed technologies applied for lean NOx reduction, the selective catalytic reduction (SCR) of NOx with ammonia (as a reducing agent) is presently the most used method. Hence, the development of catalysts for efficient lean NOx reduction that do not form N2O (an unwanted by-product in the SCR reaction) in the process, or only form N2O to a very small extent from the exhaust gases is of crucial significance. One of the types of catalysts that today are used for this purpose are zeolite-based catalysts. These have been extensively investigated owing to their extraordinary catalytic performance under practical reaction conditions such as high thermal stability and high N2 selectivity. Among all zeolites, Cu ion-exchanged zeolites, with MFI framework structure, like ZSM-5 and BEA framework structure, like Beta, represent high activity and N2 selectivity. Besides, Cu ion-exchanged zeolites with CHA Framework structure, like SSZ-13, show even higher hydrothermal stability, N2 selectivity and better hydrocarbon poisoning resistance compared to Cu-based ZSM-5 and Beta zeolites. This work aims at investigating the effect of the zeolite framework structure on N2O formation during NH3-SCR reactions over three Cu-based zeolites ranging from small-pore to large-pore structures. Since Cu ions at the exchange sites play a crucial role in SCR reactions and promote different SCR pathways, the formation of different copper species has been investigated. In the zeolite framework, Cu exists in two cationic forms, which can catalyze the SCR reaction by activating NO to form NO+ and/or surface nitrate species. The nitrate species can subsequently react with NH3 to form another intermediate, ammonium nitrate (AN), which seems to be one source for N2O formation at low temperatures. These results are supported by kinetic studies in flow reactor and H 2 -TPR measurements. Furthermore, in situ infrared spectroscopy data revealed that in various NO/NO2 ratio in the inlet gas composition, higher formation of N2O is observed at low temperature which can be due to the higher formation and decomposition of ammonium nitrate. The investigations in flow reactor, are in line with the in situ infrared spectroscopy results.
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| 5. |
- Mendes, Pedro S. F., et al.
(författare)
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Conference Report: YEuCat Better Together - Collaborative Catalysis in a Changing World
- 2022
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Ingår i: ChemCatChem. - : Wiley. - 1867-3899 .- 1867-3880. ; 14:15
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- "YEuCat Better Together was the first collaborative event organized by the Young European Catalysis Network with the goal of joining young minds to propose an innovative catalytic solution to a global problem." This and more about YEuCat Better Together can be found in this Guest Editorial.+
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