| 1. |
- 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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| 2. |
- Ho, Hoang Phuoc, 1983, et al.
(författare)
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Role of the supports during phosphorus poisoning of diesel oxidation catalysts
- 2023
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 468
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus (P) poisoning is one of the main factors accounting for the deactivation of diesel oxidation catalysts (DOC) apart from sulfur poisoning and sintering of the Pt active sites. This study compares the impact of P with loading up to 2.4 wt% on the catalytic performance of monometallic and bimetallic Pt-Pd catalysts using alumina and high silica BEA zeolites as the supports. P poisoning caused deactivation for CO, C3H6, C3H8 and NO oxidation; however, the degree of the impact of P in terms of temperatures at which 50% of the component is converted (T50) depends not only on the types of the active phase (Pt and Pt-Pd) but also on the types of supports (alumina and BEA zeolite). The influence of P impregnation on the textural properties of the materials is more significant for zeolite than alumina-based catalysts, which is in line with the activity measurements. A weak interaction between P and high silica zeolite resulted in the formation of a prominent fraction of P2O5 in the P-Pt/BEA, whereas a strong binding between P and alumina accounted for a dominant fraction of phosphate in the P-Pt/Al2O3 as revealed by XPS and NMR measurements. Phosphorus compounds partially covered the available surface of the active sites and this lowered the catalytic activity. For alumina-based catalysts, P mainly reacted with the support and only deactivated a part of the active noble metals. Whereas, for zeolite-based catalysts, P existed mainly in the form of phosphorus oxides that significantly blocked the catalyst surface and thereby deactivated more of the available active sites than that on alumina-based materials, which is consistent with the CO chemisorption data.
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| 3. |
- Ho, Hoang Phuoc, 1983, et al.
(författare)
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The effect of Pt/Pd ratio on the oxidation activity and resistance to sulfur poisoning for Pt-Pd/BEA diesel oxidation catalysts with high siliceous content
- 2022
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the effect of the Pt/Pd ratio on the oxidation activity and sulfur poisoning/regeneration of diesel oxidation catalysts (DOC) using beta zeolites with high siliceous content as support. Formation of Pt-Pd alloy leads to contraction of the cell lattice of Pt in the bimetallic catalysts, improving not only the sintering resistance of Pt but also retaining a high fraction of Pd in Pd2+ form. Moreover, the Pt-Pd alloy also improves the oxidation resistance of the particles, which enhances the activity of the catalysts for CO and C3H6 oxidation. Bimetallic catalysts also favor NO reduction at a lower temperature than the monometallic Pt although they showed lower values for the absolute conversion of NO due to a decrease in the total number of the Pt active sites. In addition, the bimetallic catalysts significantly improved the sulfur resistance as compared to the monometallic Pd catalyst. Moreover, the bimetallic catalysts could easily recover their activity for NO and C3H6 oxidation by thermal treatment either in lean conditions or in H2. The reduction with H2 was necessary to recover completely the activity of the CO and C3H8 oxidation.
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| 4. |
- Shao, Jieling, 1993
(författare)
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Novel catalysts development for NOx reduction from H2 combustion engines
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogen, as a clean energy carrier, burns without producing any carbon emissions. Hydrogen internal combustion engines (H2-ICE) are considered an alternative for the transition from conventional fossil-fuel vehicles. However, the development of effective aftertreatment catalysts remains necessary to address the inevitable NOx emissions from internal combustion engines. This thesis covers the performance of various active metals supported on zeolites as catalysts for the selective reduction of NO by H2 (H2-SCR), as well as the investigation of the influence of various reaction conditions and the related reaction mechanisms. The results of the thesis work are reported in two manuscripts, namely Paper I and II. Paper I focus on catalysts with Pt supported on SSZ-13 zeolite. Their performance is evaluated with varying H2/NO feed ratios (5/10/15), Pt loadings (0.5/1.0/2.0 wt%), and with and without water co-feeding. Activity tests showed that Pt catalysts have high catalytic activities for H2-SCR at low temperatures (<150 ℃), but only NO oxidation occurs at high temperatures. The reaction process is complex and includes multiple reactions such as competing H2 oxidation and NO oxidation, as well as other side reactions. The selectivity for the by-product N2O cannot be ignored and it is even greater than that for N2 at temperatures less than 120 ℃. Higher H2 concentration promotes N2 selectivity, and the more exothermic H2 oxidation aids NO oxidation to occur at lower temperatures. The 0.5 wt% Pt catalyst was found to possess the highest N2 selectivity in the loading studies, not only because fewer active sites attenuate the competing hydrogen oxidation reaction, but also it possesses a smaller particle size and higher dispersion, and a larger portion of Pt in its metallic state. Water had a strong inhibitory effect on H2-SCR at low temperatures, with a significant reduction in N2 generation compared to anhydrous environments. It was found in in-situ DRIFTS experiments that nitrosyl species weakly adsorbed on the catalyst and could be easily removed; H2 is absorbed on the Pt active sites and is activated to interact with nitrates. Meanwhile, NH4+ ions were formed during the reaction and could play a role as reaction intermediates to assist in the reduction of NO. Simultaneous entry of NO and H2 induces a faster reaction than sequential entry and affects the binding of surface species, especially NO. The introduction of O2 to the NO+H2 mixture generates more nitrite (NO2-) species on the catalyst. Paper II focuses on extending the range of reaction temperatures for H2-SCR. It was found that Pt/SSZ-13, Pd/SSZ-13, and Ir/SSZ-13 catalyze the H2-SCR at three temperature intervals, low, medium, and high temperatures, respectively. Also, nitrogen selectivity increases sequentially with temperature. Combining them in series in the order of iridium-palladium-platinum is an interesting option. Due to the low reactivity of Ir, two strategies, a reduction pretreatment and replacement of the support with BETA zeolite, were examined and found to be successful in increasing its nitrogen generation. Similarly, the difference in H2-SCR reaction properties on the three active centres was investigated using in-situ DRIFTS measurements, and it was found that the Ir had the strongest NO adsorption, which was one of the reasons for its weak activity. No H2-SCR reaction occurred based on observation from the spectra at 200 ℃. After the reduction pretreatment, NO adsorption was weakened due to the metal present more in its metallic state and this contributed to the occurrence of H2-SCR.
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| 5. |
- 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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| 6. |
- Sharma, Poonam, 1990, et al.
(författare)
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Role of ZrO 2 and CeO 2 support on the In 2 O 3 catalyst activity for CO 2 hydrogenation
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 331
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Tidskriftsartikel (refereegranskat)abstract
- Methanol synthesis from CO2 hydrogenation has drawn global attention as catalytic CO2 hydrogenation is an attractive choice to mitigate CO2 emissions and lessen dependency on fossil resources. In the present study, we have synthesized ZrO2 and CeO2-supported In2O3 catalysts for methanol synthesis from CO2 hydrogenation and the catalytic performances of Inx/ZrO2, and Inx/CeO2 (x = 1 % and 13 %) were compared. Specifically, the effect of the ZrO2 and CeO2 supports on In2O3 catalyst during CO2 hydrogenation was explored. This study reveals that ZrO2 support increased the catalytic activity while the CeO2 support decreased although both supports have almost the same indium loading and surface area. Various characterizations like XRD, DRIFT, CO2-TPD, H2-TPR and XPS analysis of catalysts provided insight into changes that arise after mixing the two oxides and during the reaction as well as after the reaction. The stabilities of In2O3, In13/ZrO2, and In13/CeO2 were tested for up to 50 h and we found In13/ZrO2 was stable during this time-on-stream, while In13/CeO2 lost activity after 2 h of reaction. XPS results of spent catalysts showed that In(OH)3 was observed significantly over the spent In13/CeO2. OH groups were also verified by DRIFT experiments, however at low levels due to low CO2 conversion at atmospheric pressure. XRD analysis confirmed the sintering of CeO2 support during the reaction. Thus, the hydrophilic nature of CeO2, redox properties of CeO2 and sintering of CeO2 support in the presence of water, were the main reasons for the early deactivation of In13/CeO2. A regeneration study was carried out to regenerate the catalyst and the results showed that partial regeneration of the In13/CeO2 catalyst is possible by Ar flushing. We, therefore, suggest that the build-up of OHgroups deactivate the In13/CeO2 catalyst and some of these OH groups could be removed during flushing with inert gas, causing a partial regeneration. However, the decreased surface area is not reversible, and this results in a continuous decrease in the activity of the catalyst after repeated experiments, even if the catalyst is flushed with Ar between the experiments.
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