| 1. |
- Bounechada, Djamela, 1984, et al.
(författare)
-
Mechanisms behind sulfur promoted oxidation of methane
- 2013
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:22, s. 8648-8661
-
Tidskriftsartikel (refereegranskat)abstract
- The promoting effect of SO2 on the activity for methane oxidation over platinum supported on silica, alumina and ceria has been studied by flow-reactor, in situ infrared spectroscopy and in situ high-energy x-ray diffraction experiments under transient reaction conditions. The catalytic activity is clearly dependent on the support material and its interaction with the noble metal both in absence and presence of sulfur. On platinum, the competitive reactant adsorption favors oxygen dissociation such that oxygen self-poisoning is observed for Pt/silica and Pt/alumina. Contrarily for Pt/ceria, no oxygen self-poisoning is observed, which seems to be due to additional reaction channels via sites on the platinum-ceria boundary and/or ceria surface considerably far from the Pt crystallites. Addition of sulfur dioxide generally leads to the formation of ad-SOx species on the supports with a concomitant removal and/or blockage/rearrangement of surface hydroxyl groups. Thereby, the methane oxidation is inhibited for Pt/silica, enhanced for Pt/alumina and temporary enhanced followed by inhibition after long-term exposure to sulfur for Pt/ceria. The observations can be explained by competitive oxidation of SO2 and CH4 on Pt/silica, formation of new active sites at the noble metal-support interface promoting dissociative adsorption of methane on Pt/alumina, and in the case of Pt/ceria, formation of promoting interfacial surface sulfates followed by formation of deactivating bulk-like sulfate species. Furthermore, it can be excluded that reduction of detrimental high oxygen coverage and/or oxide formation on the platinum particles through SO2 oxidation is the main cause for the promotional effects observed.
|
|
| 2. |
- Fouladvand, Sheedeh, 1984, et al.
(författare)
-
Methane oxidation over Pd supported on ceria–alumina under rich/lean cycling conditions
- 2013
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 410-415
-
Tidskriftsartikel (refereegranskat)abstract
- Catalysts with highly dispersed palladium on alumina, alumina doped with 20 wt% ceria and ceria have been prepared, characterized and examined for net-lean methane oxidation. In particular, the activity and selectivity were investigated during rich/lean cycling of the feed. The ceria content is found to influence both the general and the instantaneous activity responses. The results indicate that the active phase of palladium changes between reduced and oxidised Pd during the rich/lean cycling, and that the process is influenced by the presence of ceria.
|
|
| 3. |
- Nilsson, Johan, 1987, et al.
(författare)
-
Chemistry of supported palladium nanoparticles during methane oxidation
- 2015
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 5:4, s. 2481-2489
-
Tidskriftsartikel (refereegranskat)abstract
- Time-resolved in situ energy-dispersive X-ray absorption spectroscopy and mass spectrometry are used to correlate changes in chemical state of alumina and ceria supported palladium nanoparticles with changes in activity and selectivity for methane oxidation. Specifically, modulation excitation spectroscopy experiments are carried out by periodically cycling between net-reducing and net-oxidizing reaction conditions. The XANES and EXAFS data show that the palladium nanoparticles are readily bulk oxidized when exposed to oxygen, forming a PdO-like phase, and reduced back to a reduced (metal) phase when oxygen is removed from the feed. The difference between the two support materials is most noticeable at the switches between net-oxidizing and net-reducing reaction conditions. Here, a brief reduction in conversion is observed for the alumina supported catalyst, but for the ceria this reduction in conversion is minor or not observed at all. This difference is attributed to differences in the oxidation kinetics and the oxygen storage capability of ceria.
|
|
| 4. |
- Pingel, Torben, 1984, et al.
(författare)
-
Three-dimensional probing of catalyst ageing on different length scales: A case study of changes in microstructure and activity for CO oxidation of a Pt-Pd/Al2O3 catalyst
- 2017
-
Ingår i: ChemCatChem. - : Wiley. - 1867-3899 .- 1867-3880. ; 9:18, s. 3544-3553
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study the effects of thermal treatment on the microstructure of a Pt-Pd/Al2O3 oxidation catalyst and its activity for CO oxidation have been studied. The microstructural analysis was performed using several high-resolution electron microscopy techniques like STEM, FIB/SEM slice & view, SEM and EDX. A combination of these analysis techniques and advanced TEM specimen preparation allowed for three-dimensional probing at different length scales avoiding the random character of conventionally crushed powder specimens due to site specificity. A core-shell distribution of Pt-Pd nanoparticles within the alumina support particles, with enlarged nanoparticles (≈ 1.5 to 40 nm) being present in the shell and small nanoparticles (
|
|
| 5. |
- Auvray, Xavier, 1986, et al.
(författare)
-
Comparative Study of SO 2 and SO 2 /SO 3 Poisoning and Regeneration of Cu/BEA and Cu/SSZ-13 for NH 3 SCR
- 2021
-
Ingår i: Emission Control Science and Technology. - : Springer Science and Business Media LLC. - 2199-3629 .- 2199-3637. ; 7:4, s. 232-246
-
Tidskriftsartikel (refereegranskat)abstract
- Two copper-exchanged zeolites, Cu/SSZ-13 and Cu/BEA, were studied as catalysts for the selective reduction of NOx by NH3 (NH3-SCR). Their activities for standard SCR (NOx = NO) and fast SCR (NOx = 50% NO + 50% NO2) were measured before and after sulfur poisoning at 250 °C. The effect of 30 ppm SO2 and a mixture of 24 ppm SO3 + 6 ppm SO2 was evaluated. The repetition of subsequent activity measurements served as regeneration method in SCR conditions. SO2 deactivated Cu/SSZ-13 whereas Cu/BEA was only moderately affected. SO3 led to stronger deactivation of both catalysts than SO2. However, also for this case, the Cu/BEA was significantly less affected than Cu/SSZ-13, even though Cu/BEA contained larger amount of stored sulfur. One possible reason for this could be the large pores of Cu/BEA, where the sulfur species possibly resulted in less sterical hindrance than in the small pore SSZ-13 structure. NH3 temperature-programmed desorption (NH3-TPD) showed no loss of storage sites upon sulfur treatment and subsequent regeneration. Partial activity recovery was observed after a period in SCR conditions at 400 °C and 500 °C. Temperature at 300 °C was insufficient to regenerate the catalysts. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NO adsorption suggested that SO2 interacts with the ZCuOH sites on Cu/SSZ-13, causing the strong poisoning.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Chaoquan, Hu, 1981, et al.
(författare)
-
Methyl crotonate hydrogenation over Pt: Effects of support and metal dispersion
- 2016
-
Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 511, s. 106-116
-
Tidskriftsartikel (refereegranskat)abstract
- Gas-phase hydrogenation of methyl crotonate (MC) has been studied over Pt supported on Al2O3, C, SiO2,and TiO2. The physicochemical properties of the catalysts were characterized by use of N2 physisorption,transmission electron microscopy and CO chemisorption. The effects of Pt dispersion and nature of the support on the catalytic properties of the catalysts were determined by measurements of the kinetic parameters for MC hydrogenation. The results clearly display MC inhibition effects on the hydrogenation over the catalysts. However, the degree of MC-inhibition is found to depend on both the Pt dispersion and the support used. For alumina a high Pt dispersion can promote the resistance of the catalyst against MC-inhibition, and even allow hydrogen adsorption to become equilibrated on the Pt surface. Compared to SiO2 and C supports, Al2O3 improves the resistance of the Pt surface against MC inhibition, whereas TiO2reduces the resistance. Possible reasons are suggested to understand the positive effect of Al2O3 on Pt against MC inhibition.
|
|
| 9. |
- Fouladvand, Sheedeh, 1984, et al.
(författare)
-
A transient in situ infrared spectroscopy study on methane oxidation over supported Pt catalysts
- 2014
-
Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 4:10, s. 3463-3473
-
Tidskriftsartikel (refereegranskat)abstract
- Catalysts with platinum dispersed on alumina, ceria and mixed alumina-ceria have been prepared by incipient wetness impreg- nation, characterized with transmission electron microscopy and X-ray diffraction, and evaluated for total oxidation of methane under both stationary and transient gas compositions (oxygen pulsing). Further, in situ diffuse reflectance Fourier transformed infrared spectroscopy has been used to monitor the evolution of surface species during precise transient gas composition changes using high-speed gas switching valves. The results show that platinum interacts sufficiently strong with all the supports so as to form small platinum particles. The smallest sizes are observed for the Pt/Ce sample. The alumina con- taining samples show, in contrast to the Pt/Ce sample, a decreased methane conversion with the increasing oxygen concentration and a clear kinetic bistability between increasing and decreasing oxygen concentrations. The bistable kinetics is likely connected to oxidation and reduction of platinum occurring at different stoichiometric gas mixtures depending on the history of the system, for which an oxidation of the platinum particles effectively inhibits the dissociative adsorption of methane leading to low reaction rate. It is shown for the alumina containing samples that the adverse effects of oxygen excess can be circumvented by the use of periodic operation so that the the average methane conversion is improved. Further, Pt/Ce seems to exhibit additional active sites at the platinum-ceria interface explaining the generally higher conversion of methane for this sample.
|
|
| 10. |
- Fouladvand, Sheedeh, 1984, et al.
(författare)
-
Fault Tree Analysis, Strengths and Weaknesses
- 2010
-
Ingår i: SHO2010: INTERNATIONAL SYMPOSIUM ON OCCUPATIONAL SAFETY AND HYGIENE. - 9789729950469 ; , s. 253-255
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fault Tree Analysis (FTA) is a tool of hazard identification techniques. As a useful method it is applied in various industries, social and environmental problems for reconstruction, failure analysis, and failure frequency estimation. ETA is a graphical and logic combination of causes of a defined undesired event where Boolean algebra is used. It is a backward method which is used to think about the consequences which may occur. This analysis method is mainly used in the field of safety engineering to quantify the probability of an undesired event and is used to reconstruct it. It can also be used to reconstruct an accident. Besides its advantages, there are a number of shortcomings which imply that the method still has rooms for improvement. Among the disadvantages are the uncertainties in covering all failure modes, inaccuracy in human error in investigation of complex man-made systems and inefficiency of the tool in case of scarce or insufficient data. These problems demand some revision study to find the research questions in detail. The purpose of this paper is to conduct a literature review in order to find weaknesses and strengths of FTA to indicate a platform for future research works.
|
|
