Cu-Zeolite SCR Catalyst Thermal Deactivation Studied with FTIR Spatial Resolution
Bibliographic record
Abstract
The performance of a commercial Cu-zeolite SCR catalyst after differing degrees of hydrothermal aging (aged for 72 hours at 500, 700 and 800°C with 10% moisture balanced with air) was studied by spatially resolving different key reactions using gas-phase FTIR measurements. Gases were sampled along a channel at different positions and analyzed using FTIR, which overcomes the interference of water and nitrogen on ammonia concentration detection encountered in standard mass spectrometer-based spatial resolution measurements. The NO:NO₂ concentration ratio was changed so that the standard (NO:NO₂ = 1:0), fast (NO:NO₂ = 1:1) and NO₂ (NO:NO₂ = 0:1) SCR reactions could be investigated as a function of the catalyst's hydrothermal aging extent. In addition, the effects of hydrothermal aging on the activity of NH₃ and NO oxidation were also investigated. Hydrothermal aging had little effect on NO oxidation activity. For standard and fast SCR processes, NOx conversion attained its maximum at 300°C. Hydrothermal aging decreased reaction rates for SCR and NH₃ overconsumption simultaneously. However, selectivity to NH₃ overconsumption was high over the highly aged catalyst at high temperatures. NO was oxidized to NO₂ at the outlet portion of the catalyst under standard SCR conditions at high temperatures, suggesting a balance between NO oxidation and SCR at limited NH₃ concentrations. NO conversion under standard SCR conditions decreased more with hydrothermal aging compared to NOx conversion under fast SCR conditions. Coincidently, NH₃ overconsumption was more significant under standard SCR versus fast SCR conditions. Along a monolithic catalyst channel, the extent of reaction changed with the NO:NO₂ composition. When both NO and NO₂ were present in the inlet gas, the fast SCR reaction dominated. At temperatures below 200°C, a small amount of reaction between NH₃ and NO₂ was also observed. Standard SCR became more significant with NO₂ depletion along the catalyst. However, the fast SCR reaction at high temperatures can be limited by the decomposition of NO₂ at the front of the catalyst. Hydrothermal aging decreased the extent of NO₂ decomposition into NO at high temperatures, which helps maintain fast SCR reaction conditions in the system. The effects of hydrothermal aging on NH₃ oxidation was more complicated. Generally, aging reduced NH₃ oxidation activity, but it did not change monotonically with aging extent and neither did NOx produced via NH₃ oxidation. However, the highly aged catalyst did produce a high proportion of NOx.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".