New Insights into Formation of Molecular Sieve SAPO-34 for MTO Reactions
Bibliographic record
Abstract
Small-pore molecular sieve SAPO-34 is well-known as the most promising and effective catalyst for the conversion of methanol to olefins (MTO). In this paper, we have investigated the formation of SAPO-34 under different dry gel conversion (DGC) conditions using two types of synthesis gels with one containing hydrofluoric acid (HF) and the other not. Particular attention was paid to the Si incorporation and distribution in final SAPO-34 products. The results indicate that under DGC (with HF) conditions SAPO-34 is formed from the transformation of a highly crystalline, layered prephase that is held by covalent bonds. The final SAPO-34 product is a mixture of triclinic and trigonal phases containing six framework Si species. The Si distribution in triclinic and trigonal SAPO-34 is drastically different. The majority of Si species are located in the aluminosilicate domains in trigonal phase. Conversely, under DGC (without HF) conditions, the crystallization of SAPO-34 involves three transformational stages. Initially, a layered, crystalline intermediate forms and then transforms to a semicrystalline phase. The structures of both intermediates are held by weak noncovalent bonding interactions. The final SAPO-34 product is in pure trigonal form and contains two major Si species. Despite the difference in Si distribution, the SAPO-34 products prepared by using different gels have similar bulk Si contents. MTO reaction tests show that before 50 min of time-on-stream the DGC (with HF) product gives lower ethylene and propylene selectivity but higher propane selectivity than the DGC (without HF) product. After 50 min on stream, similar light olefin and propane selectivities are observed over the two SAPO-34 samples.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".