Sol-Gel Entrapped Cobalt Pyridine-Carboxylate and Its Catalytic Performance for Oxidative Carbonylation of Methanol
Bibliographic record
Abstract
The sol-gel method has advantages over the immobilization procedures employed in the preparation of heterogeneous catalysts. The physical entrapment of homogeneous transition-metal catalysts into silica sol-gel matrices is a simple procedure which makes it possible to convert a variety of soluble metal compounds into recyclable leach-proof catalysts that are more stable than their homogeneous analogues. In this paper, the sol-gel entrapment of cobalt pyridine-carboxylate Co(pic) 2·4H 2O and synthesis of dimethyl carbonate by oxidative carbonylation of methanol were systematically investigated in order to reveal the relation between the preparative conditions and the physico-chemical and catalytic properties of the xerogels. Co(pic) 2·4H 2O was physically entrapped in SiO 2 sol-gel matrices under mild conditions by the sol-gel method using tetraethoxysilane (TEOS) as the precursor. The xerogels were obtained by conventional drying at 80 ℃ for 12 h and then washed with boiling water. The content of cobalt in water was measured by atom absorption spectroscopy and a corporation degree of cobalt in a sol-gel matrix was found to be 2.8% (Co/Si molar ratio).FT-IR and TG-DTA characterization results showed that Co(pic) 2·4H 2O was entrapped in the three-dimensional network of silica and the decomposition temperature of the xerogel is increased by 15 ℃. N 2 adsorption measurement confirmed that the xerogels have high surface areas of 320 to 458 m 2/g. The gelation time was observed to extend with increasing water/TEOS molar ratio (R) or decreasing pH under acid conditions. The xerogel catalyst prepared at R=6 and pH=4 showed the highest activity for the oxidative carbonylation of methanol to dimethyl carbonate. The methanol conversion reached 5.73% after reaction for 3 h, while the conversion over the homogeneous catalyst Co(pic) 2·4H 2O was 6.53%. The xerogel catalyst could be used for 6 reaction cycles without any loss of activity. This suggested that the entrapment of homogeneous metal complex catalysts into sol-gel matrices is a promising procedure.
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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".