Consequences of Surface Oxophilicity of Ni, Ni-Co, and Co Clusters on Methane Activation
Bibliographic record
Abstract
This study describes a new C–H bond activation pathway during CH 4 –CO 2 reactions on oxophilic Ni-Co and Co clusters, unlike those established previously on Ni clusters. The initial C–H bond activation remains as the sole kinetically relevant step on Ni-Co, Ni, and Co clusters, but their specific reaction paths vary. On Ni clusters, C–H bond activation occurs via an oxidative addition step that involves a three-center (H 3 C···*···H) ⧧ transition state, during which a Ni-atom inserts into the C–H bond and donates its electron density into the C–H bond’s antibonding orbital. Ni-Co clusters are more oxophilic than Ni; thus, their surfaces are covered with oxygen adatoms. An oxygen adatom and a vicinal Co-atom form a metal–oxygen site-pair that cleaves the C–H bond via a σ bond metathesis reaction, during which the Co inserts into the C–H bond while the oxygen abstracts the leaving H-atom in a concerted, four-center (H 3 C···*···H···O*) ⧧ transition state. Similarly, Co clusters also catalyze the σ bond metathesis step, but much less effectively because of their higher oxophilicities, much stronger binding to oxygen, and less effective hydrogen abstraction than Ni-Co clusters. On Ni-Co and Co clusters, the pseudo-first-order rate coefficients are single-valued functions of the CO 2 -to-CO ratio (or H 2 O-to-H 2 ratio), because this ratio prescribes the oxygen chemical potentials and the relative abundances of metal–oxygen site-pairs through the water–gas shift equilibrium. The direct involvement of reactive oxygen in the kinetically relevant step leads to more effective CH 4 turnovers and complete elimination of coke deposition on Ni-Co bimetallic clusters.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".