Mechanistic Role of the Proton–Hydride Pair in Heteroarene Catalytic Hydrogenation
Bibliographic record
Abstract
Kinetic and density functional theory studies probe the catalytic involvements of proton–hydride pairs in breaking the strong aromaticity of N-containing heteroarenes (pyridine and pyrrole) on sulfided Ru cluster surfaces. Under the sulfur chemical potentials relevant to hydrodenitrogenation catalysis, Ru clusters remain covered with a layer of sulfur-deficient RuS x on which a variety of reactive hydrogen species, which bind to Ru 4+, S 2–, or Ru 4+ –S as Ru 4+ –(H δ− ), S 2– –(H δ+ ), and Ru 4+ –(SH 2 ), respectively, coexist. These reactive hydrogen species exhibit either proton or hydride character, depending on the electronegativity of their ligands (ruthenium and sulfur). For this reason, they participate in different hydrogen addition steps during the hydrogenation of heterocyclic-N compounds. Pyridine as the basic and pyrrole as the nonbasic heterocyclic model compounds undergo hydrogenation via distinctly different kinetically relevant steps because of their different proton affinities, which influence their interactions with the various reactive hydrogen species and in turn adsorption configurations. The hydrogenation of pyridine initiates from an initial, quasi-equilibrated proton attack onto the N atom, followed by a second hydridic hydrogen addition as the kinetically relevant step. In the contrasting case of pyrrole, the hydrogenation initiates via a kinetically relevant proton attack to its β-carbon that breaks its aromaticity before a hydride addition onto its α-carbon. Both reactions require a proton attack followed by a hydride attack, but their mechanistic differences lead to contrasting rate dependences with H 2 S pressure because the H 2 S pressure, together with H 2 pressure, gives the H 2 S:H 2 ratio that dictates the sulfur chemical potentials, the relative abundance of S anions and Ru cations coordinating to the hydrogen species, and in turn the surface concentrations of proton and hydride intermediates on Ru cluster surfaces. The catalytic involvements of proton–hydride pairs described here are general for hydrogenation reactions and, in particular, heteroarene hydrogenation in hydrotreatment processes.
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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 | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".