Is palladium on carbon acting as an oxidising or reducing agent?

Question

In the conversion of piperidine to pyridine, palladium on carbon (Pd/C) is used. But it is reducing agent.

Clear the confusion, please.

Answer 1

Palladium on carbon ($\ce{Pd/C}$) is neither an oxidant nor a reductant. The reaction is the dehydrogenation of piperidine: $\ce{C5H11N -> C5H5N + 3H2}$ and here, $\ce{Pd/C}$ is merely a catalyst.

Even in standard hydrogenation reactions using $\ce{H2(g) + Pd/C}$, the $\ce{Pd/C}$ is not a reducing agent. The $\ce{H2}$ is the reducing agent and Pd/C is again only a catalyst.

Answer 2

(The above answer brings up hydrogenation using Pd/C, be weary of the answer because they're not addressing the question.)

The above answer is partly true, but on the whole incorrect and would fail in a test scenario.

Yes, Pd/C is a catalyst therefore in a full reaction cycle the Pd/C should return to its original oxidation state.

However, Pd/C can only accept the N-H bond via oxidative addition onto Pd metal. By this definition, because the Pd is oxidized while adding the N-H bond across Pd, then Pd must begin the cycle as a "reductant" (i.e. the Pd metal initially reduces the N-H bond). The organic compound must be the "oxidant" because it oxidizes the Pd (i.e. oxidative-addition to Pd).

Where the first answer fails to be correct is: if Pd/C has been previously oxidized, it cannot perform the first step in the catalytic cycle and cannot be catalytic. It is more correct to say that Pd/C is a reducing agent (reductant, what have you).

Where the first answer fails more is: most Pd/C reductions in a lab setting are NOT catalytic and require a molar equivalent or even excess of Pd/C for a reduction, which goes against the definition of a catalyst.