Can oxidation occur without accompanying reduction?
Ordinarily, the answer is "No". Electrons given off by one reagent (the reducing agent) must be taken up by another (the oxidizing agent).
There is, however, one type of reaction where the electrons are not taken up by anything, but remain as a product of reaction (at least temporarily). This involves certain highly electropositive metals, especially alkali metals, dissolving in solvents such as liquid ammonia to form the metal ions plus solvated electrons (https://en.wikipedia.org/wiki/Solvated_electron). The metal is oxidized but nothing is reduced, at least not right away; the electrons given off by the metal remain as a product.
Over time, however, the ammonia does get reduced releasing hydrogen gas, and then we have a conventional redox reaction.