Surface effects on the Formation of Hydrogen Peroxide from dissociated water vapour

The formation of hydrogen peroxide at 77°K from water vapour dissociated in a low‐pressure electrodeless discharge was investigated as function of the surface‐to‐volume ratio. S/V, of both coated and uncoated tubular reactors interposed between the discharge exit and the coolant level. As S/V was increased, the peroxide yield increased to a maximum value and then decreased; this maximum shifted to much lower values of S/V for KCl‐coated and H 3 PO 4 ‐coated surfaces. Compared with uncoated Pyrex surfaces, H 3 PO 4 ‐coatings gave higher H 2 0 2 yields whereas KCl‐coatings gave lower yields. Surfaces coated well with ice did not show much effect, but condensed water films decreased the H 2 O 2 yield. Similar results were obtained when the surface area and the volume traversed by the dissociated vapour were varied at constant S/V. These surface effects are discussed to show that the formation of H 2 O 2 occurs via the cold surface reactions H + O 2 → O a H and H + 0 2 H → H 2 O 2 and not by the dimerization of OH radicals.