Photocatalytic degradation of gaseous VOCs over Tm3+-TiO2: Revealing the activity enhancement mechanism and different reaction paths

Oxygen Isotope Tracing Study to Directly Reveal the Role of O2 and H2O in the Photocatalytic Oxidation Mechanism of Gaseous Monoaromatics

“…It is necessary to understand the formation sequence of these three kinds of intermediates to clarify the oxidation mechanism of xylenes. Previous works proposed that MBA was formed first during the oxidation of xylenes and then converted to MBAD and finally to MBAC. , A similar formation order of aromatic alcohols, aldehydes, and acids has also been deduced from the oxidation of other monoaromatics, such as toluene, ethylbenzene, and styrene . So far, no direct and solid evidence has been obtained to support the above formation order.…”

“…The low H 2 18 O content suppressed the formation of benzenedicarboxaldehydes during the oxidation of xylenes and 16O 2 greatly affected the yield of total intermediates, while neither of them altered the percentage order of the products. Methylbenzaldehydes, methylbenzyl alcohols, and benzenedicarboxaldehydes possessed greater 16 O percentage (≥69.49%), while higher 18 O distribution was observed in methylbenzoic acids and phthalide (≥59.51%). Together with the interconversion results of the products revealed, 16 O 2 determined the transformation of xylenes initially to methylbenzaldehydes and then to methylbenzyl alcohols or benzenedicarboxaldehydes, while H 2 18 O mainly contributed to conversion of methylbenzaldehydes to methylbenzoic acids or phthalide.…”

“…Methylbenzaldehydes, methylbenzyl alcohols, and benzenedicarboxaldehydes possessed greater 16 O percentage (≥69.49%), while higher 18 O distribution was observed in methylbenzoic acids and phthalide (≥59.51%). Together with the interconversion results of the products revealed, 16 O 2 determined the transformation of xylenes initially to methylbenzaldehydes and then to methylbenzyl alcohols or benzenedicarboxaldehydes, while H 2 18 O mainly contributed to conversion of methylbenzaldehydes to methylbenzoic acids or phthalide. Further interaction sites of xylene and its products with H 2 O and O 2 were confirmed by molecular dynamics calculations.…”

“…In general, photocatalytic oxidation of gaseous monoaromatics proceeds in the presence of O 2 and/or H 2 O, which may influence the formation of intermediates. For instance, identical intermediates (e.g., 2-methylbenzaldehyde, 2-methylacetophenone, and phthalide) are obtained from the oxidation of o-xylene under the same dry air conditions, 15,16 indicating that O 2 is more involved in the formation of these products. Under 20% relative humidity (RH) condition, 2-methylbenzoic acid is additionally produced, 17 suggesting that the formation of this acid is related to H 2 O.…”

“…Hence, in this work, photocatalytic oxidation of seven gaseous monoaromatics was carried out under varied 16 O 2 / H 2 18 O molar ratios. First, three monoaromatics, m-xylene, oxylene, and p-xylene, were selected as representatives to study the effect of 16 O 2 /H 2 18 O molar ratio on the composition, amount, and percentage of their intermediates. Furthermore, the percentages of 16 O and 18 O in the intermediates were analyzed to reveal the origin of the oxygen atom from O 2 or H 2 O.…”