Evaluating Metal–Support Interaction in Formaldehyde Oxidation Using Pd/TiO₂ Catalysts: The Key Role of Mono-Oxygen Vacancies

Metal-support interactions (MSI) have been widely recognized as playing a key role in regulating the catalytic activity in various reactions. However, clarifying the relationship linking catalyst defect structures, active sites, and catalytic performance for catalysts with a constructed MSI remains a challenge. Here, Pd/TiO₂ catalysts with adjustable MSI were designed and fabricated based on defect engineering. Comprehensive characterization analysis revealed that as the catalyst reduction temperature and defect content increase, the MSI gradually increases, subsequently enhancing the intrinsic activity of the catalyst to oxidize formaldehyde (HCHO). However, the activity of the catalyst exhibited a volcano-shaped trend, which was caused by the collapse of the support structure at a high reduction temperature. Through comparative analysis of the HCHO oxidation reaction and CO oxidation reaction activity tests, it was confirmed that the ratio of mono-oxygen vacancies to oxygen vacancy clusters (<i>I</i>₁/<i>I</i>₂) in this study system could reliably serve as a valid "descriptor" for HCHO oxidation apparent activity.