Abnormal inhibiting effect of H2O on Pd/SiO2 and Na–Pd/SiO2 catalysts for HCHO oxidation

Abstract

Active hydroxyl groups (OH) are very important in HCHO oxidation, due to the fact that OH is the main active species in the degradation of formate and dioxymethylene (DOM) groups, especially for noble metal supported catalysts with alkali metal addition. Interestingly, in this study we found that sodium (Na) can also promote HCHO oxidation activity of Pd/SiO₂ catalysts without activated surface OH. Though Na addition could effectively improve the dispersion of Pd and the oxygen activation capacity of the catalyst, no effect on H₂O activation to form surface OH was found. Notably, different from Pd/TiO₂ or Pt/TiO₂ catalysts with TiO₂ as support, H₂O caused the deactivation of Pd/SiO₂ and even Na–Pd/SiO₂ catalysts. Investigation of the catalysts showed that the aggregation of Pd particles, reduction of effective interface and accumulation of intermediate products were the main factors leading to the deactivation of the catalysts. However, the addition of Na could improve the regeneration ability of the Pd/SiO₂ catalyst.