Promoting effect of potassium over Pd/SiO₂ catalyst for ambient formaldehyde oxidation

Highly dispersed noble metals are acknowledged for its pivotal role in influencing the efficiency of catalysts during the HCHO oxidation process. Interestingly, in this work, an innovative approach was employed to augmenting the stabilization of noble metals on irreducible carriers supported noble metal catalyst (Pd/SiO₂) by adding alkali metal potassium (K). A formidable promotion effect was observed when the K doping to Pd/SiO₂ catalysts. It achieves a conversion rate of 93% for 270 ppmV of HCHO to harmless CO₂ and H₂O at a weight hourly space velocity (WHSV) of 300,000 mL/(g·hr) at 25°C. Multiple characterization results illustrated that a strong interaction between added K and Pd species was formed after K addition, which not only stabilized Pd species on the carrier surface but also markedly enhanced its dispersal on the SiO₂ carrier. The increasing Pd dispersion induced more oxygen vacancies on the surfaces of the Pd/SiO₂ catalysts. The formation of these oxygen vacancies can be attributed to the phenomenon of hydrogen spillover, which also contributed to elevating the electron density on the Pd sites. Meanwhile, the oxygen vacancies favored the O₂ activation to form more reactive oxygen species participating in the HCHO oxidation reaction, thus improving the performance of Pd/SiO₂ catalysts displayed for HCHO oxidation. This study provides a simple strategy to design high-performance irreducible carriers supported noble metal catalysts for HCHO catalytic oxidation.