Effect of Ba addition amounts on Pd/TiO2 catalyst for formaldehyde oxidation
[Objective]Formaldehyde is a major pollutants in indoor environments,and long-term exposure to formaldehyde could pose a severe health hazard.Therefore,developing efficient formaldehyde purification technologies or materials is significant to the environment and human health.Catalytic oxidation technology has great application potential.Compared with metal oxide catalysts(Mn,Co,Ag,and other oxides),supported noble metal catalysts(Au,Pt,Pd,etc.)exhibit excellent room temperature oxidation activity of formaldehyde.Previous studies have shown that the addition of alkali metals can significantly improve Pd-based catalyst activity for formaldehyde oxidation at room temperature.Alkaline earth metals share similarities with alkali metals in chemical properties.It is worth studying whether alkaline earth metals can promote the performance of Pd-based catalysts for formaldehyde oxidation at room temperature.[Methods]TiO2(P25)supported noble metal Pd catalysts modified by different alkaline earth metals(Mg,Ca,Sr,Ba)were prepared using the impregnation method,and their formaldehyde catalytic oxidation performance was investigated.The effect of Ba addition was investigated using X-Ray diffraction(XRD),N2 Brunauer-Emmett-Teller(BET)test,high-angle annular dark-field scanning transmission electron microscopy(HAADF/STEM),electron spin resonance(ESR),Fourier transform infrared spectroscopy(FTIR),and O2-temperature programmed desorption(O2-TPD).[Results]When the Pd mass fraction was 1.0％,compared with Mg,Ca,Sr,it was found that the addition of 25.8％(mass fraction)Ba(marked as 25.8Ba-1.0Pd/TiO2)significantly improved the Pd/TiO2 formaldehyde oxidation activity at room temperature.Nearly 95％formaldehyde conversion could be achieved at 25 ℃,0.015％formaldehyde(volume fraction),weight hourly space velocity(WHSV)of 4 × 105 mL/(g·h).The XRD results showed that the Pd species were well dispersed on the catalysts.According to the result of HAADF/STEM,compared with 1.0Pd/TiO2 catalyst,the average Pd particle size of 25.8Ba-1.0Pd/TiO2 catalyst decreased from 6.4 nm to 4.1 nm,and the particle size distribution become more uniform after Ba addition.ESR result showed that abundant oxygen vacancies had been generated on the 25.8Ba-1.0Pd/TiO2 catalyst.FTIR results indicated that the Ba addition enhanced the generation of hydroxyl groups on the 25.8Ba-1.0Pd/TiO2 catalyst.[Conclusion]The characterization results show that the introduction of Ba can stabilize Pd species and improve the dispersion of Pd.The highly dispersed Pd species provide abundant reaction sites,and the highly dispersed Pd particles also promote the formation of surface defects on TiO2 due to hydrogen overflow.Improvement of surface oxygen vacancies on the carrier brings better activation of O2 and H2O,enhances the mobility of surface chemisorbed oxygen,improves the number of surface hydroxyl groups,and thus enhances the activity of Pd/TiO2 catalyst for room temperature oxidation of formaldehyde.
formaldehydePd/TiO2Bacatalytic oxidationroom temperature
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