| As one of the most important sources of indoor air pollution,the removal of formaldehyde has been a matter of great concern.Among those major methods of removing formaldehyde such as purification,catalytic oxidation and the chemical adsorption in plant,the catalytic oxidation is mainly affected by the attention of researchers due to its low energy consumption,long catalyst lifetime,and no secondary pollution.According to the related researches in recent ten years,noble metal catalyst has the advantages to the catalytic oxidation of formaldehyde in low temperature.By contrast,precious metal Pt shows excellent catalytic activities for the complete oxidation of formaldehyde out of other precious metals such as Au,Ag and Pd.In summary,Pt catalyst becomes the focus of formaldehyde catalytic oxidation research at room temperature.In this paper,a serie of Pt/MORn catalysts was successfullly synthesized using natural zeolite as the carrier for complete catalytic oxidation of formaldehyde at room temperature.The first major part of this study focuses on the pretreatment effects on natural Mordenite and furthermore their influences towards catalytic activity for HCHO.The applied pretreatment methods include acid treatment,alkali treatment and ion exchange treatment.The comparative study among those treatments presents that the best catalytic activity is found after acid treatment,and alkali treatment of natural zeolite shows lower activity for HCHO oxidation,while ion exchange treatment shows no improvement of formaldehyde oxidation on MORn and even inhibition of catalytic activity when applied on natural mordenite with acid treatment.The acid treatment with different HNO3 concentrations and frequence on zeolite changes the impurity and dealumination degree of natural zeolite regularly.When the acid treatment comes up to a certain extent,its role in promoting catalytic activity is significantly reduced.Through comprehensive comparison among different acid treatments,the HNO3 treatment with 6M concentration of acid shows the best reactivity for formaldehyde oxidation.As for alkali treatment,due to the introduction of alkali metal ions and hydroxyl,it also significantly improves the catalytic activity of Pt/MORn.However,alkali treatment is poor in removing hetero-metal oxides such as Al2O3,Fe2O3,and MgO,and it does not achieve the dealumination and improve the specific surface area effectively,so that the catalytic activity of MORn with alkali treatment is lower than that with acid treatment;Ion exchange treatment shows no improvement of the activity.Even though applying the treatment to zeolite with acid treatment can not further accelerate its catalytic activity.In addition to the study of support effects,this paper also discusses the effect of the load of precious metals,the different amount of Na+ addition and the Na+ sources on the catalytic activities.The results show that after 6M acid treatment,natural mordenite with different Pt loading amounts ranged from 0.1 to 2.0 wt.%represents variant catalytic activities and the optimal Pt loading is 0.5 wt.%;The effect of calcination temperature ranged from 200 to 500 ? on the catalytic activity of catalysts is small:NaOH and Na2CO3 are used as the sodium additives on Pt/MORn catalyst,they show a similar trend.The extra introduction of hydroxyl has no obvious promotion on the catalyst activity compared with Na+ content on the catalyst.The variation tendency on activity with continuously increasing of Na+ content is not entirely consistent the literature in this study.An Na+ addition amount of 0.5 wt.%will significantly inhibit the catalystic activity;when further increasing the amount of Na+,the catalyst activity will increase continuously and the conversion rate of formaldehyde at room temperature is more than 95%when adding 2.0 wt.%of sodium. |
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