Synthesis Of Mn0₂Supported Catalysts And Their Catalytic Performance For Decomposition Of Formaldehyde

As an important and major place for working and living, air quality of indoor environmenthas huge relationship with health of human being. Nowadays, formaldehyde （HCHO） hasbeen regarded as one of the most harmful indoor pollutants. Therefore, to resolve thepollution of indoor formaldehyde has become a focus of widespread concern in whole society,more and more methods have been applied for decomposition of indoor HCHO. Among them,catalytic oxidation technology is the most suitable for HCHO decomposition and has broaddevelopment prospects, for it can oxidize HCHO into CO₂and H₂O at low cost and higheffect. However, the development of highly effective catalysts remains a major restrictedfactor for extensive application of catalytic oxidation technology.In this paper, the main studies were based on earlier period work in laboratory. A series ofmanganese dioxide （MnO₂） with different morphologies and crystal forms were prepared by asimple method. Then, two kinds of supported catalysts including Pt/MnO₂and bimetallicalloy Au1-xPtx/MnO₂were synthesized by MnO₂as supporter. Finally,Au_0.5Pt_0.5/MnO₂/cottoncatalyst was prepared by a simple method with cotton as supporter. The above catalysts wereapplied to oxidative decomposition of HCHO and some interesting results were obtained.Experiment contents and results were shown as follows.（1） With potassium permanganate （KMnO4） and hydration acid manganese （MnSO4·H₂O）as raw materials, three kinds of MnO₂with different morphology and crystal form wereprepared through changing the reaction conditions, such as reaction temperature （T）, pH value,reaction time （t） and so on. All of prepared MnO₂materials have catalytic performance fordecomposition of HCHO. The nest-like MnO₂with cryptomelane-M shows the highestcatalytic activity for oxidative decomposition of HCHO and the complete decompositiontemperature for HCHO is180oC.（2） A series of Pt/MnO₂catalysts were obtained by polyvinylpyrrolidone （PVP）, sodiumcitrate and ascorbic acid as dispersant, protective agent and reducing agent, respectively. Theinfluence of factors, including reduction time （t）, reaction temperature （T）, PVP dosage and Ptloading, were studied on grain diameter, size distribution and dispersion of Pt nanoparticles（NPs）. Pt NPs of1-4nm were dispersed on the surface of MnO₂supporter, and no Ptnanoparticles agglomeration was observed in the Pt/MnO₂catalysts when T=80oC、t=1h、 PVP:Pt=20:1（molar ratio）. The catalytic performance of Pt/MnO₂with different morphologyand Pt loading were evaluated. The synthesized Pt/MnO₂shows high catalytic activity whenPt loading rise to2wt%, while the sample with nest-like MnO₂supporter has the highestcatalytic activity among the Pt/MnO₂catalysts, the temperature for complete decompositionof HCHO reached as low as70oC.（3） Au-Pt bimetallic NPs were facilely prepared by co-reduction method in aqueoussolutions using KBH4and PVP as reducing and protective agent, respectively. The NPs wereloaded on nest-like MnO₂supporters, forming Au1-xPtx/MnO₂and [（100%-y）Au/yPt]/MnO₂catalysts. Grain diameter, size distribution and dispersion of Au-Pt bimetallic NPs werestudied by changing the structure of Au-Pt bimetallic NPs and molar ratio of Au and Pt. Noblemetal NPs of2-5nm were completely loaded on the surface of nest-like MnO₂supporter andno agglomeration was observed. The forms of noble metal NPs and the Au/Pt molar ratio havesignificant effects on the catalytic performance.Au_0.5Pt_0.5/MnO₂has the highest catalyticactivity and the temperature for complete decomposition of HCHO reached as low as40oC.（4） The powderAu_0.5Pt_0.5/MnO₂catalyst was successfully loaded on cotton by a simplemethod. The powderAu_0.5Pt_0.5/MnO₂was uniformly loaded on the surface of cotton throughchanging of disperse concentration in water and loading ofAu_0.5Pt_0.5/MnO₂. The practicalloading dosage increases at first and then goes to stable with increasing of theory loading. TheAu_0.5Pt_0.5/MnO₂/cotton has the best catalytic performance for decomposition of HCHO whenAu_0.5Pt_0.5/MnO₂loading is15wt%. Compared with the powderAu_0.5Pt_0.5/MnO₂, theAu_0.5Pt_0.5/MnO₂/cotton catalyst has higher catalytic activity in the decomposition of HCHOwhen mass of active component are equal.