Pt/MnO2 nanostructured catalysts with cocoon-, urchin-, and nest-like morphologies were synthesized by a facile method. The synthesized MnO2 nanostructures and Pt/MnO2 catalysts were characterized by means of X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). TEM analyses showed that Pt nanoparticles of 1–4 nm were evenly dispersed on the surface of three MnO2 nanostructures, and no Pt nanoparticle agglomeration occurred in the Pt/MnO2 catalysts. These Pt/MnO2 catalysts showed much higher catalytic activities than the corresponding MnO2 nanostructures for oxidative decomposition of formaldehyde. Comparison of Pt/MnO2 catalysts with varied Pt loadings and MnO2 morphologies revealed that 2 wt % is the optimal Pt loading, and 2 wt % Pt/nest-like MnO2 showed the highest catalytic activity for oxidative decomposition of formaldehyde (temperature for complete decomposition of HCHO is 70 °C). The high dispersion and small size of Pt nanoparticles and the synergistic effect between the Pt nanoparticle and MnO2 nanostructure are considered to be the main reasons for the observed high catalytic activity of Pt/nest-like MnO2.

In situ synthesis of manganese dioxide was carried out under ambient conditions on porous cellulose fibers as support. MnO 2 /cellulose composites with different MnO 2 loadings were obtained by tuning the concentration of aqueous KMnO 4 . Physical and chemical properties of the MnO 2 / cellulose composites were characterized by SEM, TEM, and XRD. When the concentration of aqueous KMnO 4 falls in the range of 6.33À12.6 mM, the obtained MnO 2 shows a nanosheet morphology and is uniformly coated on the cellulose fiber. The catalytic activities of MnO 2 /cellulose composites were investigated for the oxidative decomposition of HCHO. The nanostructured MnO 2 /cellulose composites show excellent catalytic performance for the oxidative decomposition of HCHO. Among them, 8.86 wt % MnO 2 /cellulose has the highest catalytic activity. The HCHO conversion per milligram of MnO 2 of 8.86 wt % MnO 2 /cellulose is about 9À17 times as high as that of birnessite MnO 2 powder prepared by a hydrothermal method. The catalytic activity was found to be dependent not only on the content of MnO 2 , but also on the adsorption of HCHO on cellulose fibers as well. These two factors are supposed to give rise to the highest catalytic activity for 8.86 wt % MnO 2 /cellulose. The high efficiency combined with the easy applicability makes the MnO 2 /cellulose composites more promising for practical applications as compared to MnO 2 powders.

Heteropolyacids (HPAs) possess both acidic and redox catalytic properties and held extensive promise of practical application. These type of compound display a great potential of specific synthesis reactions for replacing sulfuric acid to satisfy the requirements of environmental protection. Heterogenizing HPAs would not only make them more useful in liquid phase oxidation with oxygen and in acid-catalyzed reaction, as the catalyst is often difficult to separate from the reaction products, but also create favorable factors for realizing heterogenization of homogeneous reaction and even utilizing new technology of catalytic distillation. In this paper, different kinds of porous materials which are well characterized, including oxides such as Al2O3, SiO2, TiO2, diatomite, bentonite, and active carbon of different sources, were used as support for heterogenizing HPAs (in different media), and the obtained results, the intrinsic characters of supports which may influence both the nature of the interaction between HPAs and supports in the heterogenization and the activity in the catalytic reaction, are explored. It is expected that these can provide a referential model for preparing supported acid catalyst used in liquid phase.

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