Preparation And Properties Of Porous Materials For Catalytic NO_x Removal

Nitrogen oxides (NOx) have been a major source of air pollution, causing a variety ofenvironmentally harmful effects such as photochemical smog, acid rain, ozone depletion andgreenhouse effects. Selective catalytic reduction of NOxwith NH3(NH3-SCR) has been usedextensively for the removal of NOx. Among the NH3-SCR catalysts, porous catalysts are idealcandidates for applications because of their large surface areas and high porosity whichfacilitate the spread of gas molecules. Therefore, the development of novel and efficientporous NH3-SCR catalysts is a research hotspot in environmental catalysis.In this paper, we first used a novel wet ammonia gas infiltration-precipitation method toprepare three dimensional ordered macroporous (3DOM) metal oxide and hierarchicallystructural catalysts. In this method, poly (methyl methacrylate) or polystyrene beads and P123were used as the hard and soft templates, respectively. The strategy was to use a soft surfactantaqueous solution of mixed metal salts, which could be converted to the corresponding metalhydroxides in-situ by wet ammonia gas in filtration and precipitation processes at roomtemperature within the interstices of a template before removal of the template. Furthermore,calcinations in an inert atmosphere made the polymer template and soft surfactant convert toan amorphous carbon template, and a subsequent calcination in air then removed the carbontemplate, resulting in well-ordered3DOM oxides with mesoporous skeletons andhierarchically structural catalysts in high yields. X-ray powder diffraction (XRD), scanningelectron microscopy (SEM) techniques are used to characterize the catalysts.The characterization results can be obtained:(1) By investigating the impact on themorphology of the catalyst using different metal precursors, ammonia steam time andcalcination conditions, we obtained the optimal preparation procedure;(2) Using vaporinfiltration-precipitation synthetic methods and the optimal preparation condition, We made aseries of metal oxides which have a good three-dimensional ordered macroporous structure;(3)By variation of ammonia steam time, we prepared hierarchically flower-like Mn2O3consistedof rods.In this paper, Mn3O4and CeO2loaded graphene nanosheets (GNS) catalysts were alsoprepared by the one step in-situ transformation in an aqueous solution mixed with precursor and graphite oxide (GO). XRD, SEM and Fourier transform infrared (FT-IR) were used tocharacterize the samples. These metal oxides/GNS materials were used as NH3-SCR catalystsfor the first time and the SCR activity of Mn3O4/GNS was significantly improved compared tothat of graphene.A series of small-pore molecule sieves were prepared by one-pot method includingSAPO-56, Cu-SAPO-56, Ce-SAPO-56, SAPO-34and Ce-SAPO-34. Moreover, thesmall-pore molecule sieves with different amount of loaded Cu were prepared using differentmethods. XRD, FT-IR and SEM were used to characterize the structure and morphology. Theobtained Cu-SAPO-56and Ce-SAPO-56samples were used as the SCR catalysts for the firsttime. The SCR activity of the small-pore molecule sieves were investigated. The resultsshowed that: neither SAPO-56nor SAPO-34samples have SCR activity; SCR activity of thesmall-pore molecule sieves were significantly improved by the loaded Cu and Ce; the SCRactivity was enhanced with the increasing of Cu content in Cu-SAPO-56; the SCR activity ofCe-SAPO-56and Ce-SAPO-34were lower than those of Cu-SAPO samples; the small-poremolecule sieves catalysts have good thermal stability.