Preparation And Catalytic Activity For CO Selective Oxidation Of Silver Nanoparticles Confined In The Channels Of Mesoporous SBA-15

The polymer electrolyte membrane fuel cell (PEMFC) has been attracting much attention in the application to electric vehicles or residential power-generations because of its many attractive features such as high power density, rapid start-up, and high efficiency. Since the PEMFC is typically operating around 80℃, its Pt-anode catalyst is extremely sensitive to CO contaminant (1%) in reformed gases, which will poison the catalyst and decrease the performance. Among the currently available methods for removing CO from H2-rich feed gas, the selective catalytic oxidation of CO with molecular oxygen is undoubtedly the most straightforward, simplest, and the most economic one. Catalysts so far proposed for this process are mainly noble metals, such as Pt, Rh, Au. Compared with the noble metals, the price of silver is the most economic one. Therefore silver catalyst has the application prospect for CO selective oxidation.The effect factors for tuning the pore size of SBA-15 are investigated in this paper. First of all, modification on the exterior of SBA-15 by -SiMe3 groups (TMS) was carried out. Subsequently, grafting -Si (CH2)3-NH2 groups (APTS) on the inner surface of the pore walls of SBA-15. Silver catalysts supported on amino-modified and silylated SBA-15 have been prepared by leading in the silver precursor Ag (NH3)2NO3 with two methods. The catalysts were characterized using different techniques such as inductively coupled plasma spectrometer (ICP-AES), X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption. The catalytic properties for CO selective oxidation reaction were evaluated in a fixed-bed reactor. The main results are as follows:1. Ordered mesoporous structure of the SBA-15 was retained in the synthesized large-pore mesoporous molecular sieve SBA-15 by adding inorganic salt ammonium nitrate. Without the addition of ammonium nitrate, mesoporous material with ordered mesoporous structure was not obtained. Hexane was identified as the best micelle expanders in Pluronic-templated synthesis of SBA-15. The effect of enlarging the pore size for SBA-15 is conspicuous with the increase of the hexane.2. The 2-D hexagonal structure of the original support was retained in the L-SBA-15-M-A support; Silver nanoparticles were dispersed uniformly within the channels of SBA-15; The silver cluster size increases with the increase of the silver loading; The preparation method of the L-Ag/SBA-15-Cal catalyst overcomes the migration of silver ion in high-temperature treatment process.3. Ag/SBA-15 catalysts have a good performance for CO selective oxidation at low temperatures, and are quite stable. Oxygen preferentially reacts with carbon monoxide at low temperatures, but with hydrogen at high temperatures. It is found that the catalytic activities for CO selective oxidation increase with the increase of the silver loading, meanwhile, the reaction temperature of the carbon monoxide and the oxygen was reduced. The catalytic activities for CO selective oxidation are related with the pore size of the catalysts supports. The catalytic activities increased due to the large-pore size of the catalysts supports. Compared with L-Ag/SBA-15-Red catalysts, L-Ag/SBA-15-Cal catalysts were beneficial to increase the catalytic activities for CO selective oxidation.