Studies On The Preparation Of High-temperature Resistant Catalytic Materials For Methane Combustion

Catalytic combustion is considered a promising method for the effective combustion of lean fuel-air mixture with minimum emissions of NOX. The main problem in the development of catalytic combustion processes is to find suitable catalysts, which have high stability and high activity. In this work, a hydrothermal synthesis method based on urea hydrolysis was first developed for preparation of Mn-substituted hexaaluminate catalysts. The mixture of carbonates and hydroxides produced in the hydrothermal process can be easily converted to hexaaluminate catalysts compared to what produced by co-precipitation of (NH4)2CO3 or NH3.H2O. The results of 100h life test of LaMnAl11O19-a catalyst showed that the catalyst had not only high combustion activity but also high stability. A ternary water/isopropanol/butanol system was expanded as the reaction media for the hydrolysis of metal alkoxides to prepare of Mn substituted hexaaluminate catalysts. The results from H'NMR, FT-IR, electrical conductometry and laser light scattering demonstrated that such a ternary system could control the condensation of precursors came from hydrolysis of metal alkoxides by hydrogen bonding among water, isopropanol and butanol. The catalyst synthesized with the ternary system had a larger surface area and allowed a higher combustion activity. Effects of dryingmethods on BET specific surface area, pore size distribution, particle size, redox of Mnn+ ions, and combustion activity were investigated. The homogeneity of precursor obtained by sol-gel process can be maintained by supercritical dying. The catalysts obtained by supercritical dying have a larger surface area due to the thinner hexagonal facet of hexaaluminate crystals.