Catalytic Performance Of Pure Silica βZeolite Washcoated Palladium Monoliths For Volatile Organic Compounds Abatement

Catalytic combustion technology has been regarding as the most effective way for the treatment of volatile organic compounds. The catalyst is the key of catalytic combustion. In order to lower the pressure drop and improve the efficiency of mass transfer, catalysts usually are made into ceramic honeycomb monoliths in practical use. The washcoat is very important for the honeycomb ceramic nonolith catalysts.This study is tried to synthesize the β zeolites with different silica alumina ratio and use them as the washcoats supported Pd on cordierite honeycomb, based on high properities of VOCs catalytic combustion of supported-Pd catalysts. The activity tests for complete catalytic oxidation of toluene were tested. Conclusions were listed as follows:Firstly, compared to β molecular sieve with other silica alumina rate, the pure-silica p washcoat increased the activity and hydrophobicity more clearly. The monolith with pure silica β washcoat coulud fully convert toluene at about240℃. The presence of50%water vapor in the feed gas have little effect on the catalytic combustion property.Secondly, the effects of loading procedure, pure-silica β molecular sieve loading, Pd content and space velocity on the activity of Pd/pure-silica (3/cordierite monolith catalyst for toluene oxidation were investigated. The results showed that impregnation-coating procedure increased the activity and the catalytic activity was influenced not only by the Pd content, but also the loading of pure-silica β zeolite. When the pure-silica β zeolite loading on the cordierite monolith was about7.9%and the Pd content0.5%. The activity decreased a little with the increase of space velocity.Thirdly, in order to improve the adhesion degree of P onto cordierite, the loading technology was studied in this paper. β molecular sieve was in-situ synthesized on the cordierite support with hydrothermal method. The results show that a coating of P grows preferably on the cordierite support. The optimal preparation conditions were confirmed as follows: silicon-aluminum sol was prepared by the molar composition of0.52TEAOH:1SiO2:0.0033Al2O3:0.37HF:14.25H2O; Aging time was5h and the cordierite support was pretreated by10%nitric acid solution; Crystallization temperature was140℃and crystallization time was5d. Finally, on the basis of the above synthesis, comparison studies carried out on Pd/β/cordierite with different loading method(in situ technology and impregnation) showed that the former catalyst was much more active than the latter. The β washcoats prepared by in-situ technology can anchor better than the catalyst by impregnation.