KIST Nano Vanadia-Titania Catalyst KO's Toxic Incinerator Exhaust, Proven Superior to Commercial Counterparts

 Korean scientists are using nanotechnology to create a catalyst to better knock toxic compounds out of incinerator exhaust and transform compounds like dioxin and 1,2-dichlorobenzene (1,2-DCB),  two of the most toxic chlorinated organic compounds present in the exhaust gas, into harmless materials.

Korea Institute of Science and Technology (KR) inventors Jong Soo Jurng, Sung Min Chin, Ju Young Jeong, Jung Eun Lee and Gwi-Nam Bae disclose an improved method for preparing a vanadia-titania catalyst having a nano structure.  The nano-catalyst is obtained by a solvothermal procedure for the conversion of chlorinated organic compounds into harmless materials.  According to  U.S. Patent 7,632,780, the vanadia-titania catalyst has a core-shell structure, which is highly active in decomposing chlorinated organic compounds such as dioxin present in the exhaust of an incinerator. 

The vanadia-titania catalyst prepared by the solvothermal method showed an activity which was higher by about 70% at 200.degree. C., and about 50% at 250.degree. C., as compared with that of the catalyst prepared by the wet method in decomposing toxic gases.  Further, the nano vanadia-titania catalyst showed an activity which was higher by about 25% at 200.degree. C., and about 30% at 250.degree. C., as compared with that of the commercial catalyst. 

Vanadia-titania catalysts have been broadly used to decompose environmentally harmful chlorinated organic compounds generated during incineration or combustion of organic waste. A vanadia-titania catalyst is capable of decomposing such chlorinated organic compounds through an oxidation-reduction reaction, emitting a harmless exhaust gas to the environment.

Generally, such vanadia-titania catalyst is prepared by a wet synthetic method such as impregnation and coprecipitation methods. For example, an aqueous vanadium salt solution is impregnated to a molded titania pellet or powder, and the resulting material is dried and calcined. However, the titania used in the existing wet synthetic method is of an anatase form having a low specific surface area and low thermally stability, and the anatase form of the titania converts in part into the rutile form during the high temperature treatment step, which leads to an inactive catalyst. To avoid such problems, there has developed a modified method that involves an elaborated multi-step procedure and requires a number of days to complete.

There also has been reported another method for preparing a vanadia-titania aerogel catalyst by drying a vanadia-titania wet gel prepared by a sol-gel method, which is conducted under a supercritical condition of carbon dioxide and dried also under a supercritical condition. However, this method also has difficulties in that it takes several days to age the gel and that the drying process must be conducted under a superitical condition.

To solve the problem, the Korean scientists endeavored to develop an improved method for preparing a vanadia-titania catalyst, which can be used for converting a chlorinated organic compound into environmentally harmless products, and have found a solvothermal method for preparing a particulate form of a vanadia-titania catalyst having a core-shell structure, which effectively converts chlorinated organic compounds. 

The KIST method of using the solvothermal procedure has merit for mass producing the vanadia-titania catalyst by a simple and successive procedure, as compared with the conventional wet method. The existing wet method requires several steps such as dissolving, drying and calcinating to prepare the particle, so that the particle cannot be prepared by a single process, but the inventive method is capable of successively operating the device by a single process, thereby resulting in successively preparing the vanadia-titania catalyst particle. Their method for preparing a vanadia-titania catalyst having a nano structure by a solvothermal procedure, is comprised of the steps:  

1) transporting a solution containing a vanadia precursor and a titania precursor to a hot section of a reactor heated with an electric furnace using a carrier gas and air;  

2) subjecting the solution containing the vanadia and the titania precursors to a solvothermal procedure at the hot section to obtain a vanadia-titania catalyst particle having a core-shell structure of a titanium dioxide core coated with vanadia particles; and  

3) cooling and collecting the vanadia-titania catalyst particle having the core-shell structure.