TiO2 계열 광촉매를 이용한 도데칸의 부분산화반응 연구

Abstract

Photocatalytic conversion of dodecane was performed at various reaction conditions for selective catalytic reduction of nitrogen oxides (NOx) by controlling flow rate, gas composition, reaction temperature, and the amount and nature of the photocatalysts. Commercial anatase phase TiO2 was the main photocatalyst studied in addition to surface-modified TiO2 such as Pt/TiO2 and F-TiO2. C1-C5 aldehydes were main oxygenated hydrocarbons (OHCs) products

acetaldehyde > propanal, butanal > pentanal > hexanal >> formaldehyde. Small amounts of hydrogen were also produced and CO2 was the main byproducts by total oxidation of dodecane. In the best case, the conversion of dodecane and selectivity of OHCs were 90 and 70%, respectively. Decrease in O2/dodecane feed ratio and total feed flow rate resulted in conversion and selectivity improvements.To increase OHCs selectivity and yield, photocatalytic conversion of dodecane was performed using TiO2-SiO2 mixed phase oxide prepared by sol-gel hydrolysis with soft templates (TBAOH, TMAOH) for deNOx application in diesel engine exhaust gas system. Photocatalyst was characterized by various kinds of tools (XRD, UV-Vis DRS, ICP, EA, BET, FTIR, XPS, HRTEM, EELS, SAED, SAXS, Isotherm, BJH, t plot method, XAFS, DRIFT. As a result, we confirmed the formation well distributed nano sized (less than 1nm minimum) TiO2 domain in the inactive amorphous SiO2 matrix. The average distance between each TiO2 cluster was approximately far longer than 8nm far enough for dodecane not to be adsorbed simultaneously on both of TiO2 clusters so that carbon-carbon fission is restricted and thus photocatalytic partial oxidation has become enhanced. In line with the nano size of TiO2 cluster, bonding type of Ti was confirmed that Ti-O-Si was dominant and configuration of tetrahedral symmetry of Ti was remarkable as Ti/Si become smaller. This means substitution of Ti for Si was successfully occurred during the synthesis process configuration. Peak shifts detected by lots of characterization results could support this statement.We can see the effect of small size and well distributed TiO2 active sites on the inert SiO2 lattice on the photocatalytic performance that improvement in OHCs selectivity and yield was obvious. When using TiO2-SiO2 mixed oxide with Ti/Si=0.04, the lowest value I prepared, OHCs selectivity was much higher and its yield was 2.18 times greater than that of pure anatase TiO2. This results came from sophisticatedly build continuous flow system and delicately designed experimental plan that carbon balance between sum of carbon mole number of reactants and products was more than 90% and BET and other textural properties’ variation among the tested samples was tiny. During the graduate course, I have demonstrated a novel scheme of NOx after-treatment system for diesel engine exhaust line involving the new photocatalytic reaction, where on-board photocatalytic partial oxidation of a small amount of diesel fuel for OHCs production that were supplied to the deNOx system as NOx reductant. Installation of the photocatalytic reactor with a UV lamp inside the vehicle is not convenient, yet it could be more environment friendly than carrying the urea tank on board, currently considered the most promising technology. In scientific point of view, the number of study regarding photocatalytic partial oxidation of organic compound is rather scarce than that of photocatalytic mineralization or total oxidation process. To the best of our knowledge, the reaction has never been studied before, and is a rare example of photocatalytic partial oxidation for cracking and functionalizing a long chain organic alkane into smaller OHC molecules at low temperatures (< 100 °C) without water.