The Catalytic Performance Of Carbon Nanotubes On Cumene Oxidation

Nano-sized carbon materials are good catalytic materials due to their special propertiesof outstanding electron cunductivity, high surface area, and easy doping. Compared withmetal catalyst, nano-sized carbon materials have the advantage of environmental friendnessand low cost, resulting in a wide application in electrochemistry and catalytic reactions ofhydrocarbons in recent years. In this thesis, carbon nanotubes as catalyst were studied in theliquid-phase oxidation of cumene, which is an important petrochemical process. Therelationship between structure and catalytic performance, and the reaction mechanism werediscussed in detail. The main contents and results are as follows:(1) The pristine carbon nanotubes (CNTs) showed good catalytic performance in theoxidation of cumene, and major product was cumene hydroperoxide (CHP). Under thereaction temperature of80oC, the reaction time of8h, mCNTs/mcumeneratio of0.012and O2flow rate of10cm3/min, cumene conversion of24.1%with CHP selectivity of88.4%wasobtained. CNT catalyst showed desirable recyclability, after five cycling tests, cumeneconversion and CHP selectivity remained24.3%and86.4%, respectively.Through systematiccharacteration analysis, it was found oxygenous functional groups and defect on the surface ofCNTs decreased the catalytic performance of CNTs in cumene oxidation. This is possiblyattributed to the destruction of electrons delocalization after the introducing of defects andoxygenous functional groups, which is unfavorable for the interaction between CHP andCNTs.(2) A series of N doped CNTs with nitrogen contents of0-4.36at.%were prepared viachemecal vapor deposition (CVD) method. In the catalytic oxidation of cumene, the doping ofnitrogen was found to effectively tune reaction activity and products destribution. With theincreasement of nitrogen content, the cumene conversion and selectivity to acetophenone and2-benzyl-2-propanol increased, while the selectivity to CHP decreased. For NCNTs-3catalystwith nitrogen content of3.44at.%, cumene conversion of86.4%was abtained after24h ofreaction, with total selectivity to acetophenone and2-benzyl-2-propanol as high as99.0%.The residual metal impurities in the catalyst did not effect the catalytic performance, while Ndoping played an important role. N doped CNTs also showed a desirable recyclability,indicating that N-CNTs can be used as excellent catalyst for the one-step oxidationof cumeneto produce acetophenone and2-benzyl-2-propanol. (3) The reaction mechanism of cumene oxidation based on carbon catalysis wasdiscussed in detail. It was proven that the oxidation of cumene with CNTs as catalyst is aradical-involved reaction. Cumene hydroperoxide played an important role in this reaction,the reaction rate increased with CHP decomposition rate. The incorporation of nitrogen couldincrease the surface electron density of CNTs, which could remarkably strenghten theinteraction between CHP, oxygenated radicals and CNTs. Hence, the whole reaction rate andselectivity to acetophenone and2-benzyl-2-propanol were improved.