Preparation And Performance Of Structured Carbon Nanotube Catalyst For Cumene Oxidation

Carbon nanotubes(CNTs) have received intensive scientific interests in the field of heterogeneous catalysis due to its exceptional physical and chemical properties. However, for catlytic applications, the direct use of CNTs in a powder form is limited by the problems of catalyst recovery, low efficient mass transfer and poor reactor adaptability. Structured CNTs as catalysts can solve the problems and expand the applications of CNTs in the field of catalysis. In this context, we prepared a structured CNT catalyst via chemical vapor deposition(CVD), which was used both as catalysts and as stirrer in a rotating foam stirrer reactor. The performance of structured CNT catalyst was investigated in the aerobic oxidation of cumene. We also studied the kinetic of cumene oxidation catalyzed by CNTs. The study on the kinetic of cumene oxidation may provide a reliable basis for the reactor modeling. The main contents and results are described as follows:(1) CVD method was used to grow a layer of CNT on the surface of Ni foam modified by alumia sol. Typically, the structured CNT catalyst with a dense and homogeneous layer of CNTs was synthesized in a gas mixture containing LPG/H2/ Ar at 750℃ for 9 min. The LPG, H2 and Ar flow rates were 60, 140 and 640 mL/min, respectively. The preparaed structured CNT catalyst showed good catalytic performance in the oxidation of cumene. At 353 K and 0.4 MPa O2, the similar activity as commercial CNT powder can be achieved upon the structured CNT catalyst, with 1.2g CNTs and dimensions of Φ45*30mm. The structured CNT catalyst showed desirable recyclability. After five cycling tests, the cumene conversion and product yields remianed constant.(2) A kinetic model based on the radical reaction meachanism of cumene oxidation was established, which contains 7 major elemental steps. The kinetic parameters of cumene oxidation upone CNTs and N-doped CNTs(NCNTs) were obtained by the non-linear aggression of the experimental concentration-time data. A good agreement was obtained for the experimental and calculated concentrations. Mechanical insights into the effect of N-doping on carbon catalysis was reached by comparing the kinetics parameters of CNTs and NCNTs. The incoporation of nitrogen could reduce the activation energy of CHP decomposition, thereby could remarkably improve the overall reaction rate of cumene oxidation and reduce the selectivity of CHP. The incoporation of nitrogen also could increase the surface electron density of CNTs, which could strengthen the interactions between O2, RO?, RO2? and catalyst. Hence, the slectivities to acetophenone and 2-benzyl-2-propanol were improved.