Preparation of Carbon Nanotubes (CNTs)-Cordierite Monoliths by Catalytic Chemical Vapor Deposition as Catalyst Supports for Ammonia Synthesis

摘要

Tunable carbon nanotubles (CNTs)-coated monoliths as catalyst supports were prepared by catalytic chemical vapor deposition (CCVD) over deposited cobalt on cordierite. The influence of the preparation conditions such as the cobalt nitrate loading on the cordierite monoliths, the flow rate of reaction gases, reaction time and temperature on CNTs yield, thermal properties and structural features of the resulting materials were studied. The CNTs-cordierite was characterized by TEM/HREM, SEM, N2 physisorption and TGA. The SEM showed that a relatively homogeneous mesoporous layer of CNTs covered on the surface of the cordierite monoliths. Comparing with the bare cordierite, the BET surface area and pore volume of CNTs-cordierite increased significantly. CNTs have penetrated into the cordierite substrate and led to a remarkable mechanical stability of the CNTs-cordierite monoliths against ultrasound maltreatment. The CNTs content, BET surface area, pore volume and thermal properties of CNTs-cordierite monoliths all could be changed by the variation of the synthesis conditions. Barium promoted ruthenium catalysts supported on the as-synthesized materials showed much higher activity for ammonia synthesis than their counterparts deposited on bare cordierite monoliths. Furthermore, the catalytic activity linearly increased with the BET surface area of CNTs-cordierite monoliths. The CNTs-cordierite monoliths were proved to be promising candidates as catalyst supports and the performance of catalysts supported on as-prepared materials would be easily modified by changing the growth conditions of CNTs.