Carbon deposition mechanism and structural changes for zeolite-templated carbons

Abstract

The process of synthesizing a zeolite/carbon composite (ZCP) is the first chemical event for preparing a zeolite-templated carbon (ZTC) via the chemical vapor deposition (CVD) process. The purpose of this work was to investigate the effect of CVD time duration (up to 446 min) at 600 °C and then heat treatment at 800 °C on the structure of the pyrolytic carbon formed. The CVD process with 13X zeolite as the template was performed in a thermogravimetric analyzer (TGA) using a low acetylene concentration (2 % by vol. In N 2 ). A thermogravimetric analyzer connected to a mass spectrometer (TG-MS) characterized the in-situ mass change that a zeolite particle underwent during a TGA run, while the MS monitored the decrease in C 2 H 2 concentration and the appearance of C 2 H 2 decomposition products (H 2 , CH 4 , C 6 H 6 ). Optical analysis and SEM/EDS of the macro- and micro-morphology of the ZCP indicated that pyrolytic carbon was deposited gradually in the nano-pores, starting from the edge of the spherically shaped zeolite. The XPS and XRD analysis indicated that the pyrolytic carbon deposited in the nano-pores was mainly connected by C–C and C C bonds, whereas some quasi-crystal graphitic carbon was formed at the zeolite's external surface. Finally, three stages of carbon formation were identified during the CVD process in the TGA and the mass-time profile generated by the TGA curve was well predicted by a diffusion-reaction equation model. Findings from this work provided useful insight for designing, and optimizing a CVD process used for the synthesis of ZCP. • One particle zeolite was used to synthesis ZCP in a TGA analyzer by the CVD process. • TG-MS monitored the mass change of ZCP and the evolution of gaseous by-products. • DRE model was presented to predict the mass increase of ZCP with time. • Mechanisms of carbon deposition in the zeolite nano-pores has been revealed.