Carbon deposition mechanism and structural changes for zeolite-templated carbons

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 N2). 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 C2H2 concentration and the appearance of C2H2 decomposition products (H2, CH4, C6H6). 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 CC 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.