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 zeolitetemplated 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 degrees C and then heat treatment at 800 degrees 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 micromorphology 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.

Automated summary

The study investigated the impact of CVD time and temperature on the structure of pyrolytic carbon in ZCP synthesis, confirming that pyrolytic carbon is mainly connected by C-C and C--C bonds, while some graphitic carbon forms on the zeolite surface. The experimental results from TGA and mass spectrometer analysis provided valuable insights for designing and optimizing CVD processes for ZCP synthesis.