X-ray diffraction (XRD) studies on the chemical states of some metal species in cellulosic chars and the Ellingham diagrams

Samples of carboxy methyl cellulose, subjected to ion exchange with different metal ions (Cu, Ni, Co, Fe, and Ca), were pyrolyzed in the temperature range of 300-1000 °C to obtain chars that were doped with metal species. X-ray diffraction (XRD) profiles of these chars showed that the metal species in the char existed as an oxide or elemental metal or carbide, depending on the heat-treatment temperature. The thermodynamic feasibility of formation of the metal via the reduction of the oxide by carbon (char) was examined using Ellingham diagrams, and the predictions agreed fairly well with the XRD results. The XRD peaks of metals were observed near the predicted temperatures. However, metal oxides showed their peaks only at temperatures higher than the temperatures of their formation, possibly because of their high Tammann temperatures and their nanodispersion in the char matrix. The Ellingham diagrams, in combination with XRD data, provide valuable insight into the chemical state of the catalyst species in chars. © 2007 American Chemical Society.