13C n.m.r. quantitative analysis of catalyst carbon deposits

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

“…15% expected for nonprotonated C (Fonseca et al, 1996), and were higher for the 480 C chars. We also found high aromaticity in the difference spectra showing protonated C. Apart from the shoulders due to phenolic and C-substituted C, the main aromatic peak is therefore likely due to a mixture of bridgehead C (shared by two or more aromatic rings), and protonated aromatic C with similar ranges of chemical shifts (Sullivan and Maciel, 1982;Netzel et al, 1996;Smernik and Oades, 2000;Solum et al, 2001).…”

“…Low CP efficiency is typical of highly-condensed aromatic structures such as high-temperature biomass chars (Freitas et al, 1999(Freitas et al, , 2001Maroto-Valer et al, 1996) and coke deposits (Fonseca et al, 1996;Maroto-Valer et al, 1998). Approximately 27% of the carbon was observed by CP for highly aromatic photooxidation residues of soil organic matter .…”

“…We also found high aromaticity in the difference spectra showing protonated C. Apart from the shoulders due to phenolic and C-substituted C, the main aromatic peak is therefore likely due to a mixture of bridgehead C (shared by two or more aromatic rings), and protonated aromatic C with similar ranges of chemical shifts (Sullivan and Maciel, 1982;Netzel et al, 1996;Smernik and Oades, 2000;Solum et al, 2001). The proportion of bridgehead vs. protonated aromatic C is determined by cluster size distribution, linkages, and the proportion of linear vs. cyclic condensation (Solum et al, 1995;Fonseca et al, 1996;Maroto-Valer et al, 1998). The higher DD losses, narrower aromatic peaks, and slightly higher CP efficiencies for the 480 C chars are consistent evidence that loss of phenolic and alkyl substituents resulted in a relative increase of protonated aromatic C. This occurs as chars produced around this temperature form relatively small clusters of condensed C (including linear structures), that still have high proportions of protonated C (Solum et al, 1995).…”

Investigation of the mechanism of sediment formation in residual oil hydrocracking process through characterization of sediment deposits

“…13 C solid-state NMR spectra were obtained from original sediments and its THFIS fractions. The spectra of dried and ground samples were measured using proton gated decoupled single pulse excitation at high MAS (SPE/MAS) [16] and cross polarization with polarization inversion at low or moderate MAS (CP/PI/ MAS) [17]. For more details see Hauser et al [18].…”

“…NMR has become a powerful tool for structural characterization of solid carbonaceous deposits [16,19] and liquid hydrocarbons [20]. In liquid and solid-state NMR, for example, different types of structural entities can be identified and quantified [20].…”