C-13 NMR ANALYSIS OF CATALYST CARBON DEPOSITS SIMULATED BY MODEL COMPOUNDS

Mixtures of pyrene and cholestane adsorbed on Haldor Topsoe TK551 cata lyst were studied as model compounds for carbonaceous deposits (coke) formed during use of the same catalyst. Several techniques were screen ed for quantitative analysis of the carbonaceous compounds by C-13 n.m .r. and the best results were obtained using the proton gated decoupli ng pulse sequence coupled with depth pulses. These quantitative analys es are performed using an external model compound calibration line. Qu antitative C-13 n.m.r. analysis of different types of coke revealed th at not all the carbons in the coke were observable. The 'invisible' ca rbons are attributed to graphitic material, since pure graphite is als o completely invisible to C-13 n.m.r. under these conditions.