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| - XPS and 15N NMR Study of Nitrogen Forms inCarbonaceous Solids
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| - A combination of XPS and solid-state 15N NMR have been used to characterize the nitrogenforms in a variety of different carbonaceous samples having high natural nitrogen abundance. Itis currently difficult to unequivocally interpret and quantify individual 15N NMR and XPS spectra.The advantages of using a multiple technique approach for nitrogen speciation as well as thelimitation of XPS nitrogen (1s) and 15N NMR spectroscopy are discussed. XPS and 15N NMRresults show that pyridinic and pyrrolic nitrogen are present in quinoline and isoquinolinepyrolysis chars. Pyridinic nitrogen is the most abundant form in quinoline pitch while isoquinolinepitch produced the most pyrrolic nitrogen. A small amount of quaternary nitrogen (∼10 mol %)appeared in the XPS spectrum of the chars, however, no additional nitrogen forms were identifiedabove the noise level in the 15N NMR spectra. The 15N NMR spectrum of Green River kerogenshows a single broad feature centered around −245 ppm in the 15N NMR, consistent with theposition of pyrrolic nitrogen forms. XPS spectra of Green River kerogen show a large peak at400.2 eV and the peak at this position in the curve-resolved nitrogen (1s) spectrum is consistentwith pyrrolic nitrogen forms. Other XPS peaks were consistent with and attributed to pyridinicquaternary and amine nitrogen species. Acid treatment of Green River kerogen resulted in anincrease in the quaternary nitrogen feature in both the XPS and 15N NMR spectra with aconcomitant decline in the XPS pyridinic and amine nitrogen features. Pyrolysis of kerogenresulted in the appearance of a peak near −80 ppm in the 15N NMR spectrum attributed topyridinic nitrogen forms. XPS spectra also show an increase in pyridinic nitrogen upon pyrolysis.XPS results show that the major peak in the curve-resolved nitrogen (1s) spectrum of both freshand pyrolyzed peats appears at 400.2 eV. Both amide and pyrrolic nitrogen appear at this energyposition and it is impossible to distinguish between these two species based on XPS data alone.For fresh peat, the major peak in the 15N NMR spectrum occurs at chemical shift positionsconsistent with the presence amide nitrogen forms. The main peak in the 15N NMR spectrum ofpyrolyzed peats broadens and shifts toward higher field. This change is associated with the lossof amide forms and the appearance of pyrrolic nitrogen forms
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