DRIFT STUDY OF TEMPERATURE-PROGRAMMED DESORPTION OF NO ADSORBED ON CO-MO AL2O3 SULFIDED AT HIGH-PRESSURE/

In order to make clear the coordinatively unsaturated sites (CUS) of C o-Mo/Al2O3 sulfided at high pressure, the temperature programmed desor ption of NO adsorbed on Co-Mo/Al2O3 sulfided at high pressure was stud ied by DRIFT method. The intensity of two IR bands (1835 and 1785 cm(- 1)) of adsorbed NO on Co-Mo/Al2O3 decreased simultaneously up to 393 K . The higher frequency band disappeared at 393 K, while the lower freq uency band remained even at 403 K. In the case of Mo/Al2O3, the intens ities of two bands appeared at 298 K decreased monotonously with incre asing temperature, and disappeared simultaneously over 433 K. In the c ase of Co/Al2O3, two bands disappeared simultaneously over 393 K. Thes e results suggest that two kinds of nitrosyl species are formed on Co- Mo/Al2O3. One is dinitrosyl species adsorbed on CUS of Co, and the oth er is unidentified nitrosyl species. Comparing DRIFT spectra of Co-Mo/ Al2O3 with those of a physical mixture of Mo/Al2O3 and Co/Al2O3, it is also suggested that the formation of the latter one correlates with t he interaction between Co and Mo in Co-Mo/Al2O3. The unidentified nitr osyl species might be the key to explain the dependency of DRIFT spect rum of adsorbed NO on the pressure of sulfiding. (C) 1998 Elsevier Sci ence B.V. All rights reserved.