Characteristics of CcoMo sulfide catalysts supported on carbon, Mo nitride catalysts, and CoMo nitride catalysts

Abstract

Carbon supported Co and Mo catalysts were prepared and characterized by using electron spin resonance(ESR) studies and NO titration. Carbon supported Co catalysts showed higher HDS activities and NO uptakes than Mo catalyst,and their HDS activities were well correlated with the results of ESR study and NO titration. One distinct ESR signals(carbon signal) corresponding to free radicals of carbon have been observed over activated carbon. When metal was loaded on carbon,the intensity of carbon site decreased with their metal dispersion. Other signals due to metal sulfides were not seen or not significant. In sulfide state cobalt species showed higher dispersion on carbon than molybdenum species. By simultaneous measurements of ESR study and NO titration the metal dispersion and morphology of carbon supported metal sulfide catalyst could be achieved. Also ESR study was useful tool for investigating the nature of metal cluster on carbon support. The simple schematic models for carbon supported Co and Mo catalysts were proposed. Carbon supported CoMo catalysts were prepared and characterized by using thiophene hydrodesulfurization(HDS),temperature- programmed desorption(TPD) of nitric oxide(NO) and ESR studies. Their catalytic activities for thiophene HDS were well correlated with NO TPD results. Co species showed higher dispersion on carbon in both oxide and sulfide states than Mo species. Three kinds of NO adsorption sites(i.e. catalytic sites)were characterized on Co species through NO TPD,and one of these sites represented similar properties to so-called a synergistic site assigned on CoMo/C catalyst in higher HDS activity and thermal resistance. It was suggested that Co species acted as a primary species,and Mo species as a secondary species at least on the carbon support. Molybdenum nitrides were prepared by temperature-programmed reduction of $MoO_3$ with flowing $NH_3$, and they were tested for indole HDN and benzothiophene HDS. Too low or high $NH_3# space ...