CHARACTERIZATION OF Mo, NiMo AND CoMo CATALYSTS IN THEIR SULFURED STATE
The effect of the support composition on the surface structure of Mo, CoMo and NiMo catalysts on TiO2-Al2O3 mixed oxides was characterized in the sulfided state by FT-IR spectroscopy of adsorbed NO, TPS and TPR-S techniques, before and after HDS thiophene reaction. The NO adsorption studies on the sulfided unpromoted Mo catalysts showed that the variation of total NO adsorbed and the catalytic activity follow a similar trend with the Ti content. However, in the case of the promoted catalysts the results indicate the presence of less sulfided Co and Ni species at intermediate Ti contents. Activity variations with Ti content were associated to changes in sulfidation evidenced by the NO frequency band shifts. Moreover, the changes induced by the presence of titania, on the molybdenum sulfided phases after the reaction test, can be assessed in part by the TPR-S technique. A quantitative analysis of the UV signal in the region 25-300 °C of the TPR-S patterns show that the H2S produced in this region, which is related to the number of sulfur vacancies created, coincide with the HDS activity trend
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