IR study of hydrotreating catalysts in working conditions: Comparison of the acidity present on the sulfided phase and on the alumina support

Abstract

Abstract The design of an apparatus suitable for monitoring in situ surface sites of sulfided catalysts simultaneously by transmission FTIR spectroscopy and by activity measurements is reported. It has been used to evaluate Bronsted acidity of hydrotreating catalysts in “working” conditions, i.e. at high temperature in presence of H 2 S and hydrocarbons in the flow. Acidity of Al 2 O 3 and CoMo/Al 2 O 3 has been characterized by monitoring the adsorption of 2,6-dimethylpyridine (DMP) at high temperature (100–250°C). DMP reveals a higher number of Bronsted acid sites on CoMo/Al 2 O 3 than on Al 2 O 3 . H 2 S adsorption leads to the creation of Bronsted acid sites on both catalysts but in a larger extent on CoMo/Al 2 O 3 . Evaluation of the Bronsted acidity of catalysts was also performed using 3,3-dimethyl-1-butene (33DMB1) isomerization as test reaction, carried out in situ either in the IR reactor-cell or in a conventional glass micro-reactor. Initial activities of the activated catalysts are in good agreement with the relative amounts of Bronsted acid sites probed by DMP. Isomerization activity of both catalysts is also promoted in presence of H 2 S. Simultaneous measurements of activity and DMP adsorption followed by FTIR spectroscopy during the reaction at 250°C shows that Bronsted acid sites probed by DMP are the active sites for 33DMB1 isomerization. Deactivation of the sulfide catalyst is attributed to the formation on the sulfided phase of a species which poisons Bronsted acid sites. Coke formation was also evidenced