Christian Gachet

Influence of sulphidation conditions on the properties of NiW/Al2O3 hydrotreating catalysts

Abstract The sulphidation of a nickel-tungsten catalyst has been studied by XPS and electron microscopy. These features are related to catalytic properties in test reactions characteristic of hydrotreatment (HDS, HDN, HN of aromatics) and to chemisorption measurements. It was observed that for a sulphidation temperature of 400°C, only 70% of the tungsten atoms are in a WS 2 - like form; this proportion increases to 95% at 650°C. High-resolution microscopy results indicate that a slight lateral growth of the WS 2 -like crystals occurs above 500°C. The activity in the HN of biphenyl does not vary with the sulphidation temperature in the same way as HDS reactions. These variations of catalytic activities support the existence of two different catalytic sites for hydrogenolysis and hydrogenation reactions. The crystallite length increase observed above 500°C leads to a decrease in the number of edge positions necessary for mixed site formation and therefore a decrease in the probe molecule uptake and HDS catalytic activity.

Optimization of the composition of Ni-W/A1203 hydrotreating catalysts using model molecules and real feedstock conversion studies

Abstract Alumina supported Ni-W catalysts with contents of components varying over a wide range were systematically studied in order to optimize a catalyst for further industrial use, mainly for HDN reactions. The catalytic activities were determined in different reactions representative of the hydrotreatment process, viz., piperidine HDN, biphenyl and pyridine hydrogenations, thiophene and dibenzothiphene HDS. The promoting effect of Ni is always observed but the amplitude of the synergy is greatly dependent on the type of molecule to be treated. The nature of the active sites responsible for the catalytic activities is discussed in terms of the mixed phase model. The selected most active catalyst for performing HDN reactions was tested in real feedstock conversions and compared with conventional nickel-tungsten catalysts.

Catalytic Hydrodesulfurization of Dibenzothiophene Over Y Type Zeolites

Publisher Summary This chapter discusses the catalytic hydrodesulfurization (HDS) of dibenzothiophene over Y type zeolites. The catalytic HDS of DBT over Y zeolites and decationized Y zeolites, with or without metal loadings, shows that these two catalysts have quite different behaviors. Attention must be paid to the initial activity of these catalysts and to the activity after 15 hours of work. In particular, though the three zeolites with Co have very low initial activity, after 15 hours of work the CoMo–HY zeolite is the most active and the most stable catalyst. So, neither the Co nor the association Co–Mo is active by itself, but the Co has a main influence on the activation of the catalyst during the sulfidation. Moreover, some parallelism can be done between the HY and the alumina-supported catalysts, which is a good approach for a better understanding of the interaction of Co and Mo species.

Deactivation of Hydrodesulfurization Catalysts: Influence of the Hydrogen-Pretreatment Temperature on Coo-MoO3/γ Al2O3, MoO3/γ Al2O3, CoO/γ Al2O3 Precursors

CoO-MoO 3 /γ Al 2 O 3 , MoO 3 /γ Al 2 O 3 , CoO/γ Al 2 O 3 oxides are pretreated by H 2 at different temperatures. Directly, without any presulfidation, the activities in the hydrodesulfurization of the dibenzothiophene and the sulfur uptakes are measured in function of the time of the runs. (change-para-here) For the samples pretreated at high temperature, the initial activity is great, the deactivation strong. A maximum of the steady-state activities is observed for the pretreatment temperature of about 430°C. (change-para-here) Those results suggest two types of active sites for the hydrodesulfurization: strongly reduced molybdenum ions, active but fragile, got by only reduction, and sulfided molybdenum less active but more resistant obtained by concerted reduction and sulfidation.