Sulfur uptake determination on Ni containing molybdena-alumina samples by radioisotope tracer technique

Promoter effect of nickel in thiophene hydrodesulfurization as monitored by sulfur uptake and cyclohexane conversion

“…Different from the generally accepted pretreatment method, the samples were reduced before sulfidation for possible comparison of the samples' activities in cyclohexane dehydrogenation with those in thiophene HDS. Experiments with 35 S labeled samples indicated that hydrogen treatment [7,9] and cooling in vacuum [7] did not reduce the amount of sulfur, bound irreversibly to the sample. Catalytic measurements were performed by injecting into the gas stream (60 NTP cm 3 /min) liquid pulses (5 9 10 -7 NTP l) of thiophene (Merck-Schuchardt zur Synthese [ 99%) and cyclohexane (Merck for gas chromatography min.…”

“…Experiments have been performed on the five calcined oxides of different chemical composition (Table 1) prepared before sulfidation by similar procedure [7].…”

“…In a recent paper [7], we presented data on the amounts of sulfur uptakes, by a non-promoted molybdena-alumina containing 12 mass% of MoO 3 (denoted Mo12), alumina supported Ni of 12% mass% (Ni12) and three nickel-promoted molybdenaalumina samples with 0.15, 0.35 and 0.6 Ni:Mo atomic ratios (NiMo(0.15), NiMo(0.35) and NiMo(0.6)). The amounts of reversible and irreversible sulfur uptake were determined by radiosulfur as tracer.…”

“…The dehydrogenation of cyclohexane has also been carried out on these samples in non sulfided form, as ''precursors'' of the sulfides. The aim of these ''ex-situ'' experiments was to gain information on the effect of the surface Ni 0 concentration before sulfidation on the extent of sulfur uptake and HDS activity, as XPS measurement data with the NiMo catalysts indicated [7,13] that the Ni 0 /Ni ratios were substantially different in the surface region of the non sulfided samples. Cyclohexane conversion activity is an indicator of surface zerovalent metal concentration [14], and the phenomenon is successfully applied for the determination of this quantity as a number of metals are active in cyclohexane dehydrogenation at low (\623 K) temperature, whereas metal-oxides catalyze this reaction only at significantly higher temperatures [15,16].…”

“…This motivates to compare the significant differences in irreversible sulfur uptake capacities of the five alumina supported samples [7] prepared by an identical method with their thiophene HDS activities in sulfided form. The dehydrogenation of cyclohexane has also been carried out on these samples in non sulfided form, as ''precursors'' of the sulfides.…”