On the surface coverage of alumina by molybdenum-oxide in nickel - and cobalt-promoted MoOx/Al2O3 catalysts

Abstract

The chemisorption of CO 2 has been studied on alumina-supported Co-and Nipromoted molybdenum-oxide (CoMo, NiMo) and, besides those, on monometallic Co and Ni. Chemisorbed amounts on the monometallic samples were equal to that on the alumina support. XPS measurements were performed with the NiMo and Ni samples. The amounts of surface Mo-and Al-ions were calculated. It could be established that molybdenum oxide forms a near to monomolecular layer on the Co-and Ni-promoted molybdena-alumina samples.

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

“…It is seen also from Table 1 that all Ni-containing samples catalyze the cyclohexane conversion. This indicates, in agreement with XPS data [7] cited before, that some Ni 0 is present on the NiMo(0.X) and Ni12, similarly to the observation with the NiMo-2 sample [13]. No cyclohexane conversion was observed on Mo12 at 673 K temperature in agreement with the general experience with oxide catalysts [15,16,22].…”

“…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].…”