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The kinetics for the initial stage of the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and dibenzothiophene (DBT) were comparatively examined over NiMo and CoMo sulfide catalysts and newly developed nickel phosphide catalysts. The HDS can proceed through an indirect hydrogenation (HYD) pathway and a direct desulfurization (DDS, or hydrogenolysis) pathway. The rate constants for the HYD and DDS pathways (k 1 and k 2, respectively) were estimated using a method that involved extrapolation to zero conversion for the initial selectivity ratio of primary products. The overall rate constants (k 1 + k 2) for 4,6-DMDBT on a catalyst weight basis (in units of 10-5 s-1 g·cat-1) at 573 K under a pressure of 20.4 atm increased in the order of CoMo sulfide (34.1) < Ni2P/USY (51.5) < Ni2P/SiO2 (66.4) < NiMo sulfide (83.2); however, the values based on active sites (in units of s-1 active site-1) ranked in a different order (CoMo sulfide (4.0) < NiMo sulfide (8.8) < Ni2P/USY (15.2) < Ni2P/SiO2 (23.7)). The rate constants for the HYD pathway of 4,6-DMDBT HDS at 573 K based on active sites were strongly dependent on the type of catalyst used; however, those for the DDS pathway were less sensitive to the type of catalyst, as can be observed from the corresponding values (k 1; k 2) for CoMo sulfide (2.2; 1.8), NiMo sulfide (6.7; 2.1), Ni2P/USY (12.7; 2.5), and Ni2P/SiO2 (21.6; 2.1). The NiMo sulfide catalyst, which favored the HYD pathway, was more active than the CoMo sulfide catalyst for 4,6-DMDBT. The nickel phosphide catalysts showed higher activity in 4,6-DMDBT HDS than the sulfide catalysts, based on rate constants normalized to active sites; they operated through the HYD pathway. A comparison with DBT HDS at 573 K under a hydrogen (H2) pressure of 20.4 atm showed that the presence of the methyl groups at the 4- and 6-positions dramatically inhibited the DDS pathway, because of steric hindrance around the S atom, and thus made the HYD pathway more important. Higher H2 pressure further enhanced the HYD pathway, whereas increased temperature increased the contribution of the DDS pathway for 4,6-DMDBT HDS.

Silica-supported manganese oxide catalysts with loadings of 3, 10, 15, and 20 wt % (as MnO2) were characterized with use of X-ray absorption spectroscopy and X-ray diffraction (XRD). The edge positions in the X-ray absorption spectra indicated that the oxidation state for the manganese decreased with increasing metal oxide loading from a value close to that of Mn2O3 (+3) to a value close to that of Mn3O4 (+2(2)/3). The XRD was consistent with these results as the diffractograms for the supported catalysts of higher manganese oxide loading matched those of a Mn3O4 reference. The reactivity of the silica-supported manganese oxide catalysts in acetone oxidation with ozone as an oxidant was studied over the temperature range of 300 to 600 K. Both oxygen and ozone produced mainly CO2 as the product of oxidation, but in the case of ozone the reaction temperature and activation energy were significantly reduced. The effect of metal oxide loading was investigated, and the activity for acetone oxidation was greater for a 10 wt % MnOx/SiO2 catalyst sample compared to a 3 wt % MnOx/SiO2 sample.

Supported manganese oxide catalysts were prepared by the impregnation of alumina foam blocks washcoated with alumina and silica. The manganese content based on the weight of the washcoats was 10 wt % calculated as MnO2. Fourier transform profiles of the Mn K-edge EXAFS spectra for these samples gave three distinctive peaks at 0.15, 0.25, and 0.32 nm and were close to the profiles of Mn3O4 and beta-MnO2. The number of surface active sites was determined through oxygen chemisorption measurements at a reduction temperature (Tred = 443 K) obtained from temperature-programmed reduction (TPR) experiments. Acetone catalytic oxidation was studied from room temperature to 573 K, and was found to be highly accelerated by the use of ozone on both catalysts with substantial reductions in the reaction temperature. The only carbon-containing product detected was CO2. The alumina-supported catalyst was found to be more active than the silica-supported catalyst in acetone and ozone conversion, with higher turnover frequencies (TOFs) for both reactions. The pressure drop through the foam was low and increased little (0.003 kPa/10 000 h(-1)) with space velocity. In situ steady-state Raman spectroscopy measurements during the acetone catalytic oxidation reaction showed the presence of an adsorbed acetone species with a C-H bond at 2930 cm(-1) and a peroxide species derived from ozone with an O-O bond at 890 cm(-1).