Kyung Lim Kim

Surface properties and reactivity of supported and unsupported molybdenum nitride catalysts

Abstract A series of γ-Al 2 O 3 supported molybdenum nitride catalysts (nitrided Mov γ-Al 2 O 3 (MNS), CoMo γ-Al 2 O 3 (CMNS), and NiMo γ-Al 2 O 3 (NMNS)) and unsupported molybdenum nitride catalyst (MNUS) were prepared by the temperature programmed reaction of their corresponding molybdenum oxide precursors with NH 3 . The surface properties of prepared molybdenum nitride catalysts were characterized by N 2 adsorption, XRD, and XPS methods. N 2 adsorption and XRD studies show that the supported molybdenum nitride catalysts possess a highly dispersed surface molybdenum nitride species on the alumina support, while unsupported molybdenum nitride catalyst possesses a typical crystalline Mo 2 N (FCC) structure. The XPS data of supported molybdenum nitride catalysts reveal that Mo 2+ , Mo 3+ , and Mo 4+ species were selectively produced upon nitridation. The results of dibenzothiophene (DBT) hydrodesulfurization over molybdenum nitride catalysts show that the reactivity is strongly dependent on the type of catalysts and it decreases in the order: MNS > NMNS ≥ CMNS ≥ MNUS. In addition, it was also found that the reactivity increases when increasing the reaction temperature and pressure and contact time. No synergistic effect for DBT hydrodesulfurization over Co (or Ni) promoted, nitrided Mo γ-Al 2 O 3 catalysts is observed. The major reaction product is biphenyl and cyclohexylbenzene is next in abundance regardless of the type of catalysts and reaction conditions. The reactivity for DBT hydrodesulfurization does not correlate with amounts of CO chemisorption. The reactivity is rather well correlated with the difference in heat of adsorption between thiophene and H 2 S.

Selective oxidation of hydrogen sulfide over potassium promoted vanadium oxide on a alumina catalysts

The effect of potassium addition to alumina supported vanadium catalysts on the catalytic activity for the selective oxidation of H2S is investigated. XRD, XPS and XANES have been used to characterize a series of K-V/Al2O3catalysts. The enhanced sulphur yield has been correlated with the crystallinity of vanadium.

Catalytic oxidation of carbon monoxide over CoOx/CeO2catalysts

CoOx/CeO2 catalysts of different cobalt loading have been prepared and tested for carbon monoxide oxidation in stoichiometric mixtures of carbon monoxide and oxygen. They were investigated by TPR, CO-TPD and XPS. The finely dispersed CoOx species that can absorb carbon monoxide seemed to be important in determining the catalytic activity.

SMSI effect on ceria supported Cu-Pd catalysts in the hydrogenation of 1,3-butadiene

Ceria-supported copper-palladium catalysts have been tested in the hydrogenation of 1,3-butadiene. The SMSI behavior of the bimetallic catalysts depended on the temperature of reduction. They were analyzed by H2 chemisorption and XPS.

Palladium catalysts supported on activated carbon with different textural and surface chemical properties

A commercial activated carbon was used as catalyst support in Pd/AC catalysts. The effects of the different surface oxygen groups and textural properties of the carbon supports on the metal dispersion of the supported catalysts were analyzed.

A Study on the Selective Hydrogenation of 1,3-Butadiene over Pd-Li/SiO2 Catalysts

Lithium addition to Pd supported on silica markedly improves the 1-butene selectivity and activity for hydrogenation of 1, 3-butadiene without isomerization and over-hydrogenation of the 1-butene. The activity of 1,3-butadiene in hydrogenation increased linearly with-lithium loading. This behavior indicates that there is not a physical blockage of the surface active sites. These results are in good agreement with XPS results that the addition of lithium aided Pd particles to be the metallic state as active site. The addition of lithium greatly improves l-butene selectivity till a certain level, but over which it decreased and trans-2-butene increased due to isomerization. The ratio of trans- and cis-2-butene from the result of hydrogenation of 1-butene was about 2: 1, i. e., l-butene favored the trans isomer. Therefore, it was reasonably assumed that the increase in 1-butene selectivity was reflected in an decrease in the trans-2-butene selectivity , From NH3- TPD it is suggested that the addition of lithium affects the adsorption of reactant and product and consequently 1-butene selectivity. 1-Butene selectivity results also indicated there is an optimum value creating a better environment for the desorption of l-butene without isomerization at a certain level of the lithium loading.

Indication of Interaction of Metals from TPR and XPS in Relation with Their Reactivity for 1,3-Butadiene Hydrogenation

A series of nickel base catalysts supported on silica has been used for selective hydrogenation of 1,3-butadiene. The materials were characterized by means of temperature-programmed reduction, hydrogen chemisorption, x-ray photoelectron spectroscopy, and x-ray absorption near edge structure. Cu-Ni interaction affected the reduction behavior of the catalysts. TPR results reveal the presence of more reducible nickel species formed by interaction of nickel with the surface of copper oxide. These results are in agreement with XPS results of Ni 2p spectra showing significant shifts towards lower binding energies with increasing copper loading. XPS shows that the Ni-Cu alloy is formed with enrichment of Ni on the surface. The addition of copper on Ni/SiO2 causes the conversion rate to decrease and increases selectivity to l-butene. This selectivity behavior is explained by the variation of the electronic properties of nickel induced by copper Hydrogen chemisorption results show that the dilution of the nickel surface atoms is responsible for the decrease in activity.

The Effect of MoO3 Addition to V2O5/Al2O3 Catalysts for the Selective Catalytic Reduction of NO by NH3

The effect of MoO3 addition to alumina supported vanadia catalysts on the catalytic activity for the selective catlaytic reduction of NO is investigated. Upon the addition of MoO3, catalytic activity is enhanced and the particle size of V2O5 which is shown by the results of XRD and Raman spectroscopy is decreased. The MoO3-V2O5/Al2O3 catalyst also exhibits more resistance to SO2 deactivation than V2O5/Al2O3 does.

Characterization of Ni-K catalysts Supported on γ-Alumina and Reactivity for the Hydrogenation of 1,3-Butadiene

A series of γ-Al2O3 supported K added Ni catalysts were prepared in order to investigate the effect of K on the selective hydrogenation of 1,3-butadiene. The catalysts were prepared by impregnation, with loadings of 15 wt% Ni and varying amounts of K[(K/Ni+K)atomic = 0.2-0.6] followed by calcinations at 400℃. Reduction was performed at 450℃ for 5h. They were characterized by temperature-programmed reduction (TPR), 1, 3-butadient-temperare programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS)and X-ray absorbance near edge structure (XANES) spectroscopy. Activity and product selectivities were tested for hydrogenation of 1,3-butadiene in the temperature range of 100-300℃. The set of data indicate that the addition of K modified the electron density of Ni metal and weakened the adsorption strength of butadiene. It has been established by a shift of the Ni2p3/2 binding energy in XPS measurement, Ni absorption edge in XANES spectroscopy and 1,3-butadiene-TPD measurements. The catalysts exhibited a high activity and selectivity for 1-butene particularly the added Ni catalysts due to the promotion of K for Ni based catalysts.

A study of hydrodenitrogenation of pyridine catalyzed by sulfided Ni-Mo/γ-Al2O3

The hydroprocessing of fuels containing relatively large amounts of organonitrogen compounds becomes increasingly important in the upgrading of hydrocarbon fuels. Therefore, to investigate the removal of organonitrogen compounds, the hydrodenitrogenation of pyridine dissolved in n-heplane was studied over sulfided Ni-Mo/u-Al2O3 catalysts in the range of lemperature between 513 K and 633 K and pressure between 30 bar and 50 bar in a fixed bed flow reactor. Pyridine conversion increased with the increased temperature and pressure, and the piperidine formation was found to be irreversible. Pyridine concentration reached a maximum at about 573 K and the apparent reaction order was found to be one with respect to pyridine.