Hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of petroleum products and intermediates are reviewed to provide the basis for developing processes to produce gasoline and diesel oil with very low sulfur content. The reactivity, selectivity and inhibition (susceptibility of substrate molecules to inhibitors) in the catalytic process are very important to develop efficient processes. Recent advances in the understanding of active species, supports and supporting methods are also critically reviewed to suggest the design of catalysts with adequate activity to satisfy future regulations on transportation fuels. Details of the structures of the catalysts are not discussed, but the mechanisms of hydrodesulfurization and inhibition are summarized. Catalyst deactivation and reactor design are also briefly reviewed. New approaches to achieve deep hydrodesulfurization are proposed.
Carbon-supported PtSn catalysts were prepared by impregnation using a commercial activated carbon after purification and oxidation (H2O2, 20 v/v%) treatments. The support surface chemistry of the carbon after purification and the oxidized carbon, and successive impregnation or coimpregnation procedures were the variables investigated. The catalysts obtained were characterized using the following techniques: TPD and TPR experiments, H2 chemisorption, XPS and XAFS, and activity assessment in the following reactions: cyclohexane dehydrogenation (reaction insensitive to structure), cyclopentane hydrogenolysis (reaction sensitive to structure) and carvone hydrogenation, which allows analysis of the selectivity of PtSn catalysts (carvone contains one C=O group and two C=C bonds for hydrogenation). The objective of the study is to find any relationships between the preparation procedure and the support properties, the characteristics of the resulting catalysts, and the catalytic behavior. The porosity of the carbon support together with the surface oxidation determines the accessibility of reactants to the active sites. Unusual selectivity to alcohols was found. Addition of tin caused blocking and dilution of the platinum clusters. The carbon support also affected the selectivity either because of its electronic properties or because of the particular metal structures developed.
Stabilization of SO42−/ZrO2 catalyst activity was investigated using Pt/SO42−/ZrO2 catalyst loaded with a small amount of platinum. Pt-loaded SO42−/ZrO2 catalyst showed excellent stability. Presumably the Pt acted as a promoter for removing coke precursors from the catalyst. The developed Pt/SO42−/ZrO2 catalyst had higher activity than zeolitic catalyst, and higher tolerance to both water and sulfur in feed oil than chlorided alumina catalyst. Commercial operation with the developed catalyst achieved 3 points higher research octane number (RON) of product oil at lower reaction temperature compared with the previous zeolite catalyst used for naphtha isomerization.
High-silica ZSM-5 zeolites were synthesized by the addition of pentavalent ions, such as phosphorus and arsenic ions, to the mother gel for the zeolite preparation. The Beckmann rearrangement of cyclohexanone oxime in the vapor phase was carried out over the high-silica ZSM-5 zeolites or zeolites modified with noble metals to elucidate the effects of the diluent gas and diluent solvent on the ε-caprolactam selectivity and catalyst deactivation. The catalyst lives of the zeolites modified with noble metals were much longer than that of the unmodified zeolite during the rearrangement using carbon dioxide and methanol as the diluent gas and diluent solvent, respectively. Furthermore, the life of the zeolites modified with noble metals was significantly improved by using a small amount of oxygen as the diluent gas. In this case, methanol was the most suitable diluent solvent for the improvement of catalyst life. The catalyst life decreased with increased cyclohexanone oxime concentration in methanol. Therefore, the coke or coke precursor on the acid sites was presumably removed by methanol vapor. These results indicate that a prolonged catalyst life in the vapor phase Beckmann rearrangement can be achieved by the optimum combination of catalyst and reaction atmosphere.
The catalytic activity of Ga2O3-Al2O3 for the selective reduction of NO with propene was inhibited by the presence of H2O, whereas the catalytic activity of In2O3-Ga2O3-Al2O3 was significantly promoted. Both Ga2O3-Al2O3 and In2O3-Ga2O3-Al2O3 promoted the formation of NO3−, acetate, formate, nitrile, isocyanate and amino species in the absence of H2O in the reaction gas mixture under the reaction conditions. Adsorption of organic nitro compounds, which are possible intermediates in the NO reduction, onto Ga2O3-Al2O3 and In2O3-Ga2O3-Al2O3 at the reaction temperature was detected as IR bands due to nitro, nitrite, carbonyl and isocyanate species, which were also observed in the NO reduction with propene. Surface NO3− species were highly reactive with propene, leading to the formation of the surface species of acetate, formate, isocyanate and amino species, as well as N2 and CO2. On the basis of these findings, the following reaction mechanism was proposed: organic nitro compounds are first produced through the reaction of NO3− formed by NO oxidation on the catalyst surface with propene, and then decomposed to -NCO species, and the surface -NH species generated by hydrolysis of the -NCO species react with NOx species to produce N2. Although the presence of H2O suppressed the formation of NO3− species as the initial reaction intermediate on Ga2O3-Al2O3 and In2O3-Ga2O3-Al2O3, the formation and subsequent decomposition (hydrolysis) of the -NCO species was promoted by H2O over In2O3-Ga2O3-Al2O3. Such contrasting behavior of the -NCO species is related to the different catalytic characteristics of Ga2O3-Al2O3 and In2O3-Ga2O3-Al2O3 for NO reduction by propene in the presence of H2O.
The activities of two combinations of three catalysts with different mean pore sizes were examined in the residue hydrotreating process. Packing of catalysts in the order of large to small pores enhanced the catalytic activity, such as for hydrodesulfurization (HDS) and hydrodemetallization (HDM), and the pore volume of the middle catalyst apparently controlled the catalyst life. The order of catalyst packing did not influence the product states, but did affect the molecular weight distributions of asphaltenes and maltenes in the product oil. Packing of catalysts in the order of large to small pores was found most effective for the cracking of asphaltene. In contrast, packing of the catalyst with the small pores in the middle bed enhanced the cracking of maltene and reduced the cracking of asphaltene, thus increasing sludge formation. Packing of catalysts in the order of large to small pores in the catalyst bed increased the solubility of both asphaltene and maltene, thus reducing sludge formation. Solubility parameters (δ) of maltene and asphaltene as defined by Hildebrand could explain the trends in sludge formation.
Hydrodesulfurization of feed oil stocks is essential for the industrial isomerization process of light naphtha, because the isomerization catalysts are deactivated by small amounts of sulfur compounds. In this study, the deactivation of Pt/SO42−/ZrO2 catalyst by various sulfur compounds was examined, and reactions to suppress the deactivation were proposed. Various sulfur compounds caused rapid deactivation of Pt/SO42−/ZrO2 catalyst, in the order of (n-C3)2S2 >> Et-S-Me >> i-C3SH > H2S. The order of deactivation seems to depend on the adsorption of the sulfur compound on the active site. In order to suppress deactivation of the isomerization catalyst, a two reactor process combining hydrodesulfurization (HDS) and isomerization was examined. HDS followed by Pt/SO42−/ZrO2 catalyst isomerization showed stable activity for light naphtha with relatively high sulfur content.
The high-throughput screening (HTS) reactor using the 96 well microplate system is useful for the optimization of Cu oxide catalyst for methanol synthesis. However, the number of parallel lines is sometimes insufficient for novel catalyst screening. Therefore, a low cost pipe fitting device and low cost HTS reactor for catalyst screening were designed.
Effect of pore structure of silica support on sulfur tolerance and tetralin hydrogenation activity of Pd, Pt and Pd-Pt catalysts was investigated. Pore diameter of SiO2 supports affected the sulfur tolerance of noble metals and resulting hydrogenation activity. High sulfur tolerance and tetralin hydrogenation activity were observed for the Pd-Pt and Pt catalysts supported on SiO2 having the average pore diameter of 3 nm. This sulfur tolerance was comparable to those supported on ultra stable Y (USY) zeolite having the SiO2/Al2O3 ratio of 390.