Hydrogenation of tetralin over Ir-containing mesoporous catalysts

Abstract

The yield in fluid catalytic cracking (FCC) depends on the extent of aromatic hydrogenation in the gas oil hydrotreater. To optimize the gas oil hydrotreater, it is crucial to understand the aromatic hydrogenation reaction chemistry occurring in the gas oil hydrotreater. Gas oils, which consist of hydrocarbons in the boiling point range of 290−570 °C, contain several aromatic compounds (including three rings, two rings, and one ring). Light cycle oil (LCO), which contains large concentrations of aromatics, has a poor cetane value and, hence, by itself, is a very poor-quality diesel. Because the current regulations [on cetane and polynuclear aromatic (PNA) hydrocarbons] are not stringent, LCO is currently blended with diesel. However, it is anticipated (based on existing regulations in Europe and California) that diesel quality in the near future will be more stringently regulated in terms of cetane and aromatics. To find alternative processes, it is necessary to develop new and more active catalysts to replace the current ones. Optimal design and operation of such hydrogenation processes can be achieved through the use of reliable simulation tools; however, such tools require detailed knowledge of kinetic pathways and rates.1−3 Kinetic experiments on hydrogenation are typically performed in the gas phase under atmospheric pressure on group VIII metal catalysts. Previously, Beltramone et al.4,5 reported a detailed study and a quantitative network analysis of polynuclear aromatics aromatization at industrial conditions, and Korre and Klein6 reported an exhaustive study in a batch reactor at high pressure. Otherwise, the sulfur and nitrogen compounds found in synthetic feedstocks and heavy petroleum fractions can strongly inhibit hydroprocessing reactions through competitive adsorp- tion. The presence of these species even at low concentrations can limit the observed catalytic activity and necessitate the use Article Current processes for dearomatization use catalysts combin- ing the acidity of a support and the hydrogenation and hydrogenolysis/ring-opening activity of an incorporated metal. Hydrogenation/hydrocracking is most often practiced on cyclic molecules over primarily acidic zeolite, alumina, or silica- alumina-supported noble and other group VIII metal catalysts. Different processes have used catalysts such as NiMo, CoMo, NiW, Pt, and Pd on various supports.7−17 The dominance of the acid function can lead to cracking, and thus, a primary focus is the optimization of the acid function. In fact, it was shown recently that significant enhancements in hydrogenation can be made by focusing on the metal function. The metal function is usually provided by Pt and/or Pd, but it has been shown that Ir, Ru, and Rh also have exceptional activities and selectivities for the target reaction of hydrogenation and, depending on the reaction conditions, selective ring-opening.18−20 Some alumina- supported transition-metal catalysts have much higher hydro- denitrogenation (HDN) and hydrodesulfurization (HDS) activities than the conventional NiMo system.21−25 For example, Rh, Ir, Ru, and Pt supported on silica or alumina are known to effectively catalyze nitrogen removal from methylamine, quinoline, or pyridine also in the reduced state.26 Noble-metal sulfides, either unsupported as bulk compounds27 or supported on active carbon,28 have been studied extensively in hydrorefining. It has been shown that transition-metal sulfides of the second and third rows such as those containing Ru, Rh, Os, and Ir are especially active during HDS reactions.27 Similarly, sulfides of Ir, Os, and Re were found to be most active in the HDN of quinoline,28 and sulfides of Ir and Pt were found to be most active in the HDN of pyridine.29 However, catalytic properties of metal deposited on alumina or other supports have been studied less frequently, and moreover, the primary attention to date has been devoted only to Ru.30 It was shown by Cinibulk and Vit́31 that the HDN of higher pressures and temperatures to obtain desired conversions. Therefore, the need for more active catalysts is crucial in this process. The development of highly active and selective hydrotreating catalysts is one of the most pressing problems facing the petroleum indu