Hydrotreating catalysts active sites

CA provides simultaneous sulfidation of Co and Mo favoring to the selective formation of the hydrotreating catalysts active sites. 

Nowadays, it is well known that the active sites of the hydrotreating reactions surface are the nanosized M0S2 particles with Co(Ni) atoms anchored at the edge plane[l]. From the other side, the textural properties of the supports that are optimal for different type of distillates are well distinguished [2]. The use of the pores with smaller size restricts the access of S- and N- containing compounds to the catalysts active sites. The use of pores with sizes larger than necessary results in a lower specific surface area and therefore in a decrease of the number of active sites per volume of catalyst. 

Owing largely to research over the last twenty years, the sulfided C0-M0/AI2O3 system is one of the best-characterized industrial catalysts [H. Topsoe, B.S. Clausen and F.E. Massoth, Hydrotreating Catalysis (1996), Springer-Verlag, Berlin]. A combination of methods, such as Mbssbauer spectroscopy, EXAFS, XPS, and infrared spectroscopy, has led to a picture in which the active site of such a catalyst is known in almost atomic detail. 

Figures 13 and 14 also show that hydrotreating the catalytic cracker feedstock increases the zeolite cracking. C3, and C5+ compounds are possible products of primary zeolite cracking. These figures show that hydrotreating of the feedstock results in larger yields of these primary cracking products and hence more valuable products. This improvement is most likely due to the heteroatom removal and the saturation of aromatic compounds during hydrotreating which tend to block active sites and reduce the activity of the catalyst.

D.6. Metallic Brim States as Active Sites in Hydrotreating Catalysts... 

Instead, they proposed a time on stream theory to model the catalyst deactivation. However, in an earlier work by Voorhies (2), a linear correlation between conversion and coke on catalyst for fixed-bed catalytic cracking was derived. Rudershausen and Watson (3) also observed the similar behavior. Coke on catalyst can reduce the activity by covering the active sites and blocking the pores. The effects of pore size on catalyst performance during hydrotreating coal oils in trickle-bed reactors have been studied experimentally by Ahmed and Crynes (4) and by Sooter (5). The pore size effects in other studies are also reported 7, 8). Prasher et al. (9) observed that the effective diffusivities of oils in aged catalysts were severely reduced by coke deposition. 

Researchers at Haldor Topsoe and their collaborators in academic institutions have contributed significantly to both the advances in research on fundamental aspects of catalytically active sites of transition metal sulfides and the development of new and more active commercial hydrotreating catalysts and processes.15 79 80... 

The decrease in activation energy with increasing coke content of a hydrotreating catalyst was modeled by a normal (Gaussian) variable-site activation energy fimction. Catalyst deactivation was correlated by site-selective deactivation for anthracene coke and site-preference deactivation for bitumen coke. 

As the edge sites of sulfide slabs are generally known as active sites in hydrotreating reactions [1], it seemed thus possible to us that reactions take place preferentially between sulfide edge sites and organometallic complexes, if placed in contact each other. Selective modification of edge sites could then be made by different metals like cobalt or tin. In this study, we applied SOMC to the modification of the conventional hydrotreating catalysts alumina-supported molybdenum sulfides with or without cobalt promoter. The Co and Sn... 

The effect of H2S uptake on the catalyst behaviour is an outstanding example of the concept of the catalysts system based on the principle that, the original catalyst, the reacting compounds and the products of conversion form the system responsible for the catalytic reaction , and expressed by Delmon more thoroughly, Probably all kinds of active sites in hydrotreating catalysts result from some sort of a dynamic process . ... 

Because of their high activities, carbides and nitrides of molybdenum have drawn most attention as hydrotreating catalysts. Many attempts were made to compare them with commercial sulfide catalysts. In terms of activity per active site, supported and unsupported M02C and M02N were found to be more active than sulfided Ni—M0/AI2O3 or Co—M0/AI2O3 catalysts in many HDS and HDN... 

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