Hydrotreating Catalysis*

1. Introduction
~i\ drotreating or hydroprocessing refers to a variety of catalytic hydrogena-
. in processes which satúrate unsaturated hydrocarbons and remove S, N, O
nd metáis from differentpetroleum streams in a refinery. These processes
epresent some ofthe most important catalytic processes and the annual sales
: hydrotreating catalysts represent cióse to 10% of the total worid market:or catalysts.
Hydrotreatment usually implies oniy small changes in overall molecular
'iructure but hydrocracking (HCR) reactions often occur simultaneously and
may in fact be desired. Todayhydrotreating is used extensively both for con-
ersion of heavy feedstocks and for improving the quality of final producís.
Hydrotreating aiso plays an essential role in pretreating streams for other re-:mery processes such as catalytic reforming, fluid-catalytic cracking (FCC),
-.nd HCR. More severe environmental legislation with respect to harmful
emissions has triggered an increased interestin both basic and applied
:esearch within hydrotreating catalysis. These efforts have already led to
:'iew technological developments.
Historically, hydrotreating processes have developed from thecracking
.md hydrogenation processes introduced inthe 1930s [1]. For along time, the
most important hydrotreating reaction has been the removal of sulfur from
arious fuel fractions. Consequently,hydrotreating catalysts are aiso com-
:nonly referred to as hydrodesulfurization (HDS) catalysts. Typical hydro-
jesulfurization catalysts consist of molybdenum supported on an alumina
:arrier witheither cobait or nickel added as promoters for improving the cat-
-ilytic activity. Industrial applications of such alumina-supported "cobalt-
moly" catalysts were reported already in 1943 [2].
Manynew challenges continué to arise in hydrotreating. In particular,
these have been the result of the dramatic woridwide decline in the demand
Dedicated to Dr. Haldor Tops0e on the occasion of his...