The fields of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN)
continue to attract the attention of researchers in the various
disciplines connected to these fascinating problems that represent two
of the key outstanding chemical challenges for the petroleum refining
industry in view of their very strong environmental and commercial
implications. One area that has flourished impressively over the last 15
years is the organometallic chemistry of thiophenes and other related
sulfur-containing molecules. This has become a powerful method for
modeling numerous surface species and reactions implicated in HDS
schemes, and nowadays it represents an attractive complement to the
standard procedures of surface chemistry and heterogeneous catalysis,
for understanding the complex reaction mechanisms involved in this
process. Similar developments have begun to appear in connection with
HDN mechanisms, although in a much more modest scale and depth. Some
years ago when, encouraged by Prof. B. R. James, this book was planned,
several excellent reviews and monographs treating different aspects of
HDS were already available including some on the subject of
organometallic models. However, it seemed appropriate to try to
summarize the most striking features of this chemistry in an updated and
systematic way, and inasmuch as possible in connection with the common
knowledge and beliefs of the mechanisms of heterogeneous HDS catalysis.
Hopefully, this attempt to build some conceptual bridges between these
two traditionally separated areas of chemistry has met with some
success.