Researchers have discovered two pieces of a scientific puzzle in the most widely used process for removing polluting sulfur compounds from crude oil. The discovery could help chemists tailor the catalytic process, known as hydrodesulfurization, for maximum efficiency and economy, according to Paul S. Weiss, professor of chemistry at Penn State, who conducted the research along with Penn State graduate student James G. Kushmerick.
A paper describing the research is published in the current issue of Journal of Physical Chemistry B, published on December 10.
The chemists made their discovery with one of the most powerful and stable microscopes in the world--an instrument they designed and built themselves. "It is so stable that the position we examine drifts no more than one atomic site per day, so we are able to observe individual molecules for days at a time and to measure the electronic structures that control chemical reactions on surfaces," says Weiss.
The chemists observed a cluster of three nickel atoms and its interaction with a molybdenum disulfide surface. Tiny molybdenum disulfide crystallites on an oxide base--with nickel or cobalt added as a reaction promoter--are used by refineries worldwide as catalysts for removing sulfur-containing thiophene compounds from crude oil.
"We were amazed to discover how mobile the nickel atoms were even well below room temperature," says Kushmerick, who had to cool his specimen down to just 4 (degrees) Kelvin above absolute zero and keep it sealed inside his microscope's vacuum chambers to keep the nickel atoms from skimming around the surface in a blur. "Because the bonds of the molybdenum disulfide are already saturated, there is nothing really to hold the nickel firmly in place," Weiss explains. The chemists found that, at 4K, the nickel atoms were so loosely bound they were easy to move around with the fine tip of their microscope's needle.