Chemical & Chemical Engineering News (80th Anniversary Issue), Vol. 81, No. 36, 2003, Sept. Edited by X. Lu Introduction

In John Ekerdt's lab at the University of Texas, Austin, we were studying the formation of methanol from synthesis gas, CO and H₂, over a zirconia solid catalyst. The postdoc who worked on the problem before me had identified many surface species that form on zirconia in the presence of synthesis gas. The intermediates that played a role in the route from synthesis gas to methanol were formate and methoxide. The methoxide was a methyl group attached to an oxygen that was attached to the surface through a zirconium. The formate was attached to surface zirconium through two oxygens. In our temperature-programmed desorption work--the method in which we studied this reaction--methanol was made only when a small amount of water was added to the synthesis gas. Without water, the CO and H₂ made only methane.

The key to a better understanding of the methanol-formation mechanism would come from knowing where the oxygen in the methanol came from. Was it the water? It certainly seemed the obvious choice. With my vial of H₂¹⁸O, I was thrilled that for my first independent experiment in graduate school, I was going to be just like Melvin Calvin. I was going to find out where the oxygen came from. Okay, so this wasn't photosynthesis, and I was not likely to win the Nobel Prize. Nonetheless, I somehow felt a connection with science like I never had before. I was going to find out what happened to tiny atoms on surfaces--an unbelievable feat for this once-political-science major!

I marched into my lab early on a Saturday morning, knowing that, by the end of the day, I would know where the oxygen came from. The working hypothesis was that since methanol formed only when water was present, the oxygen in the methanol came from the water. This would be demonstrated by the formation of all labeled CH₃¹⁸OH. A second, much less likely possibility, was that the water was incorporated in the intermediate formate. In that case, the methanol would be 50% CH₃¹⁶OH and 50% CH₃¹⁸OH.

I was dumbfounded by the results. They were unequivocal and unexpected: It turned out there was not a drop of ¹⁸O in the methanol. The water appeared to break the methoxide bond between the O–Zr to give methanol. When water was not around, the bond between the C–O of the methoxide broke, leading to methane. It was almost like a substitution reaction was occurring between the water and the methoxide. Later experimentation confirmed and further defined the synthesis gas mechanisms over zirconia and the pivotal role the O–Zr bond plays.

I walked into my adviser's office Monday morning and proudly announced that I had been like Melvin Calvin during the weekend: I had figured out where the oxygen came from. But more than learning the source of oxygen, that weekend I had been hooked by research. I had learned the secrets of things I could not see, I had been surprised by nature, and figuring it all out was better than any puzzle I had ever done. Eventually, my plans for a master's degree turned into a Ph.D. To this day, when I'm asked why I got a Ph.D., I think back to that first weekend I spent with zirconia.

As my long relationship with zirconia was winding up, I wondered if it would be appropriate to ask my fiancé for a fabulous engagement ring of cubic zirconia stones of many colors. He said his family would never understand if he gave his wife-to-be a cubic zirconia ring. (Not everyone understands the love between a researcher and her first catalyst.) I settled for a sapphire. A diamond would have been just a cheap imitation.

Nancy B. Jackson is manager of the Chemical & Biological Sensing, Imaging & Analysis Department at Sandia National Laboratories. She is still learning the secrets of things she cannot see and is still often surprised by nature.

ZIRCONIUM AT A GLANCE

Name: From the Persianzargun,meaning goldlike, a common color of the gemstone now known as zircon.

Atomic mass: 91.22.

History: Zircon has been known since ancient times. The mineral was not known to contain a new element until Martin H. Klaproth discovered it in 1789. The impure metal was first isolated by Jöns Jacob Berzelius in 1824.

Occurrence:Most zirconium is obtained from the minerals zircon and baddeleyite. Also found in abundance in S-type stars and moon rocks.

Appearance: Grayish white, lustrous metal. Chemically, zirconium is difficult to separate from hafnium.

Behavior: When finely divided, the metal may ignite spontaneously in air. The solid metal is very heat and corrosion resistant.

Uses: A key component of space vehicle parts because of its resistance to high temperatures. Zirconium has a low absorption cross section for neutrons, and is therefore used for nuclear energy applications. The commercial nuclear power industry uses more than 90% of the zirconium metal produced. Zirconium carbonate is used in poison ivy lotions and zircon is frequently used in jewelry.

HAFNIUM

ERIC SCERRI, UNIVERSITY OF CALIFORNIA, LOS ANGELES

Until recently, philosophers of science have usually concentrated their attention on physics and biology while carefully avoiding chemistry. One major exception seems to have been a philosopher who is arguably the most outstanding among them, namely Sir Karl Popper. Popper often mentioned chemical issues, including an article in which he referred to the discovery of element 72, or hafnium as it subsequently became known.

This element later took on a special significance for me as a Ph.D. student working on a thesis in the philosophy of chemistry. More important, it led to my meeting Popper at his home in London and my having a three-hour audience with this great man at a stage in his life when he had gone into seclusion. But before returning to my meeting with him, let me say something about hafnium and the scientific issue at stake.

Following Henry Moseley's establishment of an experimental technique for placing the elements in a definite sequence in 1914, scientists realized that precisely seven elements remained to be discovered. One of them was element 72. Gradually, some of these missing elements were isolated, but element 72 remained elusive. The story of the eventual discovery of element 72 has been told many times, but it is almost invariably incorrect.

According to the popular story, the chemists of the day believed that hafnium would be a rare-earth element. Meanwhile, the physicist Niels Bohr, who first applied the quantum theory to study atoms and the periodic system, is usually credited with having correctly predicted that hafnium would in fact be a transition element. Moreover, he is supposed to have instructed his assistants Dirk Coster and Georg Karl von Hevesy to search for the element among the ores of zirconium, where they indeed discovered it.

The episode is taken as an early vindication of the quantum theoretical approach to the explanation of the periodic system. Unfortunately, this popular account is incorrect. And yet it was this version that Popper used many years later to make an even grander claim that this represented the best illustration of the reduction of chemistry to quantum theory.

Meanwhile, I was researching the question of the reduction of chemistry to quantum theory and was being advised by the son of the radiochemist Fritz Paneth, who provided me with some of his father's scientific correspondence. These documents showed that it was not Bohr who had suggested to his assistants that they might look for hafnium in the ores of zirconium. The suggestion had actually been made by the elder Paneth, a chemist with little interest in quantum theory, through purely chemical arguments.

Upon further investigation, I found out that not all chemists had in fact expected that hafnium would be a rare-earth element [Ann. Sci., 51, 137 (1994)]. For example, Julius Thomsen, a Danish chemist who is known to have influenced Bohr, was one of the first to correctly predict, as early as 1895, that element 72 would be a transition metal. Similarly, the English chemist C. R. Bury in 1921 not only predicted the chemical nature of this element but even published its correct electronic configuration before Bohr ventured to do so in 1923.

CROSS-HATCHED A heat-tinted hafnium-crystal bar.