The following is an essay by Miguel A. Bañares
The American Chemical Society organized a symposium celebrating the three decades of Professor Israel E. Wachs in academia (January 1987 – January 2017) at its 252nd annual national meeting in Philadelphia on August 21-25, 2016.
Wachs, the G. Whitney Snyder Distinguished Professor of chemical and biomolecular engineering, has established a world class research laboratory in catalysis at Lehigh University. I had the honor, shared with Jonas Baltrusaitis (assistant professor of the department of chemical and biomolecular engineering), to organize this memorable symposium.
Contributions came from those who have been his former students, postdocs and colleagues throughout these three decades at Lehigh University. Professor Wachs has graduated ~35 PhD students, ~15 MS students and hosted ~15 post-docs over the years at Lehigh. Participants came from all over the world (South America, China, India, Europe and USA) to praise the positive impacts that training and collaborating with Professor Wachs has had on their career trajectories. For example, (i) Dr. Charles A. Roberts develops sustainable automotive catalysts at Toyota (USA), (ii) Dr. Xingtao Gao discovers new Fluid Catalytic Cracking (FCC) catalysts that reduce sulfur oxide acid rain emissions during gasoline production at BASF (USA), and (iii) Dr. Soren Rasmussen designs new catalysts for reduction of nitrogen oxide acid gas emissions from electric power plants and diesel trucks at Haldor-Topsoe (Denmark). Although some individuals could not attend because of work commitments, many of Professor Wachs’ students have gone on to work in catalysis activities for many international corporations involved in developing catalysts for air pollution control (Johnson-Matthey, Cummins, Kocat, etc.), manufacture of chemicals (Linde, Dow, Lyondell-Bassel, Huntsman Chemicals, ABB Lummus, Reliance, etc.), pharmaceutical production (Bristol-Meyers-Squibb, Wilmington Pharmaceuticals, etc.) and catalytic sensors (Scientific Instruments). In addition, 16 of Professor Wachs’ former graduate students and postdocs have gone onto successful academic and national laboratory positions (5 in USA, 4 in Europe, 2 in China, 2 in India, 1 in Taiwan, 1 in Mexico and 1 in Argentina).
Prof. Wachs received his B.E. degree in Chemical Engineering at The City College of The City University of New York and his Ph.D. with Professor Robert J. Madix at Stanford University. After graduating from the “Stanford Catalysis School” (Madix-Boudart), he was inspired to further advance the understanding of heterogeneous catalysis. Wachs studied catalysis in a land of earthquakes in California, which probably endowed him with a unique capability for groundbreaking research. His vision has always spanned from understanding catalysts at the molecular level and transferring this fundamental knowledge to engineering new and efficient catalysts that can be implemented at an industrial scale. With such a perspective, he joined the Corporate Research Science Laboratory of Exxon Research & Engineering Company in NJ where he obtained his “industrial PhD” experience and subsequently joined Lehigh University in January of 1987.
Professor Wachs’ vision of catalysis research was to understand the catalyst surface structure and relate this key information to the catalytic performance since this is where molecules interact with the catalyst and the catalytic reaction takes place for heterogeneous catalysts. He came to Lehigh University with a mission, he wanted to devote his career to reach the molecular level understanding of the structure of supported metal oxide catalysts (catalyst where the active metal oxide is present as a surface layer on an oxide support). This understanding was not known at the time despite major efforts in the literature by others and was intended to be a lifetime research goal. Little did he know that he would be able to accomplish his lifetime mission in only a few years. His seminal research determined the molecular structures of supported metal oxides (mainly the transition metal oxides of rhenium, chromium, molybdenum, tungsten, vanadium, niobium, tantalum, as well as others). His vision and the application of Raman spectroscopy, in conjunction with complementary techniques, were instrumental for this groundbreaking achievement.
His first significant achievement at Lehigh University was to endow Raman with a new power. Raman is an excellent tool to understand the molecular structures of supported metal oxides, which he knew. He demonstrated, however, that Raman can also be an excellent tool to measure molecular bonds distances of some functional groups. He developed the “diatomic approximation” that allows correlating the Raman vibrational frequency of metal-oxygen bonds with the corresponding interatomic bond lengths, with an accuracy comparable to that that reached at large synchrotron facilities. A simple spectrum taken in seconds in the lab can deliver such detailed information rather than traveling and getting precious time to access a synchrotron facility.
Professor Wachs soon demonstrated that most of the confusion in the literature about supported metal oxide catalysts was due to the effect of ambient moisture. Supported metal oxides, even if they appear to the eye as dry loose powder, are extensively hydrated with water accounting for ~10-20 % of their weight. The supported metal oxides phases are not only hydrated, but are totally solvated and follow their aqueous phase chemistry rules. The structure of supported metal oxides under ambient conditions is, thus, determined by the aqueous metal oxide concentration and pH.
This led to a significant leap in understanding the molecular structures of hydrated supported metal oxide catalysts. Heterogeneous catalysts do not typically operate at room temperature or in ambient environments, but at elevated temperatures and environments that digress from ambient conditions. This led to research on the development of in situ Raman spectroscopy to investigate the structural changes taking place at non-ambient conditions. The first approach was comparing ambient (hydrated) catalysts with in situ dehydrated catalysts. Such structures are far more relevant to those exhibited by a supported oxide at 400ºF or above, when they are at work during reactions. This work allowed him to teach us how supported metal oxides really look like under dehydrated conditions, and how the support and additives modify the surface metal structures. The metal oxide loading of supported oxides results increases the surface density of the surface species, leading to a progressive crowding effect that eventually leads to the formation of nanocrystalline metal oxide aggregates. That dispersion limit loading is known as “monolayer coverage”. Molecularly dispersed oxides are most active and his research has focus on these.
The next step was to look at the catalysts in situ, i.e., under conditions relevant to catalysis, in reaction feed flow and at reaction temperature. Those studies helped us understand the state of the catalysts at work, and how it changes. This is instrumental to understand the mechanisms of catalyst operation, activation and deactivation. Ultimately, Prof. Wachs got involved in the operando spectroscopy methodology, which monitors the state of the catalyst during genuine catalytic operation. Operando methodology brings simultaneous determination of both molecular structure and activity/selectivity data. That is all you need to understand catalysis. Probably, no researcher has ever gone so deep into the surface.
This has ultimately been Israel E. Wachs achievement in catalysis science: getting to know the catalysts under actual working conditions. Very often, we see a typo in literature when authors refers to his work, “Isreal” is quite often seen instead of “Israel”; however, it is my impression that it is a tribute rather than a typo since ISREAL may stand for IN SITU REAL.
His impact and recognition is enormous, several ground breaking contributions have made him a major mover and shaker in catalysis. He’s being cited more than 25,000 times and his 300 publications have an h index of >90, which is telling us that one third of his publications are extremely highly cited. That impact brings recognition by his peers, there are many awards, I only want to highlight few representative ones. Such as the EPA Clean Air Excellence Award, EPA (2001); the G. Olah Award in Petroleum or Hydrocarbon Chemistry, American Chemical Society (2008), the Alexander von Humboldt Award, AvH Foundation-Germany (2012), the Vanadis Award, International Vanadium Chemistry Society (2012) and most recently the R.H. Wilhelm Award in Chemical Reaction Engineering, AIChE (2016). These awards span through many years and disciplines, also they recognize very fundamental and very applied research work.
Prof. Wachs is never satisfied, he also wanted to get into the fundamental rationale behind catalysis. To do so he has engaged with many groups to achieve this objective, and this is another characteristic of Israel’s research: “collaboration”. Collaboration has been a major keyword. A single technique, a single vision may not bring the complete insight, and Israel has created multiple highly synergetic collaborations with researchers (experimentalists and theoreticians) across the States and worldwide to the point that I strongly believe that he is the most international catalysis scientist in the United States.
The participants of the symposium clearly underline his international character, in addition to many contributions from the USA, we also had participants from India, China, Taiwan, Japan, Argentina, Turkey, the Netherlands, France, Denmark and Spain.
The symposium had ExxonMobil as a major sponsor, along with the strong financial support from Harrick, Horiba, American Chemical Society, PQ corporation, Scientific Design Company and help from DuPont and Grace.
The insight developed by Israel on supported metal oxides lays the ground to unravel the actual nature of the surfaces of bulk mixed oxide catalysts, which also represent a significant fraction of supported oxides. Clearly, catalysis science has a “before” and an “after” with respect to Prof. Wachs’ contributions. Is this where we stop? No, he is still pushing ahead, with the same enthusiasm and zest than at the beginning, working with him is not only most rewarding as a scientist, but it is also fun. So, stay tuned and wait for new ideas.
Miguel A. Bañares is currently a Full Research Professor at the Institute for Catalysis, CSIC (Spanish National Research Council) in Madrid, Associate Editor for Catalysis Today (Elsevier) and was postdoc under Wachs.
