Pervasiveness of Surface Metal Oxide Phases In Mixed Oxide Catalysts

Meeting Program – October 2012

Israel E. Wachs
Operando Molecular Spectroscopy & Catalysis Laboratory
Department of Chemical Engineering
Lehigh University
Bethlehem, PA 18015 USA

Abstract – Mixed oxide catalytic materials possess two or more metal oxide components as found in bulk mixed metal oxides (stoichiometric oxides as well as solid solutions), polyoxo metalates (POMs), molecular sieves, zeolites, clays, hydrotalcites and supported metal oxides. Although it is now well established that two-dimensional surface metal oxide phases are present for supported metal oxides on traditional supports (e.g., Al2O3, TiO2, ZrO2, SiO2, etc.), it is not currently appreciated that such surface metal oxide species or phases are also present for other types of mixed oxides. For example, recent surface analyses have demonstrated that stoichiometric bulk mixed metal oxides also possess surface metal oxide phases that control their catalytic activity. For example, the catalytic active sites for methanol oxidation to formaldehyde over the bulk Fe2(MoO4)3 mixed oxide catalyst are surface MoOx species and not the bulk Fe2(MoO4)3 phase as previously thought in the catalysis literature. The nanometer sized clusters in POMs also possess surface species when a second metal oxide component is introduced (e.g., H3+xPW12-xMxO40). Deposition of metal oxides into molecular sieves, zeolites, clays and hydrotalcites also results in the metal oxide additive usually being present as surface metal oxide species that are the catalytic active sites for many redox and acid reactions. The formation of these surface metal oxide phases is driven by their low surface free energy and low Tammann temperature for many metal oxides of interest in catalysis (e.g., VOx, MoOx, CrOx, ReOx, WOx, etc.).
Biography – Israel E. Wachs received his undergraduate education at The City College of The City University of New York where he graduated with a B.E. (ChE) in June, 1973. He received several recognitions upon graduation (AIChE Award for Outstanding Senior, Heller Memorial Award for Outstanding Scholastic Achievement, and White ChE Alumni Award). He continued his graduate ChE education at Stanford University under the mentorship of Professor Robert J. Madix in the area of surface science, and graduated with a PhD (ChE) in 1978. His research findings are considered the first application of surface science to catalysis, and his thesis publications are extensively cited in the surface science and catalysis literature.
INDUSTRIAL YEARS (1977-1986) – Israel joined Exxon Research & Engineering Company in their Corporate Research Labs towards the end of 1977. At Exxon, he was involved with many different catalytic technologies over the years (selective oxidation, acid catalysis, synthesis of synthetic fuels, hydrodesulfurization (HDS) and hydrocarbon conversion). He obtained 100 USA and international patents during his industrial career. One of his inventions on the selective oxidation of o-xylene to phthalic anhydride became the leading international industrial catalyst for this technology and is still used around the world. At Exxon, he received the Research Incentive Award for one of his inventions on the synthesis of synthetic fuels and was also selected to be an Exxon Fellow for the spring semester of 1986 at California Institute of Technology (CalTech). He departed for academia at the end of 1986.
ACADEMIC YEARS (1987-present) – He joined the Chemical Engineering Department of Lehigh University in January 1987. At Lehigh, he taught many different courses over the years: Heterogeneous Catalysis, Reactor Engineering, Fluid Mechanics, Professional Development, Unit Operations, Environmental Catalysis, and Air Pollution Control. He set up a world-class catalysis research laboratory focusing on mixed metal oxide catalytic materials and their characterization under reaction conditions (in situ and operando spectroscopy). These studies have established the foundation for the molecular/electronic structure – activity/selectivity relationships and the molecular engineering of mixed metal oxide catalysts. The research performed by Wachs and his students is well known around the world. This is reflected in the many national and international honors he has received over the years as well as ~17,000 citations to his publications with an H-index of 70 (one of the highest among heterogeneous catalysis researchers).

The current focus of Wachs’ catalysis laboratory is to develop catalyst characterization techniques under reaction conditions, referred to as operando spectroscopy in the recent literature. The term operando spectroscopy implies that the catalyst characterization information is being conducted simultaneously with online product analysis. Along these lines, Professor Wachs has developed instrumentation that can simultaneously obtain Raman, IR and UV-vis spectroscopic information and product analysis with an online mass spectrometer/GC system. This cutting-edge instrument is allowing Professor Wachs’ catalysis research group to rapidly develop molecular/electronic structure – catalytic activity/selectivity relationships for many different catalytic materials and reactions (selective hydrocarbon oxidation, hydrocarbon conversion with solid acid catalysts, gas-to-liquids, photocatalytic splitting of water, enzyme catalysis, CO2 capture, WGS, nanocatalysis, rational catalyst design, etc.).