Consequences of Acid Strength and Solvation in Catalysis Mediated by Ion-pair Transition States

2012 Spring Symposium

Enrique Iglesia
Department of Chemical Engineering
University of California at Berkeley and Chemical Sciences Division
E.O. Lawrence Berkeley National Laboratory

Abstract — The rate and selectivity of reactions catalyzed by acids depend on the stability of ion-pairs at transition states that mediate kinetically-relevant steps. Rates and selectivities for alkanol dehydration and homologation, alkene and cycloalkene isomerization, and alkoxide scission and hydrogen transfer on polyoxometalate and zeolitic acids show that sensitivity to acid strength reflects differences in the amount and diffuseness of the charge in the relevant precursors and the transition states. The effects of solvation by confinement on rates and selectivities depend, in turn, on their respective differences in size. The known structures of these acids allow rigorous comparisons between experiment and theory, which confirm the mechanistic interpretations of rate data and the relevance of deprotonation energies as theoretical proxies of acid strength. These studies and insights suggest a rigorous reactivity-based ranking of acid strength that can be used to assess the strength of solid acids with uncertain or non-uniform structures.

Speaker’s Biography — Enrique Iglesia is the Theodore Vermeulen Chair in Chemical Engineering at the University of California at Berkeley and a Faculty Senior Scientist in the Lawrence Berkeley National Laboratory. He received his B.S. from Princeton University and his Ph.D. degree from Stanford University with Professor Michel Boudart and joined the Berkeley faculty in 1993 after 12 years in research and leadership positions at the Corporate Research Labs of Exxon. He has served as Editor-in-Chief of Journal of Catalysis and is the President of the North American Catalysis Society and the Director of the Berkeley Catalysis Center. He has co-authored more than 300 articles in the leading journals in chemistry and chemical engineering and is a co-inventor in 38 U.S. patents. He is a member of the National Academy of Engineering and a Fellow of the American Chemical Society. His research has been recognized with the Somorjai and Olah Awards of the American Chemical Society, the Award for Excellence in Natural Gas Conversion, the Alpha Chi Sigma and Wilhelm awards of the American Institute of Chemical Engineers, the Emmett and Burwell Awards of the Catalysis Society, the Tanabe Prize in Acid-Base Catalysis, the Canadian Chemical Society Cross Canada Lectureship, and the Francois Gault Award of the European Federation of Catalysis Societies. His research interests include the synthesis and structural and mechanistic characterization of novel inorganic solids useful as catalysts in chemical reactions of critical importance in energy conversion, sustainable synthesis of energy carriers and petrochemicals, and pollution prevention and environmental control.

Formic Acid Decomposition on Bulk Metal Catalysts

2012 Spring Symposium

Yadan Tang, Charles A. Roberts, Israel Wachs
Department of Chemical Engineering
Lehigh University

Abstract — Measured trends in catalytic reactivity over varying metal catalysts have been used to facilitate the optimization of bimetallic catalysts.[1] An important example of such a trend is the Sachtler-Fahrenfort volcano curve, in which reactivity of metal surfaces for formic acid decomposition is plotted against the stability of intermediates, i.e. the bulk heat of formation of the formate on a specific metal surface.[2] It is questionable, however, to correlate a bulk property with catalytic reactivity, a process that occurs exclusively at the surface. The current study investigates the correlation between formic acid decomposition and reactivity of bulk metal catalysts (i.e. Fe, Ru, Pd, Pt, Au, Ag, Ni, Co, and Cu) using modern techniques such as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed surface reaction (TPSR) spectroscopy. In situ DRIFTS monitors the formate structure on the surface of bulk metal catalysts during the adsorption and decomposition of formic acid. By utilizing a temperature ramping procedure, in situ DRIFTS also provides insights into thermal stability of adsorbed formates. TPSR spectroscopy detects the temperature at which the peak activity for decomposition of the adsorbed formates occurs, therefore providing a measure of the reactivity of the metal surface. In situ DRIFTS and TPSR spectroscopy experiments agree with the previous reported finding that the decomposition of HCOOH proceeds via two steps: 1) formation of surface adsorbed formate (HCOO-M) intermediates; and 2) decomposition of formate intermediates into gas phase products such as CO, CO2, H2 and H2O.[3] The formate structure on various metal catalysts are identified and assigned based on a previous study on formic acid via high resolution electron energy loss spectroscopy (HREELs).[3] The current study finds that the formate species on Fe, Ru, Pd, Pt and Au are bridged; on Co and Ni are monodentate; and on Cu and Ag are converted from monodentate to bridged at higher temperature in agreement with HREELs work on both Cu(100) and Ag(110).[4] The TPSR decomposition temperatures, Tp, were plotted versus the bulk heat of formation of formates reported by Sachtler and Farenfort[2]. Rather than a volcano trend, the plot is observed to contain two distinct linear relationships indicating that trends in reactivity of metals should be evaluated based on surface properties rather than bulk.

[1] Jacobsen, Claus J. H., Dahl, S., Clausen, Bjerne S., Bahn, S., Logadottir, A., and Nørskov, Jens K. J. Am. Chem. Soc. 123, 8404 (2001).
[2] Sachtler, W.M.H., and Fahrenfort, J., in “Proceedings, 2nd International Congress on Catalysis, Paris, 1960,” p.831. Technip, Paris, 1961.
[3] Columbia, M.R., Thiel, P.A. J. Eelectroanalytical Chem. 369, 1–14 (1994).
[4] Sexton,B.A. Surf. Sci., 88, 319 (1979).

Speaker’s Biography — Yadan Tang is a graduate student in Chemistry at Lehigh University, advised by Professor Israel Wachs. She received her B.S. in Material Science and Engineering Department at East China Univ. of Science and Technology in 2006. She received her M.S. in Chemistry Department at Lehigh Univ in 2010. Since joined in Wachs group in 2011, she has been involved in formic acid decomposition on bulk metal catalyst and supported metal oxides on zeolite.

Multifunctional Nanostructured Catalysts: From New Synthetic Methods to their Potential Applications

2012 Spring Symposium

Tewodros Asefa
Department of Chemistry and Chemical Biology, and Department of Chemical and Biochemical Engineering
Rutgers, The State University of New Jersey

Abstract — The development of novel nanomaterials with unique structures enables fundamental studies at the nanoscale, which can lead to various interesting applications. In this talk, efforts by my research group over the last few years on three different, but related, areas will be discussed. In the first part, I will describe how the rational assembly of multifunctional nanostructured materials composed of metal oxides, carbon nanofibers, metallic nanoparticles, organocatalysts or organometallic complexes leads to novel nanocatalysts for efficient synergistic catalytic reactions or for multi-step in one-pot tandem reactions of various organic compounds. The effects of how two or multiple catalytic groups that are co-placed within nanoscale cavities do synergistically catalyze reactions will be demonstrated. Furthermore, by placing these catalysts in fixed bed reactors, continuous reactions to selective products has been demonstrated.

Speaker’s Biography — Teddy Asefa was born in Ethiopia where he also completed his B.Sc. degree in Chemistry with distinction in 1992 from Addis Ababa University, Ethiopia. He came to the United States as a Fulbright Scholar in 1996 to do his graduate study. After a brief stay at the University of Delaware, he joined the Institute for Lasers, Photonics and Biophotonics (ILPB) at the State University of New York at Buffalo to complete his M.Sc. in Chemistry in 1998 with Professor Paras N. Prasad. Teddy, then, went to Toronto, Canada to complete his Ph.D. at the University of Toronto in 2002 with Professor Geoffrey A. Ozin. While at Toronto, he has co-invented new classes of nanocomposite materials called Periodic Mesoporous Organosilicas (PMOs) that are currently drawing wide range of interest world-wide. He was then an invited Miller Fellowship nominee by Professor Peidong Yang at the University of California at Berkeley and a post-doctoral fellow at McGill University with Professor R. Bruce Lennox. Teddy then joined the faculty at Syracuse University in the summer of 2005 and served as an Assistant Professor of Chemistry for four years before moving to Rutgers as an Associate Professor. He is currently a joint Associate Professor in the Department of Chemistry and Chemical Biology and the Department of Chemical and Biochemical Engineering at Rutgers University at New Brunswick. He is also a member of the Rutgers Institute for Materials, Devices, and Nanotechnology (IAMDN) and the Rutgers Energy Institute (REI). In December 2009, he helped putting together the newly formed Rutgers Catalysis Research Center (RCRC). His group at Rutgers is involved in the development of synthetic methods to a wide array of functional nanomaterials and the investigation of their potential applications in catalysis, targeted delivery of drugs at specific cells, nanocytotoxicity, solar-cells, and environmental remediation. He is an NSF CAREER Awardee, holds NSF Creativity Award, and is a recent National Science Foundation American Competitiveness Fellow (NSF-ACIF) for 2010, and also is a recipient of multiple federal and local research grants and also serves as a panelist for several federal and international agencies. He was recently awarded the Rutgers Board of Trustees Fellowships for Scholarly excellence, the highest honor given to young professors at Rutgers.

Selective Hydrodeoxygenation of m-Cresol over Bifunctional Metal-Acid Catalysts

2012 Spring Symposium

Andrew Foster, Phuong Do, Jingguang Chen and Raul F. Lobo
Department of Chemical and Biomolecular Engineering
University of Delaware

Abstract — Upgrading of biomass derived pyrolysis oil is necessary to produce liquid fuels that can seamlessly be integrated with the current transportation fuel infrastructure and hydrodeoxygenation (HDO) is one of the most effective methods to accomplish this task. In this talk we will describe the HDO of m-cresol (3-methylphenol) investigate as a model reaction for the HDO of the phenolic fraction of pyrolysis oil of lignocellulosic biomass. To facilitate selective removal of oxygen without further hydrogenation of unsaturated C-C bonds, experiments were conducted at low hydrogen pressures. Kinetic studies in a plug-flow reactor show that toluene can be selectively produced from m-cresol over a Pt/γ-Al2O3 catalyst at pressures as low as 0.5 atm H2 and 533 K. A reaction network has been developed based on investigation of the reactions of m-cresol, and the observed reaction products and intermediates over Pt/γ-Al2O3 and other supports. m-Cresol HDO proceeds by a bifunctional mechanism, requiring metal-catalyzed hydrogenation of the aromatic ring followed by acid-catalyzed dehydration. The degree of hydrogenation of the pool of intermediates prior to dehydration largely determines the resultant product distribution. The effect of the addition of a second metal (Ni and Co) on catalysts activity is also investigated. It is shown that selective production of toluene requires the dehydration to occur before saturation of the aromatic ring.

Speaker Biography — Raul F. Lobo is professor of Chemical Engineering at the University of Delaware and Director of the Center for Catalytic Science and Technology. His research interests span the development of novel porous materials for catalysis and separations, the chemistry of zeolites at high temperatures, the development of novel photocatalysts and the scientific aspects of catalyst synthesis. He has published over one hundred refereed reports and he is co-inventor in three US patents. He obtained his undergraduate degree in Chemical Engineering at the University of Costa Rica and later moved to California to pursue graduate studies in Chemical Engineering at Caltech. He worked for one year at Los Alamos National Laboratory, New Mexico as a postdoctoral fellow and started his academic career at the Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware in 1995.

Engineering Molecular Transformations over Supported Catalysts for Sustainable Energy Conversion

2012 Spring Symposium

Matthew Neurock
Departments of Chemical Engineering and Chemistry
University of Virginia

Abstract — Future strategies for energy production will undoubtedly require processes and materials that can efficiently convert sustainable resources into fuels and chemicals. While nature’s enzymes elegantly integrate highly active centers together with adaptive nanoscale environments in order to exquisitely control the catalytic transformation of molecules to specific products, they are difficult to incorporate into large scale industrial processes and limited in terms of their stability. The design of more robust heterogeneous catalytic materials that can mimic enzyme behavior, however, has been hindered by our limited understanding of how such transformations proceed over inorganic materials. The tremendous advances in ab initio theoretical methods along with high performance computing that have occurred over the past two decades provide unprecedented ability to track these molecular transformations and how they proceed at specific sites and within particular environments. This information together with the unique abilities to follow such transformations spectroscopically is enabling the design of unique atomic surface ensembles and nanoscale reaction environment that can efficiently catalyze specific molecular transformations. This talk presents the advances that have occurred within catalysis that have enabled this evolution of molecular engineering and discuss its applications to energy conversion strategies as well as chemical syntheses. More specifically, we will discuss the application to selective oxidation and hydrogenation over supported metals for biomass conversion as well as C-C bond formation reactions.

Speaker’s Biography — Matt Neurock is the Alice M. and Guy A. Wilson Professor of Chemical Engineering and Professor of Chemistry at the University of Virginia. He joined the faculty in Chemical Engineering at the University of Virginia in 1995 after receiving his Ph.D. from the University of Delaware and working as a postdoctoral Fellow at the Eindhoven University of Technology and at the DuPont Corporate Catalysis Center. He has received various awards for his research in computational catalysis and molecular reaction engineering including the 2007 R.H. Wilhelm Award in Chemical Reaction Engineering from the American Institute of Chemical Engineers and the 2005 Paul H. Emmett Award in Fundamental Catalysis from the North American Catalysis Society. He has co-authored 200 papers, two patents and two books. He is currently an editor for the Journal of Catalysis and serves on the editorial board for Applied Catalysis A: General, Electrocatalysis, and the international advisory board, ChemCatChem.

Commercialisation of a Novel Methyl Methacrylate Process – Catalyst Design and Development

2012 Spring Symposium

David W Johnson
Lucite International UK Ltd

Abstract — A brief outline of Lucite International’s new “Alpha” methyl methacrylate technology is described including process scale up and the first exploitation in Singapore in late 2008. The technology was developed from 0.5g/h lab scale to 500g/h pilot and thence directly to 12te/h commercial scale. The plant was commissioned from first introduction of chemicals to 100% rate within 3 weeks and currently operates at over 16te/h with exceptional reliability.

Two catalytic steps are key to the technology. In the first, carbon monoxide, ethylene and methanol are reacted in solution with a novel palladium phosphine catalyst which gives methyl propionate in 99.9+% selectivity in a continuous process at ppm level palladium concentrations at 100C and 10bar total pressure. The catalyst activity and life is very sensitive to operating conditions. After extensive process development, activities of 15,000 moles/mole Pd/h and life of >1x107moles methyl propionate/mole Pd are routinely achieved on the commercial plant.

The second stage catalyst, composed of caesium/zirconia/silica reacts methyl propionate with formaldehyde at 330C and 1–2barg to form methyl methacrylate (MMA) and water. The selectivity is about 93% to MMA based on methyl propionate and over 80% on formaldehyde fed. The presentation describes some of the steps in development of the catalyst including comparisons with catalysts for similar process disclosed by competitors. A discussion of the mechanism of formation of MMA and byproducts is made in terms of surface reactions between reactants and products. A 2-site model is proposed involving both strongly basic and hydroxylic, weakly acidic sites. Reactions catalysed in byproduct formation include decarboxylations, combined condensation-decarboxylations, hydride transfers and acid catalysis. Lucite has found that competitive catalysts have the wrong balance of acidity and basicity and result generally in high levels of hydride transfer and acid catalysis products.

Speaker’s Biography — The author has a BA (Natural Sciences, Chemistry) from Oxford University a PhD in radiation chemistry and carried out postdoctoral research in LEED/XPS/UPS before joining ICI Ltd in 1977. Within ICI he worked initially on nitrate promoted silver ethylene oxide catalysts followed by 4 years in ICI’s New Science Group studying the structure of novel zeolites synthesised by ICI co-workers. Since 1990 he has worked in the area of MMA process design and led the exploratory research team which defined the Alpha process and currently leads Lucite’s (formerly ICI Acrylics) chemistry team. His current interests are process improvement for the Alpha technology and introduction of biotechnology into MMA manufacture.

Shape Selectivity Revisited: Higher Catalytic Rates in Smaller Zeolite Channels

2011 Spring Symposium

Aditya Bhan
Department of Chemical Engineering and Materials Science
University of Minnesota
Twin Cities

Abstract — Zeolites are crystalline inorganic framework oxides with channel and pocket dimensions typically smaller than 1 nanometer. Their constrained environments are well known to select for chemical reactions via steric mechanisms, typically, by exclusion of molecules or transition states based on size. The strong effects of pore size and shape as they become commensurate with those of reactant species and the concomitant effects on the enthalpy and entropy of adsorption have also been broadly and convincingly noted. We inquire instead, what are the effects of confinement in small channels? In this talk, I will present three examples where reactivity in small 8-membered ring pockets of H-MOR differs from that in larger 12-membered ring channels of MOR.

(i) We show that the apparent effects of proton density and of hydroxyl group environment on DME carbonylation turnover rates reflect instead the remarkable specificity of eight-membered ring zeolite channels in accelerating kinetically relevant *CH3-CO reaction steps.

(ii) In zeolite pores large enough to accommodate ethanol dimers, ethanol preferentially dehydrates via a bimolecular pathway to generate diethyl ether since the formation of ethanol dimeric species is energetically more favorable than the formation of ethanol monomers. In zeolite channels too small to accommodate ethanol dimers, ethanol is selectively dehydrated via a unimolecular reaction pathway to generate ethylene.

(iii) For isomerization reactions of n-hexane, 8-MR channels of H-MOR minimize the free energy of required carbocationic transition states, possibly via partial confinement effects that increase the entropy of the transition state at the expense of the reaction enthalpy. These findings show that confinement in zeolite channels influences rate and selectivity of hydrocarbon reactions more fundamentally than simple considerations of size and shape.

Speaker’s Biography – Aditya Bhan received his Bachelor of Technology (B. Tech.) in Chemical Engineering from IIT Kanpur in 2000. Subsequently, he moved to West Lafayette, Indiana and joined the group of Nick Delgass at Purdue, where he developed microkinetic models to describe propane aromatization on proton- and gallium- form ZSM-5 materials for his PhD. In 2005, he moved to the University of California at Berkeley to pursue post-doctoral studies in Professor Enrique Iglesia’s group to study the kinetics, mechanism, and site requirements of dimethyl ether carbonylation. In September 2007, Dr. Bhan took up his present position as an Assistant Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota. Dr. Bhan leads a research group that focuses on the structural and mechanistic characterization of inorganic molecular sieve catalysts useful in energy conversion and petrochemical synthesis. His research at Minnesota has been recognized with the McKnight Land Grant Professor and 3M Non-tenured Faculty awards.

Catalysis Club of Philadelphia

Promoting the science of catalysis since 1949.

Consequences of Acid Strength and Solvation in Catalysis Mediated by Ion-pair Transition States

2012 Spring Symposium

Formic Acid Decomposition on Bulk Metal Catalysts

2012 Spring Symposium

Multifunctional Nanostructured Catalysts: From New Synthetic Methods to their Potential Applications

2012 Spring Symposium

Selective Hydrodeoxygenation of m-Cresol over Bifunctional Metal-Acid Catalysts

2012 Spring Symposium

Engineering Molecular Transformations over Supported Catalysts for Sustainable Energy Conversion

2012 Spring Symposium

Commercialisation of a Novel Methyl Methacrylate Process – Catalyst Design and Development

Shape Selectivity Revisited: Higher Catalytic Rates in Smaller Zeolite Channels

2011 Spring Symposium