Acetylene Hydrogenation on Alloy Catalysts Spanning Ternary Alloy Composition Space

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

Catalysts are used to accelerate production of chemicals in industrial processes, greatly increasing the efficiency of production and providing significant energy savings in chemical manufacturing. Multicomponent alloys, homogeneous mixtures of two or more metals, are used as catalysts in these reactions because they are more effective than any of the pure metal components by itself. The relative metal compositions are variable over a wide range, which presents a challenge in designing alloy catalysts in finding the optimal relative amounts of each metal component for maximum catalyst efficiency. This can become a tedious and time-consuming research activity because it requires the preparation, characterization and catalytic evaluation of hundreds of different alloy catalysts, each with a different composition. Dr. Gellman has invented a rapid, high-throughput method to accelerate the study of three-component (ternary) alloy catalysts over a wide range of possible compositions. Dr. Gellman fabricates a single material in which the composition of the alloy is varied continuously along the material surface. He then uses a number of state-of-the-art spatially-resolved analytical tools. Each measurement probes a catalyst alloy with a different composition. This methods allows 100 catalyst compositions to be prepared at once, then characterized and studied in a fraction of the time that sequential preparation of each composition would allow. Dr. Gellman is using his high-throughput method to understand how the composition of alloy catalysts influences the kinetics and selectivity of acetylene (HCCH) hydrogenation to ethylene (H2CCH2), an important chemical process in polymer production. Ultimately, Dr. Gellman's work may lead to improvement of alloy catalysts for numerous applications and may contribute to clean energy technologies for its relevance to hydrocarbon conversion. In addition to his advancement of the field of catalysis, Dr. Gellman is making broader impacts in his work with students. He mentors female undergraduate students in research to encourage their interest in pursuing advanced degrees in the STEM fields. He also is engaged in public education activities as part of his role as co-Director of the Carnegie Mellon University's Scott Institute for Energy Innovation. Understanding the complexity of multicomponent alloy catalysts is confounded by the experimental challenges of measuring the physical characteristics and the catalytic activities of alloy materials as a function of multidimensional composition. With funding from the Chemical Catalysis Program of the Chemistry Division and the Catalysis and Biocatalysis Program of the Division of Chemical, Bioengineering, Environment and Transport Systems Division, Dr. Andrew Gellman of Carnegie Mellon University addresses this challenge by using a unique set of high-throughput methods developed in his lab. The analysis employs an alloy film containing all possible compositions of alloys in a process called Composition Spread Alloy Films (CSAF). Ternary alloys, CuxAuyPd1-x-y, CuxAgyPd(1-x-y), and AgxAuyPd(1-x-y), are fabricated with x and y varied over the entire compositional range within an approximately 1 cm2 area sample size. Spatially resolved surface analysis tools are used to map alloy characteristics, including bulk composition, surface composition and valence electronic structure, as a function of composition space. A unique, 100 channel microreactor array is then used to make parallel measurements of the kinetics and selectivities of several catalytic processes, HD exchange, ethylene hydrogenation and acetylene hydrogenation, at 100 different alloy compositions. Microkinetic analysis is used to extract the fundamental reaction parameters for elementary mechanistic steps. These measurements establish correlations among kinetic parameters and alloy characteristics and yield insight into rate dependence of individual elementary steps with alloy composition. In addition to his advancement of the field of catalysis, Dr. Gellman is making broader impacts in his work with students. He mentors undergraduate female students in research to encourage their interest in pursuing advanced degrees in the STEM fields. He also is engaged in public education activities as part of his role as co-Director of the Carnegie Mellon University's Scott Institute for Energy Innovation.