Public Abstract

DE-SC0021008: Experimental and modelling studies of the role of chemical promoters in heterogeneous catalysis

Award Status: Active

Institution: Regents of the University of Michigan, Ann Arbor, MI
UEI: GNJ7BBP73WE9
PM: Schwartz, Viviane

Most Recent Award Date: 05/12/2026
Number of Support Periods: 7
PI: Linic, Suljo

Current Budget Period: 09/01/2026 - 08/31/2027
Current Project Period: 09/01/2026 - 08/31/2029

Public Abstract

Experimental and modeling studies of the role of chemical promoters in heterogeneous catalysis Suljo Linic, University of Michigan, Ann Arbor, MI Heterogeneous catalysts are often solid nanostructures (nanoparticles or zeolite frameworks) that are promoted with various additives. These additives (promoters) are usually introduced in very small amounts (mmol per gram of catalyst) covering a fraction of the catalytically active surface. While these chemical promoters have dramatic impact on the performance of many solid catalysts, in terms of enhancing rates of reactions or improving the selectivity towards the desired products, our understanding of the underlying mechanisms of promotion is rather limited. The central objective of this project is to investigate the role of chemical promoters in catalytic reactions on metal surfaces. We will focus on ethylene epoxidation on promoted silver (Ag) nanoparticle catalysts, one of the largest commercial catalytic processes, as a case study. This process employs Ag nanoparticle catalysts supported on alumina and promoted with Cesium (Cs), Rhenium (Re), Chlorine (Cl) and Molybdenum (Mo). The addition of these promoters significantly enhances the selectivity of the process towards the desired products. The central hypotheses we propose to probe is that chemical promoters (Cl, Cs, Re, …) modulate catalytic outcomes by tuning the surface concentration and electronic character of key intermediates, such as adsorbed oxygen on Ag. Specifically, we will explore this hypothesis by focusing on two limiting cases: (1) determining how single promoters (Cl, Cs, Re) individually modulate oxygen coverage and electronic structure and in doing so impact the outcome of the reaction, and (2) establishing how promoter packages (i.e., a combination of these promoters) generate cooperative or nonlinear effects that cannot be inferred from their isolated behavior. The hypothesis will be tested by deploying operando spectroscopy, reaction kinetics, and advanced first principles simulations. Specifically, we will measure the surface concentration of oxygen and other intermediates on promoted and unpromoted Ag catalysts under reaction conditions using the recently developed operando SERS method. By expressing the rates of selective and unselective pathways directly as functions of measured surface coverages rather than gas-phase partial pressures, we will test our central hypotheses regarding promoter-controlled selectivity. These experiments will be complemented by state-of-the-art neural-network–based simulations that provide first-principles accuracy for realistic catalyst models, enabling us to interpret the experimental findings and propose atomistic descriptions of the mechanism by which promoters impact catalysis. Finally, we will employ a suite of additional microscopy and spectroscopy characterization tools, including newly acquired in-operando x-ray absorption spectroscopy (XAS) capabilities, to probe catalyst structure and electronic properties of key intermediates and thereby rigorously evaluate the mechanistic conclusions. By capturing catalytic materials as they function and establishing transferable mechanistic principles, this project directly advances DOE’s strategic priorities in chemical transformations, data-driven materials discovery, and the development of efficient, selective, and durable catalytic processes.

Experimental and modeling studies of the role of chemical promoters in heterogeneous catalysis

Suljo Linic, University of Michigan, Ann Arbor, MI

Heterogeneous catalysts are often solid nanostructures (nanoparticles or zeolite frameworks) that are promoted with various additives. These additives (promoters) are usually introduced in very small amounts (mmol per gram of catalyst) covering a fraction of the catalytically active surface. While these chemical promoters have dramatic impact on the performance of many solid catalysts, in terms of enhancing rates of reactions or improving the selectivity towards the desired products, our understanding of the underlying mechanisms of promotion is rather limited. The central objective of this project is to investigate the role of chemical promoters in catalytic reactions on metal surfaces. We will focus on ethylene epoxidation on promoted silver (Ag) nanoparticle catalysts, one of the largest commercial catalytic processes, as a case study. This process employs Ag nanoparticle catalysts supported on alumina and promoted with Cesium (Cs), Rhenium (Re), Chlorine (Cl) and Molybdenum (Mo). The addition of these promoters significantly enhances the selectivity of the process towards the desired products.

The central hypotheses we propose to probe is that chemical promoters (Cl, Cs, Re, …) modulate catalytic outcomes by tuning the surface concentration and electronic character of key intermediates, such as adsorbed oxygen on Ag. Specifically, we will explore this hypothesis by focusing on two limiting cases: (1) determining how single promoters (Cl, Cs, Re) individually modulate oxygen coverage and electronic structure and in doing so impact the outcome of the reaction, and (2) establishing how promoter packages (i.e., a combination of these promoters) generate cooperative or nonlinear effects that cannot be inferred from their isolated behavior.

The hypothesis will be tested by deploying operando spectroscopy, reaction kinetics, and advanced first principles simulations. Specifically, we will measure the surface concentration of oxygen and other intermediates on promoted and unpromoted Ag catalysts under reaction conditions using the recently developed operando SERS method. By expressing the rates of selective and unselective pathways directly as functions of measured surface coverages rather than gas-phase partial pressures, we will test our central hypotheses regarding promoter-controlled selectivity. These experiments will be complemented by state-of-the-art neural-network–based simulations that provide first-principles accuracy for realistic catalyst models, enabling us to interpret the experimental findings and propose atomistic descriptions of the mechanism by which promoters impact catalysis. Finally, we will employ a suite of additional microscopy and spectroscopy characterization tools, including newly acquired in-operando x-ray absorption spectroscopy (XAS) capabilities, to probe catalyst structure and electronic properties of key intermediates and thereby rigorously evaluate the mechanistic conclusions.

By capturing catalytic materials as they function and establishing transferable mechanistic principles, this project directly advances DOE’s strategic priorities in chemical transformations, data-driven materials discovery, and the development of efficient, selective, and durable catalytic processes.