Mechanistic Understanding and the Rational Design of Sinter-Resistant Heterogeneous Catalysts

Abstract

The activity and selectivity of heterogeneous catalysts are strong functions of the morphology of the catalytic active phase, which governs both the density and type of active sites. To realize materials with the desired reactivity, cutting-edge catalysts are often the product of novel synthetic strategies and advanced computational studies. Combining these approaches allows for the prediction and fabrication of active motifs in a directed manner. However, catalyst active phases are ordinarily in the nanometer or atomic regime, and small morphological changes can result in large differences in catalytic properties. Given painstaking efforts to design and fabricate active materials at the nanoscale, it is essential that these engineered structures and superior catalytic properties are preserved during working conditions. The stability of a highly active catalyst morphology is crucial for long-term, sustained activity, especially for industrial applications. Unfortunately, catalyst sintering, or processes in which active surface area is lost due to irreversible agglomeration of atomic species or particles, inevitably leads to reduced active surface area and decreased catalytic activity. This problem has led to the development of many schemes, applied with varying degrees of success, which attempt to counteract these aging processes. Undoubtedly, for the directed development of stable, sinter-resistant, heterogeneous catalysts, a fundamental understanding of the species and mechanisms contributing to sintering processes is required. To highlight the importance of fundamental mechanistic understanding of sintering processes, the first portion of this perspective highlights recent approaches to characterize sintering dynamics in heterogeneous catalysts. Next, we showcase recent examples illustrating intentional measures taken to protect against particular sintering mechanisms. We believe that by reviewing examples with mechanistic understanding of these aging phenomena, we can select approaches with the highest probability of successful application to new catalytic systems. These approaches are divided into two main categories: chemical approaches, which are based on modification of the chemistry of the catalytic materials, and physical approaches, based on increased physical barriers to sintering. Our goal is to stimulate more work both on the fundamental understanding of sintering mechanisms, and on the production of stable catalysts by directly targeting and suppressing specific sintering processes.