Constructing and controlling of highly dispersed metallic sites for catalysis

It is well established that the high dispersion of active catalyst is vital to determine the performance in heterogeneous catalysis after decades of research on nanomaterials. Since the minimum scale for catalytic species is the single-atom metal with isolated metal atoms singly dispersed on, and/or coordinated with the surface atoms of some suitable supports, explosive growth of research on atomically dispersed metal catalysts has emerged especially in frontier heterogeneous catalysis. Such highly dispersed metallic sites (HDMS) imitate the function of site-directed mutagenesis in enzymology, not only maximizing the efficiency of metal atom of interest, but also offering a possibility to achieve the highest catalytic activity and selectivity and make up the gap between heterogeneous and homogeneous catalysis. However, the formidable challenge lies in that with the decreasing size of metal particles or the decreased coordination of metal atoms, the surface free energy of metals is significantly increased, which would lead to serious aggregation of the intended single-atom dispersed catalysts. Therefore, appropriate approaches to construct HDMS and control the HDMS in good homogeneity are importantly necessary to realize the fantastic catalytic activity of HDMS. Problems lie in how to synthesize precisely site-isolated supported metals and how to make sure the metals bond selectively to specific support surface sites. In this review, we aim to assess the above issues via summarizing the key recent progress on HDMS constructing and controlling in terms of the supports and metal precursors engineering, as well as the known interactions between the support and HDMS. We believe that the summary and discussion in the review will lead to a better understanding of HDMS configuration and constructing, and even shed light on novel design for new HDMS based on the discovered interactions between the support and HDMS. We also give a prospect for the future research on HDMS, with emphasizing on the emergence of new fabrication for HDMS with improved catalysts' thermal stability and possibility for industrial application. (C) 2018 Elsevier Ltd. All rights reserved.