Selective hydrogenation of acetylene is an essential step in petrochemical industry. Generally, a trace amount of acetylene (0.5%-2%) in ethylene must be removed by hydrogenation to avoid poisoning of the polymerization catalyst in the following process. Palladium (Pd) based catalysts are widely accepted due to their high activity and selectivity in this reaction than other metals. In addition, the introduction of second metal components, surface modification and other solutions can further improve the ethylene selectivity of Pd. However, Pd-based catalysts suffering from the drawback of high cost. Therefore, design and fabrication of non-precious metal-based catalysts with high-efficiency and low-cost is of great significance.
In the past decades, tremendous progress has been made in the design and fabrication of non-precious metal catalysts for acetylene selective hydrogenation. However, there are still obstacles impeding their utilization, such as low activity, insufficient selectivity and inconvenient preparation technics. Therefore, it is urgent for the design of novel high-efficiency non-precious metal catalysts for acetylene selective hydrogenation, which depends highly on the in-depth understanding of the structure-property relationship. Therefore, an accurate recognition of the catalyst structure is the main issue. Catalyst structure was generally characterized by ex-situ techniques. Unfortunately, most of the catalyst are sensitive to oxygen and would undergo some undesired structural changes under air condition, which block a precise establishment of the structure-property relationship. In-situ techniques are accessible for the characterization of the catalyst structure and its evolution under working conditions. The relevant studies have greatly promoted the recognition of true active structure and novel catalyst design. For instance, our previous work has visualized that the supported PdZn intermetallic structure was induced by the interfacial interstitial H (Angew. Chem. Int. Ed. 2019, 58, 4232).
Inspired by well-recognized interstitial atom governed catalytic behaviors, we propose a new strategy to design and synthesize highly-efficiency nickel (Ni) based catalysts with interstitial atom control for acetylene hydrogenation reaction based on a series of studies (ChemCatChem 2017, 9, 3435; Angew. Chem. Int. Ed. 2019, 58, 4232; Chem. Commun. 2020, 56, 6372) and the collaboration with Prof. Wei Zhang from Jilin University, Prof. Min Wei from Beijing University of Chemical Technology, and Dr. Xing Huang and Dr. Marc-Georg Willinger from ETH Zurich. In this work, we show that the desired carbon atoms can be manipulated within Ni lattice containing an expanded interstitial space for improving the selectivity in acetylene hydrogenation reaction. The radius of octahedral space of Ni is expanded from 0.517 to 0.524 Å via formation of Ni3Zn, affording the dissociated carbon atoms to readily dissolve and diffuse at mild temperatures. Such incorporated carbon atoms coordinate with the surrounding Ni atoms for generation of Ni3ZnC0.7 and thereof inhibit the formation of subsurface hydrogen structures. Thus, the selectivity and stability are dramatically improved, as it enables suppressing the pathway of ethylene hydrogenation and restraining the accumulation of carbonaceous species on surface.
For more details, please see our recent article “Manipulating interstitial carbon atoms in the nickel octahedral site for highly efficient hydrogenation of alkyne” in Nature Communications.
Figure 1. Schematic of expanded interstitial sites in the unit cells of Ni, Ni3Zn and Ni3ZnC0.7.