Size Dependence of Pd-Catalyzed Hydrogenation of 2,6-Diamino-3,5-dinitropyridine

Abstract

An in-depth understanding of the effects of metal particle sizes on reactions is crucial for tailoring and designing catalysts. Herein, the Pd/CNT catalysts with different Pd particle sizes were prepared and employed to explore the size effects on the Pdcatalyzed hydrogenation of 2,6-diamino-3,5-dinitropyridine (DADNP). The apparent turnover frequencies for DADNP conversion and target 2,3,5,6-tetraaminopyridine (TAP) formation are found to exhibit strong dependence on the Pd particle sizes, indicating that the hydrogenation of DADNP to TAP is typically structure-sensitive. The size-insensitive activation energies extracted from the kinetics studies for DADNP conversion on ≥2.6 nmsized Pd catalysts with similar electronic properties suggest the presence of only one type of active site mainly dominating the reaction. Further combining model calculations based on the cuboctahedron shape for Pd nanoparticles characterized by electron microscopy, the (111) sites are demonstrated as the dominant active sites for DADNP conversion on the ≥2.6 nm-sized Pd catalysts. However, for the Pd catalyst size <2.6 nm, the reaction is shown to be mainly dominated by the Pd electronic properties.

Mesokinetics as a Tool Bridging the Microscopic-to-Macroscopic Transition to Rationalize Catalyst Design

“…These findings also pave an explanation for the ultrahigh hydrogen generation rate of the Pt@MIL-101 catalyst with an average Pt particle size of 1.8 nm prepared by Xu et al, which should involve a large number of Pt(111) active sites . Such methodology has been successfully extended to various thermo-, electro-, and photocatalysts in different systems (e.g., chemical synthesis, hydrogen generation, and environmental applications) as shown in Figure . − All the results confirm the high universality of this methodology in the identification and qualification of an active site, which lays a solid foundation for the following identification and quantitative determination of catalytic descriptor.…”

Multi-functionalized carbon nanotubes towards green fabrication of heterogeneous catalyst platforms with enhanced catalytic properties under NIR light irradiation

“…The particle dimension and electron structure of catalytic metal particles on the surface have been reported to influence the adsorption/desorption behavior of 4-NP molecules. 45,46 Hence, the fast conversion of 4-NP could be predominantly explained by the small size as well as the intrinsic catalytic activity of Pd when applied to the reduction of 4-NP. As a refer-ence, acid-oxidized CNTs were also used as the template for the preparation of Pd/CNT composites (denoted as a-CNTs-Pd).…”

Kinetics‐assisted identification and regulation of active sites for Pd‐catalyzed propyne selective hydrogenation

“…The numbers of such differently typed surface sites with distinct activities and selectivities vary with the increasing Pd particle size, which gives rise to the size‐dependent performances for the catalytic hydrogenation 18 . Systematic investigations on such size‐dependent performances and structure sensitivity can gain more insights into the active sites for catalytic reactions 17,22–26 . For instance, we previously proposed a kinetics‐assisted method to understand the structure sensitivity of Pd‐catalyzed acetylene semi‐hydrogenation, based on which the dominant active sites for the acetylene conversion and products formation were discriminated.…”

“…18 Systematic investigations on such size-dependent performances and structure sensitivity can gain more insights into the active sites for catalytic reactions. 17,[22][23][24][25][26] For instance, we previously proposed a kinetics-assisted method to understand the structure sensitivity of Pd-catalyzed acetylene semi-hydrogenation, based on which the dominant active sites for the acetylene conversion and products formation were discriminated. As a consecutive attempt, employing this method for exploring the structure sensitivity of propyne hydrogenation with the objective of identifying the active sites is highly desirable for rationally regulating active sites toward enhanced performances.…”