Professor Fu Yu's team from the College of Sciences at NEU and Professor Huo Fengwei's team from Nanjing University of Technology recently published a paper titled "Water-assisted hydrogen spillover in Pt nanoparticle-based metal-organic framework composites" in the journal "Nature Communications". Gu Zhida, a Ph.D. student in the College of Sciences, is the primary author of the study, and NEU is the primary institution of the paper. This research outcome advances the College of Sciences' advancements in the area of porous crystal materials and expands the research scope of the research team to include the phenomenon of hydrogen overflow.
Hydrogen overflow refers to the process in the hydrogenation reaction when hydrogen gas is split into active hydrogen atoms at the active center of the precious metal and afterward moves to the carrier material, continuing to migrate on it. The hydrogen overflow phenomenon refers to the creation of additional hydrogenation active sites on the support, which has the potential to enhance the catalyst's activity, selectivity, and stability. Metal-organic frameworks (MOFs) have garnered significant interest among researchers as catalytic support materials because of their properties of low density, high specific surface area, and well-defined pore structure. Nevertheless, the hydrogen overflow phenomena seen in MOF materials present challenges regarding characterization, limited overflow effect, and an unexplained mechanism. These issues hinder the theoretical investigation and catalytic application of the hydrogen overflow phenomenon in catalysts based on MOFs.
Professor Fu Yu's team constructed a study model to investigate the hydrogen overflow event in MOF-801 by utilizing ligand hydrogenation and structural conversion as a detector (see Figure 1a). The researchers discovered that the introduction of minute quantities of water molecules into the Pt@MOF-801 complex during hydrogen heat treatment leads to the following issues: Fig. 1b shows a clear reduction in crystallinity, Fig. 1c demonstrates a drop in specific surface area, Fig. 1d indicates an increase in hydrogen consumption, and Fig. 1e illustrates an increase in ligand conversion rate. This demonstrates that the incorporation of water molecules can greatly amplify the hydrogen overflow phenomenon in MOF-801. By conducting model calculations on ligand conversion, it has been determined that under the condition of a hydrogen pressure of 200°C, the phenomena of enhanced hydrogen overflow can occur, covering an area with a diameter of around 100 nm. The isotope tracing approach indicates that the excessive active hydrogen originates from hydrogen gas, not water molecules, hence confirming the supplementary enhancement impact of water molecules in the process of hydrogen overflow. Theoretical calculations demonstrate that water molecule clusters within the pores provide a hydrogen migration pathway with a reduced energy barrier (see Figure 1f). This, in conjunction with the ligand overflow pathway, enhances the efficiency of active hydrogen migration (see Figure 1g). Furthermore, this strategy of enhancing hydrogen overflow with the assistance of water molecules has been demonstrated to be effective in a range of different metal-organic frameworks (MOFs) including UiO-66, UiO-67, ZIF-8, ZIF-67, HKUST-1, and Fe-MIL-53, as well as various covalent organic frameworks (COFs) materials such as TAPT-DHTA and TaPa-1, demonstrating the robust universality of this approach. Crucially, empirical studies have demonstrated that this approach yields an augmented hydrogen overflow effect, leading to greater efficiency in catalytic reactions and improved stability of the catalyst. This marks the pioneering application of the hydrogen overflow effect in catalysts based on Metal-Organic Frameworks (MOFs) (see Figure 1h).
This research methodology offers novel insights into investigating the phenomenon of hydrogen overflow in porous crystal materials. The research findings offer novel avenues for the future design and development of porous crystal catalyst materials that exhibit exceptional activity, stability, selectivity, and environmental compatibility.
