(382ae) Metal Nanoparticle-Supported Mesoporous Zeolites for Catalytic Reactions

The mesoporous zeolites can be effectively used not only as the solid acid catalyst itself but also as the supporting material for other catalysts such as metal nanoparticles. Particularly, the nanosponge MFI zeolite is beneficial for achieving high metal dispersion due to the confinement effect by the mesopore walls. For this reason, light transition metals (e.g., Ni and Co), which is vulnerable to thermal sintering into large particle due to the low polarizability giving poor metal-support interaction, could be supported in a form of tiny nanoparticles inside the mesopores of nanosponge MFI zeolites. By using this advantage for the high metal dispersion, I demonstrated that the use of nanosponge zeolites could enable the replacement of Pt by Ni in the metal-zeolite bifunctional catalyst without any loss of catalytic performance for hydroisomerization of n-dodecane [1]. Furthermore, the isomerization yield of Ni/nanosponge zeolite was much higher even compared with that of Pt/bulk zeolite, which is used in current industrial processes.

In 2020, we discovered a new principle to obtain intermetallic compound-type alloy nanoparticles composed of Pt and rare earth metals (REEs) [2]. It was regarded as impossible to form Pt-REE alloy nanoparticles by conventional H₂ treatment due to the fact that the bulk oxide of REEs, such as Y, La, and Ce, have very negative reduction potential. Nevertheless, we enabled the formation of Pt-REE alloy nanoparticles by using a specially designed mesoporous MFI zeolites as the support. The mesoporous MFI zeolite was first synthesized in a gallosilicate composition, and subsequently, the framework Ga was removed by treatment with concentrated HNO₃ solution. The Ga removal generated the framework defects in the resulted mesoporous MFI zeolite, where the three or four adjacent silanols (Si-OH) are clustered with hydrogen bonding. This framework defects are often called as ‘silanol nest’. When the REE precursors were loaded onto the mesoporous MFI zeolite, the supported REEs could exist as a single-atomic species by the assistance of silanol nests, which have highly activated chemical potential and mobility along the silanol nests. This enabled the atomistic alloying process as shown in the figure above. As a result, the Pt-REE intermetallic alloy nanoparticles with L1₂ structure could be supported on the mesoporous MFI zeolite. The Pt-REE/mesoporous MFI zeolite catalysts exhibited excellent catalytic longevity with high propylene selectivity and propane conversion in direct dehydrogenation of propane. Particularly, the catalytic lifetime over Pt-La/mesoporous MFI zeolite was almost 20-times longer than that over the current industrial PDH catalyst of PtSn/alumina. This atomistic alloying strategy is believed to be applicable to other common Pt-based alloys with late transition metals (e.g., Co, Cu, and Zn) and Pd- or Ni-based bimetallic alloys.

[1] Jaeheon Kim, Seung Won Han, Jeong-Chul Kim, Ryong Ryoo*, “Supporting nickel to replace platinum on zeolite nanosponges for catalytic hydroisomerization of n-dodecane”, ACS Catal. 8, 10545-10554 (2018).

[2] Ryong Ryoo*, Jaeheon Kim, et al., “Rare-earth–platinum alloy nanoparticles in mesoporous zeolite for catalysis”, Nature 585, 221-224 (2020).

Research Interests

My research interest lies in discovering new catalytic materials to revolutionize industrially important catalytic processes. My strategy involves generating catalytic active sites based on novel working principles and developing cost-effective synthesis methods for catalytic materials. Systematic studies of catalyst synthesis will enable a deep understanding of the structure–property relationships of these materials. The newly developed catalysts will be applied to practically important reactions, such as propane dehydrogenation.