One-step synthesis of hybrid zeolite membranes containing catalytic metal nanoclusters

Metal-loaded zeolitic membranes have promising applications as catalytic membranes that function simultaneously as reactors and separation devices. Post-treatment methods such as impregnation and ion exchange of metals need at least two or three steps, which increase the membrane production cost. Recent research has shown that a one-step synthesis method to encapsulate metal nanoparticles in zeolite powders offers a promising alternative to greatly improve the synthesis efficiency. However, to the best of our knowledge, the use of a one-step synthesis of zeolite membranes containing metal clusters has not yet been described in the literature. We will discuss a one-step synthesis method to incorporate metal nanoparticles in zeolite membranes. The hybrid metal-zeolite membranes were prepared by one-step colloidal hydrothermal synthesis with addition of 3-mercaptopropyl-trimethoxysilane (MPS) and a metal precursor to the initial synthesis mixture. We show that Pt ions/clusters are uniformly distributed along the membrane cross sectional layer. High magnification scanning transmission electron microscopy (STEM) shows that the Pt metal clusters in the hybrid zeolite membrane have a narrow size distribution of 0.5-2.0 nm. In contrast, a pure-silica MFI membrane obtained from MPS-free precursor, shows negligible loading of Pt metal clusters throughout the zeolite membrane layer. We then show that hybrid metal-zeolite membranes can be used as catalytic membrane reactors (CMR) to investigate a high-temperature propane dehydrogenation (PDH) at 600°C and 1 atm. The results indicate that Pt metal clusters formed within hybrid MFI zeolite membrane provide effective catalysts for high-temperature PDH reaction along with successful H₂ removal through the membrane permeation. The hybrid zeolite MR was further tested for high-temperature PDH reaction at extended operating times, and showed excellent stability in performance.