Preparation of PtCu@zeolite propane dehydrogenation catalyst by ion exchange combined with displacement reaction strategy

CAS Academician, Prof. Jihong Yu, and her team from Jilin University developed a post-treatment strategy based on metal replacement reaction using commercial ZSM-5 zeolite as a carrier, and successfully encapsulated a highly active PtCu alloy catalyst in the pores of the zeolite. In the study, Cu²⁺ ions were first introduced into the pores of the zeolite through ion exchange, and then reduced at high temperature to form a Cu@MFI intermediate; then the Pt component was introduced through a metal replacement reaction, and a PtCu alloy was formed in the pores of the zeolite through high temperature reduction. The prepared PtCu₅@MFI-K (Pt/Cu=1/5) showed excellent catalytic performance in the propane dehydrogenation reaction, with a propane conversion rate of 49.7%, a propylene selectivity of more than 90%, and good cyclic stability. This study provides a new low-cost and efficient synthesis strategy for the development of high-performance alloy@zeolite catalysts. These results were published as an open access article in CCS Chemistry, the flagship journal of the Chinese Chemical Society.

Background:

Noble metal catalysts are widely used in a variety of catalytic systems due to their high activity, but under high-temperature reaction conditions and during recycling and regeneration, metal sintering and agglomeration often lead to catalyst deactivation. Therefore, the preparation of noble metal catalysts with both high dispersibility and sintering resistance has become a key challenge in the field of catalysis. Zeolite is a class of inorganic crystalline materials with a regular microporous structure, adjustable acidic sites and good thermal stability/hydrothermal stability, which can be used as a carrier to encapsulate and stabilize ultra-small metal particles. Organic ligands are often used to stabilize metal precursors and enter the pores of molecular sieves during hydrothermal synthesis. However, this method has problems such as high cost and low metal utilization, which limit its industrial application. At present, the development of a synthesis strategy for molecular sieve-encapsulated metal catalysts suitable for industrial production remains a research hotspot in this field.

Highlights of this article:

The preparation of zeolite-encapsulated alloy catalysts (alloy@zeolite) primarily relies on in situ encapsulation methods protected by organic ligands, a method that suffers from high cost and low metal utilization. To achieve efficient and cost-effective preparation of alloy@zeolite catalysts, this study proposes a post-treatment strategy based on ion exchange combined with a displacement reaction. Using commercial zeolites as supports, Cu²⁺ is first introduced into the zeolite crystals and reduced. Subsequently, Cu is used as a sacrificial metal to displace the subsequently introduced [Pt(NH ₃)₄](NO₃)₂. Furthermore, Cu acts as a catalyst promoter to promote the dispersion of Pt atoms, thereby enhancing the catalytic performance of Pt. Based on this strategy, a PtCu alloy species (PtCu@MFI) was successfully encapsulated in a ZSM-5 (MFI) zeolite. The Pt/Cu ratio was effectively tunable by manipulating the Si/Al ratio and metal loading of the ZSM-5 zeolite. Among them, the PtCu₅@MFI-K sample (Pt/Cu molar ratio = 1/5) demonstrated excellent performance in propane dehydrogenation, achieving a propane conversion of 49.7% and a propylene selectivity exceeding 90% at 550 °C and a weight hourly space velocity (WHSV) of 3.6 h⁻¹. At a WHSV of 108 h⁻¹, the initial propane conversion was 41.0% and the propylene selectivity reached 97.7%. Furthermore, the catalyst exhibited excellent cycling stability, further demonstrating its potential for application in propane dehydrogenation.

Summary and Outlook:

In summary, this paper developed a post-treatment strategy based on ion exchange combined with a displacement reaction. Using commercial zeolites as supports, metal species were introduced via ion exchange. Following a displacement reaction and hydrogen reduction, a zeolite-encapsulated PtCu alloy catalyst was successfully prepared. Benefiting from the spatial confinement effect of the zeolite, the prepared PtCu₅@MFI-K sample exhibited excellent catalytic activity and stability in propane dehydrogenation. This strategy effectively overcomes the high cost and low metal utilization of organic ligand protection methods, providing a new approach for the large-scale preparation and industrial application of zeolite-confined alloy catalysts.

The research results were published as a research article in CCS Chemistry. Jilin University doctoral student Jialiang Li and Associate Professor Qiang Zhang are co-first authors of the paper, with Prof. Jihong Yu as the corresponding author. This research was funded by the National Key R&D Program of China (2021YFA1501202), the National Natural Science Foundation of China (22288101), and the Higher Education Discipline Innovation and Talent Attraction Program (B17020).

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About the journal: CCS Chemistry is the Chinese Chemical Society’s flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem.

About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman’s Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/.